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4.1 Types of Tissues
Tissues are composed of specialized cells of the same type that perform a common function in the body. The tissues of the human
body can be categorized into four major types: connective tissue, muscular tissue, nervous tissue, and epithelial tissue.
4.2 Connective Tissue Connects and Supports
Connective tissues bind body parts together. Although quite diverse in structure and function, connective tissues all contain
specialized cells, ground substance, and protein fibers. The term matrix includes the ground substance and fibers. Three types of
fibers, collagen, reticular, and elastic fibers, give each type of connective tissue unique qualities.
Fibrous Connective Tissue
In these tissues fibroblasts are separated by jelly-like matrix containing collagen and elastic fibers. Loose fibrous connective
tissue supports internal organs; dense fibrous connective tissue makes up tendons and ligaments. The fibroblasts in adipose
tissue enlarge and store fat.
Supportive Connective Tissue
Both cartilage and bone have cells within lacunae, but the matrix for cartilage is more flexible than that for bone. The three
types of cartilage include hyaline cartilage (at the ends of bones and comprising the fetal skeleton), elastic cartilage (forming
a flexible frame for the outer ear), and fibrocartilage (making pads in the knee and vertebral column).
Bone
The matrix of bone is hard because it contains inorganic salts, particularly calcium salts. In compact bone, the lacunae lie in
concentric circles within an osteon (or Haversian system) about a central canal. Spongy bone is made up of bars and bony
plates and is lighter than compact bone.
Fluid Connective Tissues
Body tissues are bathed in tissue fluid. Blood is a connective tissue in which the matrix is a liquid called plasma. Red blood
cells, white blood cells, and platelets are in blood. Lymph is also a fluid connective tissue. It is a clear, watery fluid derived
from tissue fluid that contains white blood cells.
4.3 Muscle Tissue Moves the Body
Muscular tissue is of three types: skeletal, smooth, and cardiac. Both skeletal and cardiac muscles are striated; both cardiac and
smooth muscles are involuntary. Skeletal muscle is found in muscles attached to bones, and smooth muscle is found in internal organs.
Cardiac muscle makes up the heart.
4.4 Nervous Tissue Communicates
Nervous tissue consists of nerve cells, called neurons, and neuroglia, the cells that support and nourish the neurons.
Neurons
A neuron has three parts: dendrites, to receive signals from sensory receptors or other neurons, a cell body where the nucleus
is located, and an axon, to conduct nerve impulses.
Neuroglia
There are several types of neuroglial cells which support, nourish, and protect neurons.
4.5 Epithelial Tissue Protects
Epithelial tissue covers the body and lines its cavities. A basement membrane joins epithelium to underlying connective tissue.
Simple Epithelia
Simple epithelia have only a single layer of cells, which can be either flattened (squamous), cube-shaped (cuboidal), or
rectangular columns (columnar). This type can be found in the air sacs of lungs, walls of blood vessels, covering the ovaries,
lining kidney tubules, and lining the digestive tract.
Pseudostratified Columnar Epithelium
These cells appear to be layered, but each cell actually touches the basement membrane. This type can be found in the lining
of the trachea.
Transitional Epithelium
This type of epithelial tissue changes in response to tension. It forms the lining of the urinary bladder.
Stratified Epithelia
Stratified epithelia have layers of cells piled one on top of the other. This type can be found in the nose, mouth, esophagus,
anal canal, outer portion of the cervix, and vagina.
Glandular Epithelia
When an epithelium secretes a product, it is said to be glandular. Exocrine glands secrete their product onto the outer surface
or into a cavity, while endocrine glands secrete their products internally.
4.6 Cell Junctions
Tight junctions (form an impermeable barrier), gap junctions (allow materials to pass from cell to cell), and adhesion junctions (allow
tissues to stretch) occur between epithelial cells.
4.7 Integumentary System
The integumentary system, or skin, is an example of an organ system because it contains accessory structures such as nails, hair, and
glands. Skin protects underlying tissues from physical trauma, pathogen invasion, and water loss. Skin helps regulate body
temperature, and because it contains sensory receptors, skin also helps us to be aware of our surroundings.
Regions of the Skin
The skin has two regions: the epidermis and the dermis. A subcutaneous layer is found between the skin and any underlying
structures.
The Epidermis
The epidermis contains basal cells that produce new epithelial cells that become keratinized as they move toward the
surface. Specialized cells called Langerhans cells phagocytize pathogens and protect the body from invading
organisms. Melanocytes produce melanin, the main pigment responsible for skin color and protect the skin from the
damaging effects of ultraviolet radiation.
Skin Cancer
Too much ultraviolet radiation is dangerous and can lead to skin cancer. Basal cell carcinoma is the more
common type of skin cancer and the most curable. Melanoma is extremely serious. Steps should be taken
to protect the skin from ultraviolet radiation.
The Dermis
The dermis, a largely fibrous connective tissue, contains epidermally derived glands and hair follicles, nerve
endings, and blood vessels. Sensory receptors for touch, pressure, temperature, and pain are present.
The Subcutaneous Layer
A subcutaneous layer, which is made up of loose connective tissue containing adipose cells, lies beneath the skin.
Accessory Organs of the Skin
The accessory structure of the skin includes the nails, hair follicles, oil glands and sweat glands.
4.8 Organ Systems
The systems of the body work together to maintain homeostasis.
Integumentary System
The integumentary system contains skin and also includes nails, hairs, muscles, oil and sweat glands, blood vessels, and
nerves. It has many homeostatic functions.
Cardiovascular System
The heart pumps blood and sends it out under pressure into the blood vessels. Blood distributes heat produced by the
muscles and transports nutrients and oxygen to the cells. It also removes their waste products. Specialized cells in the blood
are also involved in fighting infections and blood clotting.
Lymphatic and Immune Systems
The lymphatic system consists of lymphatic vessels, lymph nodes, the spleen, and other lymphatic organs. It is involved in
collecting excess tissue fluid, absorbing lipoproteins, and transporting lymph. The immune system consists of all the cells in
the body that protects us from disease.
Digestive System
The digestive system consists of the mouth, esophagus, stomach, small intestine, large intestine, and associated organs. It
receives food and digests it.
Respiratory System
The respiratory system consists of the lungs and the tubes that take air to and from them. It brings oxygen into the body and
removes carbon dioxide.
Urinary System
The urinary system contains the kidneys, the bladder, and the tubes that carry urine. The kidneys rid the body of metabolic
wastes and help regulate the salt-water balance and acid-base balance of the blood.
Skeletal System
The bones of the skeletal system protect and move body parts. It also stores minerals and produces blood cells.
Muscular System
Skeletal muscle maintains posture and accounts for the movement of the body. Muscle contractions also help to warm the
body. Cardiac muscle pumps blood. Smooth muscle moves other substances such as urine and food.
Nervous System
The nervous system consists of the brain, spinal cord, and associated nerves. This system allows us to respond to both
external and internal stimuli.
Endocrine System
The endocrine system consists of hormonal glands which secrete chemical messengers. Hormones have a wide range of
effects on the body. Both the nervous and endocrine systems coordinate and regulate the functioning of the body’s other
systems.
Reproductive System
The reproductive system differs between males and females, but is responsible for the continuance of the species.
Body Cavities
Internal organs occur within cavities; the dorsal cavity contains the brain and spinal cord; the thoracic cavity contains the
heart and lungs; the abdominal cavity contains the organs of the digestive, urinary, and reproductive systems, among others.
Body Membranes
Membranes line body cavities and internal spaces of organs. Mucous membrane lines the tubes of the digestive
system; serous membrane lines the thoracic and abdominal cavities and covers the organs they contain. Synovial
membranes line joint cavities and meninges line the dorsal cavity.
4.9 Homeostasis
Homeostasis is the body’s ability to maintain a relative constancy of its internal environment by adjusting its physiological processes.
The Internal Environment
The internal environment has two parts: blood and tissue fluid. Blood delivers oxygen and nutrients to the tissues and carries
carbon dioxide and wastes away. Tissue fluid is the medium through which substances are exchanged between cells and
blood.
The Body Systems and Homeostasis
The nervous and endocrine systems are particularly important in coordinating the activities of all the other organ systems as
they function to maintain homeostasis. All of the organ systems must do their part in order to keep us alive and healthy.
Negative Feedback
Negative feedback is the primary homeostatic mechanism that keeps a variable close to a particular value. It has at least two
components: a sensor and a control center.
Mechanical Example
A home heating system is often used to illustrate how a more complicated negative feedback mechanism works.
The thermostat determines the set point and contains a thermometer, the sensor that detects when the room
temperature is above or below the set point. It also contains the control center that turns the furnace on and off.
Human Example: Regulation of Body Temperature
The sensor and control center for body temperature is located in a part of the brain called the hypothalamus.
Above Normal Temperature
When the body temperature is above normal, the control center directs the blood vessels of the skin to
dilate allowing more blood to flow near the surface of the body where heat can be lost to the environment.
The nervous system activates the sweat glands and evaporation of sweat helps lower body temperature.
Below Normal Temperature
When the body temperature falls below normal, the control center directs the blood vessels of the skin to
constrict. It also sends nerve impulses to the skeletal muscles and shivering occurs to generate heart.
Positive Feedback
Positive feedback brings about a greater change in the same direction. One example of positive feedback is the release of
oxytocin during childbirth.
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5.1 Overview of the Cardiovascular System
The cardiovascular system consists of the heart, which pumps blood, and the blood vessels through which blood flows.
Circulation Performs Exchanges
The purpose of circulation is to service the cells. Blood brings cells the oxygen and nutrients they need and removes their
waste products. Blood is purified of its wastes at the kidneys, liver, and lungs. It gains nutrients at the lungs and intestines.
Functions of the Cardiovascular System
The heart pumps blood through blood vessels where exchange can take place with the interstitial fluid. The heart and blood
vessels regulate blood flow according to the needs of the body.
Lymphatic System
The lymphatic system collects excess tissue fluid and returns it to the cardiovascular system.
5.2 The Types of Blood Vessels
The three types of blood vessels are arteries, capillaries, and veins.
The Arteries: From the Heart
Arteries and arterioles take blood away from the heart. The middle layer of arteries consists of smooth muscle that can
constrict to regulate blood flow and blood pressure.
The Capillaries: Exchange
The capillaries have walls that are only one cell thick and allow exchange of substances with tissue fluid. Not all capillary
beds are open at the same time. Contraction of a sphincter muscle closes off the bed and then blood flows through an
arteriovenous shunt bypassing the capillary bed.
The Veins: To the Heart
Venules drain into veins that return blood to the heart. Veins have much less smooth muscle and connective tissue than an
artery. Veins often have valves that prevent the backward flow of blood when closed.
5.3 The Heart is a Double Pump
The cone-shaped, muscular heart is made up of myocardium lying inside a fibrous pericardium. Coronary arteries supply the
myocardium with oxygen and nutrients. In the heart the right and left atria empty into the right and left ventricles respectively.
Atrioventricular valves occur between the atria and ventricles, and semilunar valves occur between the ventricles and the attached
arteries. Chordae tendinae strengthen atrioventricular valves.
Passage of Blood Through the Heart
This sequence traces the path of blood from the body through the heart: superior and inferior vena cava, right atrium, right
ventricle, pulmonary arteries to the lungs. Then from the lungs blood goes back to the heart via pulmonary veins, left atrium,
left ventricle, and then to the body through the aorta.
The Heartbeat is Controlled
Each heartbeat is called a cardiac cycle. Systole refers to the contraction of heart chambers and diastole refers to their
relaxation. The heart sounds, lub-dup, are due to the closing of the atrioventricular valves, followed by the closing of the
semilunar valves.
Internal Control of Heartbeat
The sinoatrial (SA) node (pacemaker) initiates the beat and causes the atria to contract. The atrioventricular (AV)
node conveys the stimulus and initiates contraction of the ventricles. The signal for the ventricles to contract travels
from the AV node through the atrioventricular bundle to the smaller Purkinje fibers.
External Control of Heartbeat
A cardiac control center in the medulla oblongata regulates the heartbeat by way of the parasympathetic (slows heart
rate) and the sympathetic (increases heart rate) systems.
The Electrocardiogram is a Record of the Heartbeat
An electrocardiogram (ECG) is a recording of the electrical changes that occur in myocardium during a cardiac cycle. The P
wave signals the atria are about to contract; the QRS wave signals the ventricles are about to contract, and recovery of the
ventricles produces the T wave.
5.4 Features of the Cardiovascular System
When the left ventricles contracts, a surge of blood flows through the arteries. Blood pressure is highest in the large arteries nearer the
heart.
Pulse Rate Equals Heart Rate
The surge of blood entering the arteries following a heartbeat causes their elastic walls to stretch and then recoil. This is felt
as a pulse. The pulse rate of the radial and carotid artery tells the heart rate.
Blood Flow is Regulated
The beating of the heart creates the pressure that propels blood in the arteries and the arterioles.
Blood Pressure Moves Blood in Arteries
Blood pressure is the pressure of blood against the wall of a blood vessel. It is usually measured in the brachial
artery of the arm with a sphygmomanometer. The higher number is the systolic pressure and the lower number is
the diastolic pressure. Normal blood pressure is 120/80.
Blood Flow is Slow in the Capillaries
Blood moves slowly in capillaries because there are more capillaries than arterioles. This slow pace allows time for
exchanges between capillary blood and tissue cells.
Blood Flow in Veins Returns Blood to Heart
Venous return is dependent upon skeletal muscle contraction, presence of valves in veins, and respiratory
movements. Once blood has moved past a valve it closes preventing backward return.
5.5 Two Cardiovascular Pathways
The blood flows in two circuits: the pulmonary and the system circuit.
The Pulmonary Circuit Exchange of Gases
In the pulmonary circuit, pulmonary arteries take blood from the right ventricle to the lungs, carbon dioxide is given off and
oxygen is picked up, and pulmonary veins return it to the left atrium. Pulmonary arteries carry oxygen-poor blood while
pulmonary veins carry oxygen-rich blood.
The System Circuit: Exchanges with Tissue Fluid
To trace the path of blood in the systemic circuit, start with the aorta from the left ventricle. Follow its path until it branches
to an artery going to a specific organ. It can be assumed that the artery divides into arterioles and capillaries, and that the
capillaries lead to venules. The vein that takes blood to the vena cava most likely has the same name as the artery that
delivered blood to the organ. In the adult systemic circuit, unlike the pulmonary circuit, the arteries carry blood that is
relatively high in oxygen and relatively low in carbon dioxide, and the veins carry blood that is relatively low in oxygen and
relatively high in carbon dioxide.
Coronary Circulation
The coronary arteries and veins serve the heart muscle itself.
Hepatic Portal System
The hepatic portal system carries nutrient-rich blood from the small intestines to the liver, the organ that monitors
the blood’s composition.
5.6 Exchange at the Capillaries
Osmotic pressure and blood pressure control movement of fluid through the capillary wall. At the arterial end of a capillary, blood
pressure is higher than osmotic pressure and water exits a capillary at this end. At the venule end of a capillary, osmotic pressure is
greater than blood pressure, and water tends to move into the capillary.
5.7 Cardiovascular Disorders
Cardiovascular disease is the leading cause of untimely death in the Western countries.
Disorders of the Blood Vessels
Disorders of the blood vessels include hypertension and atherosclerosis that most often lead to a stroke or a heart attack.
Another possible outcome is an aneurysm.
High Blood Pressure
Hypertension is high blood pressure, which can lead to heart disease. The best defense against hypertension is a lifestyle that lowers the risk of hypertension. Hypertension is often seen in individuals with atherosclerosis, an
accumulation of plaque in the linings of arteries.
Stroke, Heart Attack, and Aneurysm
If a blood clot lodges in a cerebral blood vessel or a cerebral blood vessel bursts, a stroke has occurred and a portion
of the brain dies. If a blood clot lodges in a coronary blood vessel, a heart attack occurs. An aneurysm is a
ballooning of a blood vessel. If a major blood vessel like the aorta bursts, death is likely.
Dissolving Blood Clots
There are medical treatments for dissolving and perhaps preventing the occurrence of blood clots.
Treating Clogged Arteries
In a coronary bypass operation, a vessel is grafted onto the heart to bypass an obstructed vessel.
Angioplasty is also a common surgical procedure for treating clogged arteries.
Disorders of the Heart
In heart failure the heart no longer pumps as it should. Various medical procedures assist the heart in pumping and in
regulating the heartbeat.
Heart Transplants
Heart transplants are routinely performed but there is a shortage of human hearts. Work still goes forward on an
artificial heart.
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6.1 Blood: An Overview
Functions of Blood
Blood is the primary transport medium of the body. Blood transports gases and nutrients and carries away wastes from all
parts of the body. Hormones are also transported in the blood. Blood defends the body against invasion by pathogens in
several ways, and blood has regulatory functions for temperature, water/salt balance, and pH.
Composition of Blood
Blood is a tissue that contains cells and cells fragments suspended in a liquid called plasma.
The Formed Elements
The formed elements are red blood cells, white blood cells, and platelets. Red blood cells are two to three times
smaller than white blood cells but there are many more of them.
Plasma
Plasma is the liquid portion of blood, made up mostly of water, but also containing salts, small organic molecules,
hormones, and plasma proteins. The liver makes most plasma proteins that function to buffer the blood, transport
molecules, and maintain osmotic pressure. They also have specific functions: Albumin transports bilirubin; globulin
is a component of lipoproteins, which transport cholesterol; gamma globulins are the antibodies of immunity;
fibrinogen is involved in blood clotting.
6.2 Red Blood Cells and Transport of Oxygen
Red blood cells (erythrocytes) are small, biconcave disks that lack a nucleus when mature. There are 4–6 million red blood cells per
mm3 of whole blood.
How Red Blood Cells Carry Oxygen
Red blood cells contain hemoglobin, the respiratory pigment that transports oxygen. Each hemoglobin molecule has four
polypeptides that comprise the protein globin and an iron-containing, oxygen-carrying heme portion.
How Red Blood Cells Help Transport Carbon Dioxide
Hemoglobin directly transports about 25% of carbon dioxide which binds to the terminal amino groups of the globin
molecules.
Red Blood Cells are Produced in Bone Marrow
Red blood cells are produced in the bone marrow. Red blood cells live only about 120 days and are destroyed in the liver and
the spleen. Hemoglobin is released when blood cells are broken down. Iron is recovered and recycled to the bone marrow.
Pigments from hemoglobin are excreted as bile pigments.
Blood Doping
Blood doping is any method of increasing the supply of RBCs for the purpose of delivering oxygen more efficiently,
reducing fatigue, and giving athletes a competitive edge.
Disorders Involving Red Blood Cells
Anemia results from too few red blood cells and/or insufficient hemoglobin. Sickle-cell disease is a hereditary condition in
which the individual has sickle-shaped red blood cells that tend to rupture as they pass through the narrow capillaries.
6.3 White Blood Cells and Defense Against Disease
White blood cells (leukocytes) are large and nucleated, and function in immunity. They squeeze through capillaries and invade tissues
when needed. Some white blood cells are very good at phagocytosis while others produce antibodies. Colony-stimulating factors
(CSFs) are proteins that regulate the production of white blood cells.
Types of White Blood Cells
White blood cells are classified into the granular leukocytes and the agranular leukocytes because of the presence of
noticeable granules.
Granular Leukocytes
Neutrophils engulf bacteria and debris through phagocytosis. Eosinophils are numerous during allergic reactions or
parasitic infections. Basophils become mast cells in tissues, releasing histamine.
Agranular Leukocytes
Agranular leukocytes include monocytes, which become macrophages that phagocytize pathogens and cellular
debris in tissues, and lymphocytes (B lymphocytes and T lymphocytes) responsible for immunity.
Disorders Involving White Blood Cells
Inherited immune deficiencies such as severe combined immunodeficiency disease (SCID) result from disorders with the
production and/or function of white blood cells. Cancer of white blood cells is called leukemia. Mononucleosis is an
infectious disease in which a virus infects lymphocytes.
6.4 Platelets and Blood Clotting
Platelets result from the fragmentation of megakaryocytes in the red bone marrow. These are involved in the process of blood
clotting.
Blood Clotting
When tissues are damaged, platelets stick to the damaged area, partially sealing torn blood vessels. Injured tissues release
prothrombin activator, which converts prothrombin to thrombin. This step requires calcium ions. Thrombin functions as an
enzyme to convert fibrinogen into insoluble fibrin.
Disorders Related to Blood Clotting
An insufficient number of platelets is called thrombocytopenia. Hemophilia is an inherited clotting disorder due to a
deficiency in a clotting factor.
6.5 Blood Typing and Transfusions
A blood transfusion is the transfer of blood from one individual into the blood of another. Blood typing involves determining the
ABO blood group and Rh factor so that the transfusion can be done safely.
ABO Blood Groups
The most common system for typing blood is the ABO system. Blood types A, B, and AB correspond with having specific
antigens on the surface of RBCs; type O is an absence of these antigens. All persons have antibodies in their plasma for the A
and/or B antigen not carried on their own RBCs. If the corresponding antigen and antibody are combined, clumping, or
agglutination, occurs; in this way the blood type of the individual may be determined.
Blood Compatibility
The antibodies in the plasma must not combine with the antigens on the surface of the red blood cells or
agglutination will occur. Type O is sometimes called the universal donor because it has neither type A nor type B
antigens on the red blood cells, and type AB blood is sometimes called the universal recipient because this blood
type has neither anti-A or anti-B antibodies in the plasma.
Rh Blood Groups
The Rh system represents another antigen on the surface of RBCs. Rh positive (Rh+) indicates presence of the antigen; Rh
negative (Rh-) indicates its absence. Rh factor is especially important in Rh - mothers who carry Rh+ fetuses because of the
possibility of hemolytic disease of the newborn.
6.6 Homeostasis
All of the human systems work together to maintain homeostasis.
How Body Systems Work Together
The cardiovascular system delivers oxygen and nutrients to, and takes away metabolic wastes from, the tissue fluid that
surrounds cells. The lymphatic system returns tissue fluid to the bloodstream.