Download Anatomical terms for describing planes

Lecture 1
The subject, tasks and research methods of anatomy. History.
The history of anatomy extends from the earliest examinations of sacrificial victims to the
sophisticated analyses of the body performed by modern scientists. It has been characterized,
over time, by a continually developing understanding of the functions of organs and structures in
the body. Human anatomy was the most prominent of the biological sciences of the 19th and
early 20th centuries. Methods have also improved dramatically.
Egypt
The study of anatomy begins at least as early as 1600 BC, the date of the Edwin Smith
Surgical
Papyrus.
This
treatise
shows
that
the heart,
its
vessels, liver,spleen, kidneys, hypothalamus, uterus and bladder were recognized, and that
theblood vessels were known to emanate from the heart. Other vessels are described, some
carrying air, some mucus, and two to the right ear are said to carry the "breath of life", while two
to the left ear the "breath of death". The Ebers Papyrus (c. 1550 BC) features a treatise on the
heart. It notes that the heart is the center of blood supply, and attached to it are vessels for every
member of the body. The Egyptians seem to have known little about the function of the kidneys
and made the heart the meeting point of a number of vessels which carried all the fluids of the
body – blood, tears, urine and semen. However, they did not have a theory as to where saliva and
sweat came from.
Greek advances in anatomy
Nomenclature, methods and applications for the study of anatomy all date back to the
Greeks. The early scientist Alcmaeon began to construct a background for medical and
anatomical science with the dissection of animals. He identified the optic nerves and the tubes
later termed the Eustachius. Others such as Acron(480 BC), Pausanias (480 BC), and Philistion
of Locri made investigations into anatomy. One important figure during this time
was Empedocles (480B.C.) who viewed the blood as the innate heat which he acquired from
previous folklore. He also argued that the heart was the chief organ of both the vascular system
and the pneuma (this could refer to either breath or soul; it was considered to be distributed by
the blood vessels).
Many medical texts by various authors are collected in the Hippocratic Corpus, none of
which can definitely be ascribed to Hippocrates himself. The texts show an understanding
of musculoskeletal structure, and the beginnings of understanding of the function of certain
organs, such as the kidneys. Thetricuspid valve of the heart and its function is documented in the
treatise On the Heart.
In the 4th century BCE, Aristotle and several contemporaries produced a more empirically
founded system, based on animal dissection. Through his work with animal dissections and
evolutionary biology, Aristotle founded comparative anatomy. Around this time, Praxagoras is
credited as the first to identify the difference between arteries and veins, and the relations
between organs are described more accurately than in previous works.
The first recorded school of anatomy was in Alexandria from about 300 to 2nd century
BC. Ptolemy I Soter was the first to allow for medical officials to cut open and examine dead
bodies for the purposes of learning how human bodies operated. On some occasions King
Ptolemy even took part in these dissections. Most of the early dissections were done on executed
criminals. The first use of human cadavers for anatomical research occurred later in the 4th
century BCE when Herophilos and Erasistratus gained permission to perform live dissections, or
vivisection, on criminals in Alexandria under the auspices of the Ptolemaic dynasty. Herophilos
in particular developed a body of anatomical knowledge much more informed by the actual
structure of the human body than previous works had been. Herophilos was the first physician to
dissect human bodies and is considered to be the founder of Anatomy. He reversed the
longstanding notion made by Aristotle that the heart was the "seat of intelligence." He argued
instead that this seat was the brain. However, Herophilos was eventually accused by his
contemporaries of dissecting live criminals. The number of victims is said to be around 600
prisoners.
Early modern Anatomy
From the third century B.C.E until the twelfth century C.E. human anatomy was mainly
learned through books and animal dissection. Human dissection became restricted after Boniface
viii past a bull that forbade the dismemberment and boiling of corpses for funerary purposes. For
many decades human dissection was thought unnecessary when all the knowledge about a
human body could be read about from early authors such as Galen. In The twelfth century as
universities were being established in Italy, Emperor Frederick ii made it mandatory for students
of medicine to take courses on human anatomy and surgery. In the universities the lectern would
sit elevated before the audience and instruct someone else in the dissection of the body, but in his
early years Mondino de Luzzi performed the dissection himself making him one of the first and
few to use a hands on approach to teaching human anatomy.
Mondino de Luzzi "Mundinus" was born around 1276 and died in 1326,from 1314 to 1324 he
presented many lectures on human anatomy at Bologna university. Mondino de'Luzzi put
together a book called "Anathomia" in 1316 that consisted of detailed dissections that he had
performed, this book was used as a text book in universities for 250 years. "Mundinus" carried
out the first systematic human dissections since Herophilus of Chalcedon and Erasistratus of
Ceos 1500 years earlier. The first major development in anatomy in Christian Europe since the
fall of Rome occurred at Bologna, where anatomists dissected cadavers and contributed to the
accurate description of organs and the identification of their functions. Following de Liuzzi's
early studies, fifteenth century anatomists included Alessandro Achillini and Antonio Benivieni
Pathological anatomy.
17th and 18th centuries
he study of anatomy flourished in the 17th and 18th centuries. The advent of the printing
press facilitated the exchange of ideas. Because the study of anatomy concerned observation and
drawings, the popularity of the anatomist was equal to the quality of his drawing talents, and one
need not be an expert in Latin to take part. Many famous artists studied anatomy, attended
dissections, and published drawings for money, fromMichelangelo to Rembrandt. For the first
time, prominent universities could teach something about anatomy through drawings, rather than
relying on knowledge of Latin. Contrary to popular belief, the Church neither objected to nor
obstructed anatomical research.
Only certified anatomists were allowed to perform dissections, and sometimes then only
yearly. These dissections were sponsored by the city councilors and often charged an admission
fee, rather like a circus act for scholars. Many European cities, such as Amsterdam, London,
Copenhagen, Padua, and Paris, all had Royal anatomists (or some such office) tied to local
government. Indeed,Nicolaes Tulp was Mayor of Amsterdam for three terms. Though it was a
risky business to perform dissections, and unpredictable depending on the availability of fresh
bodies, attending dissections was legal.
To cope with shortages of cadavers and the rise in medical students during the 17th and 18th
centuries, body-snatching and even anatomy murder were practiced to obtain cadavers. 'Body
snatching' was the act of sneaking into a graveyard, digging up a corpse and using it for study.
Men known as 'resurrectionists' emerged as outside parties, who would steal corpses for a living
and sell the bodies to anatomy schools. The leading London anatomist John Hunter paid for a
regular supply of corpses for his anatomy school. The British Parliament passed the Anatomy
Act 1832, which finally provided for an adequate and legitimate supply of corpses by allowing
legal dissection of executed murderers. The view of anatomist at the time, however, became
similar to that of an executioner. Having one's body dissected was seen as a punishment worse
than death, "if you stole a pig, you were hung. If you killed a man, you were hung and then
dissected." Demand grew so great that some anatomist resorted to dissecting their own family
members (William Harvey dissected his own father and sister) as well as robbing bodies from
their graves.
Many Europeans interested in the study of anatomy traveled to Italy, then the centre of
anatomy. Only in Italy could certain important research methods be used, such as dissections on
women. Realdo Colombo (also known as Realdus Columbus) and Gabriele Falloppio were
pupils of Vesalius. Columbus, as Vesalius's immediate successor in Padua, and afterwards
professor at Rome, distinguished himself by describing the shape and cavities of the heart, the
structure of the pulmonary artery and aorta and their valves, and tracing the course of the blood
from the right to the left side of the heart.
Lecture 2
Cell, tissue, organ. The symmetry of the human body.
Systems of the Human Body
A system of human body means a collective functional unit made by several organs in which the
organs work in complete coordination with one another. Organs cannot work alone because their
are certain needs of every organ that need to be fulfilled and the organ itself cannot fulfill those
needs. So all organs of human body need the support of other organs to perform their functions
and in this way an organ system is formed.
Human body is made of ten different systems. All the systems require support and coordination
of other systems to form a living and healthy human body. If any one of these systems is
damaged, human body will become unstable and this lack of stability will ultimately lead to
death. The instability caused by damage of one system cannot be stabilized by other systems
because functions of one system cannot be performed by other systems. Knowledge of human
body systems is very important for a medical professional because it is the base of all medical
sciences and clinical practices. Although, generally, the structural aspects of human body
systems are studied in anatomy and the functional aspects are studied in physiology but it is very
important to have a coordination between the two subjects because knowledge of structure is
incomplete without the knowledge of function and the knowledge of function is incomplete
without the knowledge of structure.
Human anatomy uses its own collection of terms. Many of these are taken from Latin and Greek
languages and each has a very specific meaning. It is really important to understand the basic
terms, which would be used again and again throughout the course of learning anatomy.
Therefore, it is highly recommended that you try to learn the following terms.
Anatomical terms for describing positions:
Anatomical position: In this position the body is straight in standing position with eyes also
looking straight. The palms are hanging by the sides close to the body and are facing forwards.
The feet also point forwards and the legs are fully extended. Anatomical position is very
important because the relations of all structures are described as presumed to be in anatomical
position.
Anatomical Position
Supine position: In this position the body is lying down with face pointing upwards. All the
remaining positions are similar to anatomical position with the only difference of being in a
horizontal plane rather than a vertical plane.
Person Lying in Supine Position (Source: Apers0n/Wikipedia)
Prone position: This is the position in which the back of the body is directed upwards. The body
lies in a horizontal plane with face directed downwards.
Prone Position
Lithotomy position: In this position the body is lying in a supine with hips and knees fully
extended. The feet are strapped in position to support the flexed knees and hips.
Lithotomy Position
Anatomical terms for describing planes:
Planes
Median or Mid-Sagittal plane: This is the plane which divides the body into equal right and
left halves.
Sagittal plane: It is any plane parallel to the median plane. This plane divides the body into
unequal right and left halves.
Frontal plane: It is a vertical plane at right angle to median plane. If you draw a line from one
ear to another from above the head and then divide the whole body along this line, the plane
formed will be frontal plane. It is also known as coronal plane.
Transverse plane: It is the horizontal plane of the body. It is perpendicular to both frontal and
median plane.
Oblique plane: Any plane other than the above described planes will be oblique plane.
Anatomical terms for describing relations:
Terms of Relation
Anterior means towards the front.
Posterior means towards the back.
Superior means towards the head.
Inferior means towards the feet.
Medial means towards the median plane (near the middle of the body).
Lateral means away from the median plane (away from the middle of the body).
Anatomical terms for limbs:
Proximal means near the trunk
Distal means away from the trunk
Preaxial border means the outer border in the upper limb and inner border in the lower limb.
Postaxial border means outer border in upper limb and inner border in lower limb
Flexor surface means anterior surface of the upper limb and posterior surface of the lower limb
Extensor surface means the posterior surface of upper limb and anterior surface of the lower
limb.
Anatomical terms for describing muscles:
Origin: The relatively fixed end of muscle during natural movements of the muscle
Insertion: The relatively mobile end of the muscle during natural movements of the muscle
Belly: The fat fleshy part of the muscle which is contractile in function
Tendon: The fibrous and non-contractile part of the muscle which attaches muscle to the bone.
Aponeurosis: It is a flattened tendon arising from the connective tissues around the muscle.
Anatomical terms for describing movements:
Movements of limbs
Flexion: A movement by which the angle of a joint is decreased
Extension: A movement by which the angle of a joint is increased
Adduction: Movement toward the central axis
Abduction: Movement away from the central axis
Medial rotation: Rotation toward the medial side of the body
Lateral rotation: Rotation towards the lateral side of the body
Pronation: This movement occurs in the forearm whereby the palm is turned backwards
Supination: This movement also occurs in the forearm whereby the palm is turned forwards
Lecture 3
Bones. The skeleton of the trunk.
The skeletal system includes all of the bones and joints in the body. Each bone is a complex
living organ that is made up of many cells, protein fibers, and minerals. The skeleton acts as a
scaffold by providing support and protection for the soft tissues that make up the rest of the
body. The skeletal system also provides attachment points for muscles to allow movements at the
joints. New blood cells are produced by the red bone marrow inside of our bones. Bones act as
the body’s warehouse for calcium, iron, and energy in the form of fat. Finally, the skeleton
grows throughout childhood and provides a framework for the rest of the body to grow along
with it.
The skeletal system in an adult body is made up of 206 individual bones. These bones are
arranged into two major divisions: the axial skeleton and the appendicular skeleton. The axial
skeleton runs along the body’s midline axis and is made up of 80 bones in the following regions:
Skull
Hyoid
Auditory ossicles
Ribs
Sternum
Vertebral column
The appendicular skeleton is made up of 126 bones in the folowing regions:
Upper limbs
Lower limbs
Pelvic girdle
Pectoral (shoulder) girdle
Skull
The skull is composed of 22 bones that are fused together except for the mandible. These 21
fused bones are separate in children to allow the skull and brain to grow, but fuse to give added
strength and protection as an adult. The mandible remains as a movable jaw bone and forms the
only movable joint in the skull with the temporal bone.
The bones of the superior portion of the skull are known as the cranium and protect the brain
from damage. The bones of the inferior and anterior portion of the skull are known as facial
bones and support the eyes, nose, and mouth.
Hyoid and Auditory Ossicles
The hyoid is a small, U-shaped bone found just inferior to the mandible. The hyoid is the only
bone in the body that does not form a joint with any other bone—it is a floating bone. The
hyoid’s function is to help hold the trachea open and to form a bony connection for the tongue
muscles.
The malleus, incus, and stapes—known collectively as the auditory ossicles—are the smallest
bones in the body. Found in a small cavity inside of the temporal bone, they serve to transmit
and amplify sound from the eardrum to the inner ear.
Vertebrae
Twenty-six vertebrae form the vertebral column of the human body. They are named by region:
Cervical (neck) - 7 vertebrae
Thoracic (chest) - 12 vertebrae
Lumbar (lower back) - 5 vertebrae
Sacrum - 1 vertebra
Coccyx (tailbone) - 1 vertebra
With the exception of the singular sacrum and coccyx, each vertebra is named for the first letter
of its region and its position along the superior-inferior axis. For example, the most superior
thoracic vertebra is called T1 and the most inferior is called T12.
Ribs and Sternum
The sternum, or breastbone, is a thin, knife-shaped bone located along the midline of the anterior
side of the thoracic region of the skeleton. The sternum connects to the ribs by thin bands of
cartilage called the costal cartilage.
There are 12 pairs of ribs that together with the sternum form the ribcage of the thoracic region.
The first seven ribs are known as “true ribs” because they connect the thoracic vertebrae directly
to the sternum through their own band of costal cartilage. Ribs 8, 9, and 10 all connect to the
sternum through cartilage that is connected to the cartilage of the seventh rib, so we consider
these to be “false ribs.” Ribs 11 and 12 are also false ribs, but are also considered to be “floating
ribs” because they do not have any cartilage attachment to the sternum at all.
Pectoral Girdle and Upper Limb
The pectoral girdle connects the upper limb (arm) bones to the axial skeleton and consists of
the left and right clavicles and left and right scapulae.
The humerus is the bone of the upper arm. It forms the ball and socket joint of the
shoulder with the scapula and forms the elbow joint with the lower arm bones. The radius and
ulna are the two bones of the forearm. The ulna is on the medial side of the forearm and forms a
hinge joint with the humerus at the elbow. The radius allows the forearm and hand to turn over at
the wrist joint.
The lower arm bones form the wrist joint with the carpals, a group of eight small bones that give
added flexibility to the wrist. The carpals are connected to the five metacarpals that form
the bones of the hand and connect to each of the fingers. Each finger has three bones known as
phalanges, except for the thumb, which only has two phalanges.
Pelvic Girdle and Lower Limb
Formed by the left and right hip bones, the pelvic girdle connects the lower limb (leg) bones to
the axial skeleton.
The femur is the largest bone in the body and the only bone of the thigh (femoral) region. The
femur forms the ball and socket hip joint with the hip bone and forms theknee joint with the
tibia and patella. Commonly called the kneecap, the patella is special because it is one of the few
bones that are not present at birth. The patella forms in early childhood to support the knee for
walking and crawling.
The tibia and fibula are the bones of the lower leg. The tibia is much larger than the fibula and
bears almost all of the body’s weight. The fibula is mainly a muscle attachment point and is used
to help maintain balance. The tibia and fibula form the ankle joint with the talus, one of the
seven tarsal bones in the foot.
The tarsals are a group of seven small bones that form the posterior end of the foot and heel. The
tarsals form joints with the five long metatarsals of the foot. Then each of the metatarsals forms a
joint with one of the set of phalanges in the toes. Each toe has three phalanges, except for the big
toe, which only has two phalanges.
Microscopic Structure of Bones
The skeleton makes up about 30-40% of an adult’s body mass. The skeleton’s mass is made up
of nonliving bone matrix and many tiny bone cells. Roughly half of the bone matrix’s mass
is water, while the other half is collagen protein and solid crystals of calcium carbonate and
calcium
phosphate.
Living bone cells are found on the edges of bones and in small cavities inside of the bone matrix.
Although these cells make up very little of the total bone mass, they have several very important
roles in the functions of the skeletal system. The bone cells allow bones to:
Grow and develop
Be repaired following an injury or daily wear
Be broken down to release their stored minerals
Types of Bones
All of the bones of the body can be broken down into five types: long, short, flat, irregular, and
sesamoid.
Long. Long bones are longer than they are wide and are the major bones of the limbs. Long
bones grow more than the other classes of bone throughout childhood and so are responsible for
the bulk of our height as adults. A hollow medullary cavity is found in the center of long bones
and serves as a storage area for bone marrow. Examples of long bones include the femur, tibia,
fibula, metatarsals, and phalanges.
Short. Short bones are about as long as they are wide and are often cubed or round in shape. The
carpal bones of the wrist and the tarsal bones of the foot are examples of short bones.
Flat. Flat bones vary greatly in size and shape, but have the common feature of being very thin
in one direction. Because they are thin, flat bones do not have a medullary cavity like the long
bones. The frontal, parietal, and occipital bones of the cranium—along with the ribs and hip
bones—are all examples of flat bones.
Irregular. Irregular bones have a shape that does not fit the pattern of the long, short, or flat
bones. The vertebrae, sacrum, and coccyx of the spine—as well as the sphenoid, ethmoid,
and zygomatic bones of the skull—are all irregular bones.
Sesamoid. The sesamoid bones are formed after birth inside of tendons that run across joints.
Sesamoid bones grow to protect the tendon from stresses and strains at the joint and can help to
give a mechanical advantage to muscles pulling on the tendon. The patella and the pisiform
bone of the carpals are the only sesamoid bones that are counted as part of the 206 bones of the
body. Other sesamoid bones can form in the joints of the hands and feet, but are not present in all
people.
Parts of Bones
The long bones of the body contain many distinct regions due to the way in which they develop.
At birth, each long bone is made of three individual bones separated by hyaline cartilage. Each
end bone is called an epiphysis (epi = on; physis = to grow) while the middle bone is called a
diaphysis (dia = passing through). The epiphyses and diaphysis grow towards one another and
eventually fuse into one bone. The region of growth and eventual fusion in between the
epiphysis and diaphysis is called the metaphysis (meta = after). Once the long bone parts have
fused together, the only hyaline cartilage left in the bone is found as articular cartilage on the
ends of the bone that form joints with other bones. The articular cartilage acts as a shock
absorber and gliding surface between the bones to facilitate movement at the joint.
Looking at a bone in cross section, there are several distinct layered regions that make up a bone.
The outside of a bone is covered in a thin layer of dense irregular connective tissue called the
periosteum. The periosteum contains many strong collagen fibers that are used to firmly anchor
tendons and muscles to the bone for movement. Stem cells and osteoblast cells in the periosteum
are involved in the growth and repair of the outside of the bone due to stress and injury. Blood
vessels present in the periosteum provide energy to the cells on the surface of the bone and
penetrate into the bone itself to nourish the cells inside of the bone. The periosteum also contains
nervous tissue and many nerve endings to give bone its sensitivity to pain when injured.
Deep to the periosteum is the compact bone that makes up the hard, mineralized portion of the
bone. Compact bone is made of a matrix of hard mineral salts reinforced with tough collagen
fibers. Many tiny cells called osteocytes live in small spaces in the matrix and help to maintain
the strength and integrity of the compact bone.
Deep to the compact bone layer is a region of spongy bone where the bone tissue grows in thin
columns called trabeculae with spaces for red bone marrow in between. The trabeculae grow in a
specific pattern to resist outside stresses with the least amount of mass possible, keeping bones
light but strong. Long bones have a spongy bone on their ends but have a hollow medullary
cavity in the middle of the diaphysis. The medullary cavity contains red bone marrow during
childhood, eventually turning into yellow bone marrow after puberty.
Articulations
An articulation, or joint, is a point of contact between bones, between a bone and cartilage, or
between a bone and a tooth. Synovial joints are the most common type of articulation and feature
a small gap between the bones. This gap allows a free range of motion and space for synovial
fluid to lubricate the joint. Fibrous joints exist where bones are very tightly joined and offer little
to no movement between the bones. Fibrous joints also hold teeth in their bony sockets. Finally,
cartilaginous joints are formed where bone meets cartilage or where there is a layer of cartilage
between two bones. These joints provide a small amount of flexibility in the joint due to the gellike consistency of cartilage.
Support and Protection
The skeletal system’s primary function is to form a solid framework that supports and protects
the body's organs and anchors the skeletal muscles. The bones of the axial skeleton act as a hard
shell to protect the internal organs—such as the brain and theheart—from damage caused by
external forces. The bones of the appendicular skeleton provide support and flexibility at the
joints and anchor the muscles that move the limbs.
Movement
The bones of the skeletal system act as attachment points for the skeletal muscles of the body.
Almost every skeletal muscle works by pulling two or more bones either closer together or
further apart. Joints act as pivot points for the movement of the bones. The regions of each bone
where muscles attach to the bone grow larger and stronger to support the additional force of the
muscle. In addition, the overall mass and thickness of a bone increase when it is under a lot of
stress from lifting weights or supporting body weight.
Hematopoiesis
Red bone marrow produces red and white blood cells in a process known as hematopoiesis. Red
bone marrow is found in the hollow space inside of bones known as the medullary cavity.
Children tend to have more red bone marrow compared to their body size than adults do, due to
their body’s constant growth and development. The amount of red bone marrow drops off at the
end of puberty, replaced by yellow bone marrow.
Storage
The skeletal system stores many different types of essential substances to facilitate growth and
repair of the body. The skeletal system’s cell matrix acts as our calcium bank by storing and
releasing calcium ions into the blood as needed. Proper levels of calcium ions in the blood are
essential to the proper function of the nervous and muscular systems. Bone cells also release
osteocalcin, a hormone that helps regulate blood sugar and fat deposition. The yellow bone
marrow inside of our hollow long bones is used to store energy in the form of lipids. Finally, red
bone marrow stores some iron in the form of the molecule ferritin and uses this iron to form
hemoglobin in red blood cells.
Growth and Development
The skeleton begins to form early in fetal development as a flexible skeleton made of hyaline
cartilage and dense irregular fibrous connective tissue. These tissues act as a soft, growing
framework and placeholder for the bony skeleton that will replace them. As development
progresses, blood vessels begin to grow into the soft fetal skeleton, bringing stem cells and
nutrients for bone growth. Osseous tissue slowly replaces the cartilage and fibrous tissue in a
process called calcification. The calcified areas spread out from their blood vessels replacing the
old tissues until they reach the border of another bony area. At birth, the skeleton of a newborn
has more than 300 bones; as a person ages, these bones grow together and fuse into larger bones,
leaving adults with only 206 bones.
Flat bones follow the process of intramembranous ossification where the young bones grow from
a primary ossification center in fibrous membranes and leave a small region of fibrous tissue in
between each other. In the skull these soft spots are known as fontanels, and give the skull
flexibility and room for the bones to grow. Bone slowly replaces the fontanels until the
individual bones of the skull fuse together to form a rigid adult skull.
Long bones follow the process of endochondral ossification where the diaphysis grows inside of
cartilage from a primary ossification center until it forms most of the bone. The epiphyses then
grow from secondary ossification centers on the ends of the bone. A small band of hyaline
cartilage remains in between the bones as a growth plate. As we grow through childhood, the
growth plates grow under the influence of growth and sex hormones, slowly separating the
bones. At the same time the bones grow larger by growing back into the growth plates. This
process continues until the end of puberty, when the growth plate stops growing and the bones
fuse permanently into a single bone. The vast difference in height and limb length between birth
and adulthood are mainly the result of endochondral ossification in the long bones.
Spine
Stretching down the midline of the trunk from the base of the skull to the coccyx, the spine plays
an extremely important role in our bodies as it supports the upper body’s weight; provides
posture while allowing for movement and flexibility; and protects the spinal cord.
The spine, also known as the vertebral column or spinal column, is a column of 26 bones in an
adult body – 24 separate vertebrae interspaced with cartilage, and then additionally the sacrum
and coccyx Prior to adolescence, the spine consists of 33 bones because the sacrum’s five bones
and the coccyx’s four do not fuse together until adolescence.
The vertebrae are named by the first letter of their region (cervical, thoracic, or lumbar) and with
a number to indicate their position along the superior-inferior axis. For example, the fifth lumbar
vertebra (which is most inferior one, located beneath the fourth lumbar vertebra) is called the L5
vertebra.
Each vertebra has several important parts: the body, vertebral foramen, spinous process, and
transverse process.
The body is the main weight-bearing region of a vertebra, making up the bulk of the bone’s
mass.
Extending from the body, the transverse processes are thin columns of bone that point out to the
left and right sides of the body.
The spinous process extends from the ends of the transverse processes in the posterior direction.
Between the body, transverse processes and spinous process is the vertebral foramen, a hollow
space that contains the spinal cord and meninges.
Between the vertebrae of the spine are thin regions of cartilage known as the intervertebral discs.
Intervertebral discs are made of an outer shell known as the annulus fibrosus and a soft, pulpy
region known as the nucleus pulposus in the middle.
The annulus fibrosus is made of tough fibrocartilage that binds the vertebrae together but is
flexible enough to allow for our movements.
The inner nucleus pulposus acts as a shock absorber to support the body’s weight and prevent the
vertebrae from painfully crashing into each other while under strain.
The vertebrae of the spine align so that their vertebral canals form a hollow, bony tube to protect
the spinal cord from external damage and infection. Between the vertebrae are small spaces
known as intervertebral canals that allow spinal nerves to exit the spinal cord and connect to the
various regions of the body.
There are 5 major regions of the spine:
Cervical: The 7 vertebrae in the neck form the cervical region of the spine. Cervical vertebrae
are the thinnest and most delicate vertebrae in the spine but offer great flexibility to the neck.
The first cervical vertebra, C1, supports the skull and is named “atlas” after the Greek titan who
held the Earth on his shoulders. The skull pivots on the atlas when moving up and down. The
second cervical vertebra, C2, is also known as the “axis” because it allows the skull and atlas to
rotate to the left and right.
Thoracic: The 12 vertebrae in the chest region form the spine’s thoracic region. Thoracic
vertebrae are larger and stronger than cervical vertebrae but are much less flexible. The spinous
processes of the thoracic vertebrae point inferiorly to help lock the vertebrae together. A unique
feature of the thoracic vertebrae is that each one forms joints with a pair of ribs to form the
sturdy rib cage that protects the organs of the chest.
Lumbar: The 5 vertebrae in the lower back form the lumbar region of the spine. Lumbar
vertebrae are even larger and stronger than thoracic vertebrae, but are more flexible due to the
lack of ribs in the lumbar region. All of the upper body’s weight bears down on the lumbar
vertebrae, leading to many back problems in this region despite the size and strength of the
vertebrae.
Sacral: The sacral region of the spine contains only the sacrum, a single bone in the adult
skeleton that is formed by the fusion of 5 smaller vertebrae during adolescence. The sacrum is a
flat, triangular bone found in the lower back and wedged between the 2 hip bones.
Coccygeal: The spine’s coccygeal region contains only the coccyx, a single bone in the adult
skeleton that is formed by the fusion of 4 tiny vertebrae during adolescence. The coccyx is often
referred to as the human tailbone, as this region is homologous to the tail bones of animals that
have tails. In humans, the coccyx bears our body weight when sitting down and provides
attachment points for muscles of the pelvic and gluteal regions. While most people have a
coccyx made of 4 fused vertebrae, the coccyx may consist of as few as 3 or as many as 5
vertebrae. The length of the coccyx has no effect on the body’s function.
False ribs
The false ribs are the remaining five pairs of ribs (the other seven are called true ribs) in which
their cartilages do not reach the sternum directly. Instead, the cartilages of the upper three false
ribs join the cartilages attached to the ribs above.
True ribs
The true ribs are attached to the sternum (breastbone) directly by their costal cartilages. There
are seven true ribs. (The other ribs are termed floating or false ribs.)
Xiphoid Process of Sternum
The xiphoid process is the smallest and most inferior region of the sternum, or breastbone. At
birth, it is a thin, roughly triangular region of cartilage that slowly ossifies into a bone and fuses
with the body of the sternum. Clinically, the xiphoid process plays an important role as a bony
anatomical landmark in the trunk and may be damaged by improperly administered CPR.
The xiphoid process is located inferior to the body of the sternum. The word xiphoid comes from
the Greek word for “sword-shaped,” which describes its thin and pointed shape. It is widest at its
superior end where it is attached to the body of the sternum by a thin, slightly movable fibrous
joint (syndesmosis). From its syndesmosis, it tapers gradually to a point. There are many
common variations in the shape of the xiphoid process, including:
Perforation with a small foramen in its center
Bifurcation with a split into left and right branches at its inferior end.
These variations in anatomy apparently do not result in any sort of change in the function of the
xiphoid process and may be inherited genetically.
Developmentally, the xiphoid process begins as a structure made of hyaline cartilage at birth and
childhood, slowly ossifying into a bony part of the sternum. In fact, the ossification of the
xiphoid process is so slow that it often does not end until an individual reaches the age of 40.
The xiphoid process functions as a vital attachment point for several major muscles. It acts as
one of several origins for the diaphragm muscle that forms the floor of the ribcage and performs
the vital process of respiration. The xiphoid process also acts as an insertion for the rectus
abdominis and transverse abdominis muscles that compress and flex the abdomen. During
cardiopulmonary resuscitation (CPR), the xiphoid process may be used as a bony landmark to
determine the location for administering chest compressions. It is extremely important that
pressure is not exerted on the xiphoid process during chest compressions, as this can cause the
xiphoid process to separate from the sternum, possibly puncturing the diaphragm or liver.
Lecture 4
Skeleton upper and lower limbs.
Lower limbs.
Ilium
The ilium is the largest and most superior of the three bones that join to form the hipbone, or os
coxa. It is a wide, flat bone that provides many attachment points for muscles of the trunk and
hip. You can find the crest of your ilium by placing your hands on your hips. The superficial
location of the ilium makes it a common site for extracting bone tissue for grafting and bone
marrow for transplants.
It forms the superior region of the hipbone and joins with the pubis and ischium at the
acetabulum, or hip socket. The largest region of the ilium is the ala, an area shaped somewhat
like an elephant’s ear with a large, flat surface that is slightly concave when viewed from the
anterior direction. Along the superior edge of the ala is a widened bony ridge known as the iliac
crest. The iliac crest protrudes laterally towards the body’s surface and acts as an important and
easily located bony landmark of the body. At the ends of the iliac crest, the ilium narrows
sharply toward its center to form the anterior and posterior superior spines of the ilium. It turns
again just below these spines to form the anterior and posterior inferior spines at the base of the
ala.
Inferior to the ala, the ilium widens into a region known as the body of the ilium. Between the
ala and the body is the greater sciatic notch, a large V-shaped notch in the posterior ilium that
allows the sciatic nerve to pass through the pelvis in order to innervate the leg. The body widens
to form the sacroiliac joint on its medial surface and forms cartilaginous joints with the pubis and
ischium at the acetabulum. The acetabulum is the cup-like structure that forms the socket of the
hip joint.
The ilium forms and grows during fetal development separately from the other hip bones, the
pubis and ischium. At birth, these three bones remain separated by a thin layer of cartilage at the
acetabulum. This cartilage layer provides room for the bones to grow independently before
fusing during young adulthood when they are fully-grown.
The ilium forms the sacroiliac joint with the sacrum along its medial side and forms the superior
end of the hip joint at the acetabulum. The sacroiliac joint is a planar joint that allows a slight
degree of gliding between the pelvis and the spinal column. The hip joint is a ball-and-socket
joint that permits the thigh to have a free range of motion.
The surface of the ilium is covered in a thin fibrous membrane known as the periosteum. The
periosteum is made of dense irregular connective tissue and plays an important role in the
connection of muscles to the surface of the ilium. Deep to the periosteum is a layer of compact
bone that contains bone cells embedded in a hard mineral and protein matrix. Compact bone
provides most of the strength and structural integrity to the ilium. The inner portion of the ilium
is filled with many columns of spongy bone. Spongy bone supports the surrounding compact
bone like the girders of a bridge, while leaving hollow spaces inside the bone to reduce its
weight. These spaces are also filled with red bone marrow, which is responsible for the
production of blood cells.
Acetabulum
The acetabulum is a cup-like depression ball and socket joint. The ilium, the ischium, and the
pubis bones form it.
Anterior inferior iliac spine
The anterior inferior iliac spine is the area just below where the iliac crest terminates anteriorly.
Anterior sacroiliac ligament
The anterior sacroiliac ligament is the fibrocartilage at the front of the sacrum, which joins it to
the ilium.
Superior ramus of the pubis
The superior ramus of the pubis is the pubic bone's section that helps to form the obturator
foramen. It reaches to the median plane from the body. Here it merges with its opposite side, the
inferior ramus of the pubis. There are two parts of the superior pubic of the ramus: the lateral
narrow prismoid part and the medial flattened part.
Upper limb
Clavicle
The clavicles, or collarbones, are a pair of long bones that connect the scapula to the sternum.
The name clavicle comes from the Latin word for “little key” and describes the shape of the
clavicle as an old-fashioned skeleton key. The clavicle is one of the most commonly broken
bones in the human body. It also serves as an important and easily located bony landmark due to
its superficial location and projection from the trunk.
The clavicles are cylindrical bones around 6 inches (15 cm) long and curved in the transverse
plane like a letter S.
They are located in the thoracic region superior and anterior to the first rib. Each clavicle runs
transversely and forms a joint with the sternum on its medial end and the scapula on its lateral
end. The medial end of each clavicle is a smooth, rounded cylinder known as the sternal
extremity, which forms the sternoclavicular joint with the manubrium of the sternum. Viewed
from the anterior position, the clavicle forms a convex curve at its medial end before forming a
smaller concave curve near its lateral end. The lateral end terminates in a flattened facet known
as the acromial extremity, which forms the acromioclavicular (AC) joint with the acromion
process of the scapula.
The clavicles, along with the scapulae, form the pectoral girdle that attaches the bones of the arm
to the trunk. In fact, the sternoclavicular joints are the only bony attachments between the
pectoral girdles and the bones of the axial skeleton. The clavicles function as struts to anchor the
arms to the trunk while permitting the movement of the scapulae and shoulder joints relative to
the trunk. The movement of the clavicles increases the mobility of the shoulder joints beyond
what would be possible with only ball-and-socket joints, allowing the arm to move in a large
circle. Several muscles of the neck and shoulder also attach to the clavicle, including the
pectoralis major, sternocleidomastoid, trapezius, and deltoid.
The unique position of the clavicle in the body frequently makes it the site of fractures from
several types of accidents. When the arm is extended to break a fall, much of the force from the
fall is transmitted through the arm to the shoulder, which shifts suddenly and can fracture the
clavicle. When a strong force is applied directly to the shoulder, such as during a car accident,
tackle, or sudden fall, the shoulder bones can be pushed medially and result in a fractured
clavicle.
Costal cartilage
The costal cartilage is a set of hyaline cartilage bands that attach the medial end of the seven true
ribs to the lateral border of the sternum (breastbone). Costal (cost- = rib) cartilage also connects
the three superior false ribs to the sternum, but these false ribs are attached indirectly by way of
the seventh true rib’s cartilage band.
Function
The costal cartilage forms a semi-movable joint between the true ribs and the sternum. This joint
permits flexibility in the rib cage while keeping the ribs firmly connected to the sternum. The
flexibility of the costal cartilage allows the ribcage to expand along with the lungs during deep
inhalation. It also allows the thoracic region to bend laterally, anteriorly, and posteriorly. Finally,
the costal cartilage may act as a shock absorber to prevent blows to the anterior portion of the
chest from resulting in rib fractures.
Injuries and Disorders
After a direct impact, the costal cartilage can become separated from the end of the rib that it is
normally attached to. This painful condition is known as a rib separation. Given enough time and
rest, a rib and cartilage will fuse back together again.
The costal cartilage may also become inflamed in a condition known as costochondritis.
Costochondritis causes chest pain, which is not life threatening but may be confused with a
symptom of a heart attack. As with a rib separation, the body will repair costochondritis and
symptoms will go away on their own.
Interclavicular ligament
The interclavicular ligament is located in the arm, chest and back. The clavicle (collarbone) acts
as a brace for the freely movable scapula (shoulder blade), and helps to hold the shoulders in
place. It also provides attachments for the muscles, tendons, and the interclavicular ligaments. As
a result of its elongated double curve, the clavicle is weakly built. If it is compressed from the
end by abnormal pressures on the shoulder, it is likely to fracture.
Scapula
The scapula is the technical name for the shoulder blade. It is a flat, triangular bone that lies over
the back of the upper ribs. The rear surface can be felt under the skin. It serves as an attachment
for some of the muscles and tendons of the arm, neck, chest and back and aids in the movements
of the arm and shoulder. It is well padded with muscle so that great force is required to fracture
it. The back surface of each scapula is divided into unequal portions by a spine. This spine leads
to a head, which bears two processes-the acromion process that forms the tip of the shoulder and
a coracoid process that curves forward and down below the clavicle (collarbone). The acromion
process joins a clavicle and provides attachments for muscles of the arm and chest muscles. The
acromion is a bony prominence at the top of the shoulder blade. On the head of the scapula,
between the processes mentioned above, is a depression called the glenoid cavity. It joins with
the head of the upper arm bone (humerus).
Spine of Scapula
The spine of the scapula divides its back surface into unequal portions. This spine leads to a
head, that bears two processes - the acromion process that forms the tip of the shoulder and a
coracoid process that curves forward and down below the clavicle (collarbone). The acromion, a
bony prominence at the top of the shoulder blade, joins the clavicle and provides attachments for
muscles of the arm and chest muscles. On the head of the scapula, between the processes
mentioned above, is a depression called the glenoid cavity. It joins with the head of the upper
arm bone (humerus).
Humerus
The humerus is the both the largest bone in the arm and the only bone in the upper arm. Many
powerful muscles that manipulate the upper arm at the shoulder and the forearm at the elbow are
anchored to the humerus. Movement of the humerus is essential to all of the varied activities of
the arm, such as throwing, lifting, and writing.
At its proximal end, the humerus forms a smooth, spherical structure known as the head of the
humerus.
The head of the humerus forms the ball of the ball-and-socket shoulder joint, with the glenoid
cavity of the scapula acting as the socket. The rounded shape of the head of the humerus allows
the humerus to move in a complete circle (circumduction) and rotate around its axis at the
shoulder joint. Just below the head, the humerus narrows into the anatomical neck of the
humerus. Two small processes, the greater and lesser tubercles, extend from the humerus just
below the anatomical neck as attachment points for the muscles of the rotator cuff. The humerus
narrows below the tubercles again in a region known as the surgical neck before extending
toward elbow joint as the body of the humerus. About a third of the way to the elbow, the
humerus swells into a small process known as the deltoid tuberosity, which supports the insertion
point of the deltoid muscle.
Below the deltoid tuberosity, the humerus gradually widens, doubling its width as it approaches
the elbow. The distal end of the humerus contains two joint-forming processes known as the
capitulum and trochlea. On the medial side of the arm, the trochlea interlocks with the ulna of the
forearm to form half of the elbow joint. On the lateral side of the arm, the convex capitulum
forms a loose connection with the concave head of the radius. The shape of the joint between the
capitulum and radius allows the forearm and hand to rotate and bend at the elbow while the ulna
forms a tight hinge with the trochlea. On the posterior side of the humerus, a small cavity known
as the olecranon fossa allows the tip of the ulna, known as the olecranon, to lock into the
humerus and prevent the extension of the elbow beyond 180 degrees.
The humerus is classified structurally as a long bone because it is considerably longer than it is
wide. Like all long bones, the humerus is hollow in the middle of its shaft and is reinforced at the
ends by small columns of spongy bone known as trabeculae. Red bone marrow, the tissue that
produces new blood cells, is found in the ends of the humerus and supported by the trabeculae.
The hollow medullary cavity in the middle of the shaft of the humerus is filled with fatty yellow
bone marrow for energy storage. Compact bone forms the largest and strongest structure in the
humerus, surrounding the trabeculae in the ends and the medullary cavity in the shaft.
Surrounding the entire bone is the fibrous periosteum layer that provides a thin, yet strong
connecting material for the tendons and ligaments that bind the humerus to muscles and other
bones. Finally, the ends of the humerus are capped by a thin layer of hyaline known as articular
cartilage that acts as a shock absorber in the joints.
The adult humerus develops from three individual bones in the fetus: the diaphysis, or central
shaft, and two epiphyses that form the end caps of the bone. Between these three bones is a thin
layer of hyaline cartilage known as the epiphyseal plate or growth plate. Cartilage in the growth
plate grows throughout childhood and adolescence to elongate the humerus and provide for the
growth of the arm. The cartilage is replaced by bony tissue so that the humerus increases its
length significantly while the growth plate remains relatively thin. Finally, at the end of puberty,
the cartilage stops growing and is completely replaced by bone to form a singular, unified
humerus. The region of bone between the epiphysis and diaphysis in the mature humerus is
known as the metaphysis.
Radius
The radius is the more lateral and slightly shorter of the two forearm bones. It is found on the
thumb side of the forearm and rotates to allow the hand to pivot at the wrist. Several muscles of
the arm and forearm have origins and insertions on the radius to provide motion to the upper
limb. These movements are essential to many everyday tasks such as writing, drawing, and
throwing a ball.
The radius is located on the lateral side of the forearm between the elbow and the wrist joints. It
forms the elbow joint on its proximal end with the humerus of the upper arm and the ulna of the
forearm Although the radius begins as the smaller of the two forearm bones at the elbow, it
widens significantly as it extends along the forearm to become much wider than the ulna at the
wrist. A short cylinder of smooth bone forms the head of the radius where it meets the capitulum
of the humerus and the radial notch of the ulna at the elbow. The head of the radius allows the
forearm to flex and pivot at the elbow joint. Just distal to the head, the radius narrows
considerably to form the neck of the radius before expanding medially to form the radial
tuberosity, a bony process that serves as the insertion of the biceps brachii.
Distal to the elbow, the body of the radius continues in a straight line along the lateral side of the
forearm before suddenly widening just above the wrist joint. At its wide distal end, the radius
terminates in three smooth, concave surfaces that form the wrist joint with the ulna and the
carpals of the hand. Two of these concavities meet with the scaphoid and lunate bones of the
carpals to form the radiocarpal portion of the wrist joint. On the medial side, the ulnar notch of
the radius forms the distal radioulnar joint with the ulna, allowing the radius to rotate around the
ulna to supinate and pronate the hand and wrist. The styloid process – a small, pointy extension
of bone – protrudes from the lateral edge of the radius to anchor the radial collateral ligament of
the wrist.
One of the most important functions of the radius is anchoring the muscles of the upper arm and
the forearm. The biceps brachii muscle of the upper arm forms its insertion at the radial
tuberosity to flex and supinate the forearm at the elbow. The supinator, pronator teres, and
pronator quadratus muscles of the forearm also form insertions on the radius to supinate and
pronate the hand and wrist by rotating the distal end of the radius around the ulna. Several
muscles that move the hand and digits – including the flexor pollicis longus and flexor digitorum
superficialis muscles – also have their origins on the radius.
The radius is classified structurally as a long bone because it is much longer than it is wide. Like
all long bones, the radius is made of compact bone with a hollow center and spongy bones filling
the ends. Compact bone is the hardest and heaviest part of the radius and makes up most of its
structure. Many layers of minerals and collagen fibers give the compact bone its strength and
flexibility.
Deep to the compact bone is a hollow cavity that spans the length of the bone and is filled with
adipose-rich yellow bone marrow. Yellow bone marrow stores energy for the body’s cells in the
form of triglycerides.
At the proximal and distal end of the radius, the compact bone is reinforced by thin columns of
spongy bone that give the radius extra strength without significantly adding to its mass. Small
hollow spaces in the spongy bone house red bone marrow tissue that produces all of the body’s
blood cells.
The outer surface of the radius is covered in a thin layer of fibrous connective tissue known as
the periosteum, and at its proximal and distal ends is covered in hyaline cartilage. Periosteum
contains many collagen fibers that form strong connections between the radius and the tendons
and ligaments that connect it to the bones and muscles of the arm. Hyaline cartilage gives the
ends of the radius a smooth surface to reduce friction during movements of the forearm. It also
acts as a flexible shock absorber to reduce impact stress at the elbow and wrist joints.
At birth, the radius begins as a bony shaft, known as the diaphysis, with a cap of hyaline
cartilage on both ends. The hyaline cartilage provides extra flexibility to the elbow and wrist
joints and provides a medium for the bone to grow into. Around the age of two, the distal hyaline
cartilage near the wrist joint begins to turn into a separate bone called the distal epiphysis. A thin
layer of cartilage called the epiphyseal plate (or growth plate) separates the diaphysis and
epiphysis. The cartilage in the growth plate grows lengthwise to keep the diaphysis and epiphysis
separated and to increase the overall length of the radius.
At around five years of age, the cartilage on the proximal end of the radius near the elbow
ossifies to form the proximal epiphysis. Just like the distal epiphysis, an epiphyseal plate
separates the proximal epiphysis from the diaphysis to give the radius room to grow. The
epiphyses unite with the diaphysis by the end of puberty to form a single radius bone, at which
point it stops growing lengthwise. The region where the diaphysis and epiphyses grow together
is called the metaphysis.
Ulna
The ulna is the longer, larger and more medial of the lower arm bones. Many muscles in the arm
and forearm attach to the ulna to perform movements of the arm, hand and wrist. Movement of
the ulna is essential to such everyday functions as throwing a ball and driving a car.
The ulna extends through the forearm from the elbow to the wrist, narrowing significantly
towards its distal end. At its proximal end it forms the elbow joint with the humerus of the upper
arm and the radius of the forearm. The ulna extends past the humerus to form the tip of the
elbow, known as the olecranon The olecranon fits into a small recess in the humerus known as
the olecranon fossa, preventing the elbow’s extension beyond around 180 degrees. Just distal to
the olecranon is the concave trochlear notch that surrounds the trochlea of the humerus to form
the hinge of the elbow joint. The distal lip of the trochlear notch protrudes anteriorly to form the
coronoid process that helps to lock the ulna in place with the humerus at the elbow and fits into
the coronoid fossa of the humerus. On the lateral edge of the coronoid process is the small radial
notch that forms the proximal radioulnar joint with the radius and permits the radius to rotate
around the ulna at the elbow. A long ridge on the anterior side of the coronoid process known as
the ulnar tuberosity extends down the shaft of the ulna as a muscle attachment point.
Moving distally from the elbow, the ulna begins to taper slightly in diameter along its entire
length while curving medially. At its distal end, the ulna forms a small part of the wrist with the
radius and the carpals of the hand. A rounded process known as the head of the ulna forms the
distal radioulnar joint with the concave ulnar notch of the radius. The alignment of these jointforming processes allows the radius to rotate around the ulna at the wrist. A small bony
extension known as the styloid process protrudes from the posterior and medial corner of the
ulna and provides an attachment point for the ulnar collateral ligament of the wrist.
Functionally, the ulna provides muscle attachment sites for over a dozen muscles in the upper
arm and forearm. In the upper arm, the triceps brachii and anconeus muscles form insertions at
the olecranon to extend the forearm at the elbow. The brachialis muscle has its insertion on the
coronoid process to flex the arm at the elbow. Many muscles that act on the hand and wrist have
their origins on the ulna, including the pronators, supinators, flexors and extensors.
Like its neighbors the humerus and radius, the ulna is classified as a long bone because of its
long, narrow shape. All long bones have a similar structure, with a hollow shaft surrounded by
compact bone and reinforced at the ends with spongy bone.
The hollow medullary cavity at the center of the ulna is filled with a soft, greasy substance
known as yellow bone marrow. Yellow bone marrow contains many adipocytes and stores
energy for the body in the form of triglycerides, or fats.
Surrounding the medullary cavity is the hard, dense compact bone made of mineral matrix and
collagen fibers. The mix of collagen and minerals, including calcium, gives the ulna its great
strength and flexibility.
The ends of the ulna are reinforced by spongy bone that increases the strength of the compact
bone near the joints without significantly increasing the mass of the bone. Each region of spongy
bone is made of many thin columns known as trabeculae that act like the steel girders of a bridge
to withstand the stresses placed on the bone. Red bone marrow is found in the spaces between
the trabeculae and contains many stem cells that produce the body’s blood cells.
On the joint-forming ends of the ulna are thin layers of hyaline cartilage that cover the compact
bone and protect it from the stresses at the joints. Hyaline is as smooth as ice to help bones glide
past each other at the joints. It is also rubbery to absorb the shocks of impacts at the joints. The
outer surface of the ulna (except at the joints) is covered in a thin fibrous layer known as the
periosteum. Periosteum is made of a dense weave of collagen fibers that extend into the tendons
and ligaments that attach the ulna to the muscles and bones of the arm.
The ulna begins at birth as a long bony shaft, known as the diaphysis, capped with hyaline
cartilage at both ends. At around 4 years of age, the hyaline at the distal end by the wrist begins
to ossify and forms a small bony cap known as the distal epiphysis. A thin layer of hyaline,
known as the epiphyseal plate or growth plate, remains between the diaphysis and the newly
formed epiphysis. The ulna grows lengthwise into the growth plate, which in turn grows to
prevent the fusion of the diaphysis and epiphysis. At around age 10, the proximal tip of the
olecranon begins to ossify and forms the proximal epiphysis. These three bones continue to grow
and remain separated by the epiphyseal plates until the end of puberty and the beginning of
adulthood, when they fuse together to form a single, unified ulna. The site of the epiphyseal plate
becomes known as the metaphysis in the mature bone.
Fermur
The femur, or thigh bone, is the longest, heaviest, and strongest bone in the entire human body.
All of the body’s weight is supported by the femurs during many activities, such as running,
jumping, walking, and standing. Extreme forces also act upon the femur thanks to the strength of
the muscles of the hip and thigh that act on the femur to move the leg. The femur is classified
structurally as a long bone and is a major component of the appendicular skeleton.
On its proximal end, the femur forms a smooth, spherical process known as the head of the
femur. The head of the femur forms the ball-and-socket hip joint with the cup-shaped
acetabulum of the coxal (hip) bone. The rounded shape of the head allows the femur to move in
almost any direction at the hip, including circumduction as well as rotation around its axis. Just
distal from the head, the femur narrows considerably to form the neck of the femur. The neck of
the femur extends laterally and distally from the head to provide extra room for the leg to move
at the hip joint, but the thinness of the neck provides a region that is susceptible to fractures.
At the end of the neck, the femur turns about 45 degrees and continues distally and slightly
medially toward the knee as the body of the femur. At the top of the body of the femur on the
lateral and posterior side is a large, rough bony projection known as the greater trochanter. Just
medial and distal to the greater trochanter is a smaller projection known as the lesser trochanter.
The greater and lesser trochanters serve as a muscle attachment sites for the tendons of many
powerful muscles of the hip and groin such as the iliopsoas group, gluteus medius, and adductor
longus. The trochanters also widen and strengthen the femur in a critical region of high stresses
due to external trauma and the force of muscle contractions.
On its distal end, the femur forms the knee joint with the tibia of the lower leg. The distal end of
the body of the femur widens significantly above the knee to form the rounded, smooth medial
and lateral condyles. The medial and lateral condyles of the femur meet with the medial and
lateral condyles of the tibia to form the articular surfaces of the knee joint. Between the condyles
is a depression called the intercondylar fossa that provides space for the anterior cruciate
ligament (ACL) and posterior cruciate ligament (PCL), which stabilize the knee along its
anterior/posterior axis.
Fibula
The fibula is the long, thin and lateral bone of the lower leg. It runs parallel to the tibia, or shin
bone, and plays a significant role in stabilizing the ankle and supporting the muscles of the lower
leg. Compared to the tibia, the fibula is about the same length, but is considerably thinner. The
difference in thickness corresponds to the varying roles of the two bones; the tibia bears the
body’s weight from the knees to the ankles, while the fibula merely functions as a support for the
tibia.
At the fibula’s proximal end, just below the knee, is a slightly rounded enlargement known as the
head of the fibula. The head of the fibula forms the proximal (superior) tibiofibular joint with the
lateral edge of the tibia. From the proximal tibiofibular joint, the fibula extends slightly medially
and anteriorly in a straight line toward the ankle. Upon reaching the ankle, the fibula swells into
a bony knob known as the lateral malleolus, which can be seen and felt protruding from the
outside of the ankle joint. At the medial malleolus, the fibula forms the distal (inferior)
tibiofibular joint with the tibia and also the talocrural (ankle) joint with the tibia and talus of the
foot.
While the fibula moves very little relative to the tibia, the joints that it forms contribute
significantly to the function of the lower leg. The proximal and distal tibiofibular joints permit
the fibula to adjust its position relative to the tibia, increasing the range of motion of the ankle.
The lateral malleolus also forms the lateral wall of the talocrural joint and reinforces the ankle
joint.
Many muscles of the thigh and lower leg attach to the fibula through tendons. One of the
hamstrings, the biceps femoris muscle, has its insertion at the head of the fibula and pulls on the
fibula to flex the leg at the knee. Eight other muscles – including the three fibularis (peroneus)
muscles, the soleus, and several flexors and extensors of the toes – have their origins on the
fibula as well.
An interesting fact about the fibula is that it can be harvested for tissue to graft onto other bones
in the body. The fibula bears so little body weight that it typically has more bone mass than is
needed to support the leg, making it a good tissue donor. The bony tissue harvested from the
fibula is most commonly grafted onto the mandible to replace bone lost during oral cancer
surgery. Skin and blood vessels covering the fibula are grafted along with the osseous (bone)
tissue to maintain blood supply to the bone and to close the wound in the face. The remaining
tissue in the leg can be sutured together to heal around the donor site.
Tibia
The tibia, sometimes known as the shin bone, is the larger and stronger of the two lower leg
bones. It forms the knee joint with the femur and the ankle joint with the fibula and tarsus. Many
powerful muscles that move the foot and lower leg are anchored to the tibia. The support and
movement of the tibia is essential to many activities performed by the legs, including standing,
walking, running, jumping and supporting the body’s weight.
The tibia is located in the lower leg medial to the fibula, distal to the femur and proximal to the
talus of the foot. It is widest at its proximal end near the femur, where it forms the distal end of
the knee joint before tapering along its length to a much narrower bone at the ankle joint. The
proximal end is roughly flat with the smooth, concave medial and lateral condyles forming the
knee joint with the femur. Between the condyles is the intercondylar region, which includes the
tibial spine and provides attachment points for the meniscus and anterior and posterior cruciate
ligaments (ACL and PCL) of the knee. At the inferior edge of the lateral condyle is a small facet
where the tibia forms the proximal tibiofibular joint with the fibula. This joint is a planar joint,
allowing the tibia and fibula to slightly glide past each other and adjust the position of the lower
leg.
Just below the condyles on the anterior surface is the tibial tuberosity, a major bony ridge that
provides an attachment point for the patella through the patellar ligament. Extension of the lower
leg involves the contraction of the rectus femoris muscle to pull on the patella, which in turn
pulls on the tibial tuberosity. A thin, bony ridge known as the anterior crest continues distally
from the tibial tuberosity, giving the shaft of the tibia a triangular cross section. The tibial
tuberosity and anterior crest are clearly identifiable landmarks of the shin as they can be easily
palpated through the skin.
Approaching the ankle joint, the tibia widens slightly in both the medial-lateral and anteriorposterior planes. On the medial side, the tibia forms a rounded bony prominence known as the
medial malleolus. The medial malleolus forms the medial side of the ankle joint with the talus of
the foot; it can be easily located by palpation of the skin in this region. On the lateral side of the
tibia is a small recess known as the fibular notch, which forms the distal tibiofibular joint with
the fibula.
The tibia is classified as a long bone due to its long, narrow shape. Long bones are hollow in the
middle, with regions of spongy bone filling each end and solid compact bone covering their
entire structure. Spongy bone is made of tiny columns known as trabeculae that reinforce the
ends of the bone against external stresses. Red bone marrow, which produces blood cells, is
found in the holes in the spongy bone between the trabeculae.
The hollow middle of the bone, known as the medullary cavity, is filled with fat-rich yellow
bone marrow that stores energy for the body. Surrounding the medullary cavity and spongy bone
is a thick layer of compact bone that gives the bone most of its strength and mass. Compact bone
is made of cells surrounded by a matrix of hard calcium mineral and collagen protein that is both
extremely strong and flexible to resist stress.
Surrounding the compact bone is a thin, fibrous layer known as the periosteum. Periosteum is
made of a dense, fibrous connective tissue, which is continuous with the ligaments that connect
the tibia to the surrounding bones and the tendons that connect the muscles to the tibia. These
connections prevent the separation of the muscles and bones from each other.
Finally, a thin layer of hyaline cartilage covers the ends of the tibia where it forms the knee and
ankle joints. Hyaline is extremely smooth and slightly flexible, providing a smooth surface for
the joint to slide across and a shock absorber to resist impacts.
At birth, the tibia consists of two bones: a central shaft known as the diaphysis, and a thin cap
just below the knee known as the proximal epiphysis. A thin layer of hyaline cartilage separates
these two bones and allows them to move slightly relative to each other. The distal end of the
tibia at the ankle is made of hyaline cartilage at birth, but begins to ossify around age 2 to form
the distal epiphysis. Throughout childhood the diaphysis and the two epiphyses remain separated
by a thin layer of hyaline cartilage known as the epiphyseal plate or the growth plate. Cartilage
in the epiphyseal plate grows throughout childhood and adolescence and is slowly replaced by
bone. The net result of this growth is the lengthening of the tibia. At the end of adolescence, the
diaphysis and epiphyses grow into the last of the cartilage and fuse to form a single tibia. The
region where the diaphysis and epiphyses fuse is known as the metaphysis.
Lecture 5
The bones of the skull.
A collection of 22 bones, the skull protects the all-important brain and supports the other soft
tissues of the head. During fetal development, the bones of the skull form within tough, fibrous
membranes in a fetus’ head. As these bones grow throughout fetal and childhood development,
they begin to fuse together, forming a single skull. The only bone that remains separate from the
rest of the skull is the mandible, or jaw bone. Early separation of the bones provides the fetal
skull with the flexibility necessary to pass through the tight confines of the birth canal.
During childhood development, the skull bones remain somewhat separated, allowing for growth
of the brain and skull. Upon reaching maturity, our skull bones fuse to produce a rigid protective
shell for the soft nervous tissue of our brain.
Cranial Bones
Surrounding the brain is a region of the skull known as the cranium. In this region we have eight
cranial bones:
Frontal bone
Two parietal bones
Two temporal bones
Occipital bone
Ethmoid bone
Sphenoid bone
Collectively, these bones provide a solid bony wall around the brain, with only a few openings
for nerves and blood vessels. Our occipital bone contains the foramen magnum, the hole through
which the spinal cord enters the skull to attach to the brain. The occipital bone also forms the
atlanto-occipital joint with the atlas (the first cervical vertebra in our spine).
The frontal, ethmoid, and sphenoid bones contain small hollow spaces known as paranasal
sinuses. The sinuses help to reduce the weight of these bones and increase the resonance of the
voice during speech, singing, and humming.
Facial Bones
The 14 bones that support the muscles and organs of the face are collectively known as our facial
bones. The facial bones consist of:
Mandible
Two maxillae (singular: maxilla)
Vomer
Two palatine bones
Two nasal bones
Two zygomatic bones
Two nasal conchae (singular: concha)
Two lacrimal bones
The mandible, or jaw bone, is the only movable bone of the skull, forming the
temporomandibular joint with the temporal bone. The lower teeth are rooted into the mandible
while the upper teeth are rooted in the two maxillae. The maxillae also contain paranasal sinuses
like the frontal, ethmoid, and sphenoid bones of the cranium.
Teeth
The teeth are a group of hard organs found in the oral cavity. We use teeth to masticate (or chew)
food into tiny pieces. They also provide shape to the mouth and face and are important
components in producing speech.
A tooth can be divided into two main parts: the crown and root. Found above the gum line, the
crown is the enlarged region of the tooth involved in chewing. Like an actual crown, the crown
of a tooth has many ridges on its top surface to aid in the chewing of food. Below the gum line is
the region of the tooth called the root, which anchors the tooth into a bony socket known as an
alveolus.
Roots are tapered structures resembling the roots of plants, and each tooth may have between
one to three roots. The exterior surface of the root is covered in a bone-like mixture of calcium
and collagen fibers known as cementum. Cementum provides grip for the periodontal ligaments
that anchor the root to the surrounding alveolus.
Each tooth is an organ consisting of three layers: the pulp, dentin, and enamel.
The pulp of the tooth is a vascular region of soft connective tissues in the middle of the tooth.
Tiny blood vessels and nerve fibers enter the pulp through small holes in the tip of the roots to
support the hard outer structures. Stem cells known as odontoblasts form the dentin of the tooth
at the edge of the pulp.
Surrounding the pulp is the dentin, a tough, mineralized layer of tissue. Dentin is much harder
than the pulp due to the presence of collagen fibers and hydroxylapatite, a calcium phosphate
mineral that is one of the strongest materials found in nature. The structure of the dentin layer is
very porous, allowing nutrients and materials produced in the pulp to spread through the tooth.
The enamel – the white, outer layer of the crown – forms an extremely hard, nonporous cap over
the dentin. Enamel is the hardest substance in the body and is made almost exclusively of
hydroxylapatite.
Teeth are classified into four major groups: incisors, canines, premolars, and molars.
Incisors are chisel-shaped teeth found in the front of the mouth and have a flat apical surface for
cutting food into smaller bits.
Canine teeth, also known as cuspids, are sharply pointed, cone-shaped teeth that are used for
ripping tough material like meat. They flank the incisors on both sides.
Premolars (bicuspids) and molars are large, flat-surfaced teeth found in the back of the mouth.
Peaks and valleys on the flat apical surface of premolars and molars are used for chewing and
grinding food into tiny pieces.
Babies are born without teeth, but grow a temporary set of twenty deciduous teeth (eight
incisors, four canines, and eight molars) between the ages of six months and three years. Baby
teeth fill the child’s tiny jaws and allow the child to chew food while larger, stronger adult teeth
develop inside the mandible and maxilla bones. At about six years of age the deciduous teeth are
slowly shed one at a time and replaced by permanent adult teeth.
Adult teeth develop while hidden within the maxilla and mandible after the deciduous teeth have
erupted. When an adult tooth erupts, it triggers the roots of the deciduous tooth above it to
atrophy. This causes the baby tooth to become loose and eventually fall out. The new permanent
tooth slowly pushes up through the gums to replace the baby tooth. Eventually, a total of thirtytwo permanent adult teeth form and erupt. The adult teeth are arranged in both the upper and
lower jaws from the midline of the mouth as follows: central incisor, lateral incisor, canine
(cuspid), first premolar (bicuspid), second premolar, first molar, second molar, and third molar.
The first twenty-eight adult teeth are fully erupted by the age of eleven to thirteen with the third
molars, known as wisdom teeth, erupting in the back of the jaw several years later in early
adulthood. Sometimes the wisdom teeth become impacted when they grow and become wedged
at an abnormal position in the jaws and fail to erupt. In some cases there is not enough room in
the jaw to accommodate a third set of molars. In both cases the wisdom teeth are surgically
removed, as they are not needed to properly chew food.
Mastication, or chewing, is the main function of the teeth. The teeth are aligned in the jaws so
that the peaks of one tooth align with the valleys of its counterpart on the other jaw. Every bite
forces food into the interface of the teeth to be chopped, while lateral motion of the jaw is used
to grind food in the premolars and molars.
Tooth decay and cavities are important health concerns related to the teeth. The enamel that
covers the crown in each tooth can be broken down by acids produced by bacteria that live in the
mouth and assist in digestion of small bits of food. This process of enamel erosion by acids is
called decay. To prevent decay, good oral hygiene, consisting of daily brushing and flossing, is
necessary. Decay can eventually lead to cavities, also known as dental caries, where holes appear
in the enamel and expose the dentin. Cavities require medical intervention to prevent their
growth, usually resulting in the removal of the affected tissue and the filling of the cavity with a
hard material to restore the strength and function of the tooth.
Lecture 6
The muscles of the upper limb.
The muscles of the arm and hand are specifically designed to meet the body’s diverse needs of
strength, speed, and precision while completing many complex daily tasks. Activities such as
lifting weights or heavy boxes require brute strength from the muscles of the arm. Writing,
painting, and typing all require speed and precision from the same muscles. Complete athletic
activities such as boxing or throwing a ball require arm and hand muscles to be strong, fast, and
precise all at the same time.
The muscles of the upper arm are responsible for the flexion and extension of the forearm at the
elbow joint. Flexion of the forearm is achieved by a group of three muscles – the brachialis,
biceps brachii, and brachioradialis. These flexor muscles are all located on the anterior side of
the upper arm and extend from the humerus and scapula to the ulna and radius of the forearm.
Additionally, the biceps brachii operates as a supinator of the forearm by rotating the radius and
moving the palm of the hand anteriorly. On the posterior side of the upper arm is the triceps
brachii, which acts as an extensor of the forearm at the elbow and the humerus at the shoulder.
The triceps brachii, as its name indicates, has three heads whose origins are on the scapula and
humerus. These three heads merge to insert on the olecranon of the ulna.
Most of the muscles that move the wrist, hand, and fingers are located in the forearm. These thin,
strap-like muscles extend from the humerus, ulna and radius and insert into the carpals,
metacarpals, and phalanges via long tendons. The muscles on the anterior side of the forearm,
such as the flexor carpi radialis and flexor digitorum superficialis, form the flexor group that
flexes the hand at the wrist and each of the phalanges. The tendons of these muscles pass through
a small corridor in the wrist known as the carpal tunnel. Inflammation of this region caused by
repetitive stress or trauma may lead to pain and numbness known as carpal tunnel syndrome.
On the posterior side of the arm the extensor muscles, such as the extensor carpi ulnaris and
extensor digitorum, act as antagonists to the flexor muscles by extending the hand and fingers.
The extensor muscles run as long, thin straps from the humerus to the metacarpals and
phalanges. The extensors are generally somewhat weaker than the flexor muscles that they work
against, due to the relative ease in opening a hand compared to gripping something firmly.
Two special motions produced by the muscles of the forearm are the supination (anterior
rotation) and pronation (posterior rotation) of the forearm and hand. Supination is produced by
the biceps brachii of the upper arm and the supinator muscle of the forearm. Pronation is
likewise produced by the pronator teres of the forearm. Both supinator and pronator teres
muscles have their origins on the humerus and ulna and insert on opposite sides of the radius to
roll the wrist in opposite directions.
Biceps Brachii Muscle (Short head)
The short head of the biceps brachii is the shorter and medial of the two bodies that form the
biceps brachii muscle in the upper arm. Like the long head of the biceps brachii, the short head is
a flexor and supinator of the elbow joint. At the shoulder joint, the short head aids in adduction
of the humerus.
The biceps brachii muscle gets its name from its two origins, or immovable ends. The long head
arises from the supraglenoid tubercle of the scapula, while the short head arises from the
coracoid process of the scapula. From its origin, the short head passes anterior to the head and
shaft of the humerus and fuses with the long head around the middle of the humerus. The fused
biceps brachii muscle crosses the elbow joint along its anterior surface and inserts on the radius
at the radial tuberosity.
The short head of the biceps brachii acts upon the bones of the upper limb across both the elbow
and shoulder joints. Together with the long head of the biceps brachii, the short head flexes and
supinates the forearm at the elbow. The biceps is often incorrectly thought of as the prime flexor
at the elbow, when in actuality it is a synergist to the true prime flexor, the brachialis muscle.
The biceps does act as the prime supinator of the elbow and is assisted by the supinator muscle
of the forearm.
At the shoulder joint, the biceps brachii provides some help to the deltoid to flex the humerus or
move it anteriorly. The short head also provides some unique functions that are not provided by
the long head. It acts as an adductor to move the humerus toward the body’s midline and pull the
arm closer to the trunk. The short head also acts as a fixator to stabilize the shoulder joint.
The biceps brachii is a skeletal muscle, and as such is an organ made mostly of skeletal muscle
and connective tissues. Skeletal muscle tissue is made of many elongated cells known as fibers;
each fiber is wrapped in a thin fibrous connective tissue sheath known as endomysium. Many
fibers are further bundled into groups known as fascicles, which are in turn wrapped with more
fibrous connective tissue known as perimysium. Many blood vessels and nerves pass between
the fascicles to provide blood flow and communication to the skeletal muscle fibers. The
fascicles, nerves, and blood vessels are bundled yet again to form the whole biceps muscle,
wrapped in an outer layer of fibrous connective tissue known as epimysium. All of the layers of
connective tissue converge at the ends of the biceps brachii to form the tendons that bind it to the
scapula and radius. At the proximal end of the short head, the tendon merges with the periosteum
of the scapula at the coracoid process to form the origin of the short head. On the opposite end of
the biceps, the distal tendon merges with the periosteum of the radius at the radial tuberosity to
form the insertion of the biceps.
Biceps Brachii Muscle (Long head)
The long head of the biceps brachii muscle is the larger of the two muscle bodies that forms the
entire biceps brachii muscle. The biceps brachii gets its name from the Latin words for “twoheaded” and “arm” which describe its structure and location. The long and short heads of the
biceps brachii work together to achieve the same functions.
The long head extends from its origin on the superglenoid tubercle of the scapula and passes
over the head of the humerus before merging with the short head. From the merger point, the
entire muscle continues beyond the distal end of the humerus and inserts on the radial tuberosity
of the radius.
Together with the short head, the long head of the biceps brachii acts as a flexor of the arm at the
elbow joint and a supinator of the forearm. The biceps brachii, brachialis, and brachioradialis
muscles all act as flexors of the arm at the elbow, with the brachialis acting as the agonist and the
biceps brachii and brachioradialis acting as synergists. At the radioulnar joint in the forearm, the
biceps brachii acts as a supinator to turn the palm of the hand upwards.
Deltoid Muscle
The deltoid muscle is a rounded, triangular muscle located on the uppermost part of the arm and
the top of the shoulder. It is named after the Greek letter delta, which is shaped like an
equilateral triangle. The deltoid is attached by tendons to the skeleton at the clavicle
(collarbone), scapula (shoulder blade), and humerus (upper arm bone). The deltoid is widest at
the top of the shoulder and narrows to its apex as it travels down the arm. Contraction of the
deltoid muscle results in a wide range of movement of the arm at the shoulder due to its location
and the wide separation of its muscle fibers.
The deltoid has three origins: the lateral end of the clavicle, the acromion of the scapula at the
top of the shoulder, and the spine of the scapula. Each origin gives rise to its own band of muscle
fibers with the anterior band forming at the clavicle, the lateral fibers forming at the acromion,
and the posterior fibers forming at the spine of the scapula. The bands merge together as they
approach the insertion point on the deltoid tuberosity of the humerus.
The deltoid has three distinct functions that correspond to the three bands of muscle fibers.
Contraction of the anterior fibers flexes and medially rotates the arm by pulling the humerus
towards the clavicle. Flexion and medial rotation of the arm moves the arm anteriorly, as in
reaching forward or throwing a ball underhand. The lateral fibers abduct the arm by pulling the
humerus toward the acromion. Abduction of the arm results in the arm moving away from the
body, as in reaching out to the side. Contraction of the posterior fibers extends and laterally
rotates the arm by pulling the humerus toward the spine of the scapula. Extension and lateral
rotation moves the arm posteriorly, as in reaching backwards or winding up to throw a ball
underhand.
Muscles of the Hand and Wrist
The hand is an intricately complex structure whose muscles have evolved to permit an
unequalled array of movements. More than 30 individual muscles in the hand and forearm work
together to achieve these diverse movements. These muscles provide the hands with unsurpassed
flexibility, extremely precise control, and gripping strength that are necessary for activities
ranging from writing and typing to producing music and gripping a ball in sports.
Six flexor muscles are found in the anterior or palmar side of the forearm, These long, thin
muscles extend through the wrist via tendons to insert into the bones of the wrist, palm, and
fingers. The flexor carpus radialis, flexor carpus ulnaris, and palmaris longus muscles all have
their origins on the humerus of the upper arm and insert into the carpals and metacarpals on the
palmar side of the hand. Working together these muscles flex the hand at the wrist. The flexor
carpus radialis also abducts the hand toward the thumb side while the flexor carpus ulnaris
adducts the hand toward the little finger side. The other three flexor muscles - flexor digitorum
superficialis, flexor digitorum profundus, and flexor pollicis longus - extend from the bones of
the arm and forearm and insert into the phalanges of the hand to flex the fingers and thumb,
respectively. The tendons of the flexor muscles and the median nerve pass through a bony
passage in the wrist known as the carpal tunnel. Repetitive motion of the flexor tendons can
cause them to become inflamed and impinge the median nerve, leading to pain, numbness and
tingling known as carpal tunnel syndrome.
Nine extensor muscles found in the posterior side of the forearm extend the hand and fingers.
Just like the flexor muscles of the forearm that these muscles work against, each extensor muscle
is long and thin and extends into the hand via long tendons. The extensor carpi radialis longus,
extensor carpi radialis brevis, and extensor carpi ulnaris muscles all extend the hand at the wrist,
with the radialis muscles abducting the hand and the ulnaris adducting it. Inserting into the
phalanges of the fingers, the extensor pollicis brevis (thumb), extensor pollicis longus (thumb),
extensor indicis (index finger), extensor digitorum (middle and ring fingers), and extensor digiti
minimi (little finger) muscles extend the digits to open the hand. The abductor pollicis longus
muscle has the dual role of both abducting the thumb and assisting with the extension of the
thumb.
Several muscles in the forearm control the pivoting of the radius around the ulna that rotates the
wrist and hand. The supinator muscle inserts on the radius and supinates the hand by turning the
palm upwards or toward the front of the body. Working as antagonists to the supinator, the
pronator teres and pronator quadratus muscles pronate the hand by turning it posteriorly or palm
side down. The pronator muscles both insert on the opposite side of the radius from the supinator
so that each set of muscles can rotate the radius in opposite directions.
The muscles of the hand can be broken down into three main regions: the thenar(lateral or
thumb side of the palm), hypothenar (medial or little finger side of the palm)
and intermediate (middle of the hand) muscles.
The thenar muscles, which form the bulge of muscles evident at the base of the thumb, are
essential to the hand's flexibility and gripping ability. One of these muscles, the opponens
pollicis, moves the thumb across the hand to oppose the other fingers, allowing us to pinch a
small object between the thumb and finger to pick it up. The abductor pollicis brevis and
adductor pollicis work as antagonists to abduct and adduct the thumb respectively. Working with
the flexor pollicis longus of the forearm, the flexor pollicis brevis flexes the thumb to grip
objects or make a fist.
The three hypothenar muscles form a small bulge of muscles on the medial side of the palm
opposite from the thenar muscles. These muscles work together to provide a wide range of
motion to the little finger. The abductor digiti minimi abducts the little finger as in spreading the
fingers apart, while the flexor digiti minimi flexes the little finger. The opponens digiti minimi
rotates the fifth metacarpal and pulls it anteriorly during opposition with the thumb or while
cupping the palm of the hand.
Found in the middle of the palm between the metacarpals, the intermediate or midpalmar
muscles collectively move the second through fifth metacarpals and the second through fifth
phalanges in a variety of ways. The four lumbrical muscles, which get their names from their
worm-like shapes, attach to the tendons the flexor digitorum profundus and the extensors of the
phalanges to flex the base of the digits at the metacarpophalangeal joints while extending the
fingers at the interphalangeal joints. Each lumbrical muscle connects to just one of the digits and
causes the digit to flex at its base while remaining straight throughout its length. The four palmar
interossei muscles extend from the metacarpals and insert on each of the phalanges to adduct the
fingers and pull them together. Working as antagonists to these muscles are the four dorsal
interossei muscles that abduct, or spread apart, the fingers.
Lecture 7
The muscles of the lower limb.
Muscles of the Hip
The hip joint is one of the most flexible joints in the entire human body. The many muscles of
the hip provide movement, strength, and stability to the hip joint and the bones of the hip and
thigh. These muscles can be grouped based upon their location and function. The four groups are
the anterior group, the posterior group, adductor group, and finally the abductor group.
The anterior muscle group features muscles that flex (bend) the thigh at the hip.
These muscles include:
The iliopsoas group, which consists of the psoas major and iliacus muscles.
The quadriceps femoris group, which consists of the rectus femoris, vastus intermedius, vastus
lateralis, and vastus medialis.
Sitting up, kicking a ball, and lifting a leg to climb a ladder are all activities that involve
contraction of the anterior muscle group.
The posterior muscle group is made up of the muscles that extend (straighten) the thigh at the
hip. These muscles include the gluteus maximus muscle (the largest muscle in the body) and the
hamstrings group, which consists of the biceps femoris, semimembranosus, and semitendinosus
muscles. Climbing stairs, standing, walking, and running are all activities that require strong
contractions from the posterior muscle group to extend the leg.
The adductor muscle group, also known as the groin muscles, is a group located on the medial
side of the thigh. These muscles move the thigh toward the body’s midline. Included in this
group are the adductor longus, adductor brevis, adductor magnus, pectineus, and gracilis
muscles. Overstretching of these muscles caused by rapid lateral movement the thigh can lead to
a groin pull, a common sports injury.
The abductor muscle group is located on the lateral side of the thigh and moves the thigh away
from the body’s midline. These muscles include the piriformis, superior gemellus, inferior
gemellus, tensor fasciae latae, sartorius, gluteus medius, and gluteus minimus muscles.
Spreading the legs to do a split is an example of a movement involving the abductor muscles.
Vastus lateralis muscle
The vastus lateralis muscle is the largest of the four muscles that make up the quadriceps femoris
group. Like the other muscles in the quadriceps group, is an extensor of the leg at the knee. Its
name means “huge lateral” due to its enormous size and location on the lateral side of the thigh.
The vastus lateralis muscle arises from widespread origins on the greater trochanter of the femur
and on the linea aspera on the posterior side of the femur.
From its origins, the muscle fibers of the vastus lateralis extend anteriorly and distally to merge
with the other three muscles of the quadriceps, forming the quadriceps tendon. From this point,
the quadriceps tendon continues distally to insert on the patella.
Contraction of the vastus lateralis draws the patella towards the anterior surface of the femur.
The patellar ligament connects the patella to the tibial tuberosity on the anterior surface of the
tibia, so that anterior movement of the patella also draws the tibia anteriorly. The net result of the
contraction of the vastus lateralis is therefore extension of the leg at the knee.
Like all skeletal muscles, the vastus lateralis is made of many skeletal muscle fibers (cells)
surrounded by connective tissue. A layer of fibrous connective tissue known as the endomysium
wraps each muscle fiber. Another layer of connective tissue known as the perimysium further
wraps groups of muscle fibers, known as fascicles. Blood vessels and nerves pass through the
spaces between fascicles to provide nutrients, oxygen, and nerve signals to the muscle fibers. All
of the fascicles, vascular tissue, and nervous tissue in the muscle are wrapped up in the
epimysium, which forms the outer layer of the muscle. At the ends of the muscle, the
endomysium, perimysium, and epimysium continue beyond the ends of the muscle fibers to form
the tendons that bind the vastus lateralis to the femur and patella.
Vastus medialis muscle
The vastus medialis muscle is one of the quadriceps femoris muscle's four muscle divisions. It
occupies the sides and front of the thigh and its function is being the primary extensor of the
knee.
Rectus femoris muscle
The rectus femoris muscle is one part of the large, fleshy group of leg muscles called the
quadriceps femoris. This muscle grouping occupies the front and sides of the thigh and is
primary extensor of the knee. It is composed of four parts - rectus femoris, vastus lateralis, vastus
medialis, and vastus intermedius. These parts connect the ilium and femur to a common patellar
tendon, which passes over the front of the knee and attaches to the patella (knee cap). This
tendon then continues as the patellar ligament to the tibia (lower leg bone).
Muscles of the knee
The muscles of the knee include the quadriceps, hamstrings, and the muscles of the calf. These
muscles work in groups to flex, extend and stabilize the knee joint. These motions of the knee
allow the body to perform such important movements as walking, running, kicking, and jumping.
Extending along the anterior surface of the thigh are the four muscles of the quadriceps femoris
group (vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris). These large
muscles originate in the ilium and femur and insert on the tibia
Contraction of the quadriceps group extends the leg at the knee and flexes the thigh at the hip.
The hamstring muscle group extends across the posterior surface of the thigh from the ischium of
the pelvis to the tibia of the lower leg. Three individual muscles form the hamstrings group:
biceps femoris, semitendinosus, and semimembranosus. The hamstrings work together to flex
the leg at the knee.
In the calf region of the leg, the gastrocnemius muscle extends from the distal end of the femur
through the calcaneal (Achilles) tendon to the calcaneus of the heel. The gastrocnemius forms
the posterior muscular wall of the knee and acts as a flexor of the knee and plantar flexor of the
foot.
Some other muscles that assist with the movements of the knee include the tensor fasciae latae,
popliteus and the articularis genus muscles. The tensor fasciae latae contracts the iliotibial band
of fibrous connective tissue that helps to stabilize the femur, tibia, and thigh muscles. Flexion of
the knee requires some slight rotation of the tibia, which is provided by the contraction of the
popliteus muscle. The tiny articularis genus muscle elevates the suprapatellar bursa and capsule
of the knee joint to prevent pinching of this soft tissue during extension of the leg at the knee.
Lecture 8
Muscles of the trunk, head and neck.
The muscles of the head and neck perform many important tasks, including movement of the
head and neck, chewing and swallowing, speech, facial expressions, and movement of the eyes.
These diverse tasks require both strong, forceful movements and some of the fastest, finest, and
most delicate adjustments in the entire human body.
The muscles of the face are unique among groups of muscles in the body. While most muscles
connect to and move only bones, facial muscles mostly connect bones to skin.
These muscles, including the zygomaticus major and orbicularis oris, pull on the skin to produce
a seemingly infinite number of facial expressions and to move the lips and cheeks during speech
and eating.
Producing the body’s ability to close the mouth, bite, and chew food, the muscles of mastication
move the mandible relative to the rest of the skull. These muscles, including the masseter and
temporalis, elevate the jaw forcefully during chewing and gently during speech.
An extensive complement of tightly interlaced muscles allows the tongue a range of complex
movements for chewing and swallowing, as well as the important function of producing speech.
Of these, four extrinsic muscle sets (connecting the tongue to the surrounding bones) move the
tongue in virtually any direction, with fine shape changes (such as for speech) the province of the
four intrinsic tongue muscles.
As for the eye, six extrinsic eye muscles provide superior, inferior, lateral, and medial motion, as
well as rotation of the eyeball. These muscles produce extremely fine movements almost
constantly throughout the day with tremendous speed and accuracy. Located inside the eye, the
intrinsic eye muscles work tirelessly to dilate the pupils and focus the lens of the eye to produce
clear vision.
Even the middle ear takes part in the muscular system of the head and neck. In fact, the smallest
muscle of the skeleton is the stapedius, which measures around 1 millimeter (1/20th of an inch)
in length. The muscles of the middle ear contract to dampen the amplitude of vibrations from the
eardrum to the inner ear.
The neck muscles, including the sternocleidomastoid and the trapezius, are responsible for the
gross motor movement in the muscular system of the head and neck. They move the head in
every direction, pulling the skull and jaw towards the shoulders, spine, and scapula. Working in
pairs on the left and right sides of the body, these muscles control the flexion and extension of
the head and neck. Working individually, these muscles rotate the head or flex the neck laterally
to the left or right. Neck muscles contract to adjust the posture of the head throughout the course
of a day and have some of the greatest endurance of any muscles in the body.
Muscles of the chest and upper back
The muscles of the chest and upper back occupy the thoracic region of the body inferior to the
neck and superior to the abdominal region and include the muscles of the shoulders. These
important muscles control many motions that involve moving the arms and head – such as
throwing a ball, looking up at the sky, and raising your hand. Breathing, a vital body function, is
also controlled by the muscles connected to the ribs of the chest and upper back.
The bones of the pectoral girdles, consisting of the clavicle (collar bone) and scapula (shoulder
blade), greatly increase the range of motion possible in the shoulder region beyond what would
be possible with the shoulder joint alone. The muscles of this region both allow for this range of
motion and contract to stabilize this region and prevent any extraneous motion. On the anterior
side of the thoracic region, the pectoralis minor and serratus anterior muscles originate on the
anterior ribs and insert on the scapula. These muscles work together to move the scapula
anteriorly and laterally during pushing, throwing, or punching motions. In the upper back region,
the trapezius, rhomboid major, and levator scapulae muscles anchor the scapula and clavicle to
the spines of several vertebrae and the occipital bone of the skull. When these muscles contract,
they elevate the pectoral girdle (as in shrugging) and move the scapula medially and posteriorly
toward the center of the back (as in rowing). The trapezius also contracts along the back of the
neck to extend the head at the neck and hold it upright throughout the day.
Nine muscles of the chest and upper back are used to move the humerus (upper arm bone). The
coracobrachialis and pectoralis major muscles connect the humerus anteriorly to the scapula and
ribs, flexing and adducting the arm toward the front of the body when you reach forward to grab
an object. On the posterior side of the arm the teres major and latissimus dorsi extend and adduct
the arm towards the scapula and vertebra when you pull an object down off of a shelf above your
head. The deltoid and supraspinatus muscles run superiorly between the scapula and humerus to
abduct as well as flex and extend the arm. These muscles allow us to raise our arm in the air or
swing the arm as in throwing a ball underhand. Rotation of the humerus is achieved by the
actions of the subscapularis, infraspinatus, and teres minor muscles that run from the scapula to
the humerus. These three rotator muscles, along with the supraspinatus, end in wide tendons that
completely surround the head of the humerus and form a structure known as the rotator cuff,
which holds the humerus in place and prevents dislocation. Rotation of the humerus by the
rotator cuff muscles is necessary for activities such as throwing a ball overhand or swinging a
hammer.
In addition to moving the arm and pectoral girdle, muscles of the chest and upper back work
together as a group to support the vital process of breathing. The diaphragm is a strong, thin,
dome-shaped muscle that spans the entire inferior border of the rib cage, separating the thoracic
cavity from the abdominal cavity. Contraction of the diaphragm causes it to descend towards the
abdomen, increasing the space of the thoracic cavity and expanding the lungs, filling them with
air. Small muscles running between the ribs, known as the external intercostal muscles, lift the
ribs during deep breathing to further expand the chest and lungs and provide even more air to the
body. During exhalation, the diaphragm relaxes to decrease the volume of the thoracic cavity,
forcing air out of the lungs. Additional air can be forced out of the lungs during deep exhalation
by contraction of the internal intercostal muscles, which push the ribs together and help
compress the thoracic cavity.
Muscles of the abdomen, lower back, and pelvis
The muscles of the abdomen, lower back, and pelvis are separated from those of the chest by the
muscular wall of the diaphragm, the critical breathing muscle. Lying exposed between the
protective bones of the superiorly located ribs and the inferiorly located pelvic girdle, the
muscles of this region play a critical role in protecting the delicate vital organs within the
abdominal cavity. In addition to providing protection, these core muscles also function in
movement of the trunk, posture, and stability of the entire body.
Extending across the anterior surface of the body from the superior border of the pelvis to the
inferior border of the ribcage are the muscles of the abdominal wall, including the transverse and
rectus abdominis and the internal and external obliques. Working as a team, these muscles
contract to flex, laterally bend, and rotate the torso. The abdominal muscles also play a major
role in the posture and stability to the body and compress the organs of the abdominal cavity
during various activities such as breathing and defecation.
The muscles of the lower back, including the erector spinae and quadratus lumborum muscles,
contract to extend and laterally bend the vertebral column. These muscles provide posture and
stability to the body by holding the vertebral column erect and adjusting the position of the body
to maintain balance.
Attached to the pelvis are muscles of the buttocks, the lower back, and the thighs. These
muscles, including the gluteus maximus and the hamstrings, extend the thigh at the hip in
support of the body's weight and propulsion. Other pelvic muscles, such as the psoas major and
iliacus, serve as flexors of the trunk and thigh at the hip joint and laterally rotate the hip as well.
Lecture 9
Splanchnology. The doctrine of the heart and blood vessels. The lymphatic system.
The cardiovascular system consists of the heart, blood vessels, and the approximately 5 liters of
blood that the blood vessels transport. Responsible for transporting oxygen, nutrients, hormones,
and cellular waste products throughout the body, the cardiovascular system is powered by the
body’s hardest-working organ — the heart, which is only about the size of a closed fist. Even at
rest, the average heart easily pumps over 5 liters of blood throughout the body every minute.
The Heart
The heart is a muscular pumping organ located medial to the lungs along the body’s midline in
the thoracic region. The bottom tip of the heart, known as its apex, is turned to the left, so that
about 2/3 of the heart is located on the body’s left side with the other 1/3 on right. The top of the
heart, known as the heart’s base, connects to the great blood vessels of the body: the aorta, vena
cava, pulmonary trunk, and pulmonary veins.
Circulatory Loops
There are 2 primary circulatory loops in the human body: the pulmonary circulation loopand
the systemic circulation loop.
Pulmonary circulation transports deoxygenated blood from the right side of the heart to
the lungs, where the blood picks up oxygen and returns to the left side of the heart. The pumping
chambers of the heart that support the pulmonary circulation loop are the right atrium and right
ventricle.
Systemic circulation carries highly oxygenated blood from the left side of the heart to all of the
tissues of the body (with the exception of the heart and lungs). Systemic circulation removes
wastes from body tissues and returns deoxygenated blood to the right side of the heart. The left
atrium and left ventricle of the heart are the pumping chambers for the systemic circulation loop.
Blood
Vessels
Blood vessels are the body’s highways that allow blood to flow quickly and efficiently from the
heart to every region of the body and back again. The size of blood vessels corresponds with the
amount of blood that passes through the vessel. All blood vessels contain a hollow area called
the lumen through which blood is able to flow. Around the lumen is the wall of the vessel, which
may be thin in the case of capillaries or very thick in the case of arteries.
All blood vessels are lined with a thin layer of simple squamous epithelium known as the
endothelium that keeps blood cells inside of the blood vessels and prevents clots from forming.
The endothelium lines the entire circulatory system, all the way to the interior of the heart, where
it is called the endocardium.
There are three major types of blood vessels: arteries, capillaries and veins. Blood vessels are
often named after either the region of the body through which they carry blood or for nearby
structures. For example, the brachiocephalic artery carries blood into the brachial (arm) and
cephalic (head) regions. One of its branches, the subclavian artery, runs under the clavicle; hence
the name subclavian. The subclavian artery runs into the axillary region where it becomes known
as the axillary artery.
Arteries and Arterioles: Arteries are blood vessels that carry blood away from the heart. Blood
carried by arteries is usually highly oxygenated, having just left the lungs on its way to the
body’s tissues. The pulmonary trunk and arteries of the pulmonary circulation loop provide an
exception to this rule – these arteries carry deoxygenated blood from the heart to the lungs to be
oxygenated.
Arteries face high levels of blood pressure as they carry blood being pushed from the heart under
great force. To withstand this pressure, the walls of the arteries are thicker, more elastic, and
more muscular than those of other vessels. The largest arteries of the body contain a high
percentage of elastic tissue that allows them to stretch and accommodate the pressure of the
heart.
Smaller arteries are more muscular in the structure of their walls. The smooth muscles of the
arterial walls of these smaller arteries contract or expand to regulate the flow of blood through
their lumen. In this way, the body controls how much blood flows to different parts of the body
under varying circumstances. The regulation of blood flow also affects blood pressure, as smaller
arteries give blood less area to flow through and therefore increases the pressure of the blood on
arterial
walls.
Arterioles are narrower arteries that branch off from the ends of arteries and carry blood to
capillaries. They face much lower blood pressures than arteries due to their greater number,
decreased blood volume, and distance from the direct pressure of the heart. Thus arteriole walls
are much thinner than those of arteries. Arterioles, like arteries, are able to use smooth muscle to
control their aperture and regulate blood flow and blood pressure.
Capillaries: Capillaries are the smallest and thinnest of the blood vessels in the body and also the
most common. They can be found running throughout almost every tissue of the body and border
the edges of the body’s avascular tissues. Capillaries connect to arterioles on one end and
venules on the other.
Capillaries carry blood very close to the cells of the tissues of the body in order to exchange
gases, nutrients, and waste products. The walls of capillaries consist of only a thin layer of
endothelium so that there is the minimum amount of structure possible between the blood and
the tissues. The endothelium acts as a filter to keep blood cells inside of the vessels while
allowing liquids, dissolved gases, and other chemicals to diffuse along their concentration
gradients into or out of tissues.
Precapillary sphincters are bands of smooth muscle found at the arteriole ends of capillaries.
These sphincters regulate blood flow into the capillaries. Since there is a limited supply of blood,
and not all tissues have the same energy and oxygen requirements, the precapillary sphincters
reduce blood flow to inactive tissues and allow free flow into active tissues.
Veins and Venules: Veins are the large return vessels of the body and act as the blood return
counterparts of arteries. Because the arteries, arterioles, and capillaries absorb most of the force
of the heart’s contractions, veins and venules are subjected to very low blood pressures. This
lack of pressure allows the walls of veins to be much thinner, less elastic, and less muscular than
the walls of arteries.
Veins rely on gravity, inertia, and the force of skeletal muscle contractions to help push blood
back to the heart. To facilitate the movement of blood, some veins contain many one-way valves
that prevent blood from flowing away from the heart. As skeletal muscles in the body contract,
they squeeze nearby veins and push blood through valves closer to the heart.
When the muscle relaxes, the valve traps the blood until another contraction pushes the blood
closer to the heart. Venules are similar to arterioles as they are small vessels that connect
capillaries, but unlike arterioles, venules connect to veins instead of arteries. Venules pick up
blood from many capillaries and deposit it into larger veins for transport back to the heart.
Coronary Circulation
The heart has its own set of blood vessels that provide the myocardium with the oxygen and
nutrients necessary to pump blood throughout the body. The left and right coronary arteries
branch off from the aorta and provide blood to the left and right sides of the heart. The coronary
sinus is a vein on the posterior side of the heart that returns deoxygenated blood from the
myocardium to the vena cava.
Hepatic Portal Circulation
The veins of the stomach and intestines perform a unique function: instead of carrying blood
directly back to the heart, they carry blood to the liver through the hepatic portal vein. Blood
leaving the digestive organs is rich in nutrients and other chemicals absorbed from food.
The liver removes toxins, stores sugars, and processes the products of digestion before they
reach the other body tissues. Blood from the liver then returns to the heart through the inferior
vena cava.
Blood
The average human body contains about 4 to 5 liters of blood. As a liquid connective tissue, it
transports many substances through the body and helps to maintain homeostasis of nutrients,
wastes, and gases. Blood is made up of red blood cells, white blood cells, platelets, and liquid
plasma.
Red Blood Cells: Red blood cells, also known as erythrocytes, are by far the most common type
of blood cell and make up about 45% of blood volume. Erythrocytes are produced inside of red
bone marrow from stem cells at the astonishing rate of about 2 million cells every second. The
shape of erythrocytes is biconcave—disks with a concave curve on both sides of the disk so that
the center of an erythrocyte is its thinnest part. The unique shape of erythrocytes gives these cells
a high surface area to volume ratio and allows them to fold to fit into thin capillaries. Immature
erythrocytes have a nucleus that is ejected from the cell when it reaches maturity to provide it
with its unique shape and flexibility. The lack of a nucleus means that red blood cells contain no
DNA
and
are
not
able
to
repair
themselves
once
damaged.
Erythrocytes transport oxygen in the blood through the red pigment hemoglobin. Hemoglobin
contains iron and proteins joined to greatly increase the oxygen carrying capacity of
erythrocytes. The high surface area to volume ratio of erythrocytes allows oxygen to be easily
transferred into the cell in the lungs and out of the cell in the capillaries of the systemic tissues.
White Blood Cells: White blood cells, also known as leukocytes, make up a very small
percentage of the total number of cells in the bloodstream, but have important functions in the
body’s immune system. There are two major classes of white blood cells: granular leukocytes
and agranular leukocytes.
Granular Leukocytes: The three types of granular leukocytes are neutrophils, eosinophils, and
basophils. Each type of granular leukocyte is classified by the presence of chemical-filled
vesicles in their cytoplasm that give them their function. Neutrophils contain digestive enzymes
that neutralize bacteria that invade the body. Eosinophils contain digestive enzymes specialized
for digesting viruses that have been bound to by antibodies in the blood. Basophils release
histamine to intensify allergic reactions and help protect the body from parasites.
Agranular Leukocytes: The two major classes of agranular leukocytes are lymphocytes and
monocytes. Lymphocytes include T cells and natural killer cells that fight off viral infections and
B cells that produce antibodies against infections by pathogens. Monocytes develop into cells
called macrophages that engulf and ingest pathogens and the dead cells from wounds or
infections.
Platelets : Also known as thrombocytes, platelets are small cell fragments responsible for the
clotting of blood and the formation of scabs. Platelets form in the red bone marrow from large
megakaryocyte cells that periodically rupture and release thousands of pieces of membrane that
become the platelets. Platelets do not contain a nucleus and only survive in the body for up to a
week before macrophages capture and digest them.
Plasma: Plasma is the non-cellular or liquid portion of the blood that makes up about 55% of the
blood’s volume. Plasma is a mixture of water, proteins, and dissolved substances. Around 90%
of plasma is made of water, although the exact percentage varies depending upon the hydration
levels of the individual. Theproteins within plasma include antibodies and albumins. Antibodies
are part of the immune system and bind to antigens on the surface of pathogens that infect the
body. Albumins help maintain the body’s osmotic balance by providing an isotonic solution for
the cells of the body. Many different substances can be found dissolved in the plasma, including
glucose, oxygen, carbon dioxide, electrolytes, nutrients, and cellular waste products. The plasma
functions as a transportation medium for these substances as they move throughout the body.
Functions of the Cardiovascular System
The cardiovascular system has three major functions: transportation of materials, protection from
pathogens, and regulation of the body’s homeostasis.
Transportation: The cardiovascular system transports blood to almost all of the body’s tissues.
The blood delivers essential nutrients and oxygen and removes wastes and carbon dioxide to be
processed or removed from the body. Hormones are transported throughout the body via the
blood’s liquid plasma.
Protection: The cardiovascular system protects the body through its white blood cells. White
blood cells clean up cellular debris and fight pathogens that have entered the body. Platelets and
red blood cells form scabs to seal wounds and prevent pathogens from entering the body and
liquids from leaking out. Blood also carries antibodies that provide specific immunity to
pathogens that the body has previously been exposed to or has been vaccinated against.
Regulation: The cardiovascular system is instrumental in the body’s ability to maintain
homeostatic control of several internal conditions. Blood vessels help maintain a stable body
temperature by controlling the blood flow to the surface of the skin. Blood vessels near the
skin’s surface open during times of overheating to allow hot blood to dump its heat into the
body’s surroundings. In the case of hypothermia, these blood vessels constrict to keep blood
flowing only to vital organs in the body’s core. Blood also helps balance the body’s pH due to
the presence of bicarbonate ions, which act as a buffer solution. Finally, the albumins in blood
plasma help to balance the osmotic concentration of the body’s cells by maintaining an isotonic
environment.
The Circulatory Pump
The heart is a four-chambered “double pump,” where each side (left and right) operates as a
separate pump. The left and right sides of the heart are separated by a muscular wall of tissue
known as the septum of the heart. The right side of the heart receives deoxygenated blood from
the systemic veins and pumps it to the lungs for oxygenation. The left side of the heart receives
oxygenated blood from the lungs and pumps it through the systemic arteries to the tissues of the
body. Each heartbeat results in the simultaneous pumping of both sides of the heart, making the
heart a very efficient pump.
Regulation of Blood Pressure
Several functions of the cardiovascular system can control blood pressure. Certain hormones
along with autonomic nerve signals from the brain affect the rate and strength of heart
contractions. Greater contractile force and heart rate lead to an increase in blood pressure. Blood
vessels can also affect blood pressure. Vasoconstriction decreases the diameter of an artery by
contracting the smooth muscle in the arterial wall. The sympathetic (fight or flight) division of
the autonomic nervous system causes vasoconstriction, which leads to increases in blood
pressure and decreases in blood flow in the constricted region. Vasodilation is the expansion of
an artery as the smooth muscle in the arterial wall relaxes after the fight-or-flight response wears
off or under the effect of certain hormones or chemicals in the blood. The volume of blood in the
body also affects blood pressure. A higher volume of blood in the body raises blood pressure by
increasing the amount of blood pumped by each heartbeat. Thicker, more viscous blood from
clotting disorders can also raise blood pressure.
Hemostasis
Hemostasis, or the clotting of blood and formation of scabs, is managed by the platelets of the
blood. Platelets normally remain inactive in the blood until they reach damaged tissue or leak out
of the blood vessels through a wound. Once active, platelets change into a spiny ball shape and
become very sticky in order to latch on to damaged tissues. Platelets next release chemical
clotting factors and begin to produce the protein fibrin to act as structure for the blood clot.
Platelets also begin sticking together to form a platelet plug. The platelet plug will serve as a
temporary seal to keep blood in the vessel and foreign material out of the vessel until the cells of
the blood vessel can repair the damage to the vessel wall.
Immune and Lymphatic System
The immune and lymphatic systems are two closely related organ systems that share several
organs and physiological functions. The immune system is our body’s defense system against
infectious pathogenic viruses, bacteria, and fungi as well as parasitic animals and protists. The
immune system works to keep these harmful agents out of the body and attacks those that
manage to enter.
The lymphatic system is a system of capillaries, vessels, nodes.
and other organs that transport a fluid called lymph from the tissues as it returns to the
bloodstream. The lymphatic tissue of these organs filters and cleans the lymph of any debris,
abnormal cells, or pathogens. The lymphatic system also transports fatty acids from
the intestines to the circulatory system.
Red Bone Marrow and Leukocytes
Red bone marrow is a highly vascular tissue found in the spaces between trabeculae of spongy
bone. It is mostly found in the ends of long bones and in the flat bones of the body. Red bone
marrow is a hematopoietic tissue containing many stem cells that produce blood cells. All of the
leukocytes, or white blood cells, of the immune system are produced by red bone marrow.
Leukocytes can be further broken down into 2 groups based upon the type of stem cells that
produces them: myeloid stem cells and lymphoid stem cells.
Myeloid stem cells produce monocytes and the granular leukocytes—eosinophils, basophils, and
neutrophils.
Monocytes. Monocytes are agranular leukocytes that can form 2 types of cells: macrophages and
dendritic
cells.
Macrophages. Monocytes respond slowly to infection and once present at the site of infection,
develop into macrophages. Macrophages are phagocytes able to consume pathogens, destroyed
cells, and debris by phagocytosis. As such, they have a role in both preventing infection as well
as cleaning up the aftermath of an infection.
Dendritic cells. Monocytes also develop into dendritic cells in healthy tissues of the skin and
mucous membranes. Dendritic cells are responsible for the detection of pathogenic antigens
which are used to activate T cells and B cells.
Granular Leukocytes
Eosinophils. Eosinophils are granular leukocytes that reduce allergic inflammation and help the
body fight off parasites.
Basophils. Basophils are granular leukocytes that trigger inflammation by releasing the
chemicals heparin and histamine. Basophils are active in producing inflammation during allergic
reactions and parasitic infections.
Neutrophils. Neutrophils are granular leukocytes that act as the first responders to the site of an
infection. Neutrophils use chemotaxis to detect chemicals produced by infectious agents and
quickly move to the site of infection. Once there, neutrophils ingest the pathogens via
phagocytosis and release chemicals to trap and kill the pathogens.
Lymphoid stem cells produce T lymphocytes and B lymphocytes.
T lymphocytes. T lymphocytes, also commonly known as T cells, are cells involved in fighting
specific pathogens in the body. T cells may act as helpers of other immune cells or attack
pathogens directly. After an infection, memory T cells persist in the body to provide a faster
reaction
to
subsequent
infection
by
pathogens
expressing
the
same
antigen.
B lymphocytes. B lymphocytes, also commonly known as B cells, are also cells involved in
fighting specific pathogens in the body. Once B cells have been activated by contact with a
pathogen, they form plasma cells that produce antibodies. Antibodies then neutralize the
pathogens until other immune cells can destroy them. After an infection, memory B cells persist
in the body to quickly produce antibodies to subsequent infection by pathogens expressing the
same
antigen.
Natural killer cells. Natural killer cells, also known as NK cells, are lymphocytes that are able
to respond to a wide range of pathogens and cancerous cells. NK cells travel within the blood
and are found in the lymph nodes, spleen, and red bone marrow where they fight most types of
infection.
Lymph
Capillaries
As blood passes through the tissues of the body, it enters thin-walled capillaries to facilitate
diffusion of nutrients, gases, and wastes. Blood plasma also diffuses through the thin capillary
walls and penetrates into the spaces between the cells of the tissues. Some of this plasma diffuses
back into the blood of the capillaries, but a considerable portion becomes embedded in the
tissues as interstitial fluid. To prevent the accumulation of excess fluids, small dead-end vessels
called lymphatic capillaries extend into the tissues to absorb fluids and return them to circulation.
Lymph
The interstitial fluid picked up by lymphatic capillaries is known as lymph. Lymph very closely
resembles the plasma found in the veins: it is a mixture of about 90% water and 10% solutes
such as proteins, cellular waste products, dissolved gases, and hormones. Lymph may also
contain bacterial cells that are picked up from diseased tissues and the white blood cells that
fight these pathogens. In late-stage cancer patients, lymph often contains cancerous cells that
have metastasized from tumors and may form new tumors within the lymphatic system. A
special type of lymph, known as chyle, is produced in thedigestive system as lymph absorbs
triglycerides from the intestinal villi. Due to the presence of triglycerides, chyle has a milky
white coloration to it.
Lymphatic Vessels
Lymphatic capillaries merge together into larger lymphatic vessels to carry lymph through the
body. The structure of lymphatic vessels closely resembles that of veins: they both have thin
walls and many check valves due to their shared function of carrying fluids under low pressure.
Lymph is transported through lymphatic vessels by the skeletal muscle pump—contractions of
skeletal muscles constrict the vessels to push the fluid forward. Check valves prevent the fluid
from flowing back toward the lymphatic capillaries.
Lymph Nodes
Lymph nodes are small, kidney-shaped organs of the lymphatic system. There are several
hundred lymph nodes found mostly throughout the thorax and abdomen of the body with the
highest concentrations in the axillary (armpit) and inguinal (groin) regions. The outside of each
lymph node is made of a dense fibrous connective tissue capsule. Inside the capsule, the lymph
node is filled with reticular tissue containing many lymphocytes and macrophages. The lymph
nodes function as filters of lymph that enters from several afferent lymph vessels. The reticular
fibers of the lymph node act as a net to catch any debris or cells that are present in the lymph.
Macrophages and lymphocytes attack and kill any microbes caught in the reticular fibers.
Efferent lymph vessels then carry the filtered lymph out of the lymph node and towards the
lymphatic ducts.
Lymphatic Ducts
All of the lymphatic vessels of the body carry lymph toward the 2 lymphatic ducts: the thoracic
duct and the right lymphatic ducts. These ducts serve to return lymph back to the venous blood
supply so that it can be circulated as plasma.
Thoracic duct. The thoracic duct connects the lymphatic vessels of the legs, abdomen, left arm,
and the left side of the head, neck, and thorax to the left brachiocephalic vein.
Right lymphatic duct. The right lymphatic duct connects the lymphatic vessels of the right
arm and the right side of the head, neck, and thorax to the right brachiocephalic vein.
Lymphatic Nodules
Outside of the system of lymphatic vessels and lymph nodes, there are masses of nonencapsulated lymphatic tissue known as lymphatic nodules. The lymphatic nodules are
associated with the mucous membranes of the body, where they work to protect the body from
pathogens entering the body through open body cavities.
Tonsils. There are 5 tonsils in the body—2 lingual, 2 palatine, and 1 pharyngeal. The lingual
tonsils are located at the posterior root of the tongue near the pharynx. The palatine tonsils are
in the posterior region of the mouth near the pharynx. The pharyngeal pharynx, also known as
the adenoid, is found in the nasopharynx at the posterior end of the nasal cavity. The tonsils
contain many T and B cells to protect the body from inhaled or ingested substances. The tonsils
often become inflamed in response to an infection.
Peyer’s patches. Peyer’s patches are small masses of lymphatic tissue found in the ileum of
the small intestine. Peyer’s patches contain T and B cells that monitor the contents of the
intestinal lumen for pathogens. Once the antigens of a pathogen are detected, the T and B cells
spread and prepare the body to fight a possible infection.
Spleen. The spleen is a flattened, oval-shaped organ located in the upper left quadrant of the
abdomen lateral to the stomach. The spleen is made up of a dense fibrous connective tissue
capsule filled with regions known as red and white pulp. Red pulp, which makes up most of the
spleen’s mass, is so named because it contains many sinuses that filter the blood. Red pulp
contains reticular tissues whose fibers filter worn out or damaged red blood cells from the blood.
Macrophages in the red pulp digest and recycle the hemoglobin of the captured red blood cells.
The red pulp also stores many platelets to be released in response to blood loss. White pulp is
found within the red pulp surrounding the arterioles of the spleen. It is made of lymphatic tissue
and contains many T cells, B cells, and macrophages to fight off infections.
Thymus. The thymus is a small, triangular organ found just posterior to the sternum and anterior
to the heart. The thymus is mostly made of glandular epithelium and hematopoietic connective
tissues. The thymus produces and trains T cells during fetal development and childhood. T cells
formed in the thymus and red bone marrow mature, develop, and reproduce in the thymus
throughout childhood. The vast majority of T cells do not survive their training in the thymus
and are destroyed by macrophages. The surviving T cells spread throughout the body to the other
lymphatic tissues to fight infections. By the time a person reaches puberty, the immune system is
mature and the role of the thymus is diminished. After puberty, the inactive thymus is slowly
replaced by adipose tissue.
Lymph Circulation
One of the primary functions of the lymphatic system is the movement of interstitial fluid from
the tissues to the circulatory system. Like the veins of the circulatory system, lymphatic
capillaries and vessels move lymph with very little pressure to help with circulation. To help
move lymph towards the lymphatic ducts, there is a series of many one-way check valves found
throughout the lymphatic vessels. These check valves allow lymph to move toward the
lymphatic ducts and close when lymph attempts to flow away from the ducts. In the limbs,
skeletal muscle contraction squeezes the walls of lymphatic vessels to push lymph through the
valves and towards the thorax. In the trunk, the diaphragm pushes down into the abdomen during
inhalation. This increased abdominal pressure pushes lymph into the less pressurized thorax. The
pressure gradient reverses during exhalation, but the check valves prevent lymph from being
pushed backwards.
Lecture 10
The organs of digestion and excretion.
The digestive system is a group of organs working together to convert food into energy and basic
nutrients to feed the entire body. Food passes through a long tube inside the body known as the
alimentary canal or the gastrointestinal tract (GI tract). The alimentary canal is made up of the
oral cavity, pharynx, esophagus, stomach, small intestines, and large intestines. In addition to the
alimentary canal, there are several important accessory organs that help your body to digest food
but do not have food pass through them. Accessory organs of the digestive system include the
teeth, tongue, salivary glands, liver, gallbladder, and pancreas. To achieve the goal of providing
energy and nutrients to the body, six major functions take place in the digestive system:
Ingestion
Secretion
Mixing and movement
Digestion
Absorption
Excretion
Mouth
Food begins its journey through the digestive system in the mouth, also known as theoral cavity.
Inside the mouth are many accessory organs that aid in the digestion of food—the tongue, teeth,
and salivary glands. Teeth chop food into small pieces, which are moistened by saliva before the
tongue and other muscles push the food into the pharynx.
Teeth. The teeth are 32 small, hard organs found along the anterior and lateral edges of the
mouth. Each tooth is made of a bone-like substance called dentin and covered in a layer of
enamel—the hardest substance in the body. Teeth are living organs and contain blood vessels
and nerves under the dentin in a soft region known as the pulp. The teeth are designed for cutting
and grinding food into smaller pieces.
Tongue. The tongue is located on the inferior portion of the mouth just posterior and medial to
the teeth. It is a small organ made up of several pairs of muscles covered in a thin, bumpy, skinlike layer. The outside of the tongue contains many rough papillae for gripping food as it is
moved by the tongue’s muscles. The taste buds on the surface of the tongue detect taste
molecules in food and connect to nerves in the tongue to send taste information to the brain. The
tongue also helps to push food toward the posterior part of the mouth for swallowing.
Salivary Glands. Surrounding the mouth are 3 sets of salivary glands. The salivary glands are
accessory organs that produce a watery secretion known as saliva. Saliva helps to moisten food
and begins the digestion of carbohydrates. The body also uses saliva to lubricate food as it passes
through the mouth, pharynx, and esophagus.
Pharynx
The pharynx, or throat, is a funnel-shaped tube connected to the posterior end of the mouth. The
pharynx is responsible for the passing of masses of chewed food from the mouth to the
esophagus. The pharynx also plays an important role in the respiratory system, as air from the
nasal cavity passes through the pharynx on its way to the larynx and eventually the lungs.
Because the pharynx serves two different functions, it contains a flap of tissue known as
the epiglottis that acts as a switch to route food to the esophagus and air to the larynx.
Esophagus
The esophagus is a muscular tube connecting the pharynx to the stomach that is part of
the upper gastrointestinal tract. It carries swallowed masses of chewed food along its length.
At the inferior end of the esophagus is a muscular ring called the lower
esophageal sphincter or cardiac sphincter. The function of this sphincter is to close of the end of
the
esophagus
and
trap
food
in
the
stomach.
Stomach
The stomach is a muscular sac that is located on the left side of the abdominal cavity, just
inferior to the diaphragm. In an average person, the stomach is about the size of their two fists
placed next to each other. This major organ acts as a storage tank for food so that the body has
time to digest large meals properly. The stomach also contains hydrochloric acid and digestive
enzymes that continue the digestion of food that began in the mouth.
Small Intestine
The small intestine is a long, thin tube about 1 inch in diameter and about 10 feet long that is
part of the lower gastrointestinal tract. It is located just inferior to the stomach and takes up
most of the space in the abdominal cavity. The entire small intestine is coiled like a hose and the
inside surface is full of many ridges and folds. These folds are used to maximize the digestion of
food and absorption of nutrients. By the time food leaves the small intestine, around 90% of all
nutrients
have
been
extracted
from
the
food
that
entered
it.
Liver and Gallbladder
The liver is a roughly triangular accessory organ of the digestive system located to the right of
the stomach, just inferior to the diaphragm and superior to the small intestine. The liver weighs
about 3 pounds and is the second largest organ in the body. The liver has many different
functions in the body, but the main function of the liver in digestion is the production of bile and
its secretion into the small intestine. The gallbladder is a small, pear-shaped organ located just
posterior to the liver. The gallbladder is used to store and recycle excess bile from the small
intestine so that it can be reused for the digestion of subsequent meals.
Pancreas
The pancreas is a large gland located just inferior and posterior to the stomach. It is about 6
inches long and shaped like short, lumpy snake with its “head” connected to the duodenum and
its “tail” pointing to the left wall of the abdominal cavity. The pancreas secretes digestive
enzymes into the small intestine to complete the chemical digestion of foods.
Large Intestine
The large intestine is a long, thick tube about 2 ½ inches in diameter and about 5 feet long. It is
located just inferior to the stomach and wraps around the superior and lateral border of the small
intestine. The large intestine absorbs water and contains many symbiotic bacteria that aid in the
breaking down of wastes to extract some small amounts of nutrients. Feces in the large intestine
exit the body through the anal canal.
The digestive system is responsible for taking whole foods and turning them into energy and
nutrients to allow the body to function, grow, and repair itself. The six primary processes of the
digestive system include:
1.
2.
3.
4.
5.
6.
Ingestion of food
Secretion of fluids and digestive enzymes
Mixing and movement of food and wastes through the body
Digestion of food into smaller pieces
Absorption of nutrients
Excretion of wastes
Ingestion
The first function of the digestive system is ingestion, or the intake of food. The mouth is
responsible for this function, as it is the orifice through which all food enters the body. The
mouth and stomach are also responsible for the storage of food as it is waiting to be digested.
This storage capacity allows the body to eat only a few times each day and to ingest more food
than it can process at one time.
Secretion
In the course of a day, the digestive system secretes around 7 liters of fluids. These fluids include
saliva, mucus, hydrochloric acid, enzymes, and bile. Saliva moistens dry food and contains
salivary amylase, a digestive enzyme that begins the digestion of carbohydrates. Mucus serves as
a protective barrier and lubricant inside of the GI tract. Hydrochloric acid helps to digest food
chemically and protects the body by killing bacteria present in our food. Enzymes are like tiny
biochemical machines that disassemble large macromolecules like proteins, carbohydrates,
and lipids into their smaller components. Finally, bile is used to emulsify large masses of lipids
into tiny globules for easy digestion.
Mixing and Movement
The digestive system uses 3 main processes to move and mix food:
Swallowing. Swallowing is the process of using smooth and skeletal muscles in the mouth,
tongue, and pharynx to push food out of the mouth, through the pharynx, and into the esophagus.
Peristalsis. Peristalsis is a muscular wave that travels the length of the GI tract, moving partially
digested food a short distance down the tract. It takes many waves of peristalsis for food to travel
from the esophagus, through the stomach and intestines, and reach the end of the GI tract.
Segmentation. Segmentation occurs only in the small intestine as short segments of intestine
contract like hands squeezing a toothpaste tube. Segmentation helps to increase the absorption of
nutrients by mixing food and increasing its contact with the walls of the intestine.
Digestion
Digestion is the process of turning large pieces of food into its component chemicals.
Mechanical digestion is the physical breakdown of large pieces of food into smaller pieces. This
mode of digestion begins with the chewing of food by the teeth and is continued through the
muscular mixing of food by the stomach and intestines. Bile produced by the liver is also used to
mechanically break fats into smaller globules. While food is being mechanically digested it is
also being chemically digested as larger and more complex molecules are being broken down
into smaller molecules that are easier to absorb. Chemical digestion begins in the mouth with
salivary amylase in saliva splitting complex carbohydrates into simple carbohydrates. The
enzymes and acid in the stomach continue chemical digestion, but the bulk of chemical digestion
takes place in the small intestine thanks to the action of the pancreas. The pancreas secretes an
incredibly strong digestive cocktail known as pancreatic juice, which is capable of digesting
lipids, carbohydrates, proteins and nucleic acids. By the time food has left the duodenum, it has
been reduced to its chemical building blocks—fatty acids, amino acids, monosaccharides, and
nucleotides.
Absorption
Once food has been reduced to its building blocks, it is ready for the body to absorb. Absorption
begins in the stomach with simple molecules like water and alcohol being absorbed directly into
the bloodstream. Most absorption takes place in the walls of the small intestine, which are
densely folded to maximize the surface area in contact with digested food. Small blood and
lymphatic vessels in the intestinal wall pick up the molecules and carry them to the rest of the
body. The large intestine is also involved in the absorption of water and vitamins B and K
before feces leave the body.
Excretion
The final function of the digestive system is the excretion of waste in a process known as
defecation. Defecation removes indigestible substances from the body so that they do not
accumulate inside the gut. The timing of defecation is controlled voluntarily by the conscious
part of the brain, but must be accomplished on a regular basis to prevent a backup of indigestible
materials.
Lecture 11
Respiratory system.
The cells of the human body require a constant stream of oxygen to stay alive. The respiratory
system provides oxygen to the body’s cells while removing carbon dioxide, a waste product that
can be lethal if allowed to accumulate. There are 3 major parts of the respiratory system: the
airway, the lungs, and the muscles of respiration. The airway, which includes the nose, mouth,
pharynx, larynx, trachea, bronchi, and bronchioles, carries air between the lungs and the body’s
exterior. The lungs act as the functional units of the respiratory system by passing oxygen into
the body and carbon dioxide out of the body. Finally, the muscles of respiration, including the
diaphragm and intercostal muscles, work together to act as a pump, pushing air into and out of
the lungs during breathing.
Nose and Nasal Cavity
The nose and nasal cavity form the main external opening for the respiratory system and are the
first section of the body’s airway—the respiratory tract through which air moves. The nose is a
structure of the face made of cartilage, bone, muscle, and skin that supports and protects the
anterior portion of the nasal cavity. The nasal cavity is a hollow space within the nose
and skull that is lined with hairs and mucus membrane. The function of the nasal cavity is to
warm, moisturize, and filter air entering the body before it reaches the lungs. Hairs and mucus
lining the nasal cavity help to trap dust, mold, pollen and other environmental contaminants
before they can reach the inner portions of the body. Air exiting the body through the nose
returns moisture and heat to the nasal cavity before being exhaled into the environment.
Mouth
The mouth, also known as the oral cavity, is the secondary external opening for the respiratory
tract. Most normal breathing takes place through the nasal cavity, but the oral cavity can be used
to supplement or replace the nasal cavity’s functions when needed. Because the pathway of air
entering the body from the mouth is shorter than the pathway for air entering from the nose, the
mouth does not warm and moisturize the air entering the lungs as well as the nose performs this
function. The mouth also lacks the hairs and sticky mucus that filter air passing through the nasal
cavity. The one advantage of breathing through the mouth is that its shorter distance and larger
diameter allows more air to quickly enter the body.
Pharynx
The pharynx, also known as the throat, is a muscular funnel that extends from the posterior end
of the nasal cavity to the superior end of the esophagus and larynx. The pharynx is divided into
3 regions: the nasopharynx, oropharynx, and laryngopharynx. The nasopharynx is the superior
region of the pharynx found in the posterior of the nasal cavity. Inhaled air from the nasal cavity
passes into the nasopharynx and descends through the oropharynx, located in the posterior of the
oral cavity. Air inhaled through the oral cavity enters the pharynx at the oropharynx. The
inhaled air then descends into the laryngopharynx, where it is diverted into the opening of the
larynx by the epiglottis. The epiglottis is a flap of elastic cartilage that acts as a switch between
the trachea and the esophagus. Because the pharynx is also used to swallow food, the epiglottis
ensures that air passes into the trachea by covering the opening to the esophagus. During the
process of swallowing, the epiglottis moves to cover the trachea to ensure that food enters the
esophagus and to prevent choking.
Larynx
The larynx, also known as the voice box, is a short section of the airway that connects the
laryngopharynx and the trachea. The larynx is located in the anterior portion of the neck, just
inferior to the hyoid bone and superior to the trachea. Several cartilage structures make up the
larynx and give it its structure. The epiglottis is one of the cartilage pieces of the larynx and
serves as the cover of the larynx during swallowing. Inferior to the epiglottis is the thyroid
cartilage, which is often referred to as the Adam’s apple as it is most commonly enlarged and
visible in adult males. The thyroidholds open the anterior end of the larynx and protects the
vocal folds. Inferior to the thyroid cartilage is the ring-shaped cricoid cartilage which holds the
larynx open and supports its posterior end. In addition to cartilage, the larynx contains special
structures known as vocal folds, which allow the body to produce the sounds of speech and
singing. The vocal folds are folds of mucous membrane that vibrate to produce vocal sounds.
The tension and vibration speed of the vocal folds can be changed to change the pitch that they
produce.
Trachea
The trachea, or windpipe, is a 5-inch long tube made of C-shaped hyaline cartilage rings lined
with pseudostratified ciliated columnar epithelium. The trachea connects the larynx to the
bronchi and allows air to pass through the neck and into the thorax. The rings of cartilage
making up the trachea allow it to remain open to air at all times. The open end of the cartilage
rings faces posteriorly toward the esophagus, allowing the esophagus to expand into the space
occupied by the trachea to accommodate masses of food moving through the esophagus.
The main function of the trachea is to provide a clear airway for air to enter and exit the lungs. In
addition, the epithelium lining the trachea produces mucus that traps dust and other contaminants
and prevents it from reaching the lungs. Cilia on the surface of the epithelial cells move the
mucus superiorly toward the pharynx where it can be swallowed and digested in the
gastrointestinal tract.
Bronchi and Bronchioles
At the inferior end of the trachea, the airway splits into left and right branches known as the
primary bronchi. The left and right bronchi run into each lung before branching off into smaller
secondary bronchi. The secondary bronchi carry air into the lobes of the lungs—2 in the left lung
and 3 in the right lung. The secondary bronchi in turn split into many smaller tertiary bronchi
within each lobe. The tertiary bronchi split into many smaller bronchioles that spread
throughout the lungs. Each bronchiole further splits into many smaller branches less than a
millimeter in diameter called terminal bronchioles. Finally, the millions of tiny terminal
bronchioles conduct air to the alveoli of the lungs.
As the airway splits into the tree-like branches of the bronchi and bronchioles, the structure of
the walls of the airway begins to change. The primary bronchi contain many C-shaped cartilage
rings that firmly hold the airway open and give the bronchi a cross-sectional shape like a
flattened circle or a letter D. As the bronchi branch into secondary and tertiary bronchi, the
cartilage becomes more widely spaced and more smooth muscle and elastin protein is found in
the walls. The bronchioles differ from the structure of the bronchi in that they do not contain any
cartilage at all. The presence of smooth muscles and elastin allow the smaller bronchi and
bronchioles to be more flexible and contractile.
The main function of the bronchi and bronchioles is to carry air from the trachea into the lungs.
Smooth muscle tissue in their walls helps to regulate airflow into the lungs. When greater
volumes of air are required by the body, such as during exercise, the smooth muscle relaxes to
dilate the bronchi and bronchioles. The dilated airway provides less resistance to airflow and
allows more air to pass into and out of the lungs. The smooth muscle fibers are able to contract
during rest to prevent hyperventilation. The bronchi and bronchioles also use the mucus and cilia
of their epithelial lining to trap and move dust and other contaminants away from the lungs.
Lungs
The lungs are a pair of large, spongy organs found in the thorax lateral to the heart and superior
to the diaphragm. Each lung is surrounded by a pleural membrane that provides the lung with
space to expand as well as a negative pressure space relative to the body’s exterior. The negative
pressure allows the lungs to passively fill with air as they relax. The left and right lungs are
slightly different in size and shape due to the heart pointing to the left side of the body. The left
lung is therefore slightly smaller than the right lung and is made up of 2 lobes while the right
lung has 3 lobes.
The interior of the lungs is made up of spongy tissues containing many capillaries and around 30
million tiny sacs known as alveoli. The alveoli are cup-shaped structures found at the end of the
terminal bronchioles and surrounded by capillaries. The alveoli are lined with thin simple
squamous epithelium that allows air entering the alveoli to exchange its gases with the blood
passing through the capillaries.
Muscles of Respiration
Surrounding the lungs are sets of muscles that are able to cause air to be inhaled or exhaled from
the lungs. The principal muscle of respiration in the human body is the diaphragm, a thin sheet of
skeletal muscle that forms the floor of the thorax. When the diaphragm contracts, it moves
inferiorly a few inches into the abdominal cavity, expanding the space within the thoracic cavity
and pulling air into the lungs. Relaxation of the diaphragm allows air to flow back out the lungs
during exhalation.
Between the ribs are many small intercostal muscles that assist the diaphragm with expanding
and compressing the lungs. These muscles are divided into 2 groups: the internal intercostal
muscles and the external intercostal muscles. The internal intercostal muscles are the deeper set
of muscles and depress the ribs to compress the thoracic cavity and force air to be exhaled from
the lungs. The external intercostals are found superficial to the internal intercostals and function
to elevate the ribs, expanding the volume of the thoracic cavity and causing air to be inhaled into
the lungs.
Pulmonary Ventilation
Pulmonary ventilation is the process of moving air into and out of the lungs to facilitate gas
exchange. The respiratory system uses both a negative pressure system and the contraction of
muscles to achieve pulmonary ventilation. The negative pressure system of the respiratory
system involves the establishment of a negative pressure gradient between the alveoli and the
external atmosphere. The pleural membrane seals the lungs and maintains the lungs at a pressure
slightly below that of the atmosphere when the lungs are at rest. This results in air following the
pressure gradient and passively filling the lungs at rest. As the lungs fill with air, the pressure
within the lungs rises until it matches the atmospheric pressure. At this point, more air can be
inhaled by the contraction of the diaphragm and the external intercostal muscles, increasing the
volume of the thorax and reducing the pressure of the lungs below that of the atmosphere again.
To exhale air, the diaphragm and external intercostal muscles relax while the internal intercostal
muscles contract to reduce the volume of the thorax and increase the pressure within the thoracic
cavity. The pressure gradient is now reversed, resulting in the exhalation of air until the pressures
inside the lungs and outside of the body are equal. At this point, the elastic nature of the lungs
causes them to recoil back to their resting volume, restoring the negative pressure gradient
present during inhalation.
External Respiration
External respiration is the exchange of gases between the air filling the alveoli and the blood in
the capillaries surrounding the walls of the alveoli. Air entering the lungs from the atmosphere
has a higher partial pressure of oxygen and a lower partial pressure of carbon dioxide than does
the blood in the capillaries. The difference in partial pressures causes the gases to diffuse
passively along their pressure gradients from high to low pressure through the simple squamous
epithelium lining of the alveoli. The net result of external respiration is the movement of oxygen
from the air into the blood and the movement of carbon dioxide from the blood into the air. The
oxygen can then be transported to the body’s tissues while carbon dioxide is released into the
atmosphere during exhalation.
Internal Respiration
Internal respiration is the exchange of gases between the blood in capillaries and the tissues of
the body. Capillary blood has a higher partial pressure of oxygen and a lower partial pressure of
carbon dioxide than the tissues through which it passes. The difference in partial pressures leads
to the diffusion of gases along their pressure gradients from high to low pressure through the
endothelium lining of the capillaries. The net result of internal respiration is the diffusion of
oxygen into the tissues and the diffusion of carbon dioxide into the blood.
Transportation of Gases
The 2 major respiratory gases, oxygen and carbon dioxide, are transported through the body in
the blood. Blood plasma has the ability to transport some dissolved oxygen and carbon dioxide,
but most of the gases transported in the blood are bonded to transport molecules. Hemoglobin is
an important transport molecule found in red blood cells that carries almost 99% of the oxygen
in the blood. Hemoglobin can also carry a small amount of carbon dioxide from the tissues back
to the lungs. However, the vast majority of carbon dioxide is carried in the plasma as bicarbonate
ion. When the partial pressure of carbon dioxide is high in the tissues, the enzyme carbonic
anhydrase catalyzes a reaction between carbon dioxide and water to form carbonic acid.
Carbonic acid then dissociates into hydrogen ion and bicarbonate ion. When the partial pressure
of carbon dioxide is low in the lungs, the reactions reverse and carbon dioxide is liberated into
the lungs to be exhaled.
Homeostatic Control of Respiration
Under normal resting conditions, the body maintains a quiet breathing rate and depth called
eupnea. Eupnea is maintained until the body’s demand for oxygen and production of carbon
dioxide rises due to greater exertion. Autonomic chemoreceptors in the body monitor the partial
pressures of oxygen and carbon dioxide in the blood and send signals to the respiratory center of
the brain stem. The respiratory center then adjusts the rate and depth of breathing to return the
blood to its normal levels of gas partial pressures.
Lecture 12
The genitourinary system.
Female reproductive system
The female reproductive system includes the ovaries, fallopian tubes, uterus, vagina, vulva,
mammary glands and breasts. These organs are involved in the production and transportation of
gametes and the production of sex hormones. The female reproductive system also facilitates the
fertilization of ova by sperm and supports the development of offspring during pregnancy and
infancy.
Ovaries
The ovaries are a pair of small glands about the size and shape of almonds, located on the left and
right sides of the pelvic body cavity lateral to the superior portion of the uterus. Ovaries produce
female sex hormones such as estrogen and progesterone as well as ova (commonly called
"eggs"), the female gametes. Ova are produced from oocyte cells that slowly develop throughout
a woman’s early life and reach maturity after puberty. Each month during ovulation, a mature
ovum is released. The ovum travels from the ovary to the fallopian tube, where it may be
fertilized before reaching the uterus.
Fallopian Tubes
The fallopian tubes are a pair of muscular tubes that extend from the left and right superior corners
of the uterus to the edge of the ovaries. The fallopian tubes end in a funnel-shaped structure
called the infundibulum, which is covered with small finger-like projections called fimbriae.
The fimbriae swipe over the outside of the ovaries to pick up released ova and carry them into the
infundibulum for transport to the uterus. The inside of each fallopian tube is covered in cilia that
work with the smooth muscle of the tube to carry the ovum to the uterus.
Uterus
The uterus is a hollow, muscular, pear-shaped organ located posterior and superior to the urinary
bladder. Connected to the two fallopian tubes on its superior end and to the vagina (via the cervix)
on its inferior end, the uterus is also known as the womb, as it surrounds and supports the
developing fetus during pregnancy. The inner lining of the uterus, known as the endometrium,
provides support to the embryo during early development. The visceral muscles of the uterus
contract during childbirth to push the fetus through the birth canal.
Vagina
The vagina is an elastic, muscular tube that connects the cervix of the uterus to the exterior of the
body. It is located inferior to the uterus and posterior to the urinary bladder. The vagina functions
as the receptacle for the penis during sexual intercourse and carries sperm to the uterus and
fallopian tubes. It also serves as the birth canal by stretching to allow delivery of the fetus during
childbirth. During menstruation, the menstrual flow exits the body via the vagina.
Vulva
The vulva is the collective name for the external female genitalia located in the pubic region of
the body. The vulva surrounds the external ends of the urethral opening and the vagina and
includes the mons pubis, labia majora, labia minora, and clitoris. The mons pubis, or pubic
mound, is a raised layer of adipose tissue between the skin and thepubic bone that provides
cushioning to the vulva. The inferior portion of the mons pubis splits into left and right halves
called the labia majora. The mons pubis and labia majora are covered with pubic hairs. Inside of
the labia majora are smaller, hairless folds of skin called the labia minora that surround the vaginal
and urethral openings. On the superior end of the labia minora is a small mass of erectile tissue
known as the clitoristhat contains many nerve endings for sensing sexual pleasure.
Breasts
and
Mammary
Glands
The breasts are specialized organs of the female body that contain mammary glands, milk ducts,
and adipose tissue. The two breasts are located on the left and right sides of the thoracic region
of the body. In the center of each breast is a highly pigmentednipple that releases milk when
stimulated. The areola, a thickened, highly pigmented band of skin that surrounds the nipple,
protects the underlying tissues during breastfeeding. The mammary glands are a special type of
sudoriferous glands that have been modified to produce milk to feed infants. Within each breast,
15 to 20 clusters of mammary glands become active during pregnancy and remain active until
milk is no longer needed. The milk passes through milk ducts on its way to the nipple, where it
exits the body.
Male reproductive system
The male reproductive system includes the scrotum, testes, spermatic ducts, sex glands, and
penis. These organs work together to produce sperm, the male gamete, and the other components
of semen. These organs also work together to deliver semen out of the body and into the vagina
where it can fertilize egg cells to produce offspring.
Scrotum
The scrotum is a sac-like organ made of skin and muscles that houses the testes. It is located
inferior to the penis in the pubic region. The scrotum is made up of 2 side-by-side pouches with a
testis located in each pouch. The smooth muscles that make up the scrotum allow it to regulate
the distance between the testes and the rest of the body. When the testes become too warm to
support spermatogenesis, the scrotum relaxes to move the testes away from the body’s heat.
Conversely, the scrotum contracts to move the testes closer to the body’s core heat when
temperatures drop below the ideal range for spermatogenesis.
Testes
The 2 testes, also known as testicles, are the male gonads responsible for the production of sperm
and testosterone. The testes are ellipsoid glandular organs around 1.5 to 2 inches long and an
inch in diameter. Each testis is found inside its own pouch on one side of the scrotum and is
connected to the abdomen by a spermatic cord and cremaster muscle. The cremaster muscles
contract and relax along with the scrotum to regulate the temperature of the testes. The inside of
the testes is divided into small compartments known as lobules. Each lobule contains a section of
seminiferous tubule lined with epithelial cells. These epithelial cells contain many stem cells that
divide and form sperm cells through the process of spermatogenesis.
Epididymis
The epididymis is a sperm storage area that wraps around the superior and posterior edge of the
testes. The epididymis is made up of several feet of long, thin tubules that are tightly coiled into
a small mass. Sperm produced in the testes moves into the epididymis to mature before being
passed on through the male reproductive organs. The length of the epididymis delays the release of
the sperm and allows them time to mature.
Spermatic Cords and Ductus Deferens
Within the scrotum, a pair of spermatic cords connects the testes to the abdominal cavity. The
spermatic cords contain the ductus deferens along with nerves, veins, arteries, and lymphatic
vessels that support the function of the testes.
The ductus deferens, also known as the vas deferens, is a muscular tube that carries sperm
superiorly from the epididymis into the abdominal cavity to the ejaculatory duct. The ductus
deferens is wider in diameter than the epididymis and uses its internal space to store mature
sperm. The smooth muscles of the walls of the ductus deferens are used to move sperm towards
the ejaculatory duct through peristalsis.
Seminal Vesicles
The seminal vesicles are a pair of lumpy exocrine glands that store and produce some of the liquid
portion of semen. The seminal vesicles are about 2 inches in length and located posterior to the
urinary bladder and anterior to the rectum. The liquid produced by the seminal vesicles contains
proteins and mucus and has an alkaline pH to help sperm survive in the acidic environment of
the vagina. The liquid also contains fructose to feed sperm cells so that they survive long enough
to fertilize the oocyte.
Ejaculatory Duct
The ductus deferens passes through the prostate and joins with the urethra at a structure known
as the ejaculatory duct. The ejaculatory duct contains the ducts from the seminal vesicles as well.
During ejaculation, the ejaculatory duct opens and expels sperm and the secretions from the
seminal vesicles into the urethra.
Urethra
Semen passes from the ejaculatory duct to the exterior of the body via the urethra, an 8 to 10
inch long muscular tube. The urethra passes through the prostate and ends at theexternal urethral
orifice located at the tip of the penis. Urine exiting the body from the urinary bladder also passes
through the urethra.
Prostate
The prostate is a walnut-sized exocrine gland that borders the inferior end of the urinary bladder
and surrounds the urethra. The prostate produces a large portion of the fluid that makes up
semen. This fluid is milky white in color and contains enzymes, proteins, and other chemicals to
support and protect sperm during ejaculation. The prostate also contains smooth muscle tissue
that can constrict to prevent the flow of urine or semen.
Cowper’s Glands
The Cowper’s glands, also known as the bulbourethral glands, are a pair of pea-sized exocrine
glands located inferior to the prostate and anterior to the anus. The Cowper’s glands secrete a
thin alkaline fluid into the urethra that lubricates the urethra and neutralizes acid from urine
remaining in the urethra after urination. This fluid enters the urethra during sexual arousal prior
to ejaculation to prepare the urethra for the flow of semen.
Penis
The penis is the male external sexual organ located superior to the scrotum and inferior to the
umbilicus. The penis is roughly cylindrical in shape and contains the urethra and the external
opening of the urethra. Large pockets of erectile tissue in the penis allow it to fill with blood and
become erect. The erection of the penis causes it to increase in size and become turgid. The
function of the penis is to deliver semen into the vagina during sexual intercourse. In addition to
its reproductive function, the penis also allows for the excretion of urine through the urethra to
the exterior of the body.
Semen
Semen is the fluid produced by males for sexual reproduction and is ejaculated out of the body
during sexual intercourse. Semen contains sperm, the male reproductive gametes, along with a
number of chemicals suspended in a liquid medium. The chemical composition of semen gives it
a thick, sticky consistency and a slightly alkaline pH. These traits help semen to support
reproduction by helping sperm to remain within the vagina after intercourse and to neutralize the
acidic environment of the vagina. In healthy adult males, semen contains around 100 million
sperm cells per milliliter. These sperm cells fertilize oocytes inside the female fallopian tubes.
The urinary system
The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. The kidneys
filter the blood to remove wastes and produce urine. The ureters, urinary bladder, and urethra
together form the urinary tract, which acts as a plumbing system to drain urine from the kidneys,
store it, and then release it during urination. Besides filtering and eliminating wastes from the
body, the urinary system also maintains the homeostasis of water, ions, pH, blood pressure,
calcium.
Kidneys
The kidneys are a pair of bean-shaped organs found along the posterior
wall of the abdominal cavity. The left kidney is located slightly higher than the right kidney
because the right side of the liver is much larger than the left side. The kidneys, unlike the other
organs of the abdominal cavity, are located posterior to the peritoneum and touch the muscles of
the back. The kidneys are surrounded by a layer of adipose that holds them in place and protects
them from physical damage. The kidneys filter metabolic wastes, excess ions, and chemicals
from the blood to form urine.
Ureters
The ureters are a pair of tubes that carry urine from the kidneys to the urinary bladder. The ureters
are about 10 to 12 inches long and run on the left and right sides of the body parallel to
the vertebral column. Gravity and peristalsis of smooth muscle tissue in the walls of the ureters
move urine toward the urinary bladder. The ends of the ureters extend slightly into the urinary
bladder and are sealed at the point of entry to the bladder by the ureterovesical valves. These
valves prevent urine from flowing back towards the kidneys.
Urinary Bladder
The urinary bladder is a sac-like hollow organ used for the storage of urine. The urinary bladder is
located along the body’s midline at the inferior end of the pelvis. Urine entering the urinary
bladder from the ureters slowly fills the hollow space of the bladder and stretches its elastic
walls. The walls of the bladder allow it to stretch to hold anywhere from 600 to 800 milliliters of
urine.
Urethra
The urethra is the tube through which urine passes from the bladder to the exterior of the body.
The female urethra is around 2 inches long and ends inferior to the clitorisand superior to the
vaginal opening. In males, the urethra is around 8 to 10 inches long and ends at the tip of
the penis. The urethra is also an organ of the male reproductive system as it carries sperm out of
the body through the penis.
The flow of urine through the urethra
is controlled by
the internal and external urethral sphincter muscles. The internal urethral sphincter is made of
smooth muscle and opens involuntarily when the bladder reaches a certain set level of distention.
The opening of the internal sphincter results in the sensation of needing to urinate. The external
urethral sphincter is made of skeletal muscle and may be opened to allow urine to pass through
the urethra or may be held closed to delay urination.
Lecture 13
The endocrine system.
The endocrine system includes all of the glands of the body and the hormones produced by those
glands. The glands are controlled directly by stimulation from the nervous system as well as by
chemical receptors in the blood and hormones produced by other glands. By regulating the
functions of organs in the body, these glands help to maintain the body’s homeostasis. Cellular
metabolism, reproduction, sexual development, sugar and mineral homeostasis, heart rate, and
digestion are among the many processes regulated by the actions of hormones.
Hypothalamus
The hypothalamus is a part of the brain located superior and anterior to the brain stem and
inferior to the thalamus. It serves many different functions in the nervous system, and is also
responsible for the direct control of the endocrine system through the pituitary gland. The
hypothalamus contains special cells called neurosecretory cells—neurons that secrete hormones:
Thyrotropin-releasing hormone (TRH)
Growth hormone-releasing hormone (GHRH)
Growth hormone-inhibiting hormone (GHIH)
Gonadotropin-releasing hormone (GnRH)
Corticotropin-releasing hormone (CRH)
Oxytocin
Antidiuretic hormone (ADH)
All of the releasing and inhibiting hormones affect the function of the anterior pituitary gland.
TRH stimulates the anterior pituitary gland to release thyroid-stimulating hormone. GHRH and
GHIH work to regulate the release of growth hormone—GHRH stimulates growth hormone
release, GHIH inhibits its release. GnRH stimulates the release of follicle stimulating hormone
and luteinizing hormone while CRH stimulates the release of adrenocorticotropic hormone. The
last two hormones—oxytocin and antidiuretic hormone—are produced by the hypothalamus and
transported to the posterior pituitary, where they are stored and later released.
Pituitary Gland
The pituitary gland, also known as the hypophysis, is a small pea-sized lump of tissue
connected to the inferior portion of the hypothalamus of the brain. Many blood vesselssurround
the pituitary gland to carry the hormones it releases throughout the body. Situated in a small
depression in the sphenoid bone called the sella turcica, the pituitary gland is actually made of 2
completely separate structures: the posterior and anterior pituitary glands.
Posterior Pituitary: The posterior pituitary gland is actually not glandular tissue at all, but
nervous tissue instead. The posterior pituitary is a small extension of the hypothalamus through
which the axons of some of the neurosecretory cells of the hypothalamus extend. These
neurosecretory cells create 2 hormones in the hypothalamus that are stored and released by the
posterior pituitary:
Oxytocin triggers uterine contractions during childbirth and the release of milk during
breastfeeding.
Antidiuretic hormone (ADH) prevents water loss in the body by increasing the re-uptake of
water in the kidneys and reducing blood flow to sweat glands.
Anterior Pituitary: The anterior pituitary gland is the true glandular part of the pituitary gland.
The function of the anterior pituitary gland is controlled by the releasing and inhibiting
hormones of the hypothalamus. The anterior pituitary produces 6 important hormones:
Thyroid stimulating hormone (TSH), as its name suggests, is a tropic hormone responsible for
the stimulation of the thyroid gland.
Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex, the outer part of the adrenal
gland, to produce its hormones.
Follicle stimulating hormone (FSH) stimulates the follicle cells of the gonads to produce
gametes—ova in females and sperm in males.
Luteinizing hormone (LH) stimulates the gonads to produce the sex hormones—estrogens in
females and testosterone in males.
Human growth hormone (HGH) affects many target cells throughout the body by stimulating
their growth, repair, and reproduction.
Prolactin (PRL) has many effects on the body, chief of which is that it stimulates the mammary
glands of the breast to produce milk.
Pineal Gland
The pineal gland is a small pinecone-shaped mass of glandular tissue found just posterior to the
thalamus of the brain. The pineal gland produces the hormone melatonin that helps to regulate
the human sleep-wake cycle known as the circadian rhythm. The activity of the pineal gland is
inhibited by stimulation from the photoreceptors of the retina. This light sensitivity causes
melatonin to be produced only in low light or darkness. Increased melatonin production causes
humans to feel drowsy at nighttime when the pineal gland is active.
Thyroid Gland
The thyroid gland is a butterfly-shaped gland located at the base of the neck and wrapped
around the lateral sides of the trachea. The thyroid gland produces 3 major hormones:
Calcitonin
Triiodothyronine (T3)
Thyroxine (T4)
Calcitonin is released when calcium ion levels in the blood rise above a certain set point.
Calcitonin functions to reduce the concentration of calcium ions in the blood by aiding the
absorption of calcium into the matrix of bones. The hormones T3 and T4 work together to
regulate the body’s metabolic rate. Increased levels of T3 and T4 lead to increased cellular
activity and energy usage in the body.
Parathyroid Glands
The parathyroid glands are 4 small masses of glandular tissue found on the posterior side of the
thyroid gland. The parathyroid glands produce the hormone parathyroid hormone (PTH), which
is involved in calcium ion homeostasis. PTH is released from the parathyroid glands when
calcium ion levels in the blood drop below a set point. PTH stimulates the osteoclasts to break
down the calcium containing bone matrix to release free calcium ions into the bloodstream. PTH
also triggers the kidneys to return calcium ions filtered out of the blood back to the bloodstream
so that it is conserved.
Adrenal Glands
The adrenal glands are a pair of roughly triangular glands found immediately superior to the
kidneys. The adrenal glands are each made of 2 distinct layers, each with their own unique
functions: the outer adrenal cortex and inner adrenal medulla.
Adrenal cortex: The adrenal cortex produces many cortical hormones in 3 classes:
glucocorticoids, mineralocorticoids, and androgens.
Glucocorticoids have many diverse functions, including the breakdown of proteins and lipids to
produce glucose. Glucocorticoids also function to reduce inflammation and immune response.
Mineralocorticoids, as their name suggests, are a group of hormones that help to regulate the
concentration of mineral ions in the body.
Androgens, such as testosterone, are produced at low levels in the adrenal cortex to regulate the
growth and activity of cells that are receptive to male hormones. In adult males, the amount of
androgens produced by the testes is many times greater than the amount produced by the adrenal
cortex, leading to the appearance of male secondary sex characteristics.
Adrenal medulla: The adrenal medulla produces the hormones epinephrine and norepinephrine
under stimulation by the sympathetic division of the autonomic nervous system. Both of these
hormones help to increase the flow of blood to the brain and muscles to improve the “fight-orflight” response to stress. These hormones also work to increase heart rate, breathing rate, and
blood pressure while decreasing the flow of blood to and function of organs that are not involved
in responding to emergencies.
Pancreas
The pancreas is a large gland located in the abdominal cavity just inferior and posterior to
the stomach. The pancreas is considered to be a heterocrine gland as it contains both endocrine
and exocrine tissue. The endocrine cells of the pancreas make up just about 1% of the total mass
of the pancreas and are found in small groups throughout the pancreas called islets of
Langerhans. Within these islets are 2 types of cells—alpha and beta cells. The alpha cells
produce the hormone glucagon, which is responsible for raising blood glucose levels. Glucagon
triggers muscle and liver cells to break down the polysaccharide glycogen to release glucose into
the bloodstream. The beta cells produce the hormone insulin, which is responsible for lowering
blood glucose levels after a meal. Insulin triggers the absorption of glucose from the blood into
cells,
where
it
is
added
to
glycogen
molecules
for
storage.
Gonads
The gonads—ovaries in females and testes in males—are responsible for producing the sex
hormones of the body. These sex hormones determine the secondary sex characteristics of adult
females and adult males.
Testes: The testes are a pair of ellipsoid organs found in the scrotum of males that produce the
androgen testosterone in males after the start of puberty. Testosterone has effects on many parts
of the body, including the muscles, bones, sex organs, and hair follicles. This hormone causes
growth and increases in strength of the bones and muscles, including the accelerated growth of
long bones during adolescence. During puberty, testosterone controls the growth and
development of the sex organs and body hair of males, including pubic, chest, and facial hair. In
men who have inherited genes for baldness testosterone triggers the onset of androgenic
alopecia, commonly known as male pattern baldness.
Ovaries: The ovaries are a pair of almond-shaped glands located in the pelvic body cavity lateral
and superior to the uterus in females. The ovaries produce the female sex hormones progesterone
and estrogens. Progesterone is most active in females during ovulation and pregnancy where it
maintains appropriate conditions in the human body to support a developing fetus. Estrogens are
a group of related hormones that function as the primary female sex hormones. The release of
estrogen during puberty triggers the development of female secondary sex characteristics such as
uterine development, breast development, and the growth of pubic hair. Estrogen also triggers
the increased growth of bones during adolescence that lead to adult height and proportions.
Thymus
The thymus is a soft, triangular-shaped organ found in the chest posterior to the sternum. The
thymus produces hormones called thymosins that help to train and develop T-lymphocytes
during fetal development and childhood. The T-lymphocytes produced in the thymus go on to
protect the body from pathogens throughout a person’s entire life. The thymus becomes inactive
during puberty and is slowly replaced by adipose tissue throughout a person’s life.
Other Hormone Producing Organs
In addition to the glands of the endocrine system, many other non-glandular organs and tissues in
the body produce hormones as well.
Heart: The cardiac muscle tissue of the heart is capable of producing the hormone atrial
natriuretic peptide (ANP) in response to high blood pressure levels. ANP works to reduce blood
pressure by triggering vasodilation to provide more space for the blood to travel through. ANP
also reduces blood volume and pressure by causing water and salt to be excreted out of the blood
by the kidneys.
Kidneys: The kidneys produce the hormone erythropoietin (EPO) in response to low levels of
oxygen in the blood. EPO released by the kidneys travels to the red bone marrow where it
stimulates an increased production of red blood cells. The number of red blood cells increases
the oxygen carrying capacity of the blood, eventually ending the production of EPO.
Digestive System: The hormones cholecystokinin (CCK), secretin, and gastrin are all produced
by the organs of the gastrointestinal tract. CCK, secretin, and gastrin all help to regulate the
secretion of pancreatic juice, bile, and gastric juice in response to the presence of food in the
stomach. CCK is also instrumental in the sensation of satiety or “fullness” after eating a meal.
Adipose: Adipose tissue produces the hormone leptin that is involved in the management of
appetite and energy usage by the body. Leptin is produced at levels relative to the amount of
adipose tissue in the body, allowing the brain to monitor the body’s energy storage condition.
When the body contains a sufficient level of adipose for energy storage, the level of leptin in the
blood tells the brain that the body is not starving and may work normally. If the level of adipose
or leptin decreases below a certain threshold, the body enters starvation mode and attempts to
conserve energy through increased hunger and food intake and decreased energy usage. Adipose
tissue also produces very low levels of estrogens in both men and women. In obese people the
large volume of adipose tissue may lead to abnormal estrogen levels.
Placenta: In pregnant women, the placenta produces several hormones that help to maintain
pregnancy. Progesterone is produced to relax the uterus, protect the fetus from the
mother’s immune system, and prevent premature delivery of the fetus. Human chorionic
gonadotropin (HCG) assists progesterone by signaling the ovaries to maintain the production of
estrogen and progesterone throughout pregnancy.
Local Hormones: Prostaglandins and leukotrienes are produced by every tissue in the body
(except for blood tissue) in response to damaging stimuli. These two hormones mainly affect the
cells that are local to the source of damage, leaving the rest of the body free to function
normally.
Prostaglandins cause swelling, inflammation, increased pain sensitivity, and increased local body
temperature to help block damaged regions of the body from infection or further damage. They
act as the body’s natural bandages to keep pathogens out and swell around damaged joints like a
natural cast to limit movement.
Leukotrienes help the body heal after prostaglandins have taken effect by reducing inflammation
while helping white blood cells to move into the region to clean up pathogens and damaged
tissues.
Endocrine System vs. Nervous System Function
The endocrine system works alongside of the nervous system to form the control systems of the
body. The nervous system provides a very fast and narrowly targeted system to turn on specific
glands and muscles throughout the body. The endocrine system, on the other hand, is much
slower acting, but has very widespread, long lasting, and powerful effects. Hormones are
distributed by glands through the bloodstream to the entire body, affecting any cell with a
receptor for a particular hormone. Most hormones affect cells in several organs or throughout the
entire body, leading to many diverse and powerful responses.
Hormone Properties
Once hormones have been produced by glands, they are distributed through the body via the
bloodstream. As hormones travel through the body, they pass through cells or along the plasma
membranes of cells until they encounter a receptor for that particular hormone. Hormones can
only affect target cells that have the appropriate receptors. This property of hormones is known
as specificity. Hormone specificity explains how each hormone can have specific effects in
widespread parts of the body.
Many hormones produced by the endocrine system are classified as tropic hormones. A tropic
hormone is a hormone that is able to trigger the release of another hormone in another gland.
Tropic hormones provide a pathway of control for hormone production as well as a way for
glands to be controlled in distant regions of the body. Many of the hormones produced by the
pituitary gland, such as TSH, ACTH, and FSH are tropic hormones.
Hormonal Regulation
The levels of hormones in the body can be regulated by several factors. The nervous system can
control hormone levels through the action of the hypothalamus and its releasing and inhibiting
hormones. For example, TRH produced by the hypothalamus stimulates the anterior pituitary to
produce TSH. Tropic hormones provide another level of control for the release of hormones. For
example, TSH is a tropic hormone that stimulates the thyroid gland to produce T3 and T4.
Nutrition can also control the levels of hormones in the body. For example, the thyroid hormones
T3 and T4 require 3 or 4 iodine atoms, respectively, to be produced. In people lacking iodine in
their diet, they will fail to produce sufficient levels of thyroid hormones to maintain a healthy
metabolic rate. Finally, the number of receptors present in cells can be varied by cells in
response to hormones. Cells that are exposed to high levels of hormones for extended periods of
time can begin to reduce the number of receptors that they produce, leading to reduced hormonal
control of the cell.
Classes of Hormones
Hormones are classified into 2 categories depending on their chemical make-up and solubility:
water-soluble and lipid-soluble hormones. Each of these classes of hormones has specific
mechanisms for their function that dictate how they affect their target cells.
Water-soluble hormones: Water-soluble hormones include the peptide and amino-acid hormones
such as insulin, epinephrine, HGH, and oxytocin. As their name indicates, these hormones are
soluble in water. Water-soluble hormones are unable to pass through the phospholipid bilayer of
the plasma membrane and are therefore dependent upon receptor molecules on the surface of
cells. When a water-soluble hormone binds to a receptor molecule on the surface of a cell, it
triggers a reaction inside of the cell. This reaction may change a factor inside of the cell such as
the permeability of the membrane or the activation of another molecule. A common reaction is to
cause molecules of cyclic adenosine monophosphate (cAMP) to be synthesized from adenosine
triphosphate (ATP) present in the cell. cAMP acts as a second messenger within the cell where it
binds to a second receptor to change the function of the cell’s physiology.
Lipid-soluble hormones: Lipid-soluble hormones include the steroid hormones such as
testosterone, estrogens, glucocorticoids, and mineralocorticoids. Because they are soluble in
lipids, these hormones are able to pass directly through the phospholipid bilayer of the plasma
membrane and bind directly to receptors inside the cell nucleus. Lipid-soluble hormones are able
to directly control the function of a cell from these receptors, often triggering the transcription of
particular genes in the DNA to produce "messenger RNAs (mRNAs)" that are used to make
proteins that affect the cell’s growth and function.
Lecture 14
General characteristics of the nervous system.
The nervous system consists of the brain, spinal cord, sensory organs, and all of the nerves that
connect these organs with the rest of the body. Together, these organs are responsible for the
control of the body and communication among its parts. The brain and spinal cord form the
control center known as the central nervous system (CNS), where information is evaluated and
decisions made. The sensory nerves and sense organs of the peripheral nervous system (PNS)
monitor conditions inside and outside of the body and send this information to the CNS. Efferent
nerves in the PNS carry signals from the control center to the muscles, glands, and organs to
regulate their functions.
Nervous Tissue
The majority of the nervous system is tissue made up of two classes of cells: neurons and
neuroglia.
Neurons. Neurons, also known as nerve cells, communicate within the body by transmitting
electrochemical signals. Neurons look quite different from other cells in the body due to the
many long cellular processes that extend from their central cell body. The cell body is the
roughly round part of a neuron that contains the nucleus, mitochondria, and most of the cellular
organelles. Small tree-like structures called dendrites extend from the cell body to pick up
stimuli from the environment, other neurons, or sensory receptor cells. Long transmitting
processes called axons extend from the cell body to send signals onward to other neurons or
effector cells in the body.
There are 3 basic classes of neurons: afferent neurons, efferent neurons, and interneurons.
Afferent neurons. Also known as sensory neurons, afferent neurons transmit sensory signals to
the central nervous system from receptors in the body.
Efferent neurons. Also known as motor neurons, efferent neurons transmit signals from the
central nervous system to effectors in the body such as muscles and glands.
Interneurons. Interneurons form complex networks within the central nervous system to
integrate the information received from afferent neurons and to direct the function of the body
through efferent neurons.
Neuroglia. Neuroglia, also known as glial cells, act as the “helper” cells of the nervous system.
Each neuron in the body is surrounded by anywhere from 6 to 60 neuroglia that protect, feed,
and insulate the neuron. Because neurons are extremely specialized cells that are essential to
body function and almost never reproduce, neuroglia are vital to maintaining a functional
nervous system.
Brain
The brain, a soft, wrinkled organ that weighs about 3 pounds, is located inside the cranial cavity,
where the bones of the skull surround and protect it. The approximately 100 billion neurons of
the brain form the main control center of the body. The brain and spinal cord together form the
central nervous system (CNS), where information is processed and responses originate. The
brain, the seat of higher mental functions such as consciousness, memory, planning, and
voluntary actions, also controls lower body functions such as the maintenance of respiration,
heart rate, blood pressure, and digestion.
Spinal
Cord
The spinal cord is a long, thin mass of bundled neurons that carries information through the
vertebral cavity of the spine beginning at the medulla oblongata of the brain on its superior end
and continuing inferiorly to the lumbar region of the spine. In the lumbar region, the spinal cord
separates into a bundle of individual nerves called thecauda equina (due to its resemblance to a
horse’s tail) that continues inferiorly to thesacrum and coccyx. The white matter of the spinal
cord functions as the main conduit of nerve signals to the body from the brain. The grey matter
of the spinal cord integrates reflexes to stimuli.
Nerves
Nerves are bundles of axons in the peripheral nervous system (PNS) that act as information
highways to carry signals between the brain and spinal cord and the rest of the body. Each axon
is wrapped in a connective tissue sheath called the endoneurium. Individual axons of the nerve
are bundled into groups of axons called fascicles, wrapped in a sheath of connective tissue called
the perineurium. Finally, many fascicles are wrapped together in another layer of connective
tissue called the epineurium to form a whole nerve. The wrapping of nerves with connective
tissue helps to protect the axons and to increase the speed of their communication within the
body.
Afferent, Efferent, and Mixed Nerves. Some of the nerves in the body are specialized for carrying
information in only one direction, similar to a one-way street. Nerves that carry information from
sensory receptors to the central nervous system only are called afferent nerves. Other neurons,
known as efferent nerves, carry signals only from the central nervous system to effectors such as
muscles and glands. Finally, some nerves are mixed nerves that contain both afferent and
efferent axons. Mixed nerves function like 2-way streets where afferent axons act as lanes
heading toward the central nervous system and efferent axons act as lanes heading away from the
central nervous system.
Cranial Nerves. Extending from the inferior side of the brain are 12 pairs of cranial nerves. Each
cranial nerve pair is identified by a Roman numeral 1 to 12 based upon its location along the
anterior-posterior axis of the brain. Each nerve also has a descriptive name (e.g. olfactory, optic,
etc.) that identifies its function or location. The cranial nerves provide a direct connection to the
brain for the special sense organs, muscles of the head, neck, and shoulders, the heart, and the
GI tract.
Spinal Nerves. Extending from the left and right sides of the spinal cord are 31 pairs of spinal
nerves. The spinal nerves are mixed nerves that carry both sensory and motor signals between
the spinal cord and specific regions of the body. The 31 spinal nerves are split into 5 groups
named for the 5 regions of the vertebral column. Thus, there are 8 pairs of cervical nerves, 12
pairs of thoracic nerves, 5 pairs oflumbar nerves, 5 pairs of sacral nerves, and 1 pair of
coccygeal nerves. Each spinal nerve exits from the spinal cord through the intervertebral
foramen between a pair of vertebrae or between the C1 vertebra and the occipital bone of the
skull.
Meninges
The meninges are the protective coverings of the central nervous system (CNS). They consist of
three layers: the dura mater, arachnoid mater, and pia mater.
Dura mater. The dura mater, which means “tough mother,” is the thickest, toughest, and most
superficial layer of meninges. Made of dense irregular connective tissue, it contains many tough
collagen fibers and blood vessels. Dura mater protects the CNS from external damage, contains
the cerebrospinal fluid that surrounds the CNS, and provides blood to the nervous tissue of the
CNS.
Arachnoid mater. The arachnoid mater, which means “spider-like mother,” is much thinner and
more delicate than the dura mater. It lines the inside of the dura mater and contains many thin
fibers that connect it to the underlying pia mater. These fibers cross a fluid-filled space called the
subarachnoid space between the arachnoid mater and the pia mater.
Pia mater. The pia mater, which means “tender mother,” is a thin and delicate layer of tissue
that rests on the outside of the brain and spinal cord. Containing many blood vessels that feed the
nervous tissue of the CNS, the pia mater penetrates into the valleys of the sulci and fissures of
the brain as it covers the entire surface of the CNS.
Cerebrospinal Fluid
The space surrounding the organs of the CNS is filled with a clear fluid known as cerebrospinal
fluid (CSF). CSF is formed from blood plasma by special structures calledchoroid plexuses. The
choroid plexuses contain many capillaries lined with epithelial tissue that filters blood plasma
and allows the filtered fluid to enter the space around the brain.
Newly created CSF flows through the inside of the brain in hollow spaces called ventricles and
through a small cavity in the middle of the spinal cord called the central canal. CSF also flows
through the subarachnoid space around the outside of the brain and spinal cord. CSF is
constantly produced at the choroid plexuses and is reabsorbed into the bloodstream at structures
called arachnoid villi.
Cerebrospinal fluid provides several vital functions to the central nervous system:
CSF absorbs shocks between the brain and skull and between the spinal cord and vertebrae. This
shock absorption protects the CNS from blows or sudden changes in velocity, such as during a
car accident.
The brain and spinal cord float within the CSF, reducing their apparent weight through
buoyancy. The brain is a very large but soft organ that requires a high volume of blood to
function effectively. The reduced weight in cerebrospinal fluid allows the blood vessels of the
brain to remain open and helps protect the nervous tissue from becoming crushed under its own
weight.
CSF helps to maintain chemical homeostasis within the central nervous system. It contains ions,
nutrients, oxygen, and albumins that support the chemical and osmotic balance of nervous tissue.
CSF also removes waste products that form as byproducts of cellular metabolism within nervous
tissue.
Sense Organs
All of the bodies’ many sense organs are components of the nervous system. What are known as
the special senses—vision, taste, smell, hearing, and balance—are all detected by specialized
organs such as the eyes, taste buds, and olfactory epithelium. Sensory receptors for the general
senses like touch, temperature, and pain are found throughout most of the body. All of the
sensory receptors of the body are connected to afferent neurons that carry their sensory
information to the CNS to be processed and integrated.
Functions of the Nervous System
The nervous system has 3 main functions: sensory, integration, and motor.
Sensory. The sensory function of the nervous system involves collecting information from
sensory receptors that monitor the body’s internal and external conditions. These signals are then
passed on to the central nervous system (CNS) for further processing by afferent neurons (and
nerves).
Integration. The process of integration is the processing of the many sensory signals that are
passed into the CNS at any given time. These signals are evaluated, compared, used for decision
making, discarded or committed to memory as deemed appropriate. Integration takes place in the
gray matter of the brain and spinal cord and is performed by interneurons. Many interneurons
work together to form complex networks that provide this processing power.
Motor. Once the networks of interneurons in the CNS evaluate sensory information and decide
on an action, they stimulate efferent neurons. Efferent neurons (also called motor neurons) carry
signals from the gray matter of the CNS through the nerves of the peripheral nervous system to
effector cells. The effector may be smooth, cardiac, or skeletal muscle tissue or glandular tissue.
The effector then releases a hormone or moves a part of the body to respond to the stimulus.
Divisions of the Nervous System
Central Nervous System
The brain and spinal cord together form the central nervous system, or CNS. The CNS acts as the
control center of the body by providing its processing, memory, and regulation systems. The
CNS takes in all of the conscious and subconscious sensory information from the body’s sensory
receptors to stay aware of the body’s internal and external conditions. Using this sensory
information, it makes decisions about both conscious and subconscious actions to take to
maintain the body’s homeostasis and ensure its survival. The CNS is also responsible for the
higher functions of the nervous system such as language, creativity, expression, emotions, and
personality. The brain is the seat of consciousness and determines who we are as individuals.
Peripheral Nervous System
The peripheral nervous system (PNS) includes all of the parts of the nervous system outside of
the brain and spinal cord. These parts include all of the cranial and spinal nerves, ganglia, and
sensory receptors.
Somatic Nervous System
The somatic nervous system (SNS) is a division of the PNS that includes all of the voluntary
efferent neurons. The SNS is the only consciously controlled part of the PNS and is responsible
for stimulating skeletal muscles in the body.
Autonomic Nervous System
The autonomic nervous system (ANS) is a division of the PNS that includes all of the
involuntary efferent neurons. The ANS controls subconscious effectors such as visceral muscle
tissue, cardiac muscle tissue, and glandular tissue.
There are 2 divisions of the autonomic nervous system in the body: the sympathetic and
parasympathetic divisions.
Sympathetic. The sympathetic division forms the body’s “fight or flight” response to stress,
danger, excitement, exercise, emotions, and embarrassment. The sympathetic division increases
respiration and heart rate, releases adrenaline and other stress hormones, and decreases digestion
to cope with these situations.
Parasympathetic. The parasympathetic division forms the body’s “rest and digest” response
when the body is relaxed, resting, or feeding. The parasympathetic works to undo the work of the
sympathetic division after a stressful situation. Among other functions, the parasympathetic
division works to decrease respiration and heart rate, increase digestion, and permit the
elimination of wastes.
Enteric Nervous System
The enteric nervous system (ENS) is the division of the ANS that is responsible for regulating
digestion and the function of the digestive organs. The ENS receives signals from the central
nervous system through both the sympathetic and parasympathetic divisions of the autonomic
nervous system to help regulate its functions. However, the ENS mostly works independently of
the CNS and continues to function without any outside input. For this reason, the ENS is often
called the “brain of the gut” or the body’s “second brain.” The ENS is an immense system—
almost as many neurons exist in the ENS as in the spinal cord.
Lecture 15
Analyzers.
The sensory nervous system is a part of the nervous system responsible for
processing sensory information. A sensory system consists of sensory receptors, neural
pathways, and parts of the brain involved in sensory perception. Commonly recognized sensory
systems
are
those
for vision, auditory (hearing), somatic
sensation(touch), gustatory (taste), olfaction (smell) and vestibular (balance/movement). In short,
senses are transducers from the physical world to the realm of the mind where we interpret the
information, creating our perception of the world around us.
The receptive field is the specific part of the world to which a receptor organ and receptor cells
respond. For instance, the part of the world an eye can see, is its receptive field; the light that
each rod or cone can see, is its receptive field. Receptive fields have been identified for
the visual system, auditory system and somatosensory system, so far.
The Structure of The Eye
Cornea
The cornea and sclera form the outer fibrous layer of the eye. The cornea is a clear transparent
tissue, which is located forward of the eyeball.
Light rays pass through this limpid tissue, and on through the crystalline lens to reach the retina.
The cornea is convex in shape and for this reason directs or bends light rays so that they can be
focused on the retina. The cornea also provides protection to the globe.
Aqueous
Between the cornea and the crystalline lens is a space which is divided into two areas, the
anterior chamber and the posterior chamber. These areas are located either side of the iris.
Both the anterior and the posterior chambers contain aqueous fluid. The cornea and the
crystalline lens have no blood supply, so this clear aqueous fluid provides nutrients and removes
any waste deposits from the transparent structures in the front of the eye.
Iris
The Iris is located behind the cornea and in front of the crystalline lens. The Iris divides the
space behind the cornea into the anterior and posterior chamber, which contains aqueous fluid.
The Iris is a coloured tissue which extends from the ciliary body and is apparent at all times. The
colour of the Iris is determined genetically.
The purpose of the Iris is to constrict or enlarge the aperture of the pupil. By doing this it
determines the amount of light that enters the pupil. In bright light the muscles of the Iris
constrict the amount of light entering the pupil, and in low light the muscles enlarge the pupil to
allow more light to enter.
Crystalline Lens
Directly behind the pupil is a highly adaptable circular bi-convex transparent body called the
crystalline lens. This lens is dependent on the ciliary body and the suspensory ligaments to
change its thickness so that it can vary its refractive power accordingly.
When the ciliary muscle pulls on the lens it decreases its thickness, allowing objects in the
distance to become clear and in focus light on the retina. when it releases it’s pull, it increases in
thickness for near objects to come into focus on the retina.
Sclera
The eye consists of three layers of tissue which make up the wall of the eye. The sclera is the
outermost layer of tissue, also called the white of the eye. This layer is a very stable fibrous
membrane that continues to retain the shape of the eye and provides protection. Connected to the
sclera are the extra-ocular or extrinsic muscles of the eye.
Choroid
The choroid is a dark brown vascular coat of the eye between the sclera and the retina. When
light penetrates the pupil and focuses on the retina, nerve endings are triggered and then
absorbed by the choroid.
Retina
The retina is a delicate, multilayer, light sensitive membrane lining the inner eyeball. The layer
highly sensitive to light is the layer of rods and cones, when light hits the retina photosensitive
pigments within the rods and cones convert light rays into nerve impulses.
The retina covers about three-quarters of the inner surface of the eyeball, this layer lies between
the choroid and the vitreous. Towards the posterior part of the retina is the macula lutea which is
the most responsive part of this layer. Where the optic nerve leaves the eye, there is a blind spot
in the vision, this part, known as the optic disc has no light-sensitive cells.
Vitreous
The vitreous body is a soft, limpid consistency made up of about 99% water, it occupies the
cavity behind the crystalline lens whilst giving an appropriate intraocular pressure to avoid the
walls of the eyeball from collapsing. The Vitreous body and the aqueous fluid maintain the shape
of the eye due to the intraocular pressure.
Optic Nerve
The optic nerve is a motor nerve that connects the retina of the eye with the brain. This nerve
penetrates the choroid and the sclera from the rear of the eye at the optic disc where it is met
with the other optic nerve to form the optic chiasma.
This is an X shaped structure formed by the two optic nerves when they cross each other on the
undersurface of the brain. The optic nerve sends all information from the retina to the brain to
give us a picture.