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- Cardiovascular System
Introduction
A.
A functional cardiovascular system is vital for supplying oxygen and nutrients to tissues
and removing wastes from them.
Structure of the Heart
A.
The heart is a hollow, cone-shaped, muscular pump within the thoracic cavity.
B.
Size and Location of the Heart
1.
The average adult heart is 14 cm long and 9 cm wide.
2.
The heart lies in the mediastinum under the sternum; its apex extends to the fifth
intercostal space.
C.
Coverings of the Heart
1.
The pericardium encloses the heart.
2.
It is made of two layers: the outer, tough connective tissue fibrous pericardium
surrounding a more delicate visceral pericardium (epicardium) that surrounds the
heart.
3.
At the base of the heart, the visceral pericardium folds back to become the parietal
pericardium that lines the fibrous pericardium.
4.
Between the parietal and visceral pericardia is a potential space (pericardial cavity)
filled with serous fluid.
D.
Wall of the Heart
1.
The wall of the heart is composed of three distinct layers.
2.
The outermost layer, the epicardium, is made up of connective tissue and
epithelium, and houses blood and lymph capillaries along with coronary arteries.
3.
The middle myocardium consists of cardiac muscle and is the thickest layer of the
heart wall.
4.
The inner endocardium is smooth and is made up of connective tissue and
epithelium, and is continuous with the endothelium of major vessels joining the
heart.
a.
The endocardium houses Purkinje fibers.
E.
Heart Chambers and Valves
1.
The heart has four internal chambers: two atria on top and two ventricles below.
a.
Atria receive blood returning to the heart and have thin walls and ear-like
auricles projecting from their exterior.
b.
The thick-muscled ventricles pump blood to the body.
2.
A septum divides the atrium and ventricle on each side and contains an
atrioventricular orifice, each guarded by an atrioventricular (A-V) valve.
a.
The right A-V valve (tricuspid) and left A-V valve (bicuspid or mitral
valve) have cusps to which chordae tendinae attach.
b.
Chordae tendinae are, in turn, attached to papillary muscles in the inner
heart wall that contract during ventricular contraction to prevent the
backflow of blood through the A-V valves.
3.
The right ventricle has a thinner wall than does the left ventricle because it must
pump blood only as far as the lungs, compared to the left ventricle pumping to the
entire body.
4.
At the base of the pulmonary trunk leading to the lungs is the pulmonary valve,
which prevents a return flow of blood to the ventricle.
5.
The left atrium receives blood from four pulmonary veins.
6.
The left ventricle pumps blood into the entire body through the aorta, guarded by
the aortic valve that prevents backflow of blood into the ventricle.
F.
G.
H.
Skeleton of the Heart
1.
Rings of dense connective tissue lie at the plane in which the A-V orifices and
aortic and pulmonary valves lie; these rings make up the skeleton of the heart.
2.
These tough rings prevent dilating of tissue in this area.
Path of Blood through the Heart
1.
Blood low in oxygen returns to the right atrium via the venae cavae and coronary
sinus.
2.
The right atrium contracts, forcing blood through the tricuspid valve into the right
ventricle.
3.
The right ventricle contracts, closing the tricuspid valve, and forcing blood through
the pulmonary valve into the pulmonary trunk and arteries.
4.
The pulmonary arteries carry blood to the lungs where it can rid itself of excess
carbon dioxide and pick up a new supply of oxygen.
5.
Freshly oxygenated blood is returned to the left atrium of the heart through the
pulmonary veins.
6.
The left atrium contracts, forcing blood through the left bicuspid valve into the left
ventricle.
7.
The left ventricle contracts, closing the bicuspid valve and forcing open the aortic
valve as blood enters the aorta for distribution to the body.
Blood Supply to the Heart
1.
The first branches off of the aorta, which carry freshly oxygenated blood, are the
right and left coronary arteries that feed the heart muscle itself.
2.
Branches of the coronary arteries feed many capillaries of the myocardium.
3.
The heart muscle requires a continuous supply of freshly oxygenated blood, so
smaller branches of arteries often have anastomoses as alternate pathways for
blood, should one pathway become blocked.
4.
Cardiac veins drain blood from the heart muscle and carry it to the coronary sinus,
which empties into the right atrium.
Heart Actions
A.
The cardiac cycle consists of the atria beating in unison followed by the contraction of both
ventricles, then the entire heart relaxes for a brief moment.
B.
Cardiac Cycle
1.
During the cardiac cycle, pressure within the heart chambers rises and falls with
the contraction and relaxation of atria and ventricles.
2.
When the atria fill, pressure in the atria is greater than that of the ventricles, which
forces the A-V valves open.
3.
Pressure inside atria rises further as they contract, forcing the remaining blood into
the ventricles.
4.
When ventricles contract, pressure inside them increases sharply, causing A-V
valves to close and the aortic and pulmonary valves to open.
a. As the ventricles contract, papillary muscles contract, pulling on chordae
tendinae and preventing the backflow of blood through the A-V valves.
C.
Heart Sounds
1.
Heart sounds are due to vibrations in heart tissues as blood rapidly changes
velocity within the heart.
2.
Heart sounds can be described as a "lub-dup" sound.
3.
The first sound (lub) occurs as ventricles contract and A-V valves are closing.
4.
The second sound (dup) occurs as ventricles relax and aortic and pulmonary valves
are closing.
D.
Cardiac Muscle Fibers
1.
E.
F.
G.
A mass of merging fibers that act as a unit is called a functional syncytium; one
exists in the atria (atrial syncytium) and one in the ventricles (ventricular
syncytium).
Cardiac Conduction System
1.
Specialized cardiac muscle tissue conducts impulses throughout the myocardium
and comprises the cardiac conduction system.
2.
A self-exciting mass of specialized cardiac muscle called the sinoatrial node (S-A
node or pacemaker), located on the posterior right atrium, generates the impulses
for the heartbeat.
3.
Impulses spread next to the atrial syncytium, it contracts, and impulses travel to the
junctional fibers leading to the atrioventricular node (A-V node) located in the
septum.
a.
Junctional fibers are small, allowing the atria to contract before the
impulse spreads rapidly over the ventricles.
4.
Branches of the A-V bundle give rise to Purkinje fibers leading to papillary
muscles; these fibers stimulate contraction of the papillary muscles at the same
time the ventricles contract.
Electrocardiogram
1.
An electrocardiogram is a recording of the electrical changes that occur during a
cardiac cycle.
2.
The first wave, the P wave, corresponds to the depolarization of the atria.
3.
The QRS complex corresponds to the depolarization of ventricles and hides the
repolarization of atria.
4.
The T waves ends the ECG pattern and corresponds to ventricular repolarization.
Regulation of the Cardiac Cycle
1.
The amount of blood pumped at any one time must adjust to the current needs of
the body (more is needed during strenuous exercise).
2.
The S-A node is innervated by branches of the sympathetic and
parasympathetic divisions, so the CNS controls heart rate.
a.
Sympathetic impulses speed up and parasympathetic impulses slow down
heart rate.
3.
The cardiac control center of the medulla oblongata maintains a balance between
the sympathetic and parasympathetic divisions of the nervous system.
4.
Impulses from cerebrum or hypothalamus may also influence heart rate, as do body
temperature and the concentrations of certain ions.
Blood Vessels
A.
The blood vessels (arteries, arterioles, capillaries, venules, and veins) form a closed tube
that carries blood away from the heart, to the cells, and back again.
B.
Arteries and Arterioles
1.
Arteries are strong, elastic vessels adapted for carrying high-pressure blood.
2.
Arteries become smaller as they divide and give rise to arterioles.
3.
The wall of an artery consists of an endothelium, tunica media, and tunica externa.
4.
Arteries are capable of vasoconstriction as directed by the sympathetic impulses;
when impulses are inhibited, vasodilation results.
C.
Capillaries
1.
Capillaries are the smallest vessels, consisting only of a layer of endothelium
through which substances are exchanged with tissue cells.
2.
Capillary permeability varies from one tissue to the next, generally with more
permeability in the liver, intestines, and certain glands, and less in muscle and
considerably less in the brain (blood-brain barrier).
3.
D.
E.
The pattern of capillary density varies from one body part to the next.
a.
Areas with a great deal of metabolic activity (leg muscles, for example)
have higher densities of capillaries.
4.
Precapillary sphincters can regulate the amount of blood entering a capillary bed.
a.
If blood is needed elsewhere in the body, the capillary beds in less
important areas are shut down.
Exchanges in the Capillaries
1.
Blood entering capillaries contains high concentrations of oxygen and nutrients
that diffuse out of the capillary wall and into the tissues.
a.
Plasma proteins remain in the blood.
2.
Hydrostatic pressure drives the passage of fluids and very small molecules out of
the capillary at this point.
3.
At the venule end, osmosis, due to the osmotic pressure of the blood, causes much
of the tissue fluid to return to the bloodstream.
4.
Lymphatic vessels collect excess tissue fluid and return it to circulation.
Venules and Veins
1.
Venules leading from capillaries merge to form veins that return blood to the heart.
2.
Veins have the same three layers as arteries have and have a flap-like valve inside
to prevent backflow of blood.
a.
Veins are thinner and less muscular than arteries; they do not carry highpressure blood.
b.
Veins also function as blood reservoirs.
Blood Pressure
A.
Blood pressure is the force of blood against the inner walls of blood vessels anywhere in
the cardiovascular system, although the term "blood pressure" usually refers to arterial
pressure.
B.
Arterial Blood Pressure
1.
Arterial blood pressure rises and falls following a pattern established by the cardiac
cycle.
a.
During ventricular contraction, arterial pressure is at its highest (systolic
pressure).
b.
When ventricles are relaxing, arterial pressure is at its lowest (diastolic
pressure).
2.
The surge of blood that occurs with ventricular contraction can be felt at certain
points in the body as a pulse.
C.
Factors that Influence Arterial Blood Pressure
1.
Arterial pressure depends on heart action, blood volume, resistance to flow, and
blood viscosity.
2.
Heart Action
a.
Heart action is dependent upon stroke volume and heart rate (together
called cardiac output); if cardiac output increases, so does blood pressure.
3.
Blood Volume
a.
Blood pressure is normally directly proportional to the volume of blood
within the cardiovascular system.
b.
Blood volume varies with age, body size, and gender.
4.
Peripheral Resistance
a.
Friction between blood and the walls of blood vessels is a force called
peripheral resistance.
b.
As peripheral resistance increases, such as during sympathetic constriction
of blood vessels, blood pressure increases.
5.
Blood Viscosity
a.
The greater the viscosity of blood, the greater its resistance to flowing, and
the greater the blood pressure.
D.
Control of Blood Pressure
1.
Blood pressure is determined by cardiac output and peripheral resistance.
2.
The body maintains normal blood pressure by adjusting cardiac output and
peripheral resistance.
3.
Cardiac output depends on stroke volume and heart rate, and a number of factors
can affect these actions.
a.
The volume of blood that enters the right atrium is normally equal to the
volume leaving the left ventricle.
b.
If arterial pressure increases, the cardiac center of the medulla oblongata
sends parasympathetic impulses to slow heart rate.
c.
If arterial pressure drops, the medulla oblongata sends sympathetic
impulses to increase heart rate to adjust blood pressure.
d.
Other factors, such as emotional upset, exercise, and a rise in temperature
can result in increased cardiac output and increased blood pressure.
4.
The vasomotor center of the medulla oblongata can adjust the sympathetic
impulses to smooth muscles in arteriole walls, adjusting blood pressure.
a.
Certain chemicals, such as carbon dioxide, oxygen, and hydrogen ions, can
also affect peripheral resistance.
E.
Venous Blood Flow
1.
Blood flow through the venous system is only partially the result of heart action
and instead also depends on skeletal muscle contraction, breathing movements, and
vasoconstriction of veins.
Paths of Circulation
A.
The body's blood vessels can be divided into a pulmonary circuit, including vessels
carrying blood to the lungs and back, and a systemic circuit made up of vessels carrying
blood from the heart to the rest of the body and back.
B.
Pulmonary Circuit
1.
The pulmonary circuit is made up of vessels that convey blood from the right
ventricle to the pulmonary arteries to the lungs, alveolar capillaries, and pulmonary
veins leading from the lungs to the left atrium.
C.
Systemic Circuit
1.
The systemic circuit includes the aorta and its branches leading to all body tissues
as well as the system of veins returning blood to the right atrium.
Arterial System
A.
The aorta is the body's largest artery.
B.
Principal Branches of the Aorta
1.
The branches of the ascending aorta are the right and left coronary arteries that
lead to heart muscle.
2.
Principal branches of the aortic arch include the brachiocephalic, left common
carotid, and left subclavian arteries.
3.
The descending aorta (thoracic aorta) gives rise to many small arteries to the
thoracic wall and thoracic viscera.
4.
The abdominal aorta gives off the following branches: celiac, superior mesenteric,
suprarenal, renal, gonadal, inferior mesenteric, and common iliac arteries.
C.
Arteries to the Head, Neck, and Brain
1.
Arteries to the head, neck, and brain include branches of the subclavian and
common carotid arteries.
2.
D.
E.
F.
The vertebral arteries supply the vertebrae and their associated ligaments and
muscles.
3.
In the cranial cavity, the vertebral arteries unite to form a basilar artery which ends
as two posterior cerebral arteries.
4.
The posterior cerebral arteries help form the circle of Willis which provides
alternate pathways through which blood can reach the brain.
5.
The right and left common carotid arteries diverge into the external carotid and
internal carotid arteries.
6.
Near the base of the internal carotid arteries are the carotid sinuses that contain
baroreceptors to monitor blood pressure.
Arteries to the Shoulder and Upper Limb
1.
The subclavian artery continues into the arm where it becomes the axillary artery.
2.
In the shoulder region, the axial artery becomes the brachial artery that, in turn,
gives rise to the ulnar and radial arteries.
Arteries to the Thoracic and Abdominal Walls
1.
Branches of the thoracic aorta and subclavian artery supply the thoracic wall with
blood.
2.
Branches of the abdominal aorta, as well as other arteries, supply the abdominal
wall with blood.
Arteries to the Pelvis and Lower Limb
1.
At the pelvic brim, the abdominal aorta divides to form the common iliac arteries
that supply the pelvic organs, gluteal area, and lower limbs.
2.
The common iliac arteries divide into internal and external iliac arteries.
a.
Internal iliac arteries supply blood to pelvic muscles and visceral
structures.
b.
External iliac arteries lead into the legs, where they become femoral,
popliteal, anterior tibial, and posterior tibial arteries.
Venous System
A.
Veins return blood to the heart after the exchange of substances has occurred in the tissues.
B.
Characteristics of Venous Pathways
1.
Larger veins parallel the courses of arteries and are named accordingly; smaller
veins take irregular pathways and are unnamed.
2.
Veins from the head and upper torso drain into the superior vena cava.
3.
Veins from the lower body drain into the inferior vena cava.
4.
The vena cavae merge to join the right atrium.
C.
Veins from the Head, Neck, and Brain
1.
The jugular veins drain the head and unite with the subclavian veins to form the
brachiocephalic veins.
D.
Veins from the Upper Limb and Shoulder
1.
The upper limb is drained by superficial and deep veins.
2.
The basilic and cephalic veins are major superficial veins.
3.
The major deep veins include the radial, ulnar, brachial, and axillary veins.
E.
Veins from the Abdominal and Thoracic Walls
1.
Tributaries of the brachiocephalic and azygos veins drain the abdominal and
thoracic walls.
F.
Veins from the Abdominal Viscera
1.
Blood draining from the intestines enters the hepatic portal system and flows to the
liver first rather than into general circulation.
2.
The liver can process the nutrients absorbed during digestion as well as remove
bacteria.
3.
G.
Hepatic veins drain the liver, gastric veins drain the stomach, superior mesenteric
veins lead from the small intestine and colon, the splenic vein leaves the spleen and
pancreas, and the inferior mesenteric vein carries blood from the lower intestinal
area.
Veins from the Lower Limb and Pelvis
1.
Deep and superficial veins drain the leg and pelvis.
2.
The deep veins include the anterior and posterior tibial veins which unite into the
popliteal vein and femoral vein; superficial veins include the small and great
saphenous veins.
3.
These veins all merge to empty into the common iliac veins.
Blood
Introduction
A.
B.
Blood is considered a type of connective tissue.
Blood transports substances throughout the body, and helps to maintain a stable internal
environment.
Blood and Blood Cells
A.
The blood includes red blood cells, white blood cells, platelets, and plasma.
B.
Blood Volume and Composition
1.
A blood hematocrit is normally 45% cells and 55% plasma.
2.
Plasma is a mixture of water, amino acids, proteins, carbohydrates, lipids, vitamins,
hormones, electrolytes, and cellular wastes.
C.
Characteristics of Red Blood Cells
1.
Red blood cells (erythrocytes) are biconcave disks that contain one-third oxygencarrying hemoglobin by volume.
2.
When oxygen combines with hemoglobin, the resulting oxyhemoglobin is bright
red.
3.
Red blood cells discard their nuclei during development.
D.
Red Blood Cell Counts
1.
The typical red blood cell count is 4,600,000-6,2000,000 cells per mm3 for males
and 4,500,000-5,100,000 cells per mm3 for females.
2.
The number of red blood cells is a measure of the blood's oxygen-carrying
capacity.
E.
Destruction of Red Blood Cells
1.
With age, red blood cells become increasingly fragile and are damaged by passing
through narrow capillaries.
2.
Macrophages in the liver and spleen phagocytize damaged red blood cells.
3.
Hemoglobin from the decomposed red blood cells is converted into heme and
globin.
4.
Heme is decomposed into iron and biliverdin.
5.
Iron is recycled into new hemoglobin or stored in the liver.
6.
Some biliverdin is converted into bilirubin.
7.
Biliverdin and bilirubin are excreted in bile as bile pigments.
F.
Red Blood Cell Production and Its Control
1.
In the embryo and fetus, red blood cell production occurs in the yolk sac, liver, and
spleen; in the adult it occurs in the red bone marrow.
2.
The average life span of a red blood cell is 120 days.
3.
The total number of red blood cells remains relatively constant due to a negative
feedback mechanism utilizing the hormone erythropoietin, which is released in
G.
H.
I.
J.
K.
response to low oxygen levels detected in the kidneys and liver.
Dietary Factors Affecting Red Blood Cell Production
1.
Vitamins B12 and folic acid are needed for DNA synthesis, so they are necessary
for the reproduction of all body cells, especially in hematopoietic tissue.
2.
Iron is needed for hemoglobin synthesis.
3.
A deficiency in red blood cells or quantity of hemoglobin results in anemia.
Types of White Blood Cells
1.
White blood cells (leukocytes) help defend the body against disease.
2.
Five types of white blood cells are in circulating blood and are distinguished by
size, granular appearance of the cytoplasm, shape of the nucleus, and staining
characteristics.
3.
The types of white blood cells are the granular neutrophils, eosinophils, and
basophils, and the agranular monocytes and lymphocytes.
a.
Neutrophils have red-staining fine cytoplasmic granules and a multilobed
nucleus; they comprise 54-62% of leukocytes.
b.
Eosinophils have coarse granules that stain deep red, a bilobed nucleus,
and make up only 1-3% of circulating leukocytes.
c.
Basophils have fewer granules that stain blue; they account for fewer than
1% of leukocytes.
d.
Monocytes are the largest blood cells, have variably-shaped nuclei, and
make up 3-9% of circulating leukocytes.
e.
Lymphocytes are long-lived, have a large, round nucleus, and account for
25-33% of circulating leukocytes.
White Blood Cell Counts
1.
Normally a cubic milliliter of blood contains 5,000 to 10,000 white blood cells.
2.
A differential white blood cell count can help pinpoint the nature of an illness,
indicating whether it is caused by bacteria or viruses.
a.
A differential white blood cell count lists the percentages of the types of
leukocytes in a blood sample.
3.
Leukocytosis occurs after an infection when excess numbers of leuocytes are
present; leukopenia occurs from a variety of conditions, including AIDS.
Functions of White Blood Cells
1.
Leukocytes can squeeze between cells lining walls of blood vessels by diapedesis
and attack bacteria and debris.
a.
Neutrophils and monocytes are phagocytic, with monocytes engulfing the
larger particles.
b.
Eosinophils moderate allergic reactions as well as defend against parasitic
infections.
c.
Basophils migrate to damaged tissues and release histamine to promote
inflammation and heparin to inhibit blood clotting.
d.
Lymphocytes are the major players in specific immune reactions and some
produce antibodies.
Blood Platelets
1.
Blood platelets are fragments of megakaryocytes.
2.
Platelets help repair damaged blood vessels by adhering to their broken edges.
3.
Normal counts vary from 130,000 to 360,000 platelets per mm3.
Blood Plasma
A.
Plasma is the clear, straw-colored fluid portion of the blood.
1.
Plasma is mostly water but contains a variety of substances.
2.
Plasma functions to transport nutrients and gases, regulate fluid and electrolyte
B.
C.
D.
E.
Hemostasis
A.
B.
C.
balance, and maintain a favorable pH.
Plasma Proteins
1.
The plasma proteins are the most abundant dissolved substances in the plasma.
2.
Plasma proteins are not used for energy and fall into three groups--albumins,
globulins, and fibrinogen.
a.
The albumins help maintain the osmotic pressure of the blood and account
for 60% of the plasma proteins.
b.
The globulins, comprising 36% of the plasma proteins, are designated as
alpha, beta, and gamma globulins.
i.
Alpha and beta globulins function in transporting lipids and fatsoluble vitamins.
ii.
Gamma globulins are a type of antibody.
c.
Fibrinogen (4%) plays a primary role in blood coagulation.
Nutrients and Gases
1.
The plasma nutrients include amino acids, monosaccharides, nucleotides, and
lipids.
a.
Since lipids are not soluble in the water of the plasma, they are surrounded
by protein molecules for transport through the bloodstream as lipoproteins.
b.
Lipoproteins are classified on the basis of their densities, which reflects
their composition.
i.
Types of lipoproteins include HDL, LDL, VLDL, and
chylomicrons.
2.
The most important blood gases are oxygen and carbon dioxide.
Nonproteins Nitrogenous Substances
1.
Nonprotein nitrogenous substances generally include amino acids, urea, and uric
acid.
a.
Urea and uric acid are the by-products of protein and nucleic acid
catabolism.
Plasma Electrolytes
1.
Plasma electrolytes are absorbed by the intestine or are by-products of cellular
metabolism.
2.
They include sodium, potassium, calcium, magnesium, chloride, bicarbonate,
phosphate, and sulfate ions.
3.
Some of these ions are important in maintaining osmotic pressure and pH of the
plasma.
Hemostasis refers to the stoppage of bleeding.
1.
Following injury to a vessel, three steps occur in hemostasis: blood vessel spasm,
platelet plug formation, and blood coagulation.
Blood Vessel Spasm
1.
Cutting a blood vessel causes the muscle in its walls to contract reflexly, or engage
in vasospasm.
2.
This reflex lasts only a few minutes, but it lasts long enough to initiate the second
and third steps of hemostasis.
Platelet Plug Formation
1.
Platelets stick to the exposed edges of damaged blood vessels, forming a net with
spiny processes protruding from their membranes.
2.
A platelet plug is most effective on a small vessel.
Blood Groups and Transfusions
A.
B.
C.
E.
Scientists determined that blood was of different types and only certain combinations were
compatible.
Antigens and Antibodies
1.
Clumping of red blood cells following transfusion is called agglutination.
2.
Agglutination is due to the interaction of proteins on the surfaces of red blood cells
(antigens) with certain antibodies carried in the plasma.
3.
Only a few of the antigens on red blood cells produce transfusion reactions.
a.
These include the ABO group and Rh group.
ABO Blood Group
1.
Type A blood has A antigens on red blood cells and anti-B antibodies in the
plasma.
2.
Type B blood has B antigens on red blood cells and anti-A antibodies in the
plasma.
3.
Type AB blood has both A and B antigens, but no antibodies in the plasma.
4.
Type O blood has neither antigen, but both types of antibodies in the plasma.
5.
Adverse transfusion reactions are avoided by preventing the mixing of blood that
contains matching antigens and antibodies.
a.
Adverse reactions are due to the agglutination of red blood cells.
Rh Blood Group
1.
The Rh factor was named after the rhesus monkey.
2.
If the Rh factor surface protein is present on red blood cells, the blood is Rh
positive; otherwise it is Rh negative.
3.
There are no corresponding antibodies in the plasma unless a person with Rhnegative blood is transfused with Rh-positive blood; the person will then develop
antibodies for the Rh factor.
4.
Erythroblastosis fetalis develops in Rh-positive fetuses of Rh-negative mothers.