Download CH 6 Skeletal System Part I

CH 6- Skeletal System
Fun Bone Facts
• When you were born you had over 300 bones.
Now, you have 206 bones.
• Over half the body's bones are in the hands and
feet.
• Not all bones are in connection with another
bone.
• Your bones are not all solid- store water.
• The smallest bone in the body is the stirrup
(stapes) in the ear measuring about 3 mm in
length.
• The longest bone in the body is the femur.
Functions of the Skeletal System
• Support: forms the structural framework for the
body.
• Serves as a point of attachment either directly or
indirectly for the soft tissues of the body.
• Protection: protects the vital organs of the body.
• Form bony boxes or cages around vital organs like
the brain, heart and lungs.
• Assists in movement: serves as a point of
attachment for skeletal muscles.
• When a skeletal muscle contracts, it will pull on a
bone- generating movement. Where muscles attach
to and pull on bones, bone landmarks are formed.
• Mineral homeostasis (balance): stores minerals such
as calcium and phosphorus.
• If the levels of these minerals in the blood drop, they
can be released from the bone into the bloodstream.
Calcium is essential for bone strength as well as
muscle contraction.
• Hemopoiesis: the production of blood cells.
• Includes red cells, white cells and platelets.
• Happens in the red bone marrow of bone.
• Lipid storage: stores lipids for further use.
• Stored in the bone marrow
Types of Bones (shapes)
• Long bones: Longer than they are wide
– Found in the arms and the legs
– Function as levers to generate movement
• Amplify the movement of muscles- 1 inch of travel
when a skeletal muscle contracts translates to
much more gross body movement.
• Short bones: Square or cube shaped
– Found in the wrists and ankles
– Function to evenly transfer forces from the
hands and feet to the arms and legs.
• As they receive a force, they shift, causing the
force transfer to be even.
• Flat bones: Thin, flat and slightly curved
(difficult to break)
– Found on the top of the skull and on the ribcage
– Function to protect
• Irregular bones: No set shape
– Found in the spine (vertebrae), face and girdles
(shoulder and hip)
– Function in muscle attachment
• Sesamoid bones: Develop inside a tendon
– Found in the kneecap
– Function to protect the tendon of a muscle during
movement
Histology of Bone Tissue
• Classified as a connective tissue because
it contains an abundant extracellular
matrix that surrounds widely spaced cells.
• Composed of:
– 98% matrix
• 50% inorganic minerals (mainly Ca and P)
• 25% protein fibers (mainly collagen that
allows the bone to bend a little before it
breaks)
• 23% water
Bone cells- 2% of bone tissue
• Osteogenic cells: unspecified stem cells that
are found within developing bone
– As they mature, they will change in structure
and function (differentiate)
• Osteoblasts: bone forming cells
– Differentiated osteogenic cells
– Responsible for removing minerals from the
blood and placing them into the developing
bone matrix (like brick layers). This “walls”
them off from neighboring cells.
Bone cells- 2% of bone tissue
• Osteocytes: mature bone cells
– Differentiated osteoblasts
– Maintain the matrix of an area of bone tissue
• Osteoclasts: Bone destroying cells
– Contain powerful digestive enzymes that can
break down the matrix of bone tissue
• Releases minerals into the blood
• Helps with the healing process by smoothing edges
of a fracture so the osteoblasts can fill in the gap.
Types of Bone Tissue
Compact bone tissue: forms the external
layer of all bones.
• Function
• Provides strength and rigidity to the bone
• Helps bones resist force
• Structure
• Composed of smaller columns of bone matrix
held together by more matrix (adds to its
strength)
Compact Bone Structure cont…
• Osteons: the structural unit of compact bone
(bone columns)
• Lamellae: Mineral rings of matrix of an osteon.
• Lacunae: spaces within the osteons that contain
osteocytes.
–One osteocyte per lacuna which maintains
the matrix around that lacuna.
• Canaliculi: the small spaces extending from the
lacunae.
–Connect neighboring lacunae so the
osteocytes can transfer materials (oxygen &
nutrients) between one another.
• Perforating canals: horizontal canals that pass
through compact bone.
• These run perpendicular to the osteon and
let blood vessels and nerves travel
transversely in bone.
• Haversian canals: vertical canals that pass
through compact bone.
• These are at the center of every osteon
and run parallel to the osteon. They allow
blood vessels and nerves travel the length
of the bone.
Spongy Bone (Cancellous)
• Forms the internal structure of all bones and the ends of
long bones.
– Structure: Hard and not solid (“airy”)
– Function:
• Increases the strength without increasing its weight.
• Trabeculae: an irregular lattice of thin columns of
bone organized along stress lines within bone.
– Hollow spaces between trabeculae are filled with
red bone marrow.
– These thin columns fracture fairly easily;
however, when they rebuild themselves, they are
stronger and re-oriented to resist future force.
The Anatomy of a Bone
• The long bone is used as the example when studying
the anatomy of bone because all features are easily
identifiable.
• The features are:
– Diaphysis: the shaft of a long bone.
• Functions to provide the strength to the bone
because it contains a thick layer of compact bone
and a thin layer of spongy bone.
– Epiphyses (“es” is plural; “is” is singular): the ends
of a long bone.
• Function to form a joint and are rounded to allow joint
formation. These are mainly composed of spongy
bone.
– Proximal epiphysis:
• The end of the long bone that is closest to the trunk
of the body.
– Distal epiphysis:
• The end of the long bone furthest from the trunk of
the body.
• Metaphyses: the regions found between the
epiphyses and the diaphysis of a long bone.
• Function depends on the age of the bone.
– Epiphyseal plate: the name given to the metaphyses in
a developing bone.
• Made entirely of hyaline cartilage and allows for the
lengthwise growth of bone.
• Called the “growth plate” and is not visible on x-rays.
– Epiphyseal line: the name given to the metaphyses
in a mature bone.
• Once this is formed, bone growth stops because
the raw material (cartilage) has been converted to
bone.
• Articular cartilage: a thin layer of hyaline
cartilage found covering the ends of bones
(epiphyses) forming a joint.
• Functions as a shock absorber to protect the ends
of bones.
• As we age, the cartilage breaks down and wears
away.
• Periosteum: a thin layer of dense irregular
connective tissue that covers all surfaces of a
bone not covered by articular cartilage.
– Functions to protect blood vessels and nerves and is
a point of attachment for muscle tendons.
– Because it is dense irregular, the collagen fibers
running in different directions can resist any force
from muscle contraction.
• Medullary cavity: a hollow space found within
the diaphysis of a long bone.
– Function depends on the age of the bone (either
contains red or yellow bone marrow.
– Red bone marrow:
• Produces blood cells (hemopoiesis)
• Fills the medullary cavity of younger individuals
because they are growing and have a higher
metabolic need (need more oxygen so need more
red blood cells).
– Yellow bone marrow:
• Energy reserve (stores fat)
• Found in the medullary cavity of most adult bones
• Endosteum: a thin layer of fibrous connective tissue
found lining the medullary cavity that holds the bone
marrow in place.
• Nutrient foramen: small openings found throughout
compact bone that allow blood vessels and nerves to
enter the bone tissue.
Anatomy of a Long Bone
Bone Formation
• Ossification: the process responsible for converting
connective tissue into bone.
– There are two different types of ossification that occur
in the body:
• Intramembranous ossification: the formation of
bones from fibrous connective tissue
(mesenchyme).
– Occurs in flat bones like the skull
– The tissue is arranged in sheets called
ossification centers and the process starts at the
center of the sheet and works it way outwards.
– Begins before birth and doesn’t finish until midteens
– The reason for a baby’s “soft spot”
Bone Formation
• Endochondral ossification: the formation of
bones from hyaline cartilage.
–Forms all bones except flat bones.
–Begins before birth in the center of the
diaphysis (primary ossification center).
–Continues shortly after birth in the
epiphyses (secondary ossification
center).
–The growing regions meet at the
epiphyseal plate, forcing the bone to
grow lengthwise.
Bone Surface Markings
• Depressions and openings:
– Fissure: Narrow slit between adjacent parts of
bones through which blood vessels or nerves
pass
– Foramen: Opening through which blood
vessels, nerves or ligaments pass
– Fossa: Shallow depression
– Sulcus: Furrow along a bone surface that
accomodates blood vessels, nerves or
tendons.
– Meatus: Tube-like opening
Fissure
Foramen
Fossa
Sulcus
Meatus
Bone Surface Markings
• Processes that form joints:
– Condyle: Large, round protuberance with a
smooth articular surface at the end of bone
– Facet: Smooth, flat, slightly concave or
convex articular surface
– Head: Usually rounded articular projection
supported by a constricted portion (neck) of
the bone
Condyle
Facet
Head
• Processes that form points of attachment
for connective tissues:
– Crest: Prominent ridge or elongated projection
– Epicondyle: Typically roughened projection
above a condyle
– Line: Long narrow ridge or border that is less
prominent than a crest
– Spinous process: Sharp, slender projection
– Trochanter: Large projection
– Tuberosity: Variable sized projection that is
rough and bumpy
– Tubercle: Variable sized rounded projection
Crest
Epicondyle
Line
Spinous Process
Trochanter
Femur
Tuberosity
Tubercle
Bone Surface Markings Practice
A.
B.
C.
D.
E.
F.
G.
H.
I.
Fissure
Foramen
Fossa
Sulcus
Meatus
Condyle
Facet
Head
Crest
J. Epicondyle
K. Line
L. Spinous process
M. Trochanter
N. Tuberosity
O. Tubercle