Anatomy and Histology of the Cardiovascular System

7/22/2019 Anatomy and Histology of the Cardiovascular System

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Anatomy and Histology of TheCardiovascular System

Irma Savitri/0806358022/Group ATrigger 1-Cardiovascular odule

Anatomy of The Hearti

The heart is located near the anterior chest wall, directly posterior to the sternum. The great

veins and arteries are connected to the superior end of the heart at the attached base. The

base sits posterior to the sternum at the level of the third costal cartilage, centered about 1.2

cm to the left side. The inferior, pointed tip of the heart is the apex. A typical adult heart

measures approximately 12.5 cm from the base to the apex, which reaches the fifth

intercostal space approximately 7.5 cm to the left of the midline. A midsagittal sectionthrough the trun does not divided the heart into two e!ual halves, because "1# the center of

the base lies slightly to the left of the midline, "2# a line drawn between the center of the base

and the apex points further to the left, "$# the entire heart is rotated to the left around this

line, so that the right atrium and right ventricle dominate an anterior view of the heart.

The heart, surrounded by the pericardial sac, sits in the anterior portion of the mediastinum.

The mediastinum, the region between the two pleural cavities, also contains the great

vessels "the large arteries and veins lined to the heart#, thymus, esophagus, and trachea.

The lining of the pericardial cavity is called the pericardium. The pericardium is lined by a

delicate serous membrane that can be subdivided into the visceral pericardium and the

parietal pericardium. The visceral pericardium, or epicardium, covers and adheres closely to

the outer surface of the heart% the parietal pericardium lines the inner surface of the

pericardial sac, which surrounds the heart. The pericardial sac, or fibrous pericardium, which

consists of a dense networ of collagen fibers, stabili&es the position of the heart and

associated vessels within the mediastinum.

The small space between the parietal and visceral surfaces is the pericardial cavity. 't

normally contains 15(5)m* of pericardial fluids, secreted by the pericardial membranes. This

fluid acts as a lubricant, reducing friction between the opposing surfaces as the heart beats.


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Superficial Anatomy of The Heart

The four cardiac chambers can easily be identified in a superficial view of the heart. The two

atria have relatively thin muscular walls and are highly expandable. +hen not filled with

blood, the outer portion of each atrium deflates and become lumpy, wrinled flap. This

expandable extension of an atrium is called an atrial appendage, or an auricle. The coronary

sulcus, a deep groove, mars the border between the atria and the ventricles. The anteriorinterventricular sulcus and the posterior interventricular sulcus, shallower depressions, mar

the boundary between the left and right ventricles.

The connective tissue of the epicardium at the coronary and interventricular sulci generally

contains substantial amounts of fat. These sulci also contain the arteries and veins that carry

blood to and from the cardiac muscle.

The Heart Wall

A section through the wall of the heart reveals three distinct layers an outer epicardium, a

middle myocardium, and an inner endocardium.

The epicardium is the visceral pericardium that covers the outer surface of the heart. This

serous membrane consists of an exposed mesothelium and an underlying layer of loose

areolar connective tissue that is attached to the myocardium.

The myocardium, or muscular wall of the heart, forms both atria and ventricles. This layer

contains cardiac muscle tissue, blood vessels, and nerves. The myocardium consists of

concentric layers of cardiac muscle tissue. The atrial myocardium contains muscle bundles

that wrap around the atria and encircle the great vessels. -uperficial ventricular muscles

wrap around both ventricles% deeper muscle layers spiral around and between the ventricles.


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The inner surfaces of the heart, including those of the heart valves, are covered by the

endocardium, a simple s!uamous epithelium that is continuous with the endothelium of the

attached great vessels.

Internal Anatomy and Organization

The atria are separated by the interatrial septum and the ventricles are separated by themuch thicer interventricular septum. ach septum is a muscular partition. Atrioventricular

"A/# valves, folds of fibrous tissue, extend into the openings between the atria and

ventricles. These valves permit blood flow in one direction only% from the atria to the

ventricles.

The Right Atrium

The right atrium receives blood from the systemic circuit through the two great veins% the

superior vena cava and the inferior vena cava. The superior vena cava, which opens into the

posterior and superior portion of the right atrium, delivers blood to the right atrium from the

head, nec, upper limbs, and chest. The inferior vena cava, which opens into the posteriorand inferior portion of the right atrium, carries blood to the right atrium from the rest of the

trun, the viscera, and the lower limbs. The cardiac veins of the heart returns blood to the

coronary sinus, a large, thin(walled vein that opens into the right atrium inferior to the

connection with the superior vena cava.

The opening of the coronary sinus lies near the posterior edge of the interatrial septum.

0rom the fifth wee of embryonic development until birth, the foramen ovale, an oval

opening, penetrates the interatrial septum and connects the two atria of the fetal heart.

efore birth, the foramen ovale permits blood flow from the right atrium to the left atrium

while the lungs are developing. At birth, the foramen ovale closes, and the opening is

permanently sealed off within three months of delivery. The fossa ovalis, a small, shallow

depression, persists at this site in the adult heart.

The posterior wall of the right atrium and the interatrial septum has smooth surfaces. 'n

contrast, the anterior atrial wall and the inner surface of the auricle contain prominent

muscular ridges called the pectinate muscles.

The Right Ventricle

lood travels from the right atrium into the right ventricle through a broad opening bounded

by three fibrous flaps. These flaps, called cusps or leaflets, are part of the right

atrioventricular "A/# valve, also nown as the tricuspid valve. The free edge of each cusp isattached to connective tissue fibers called the chordae tendinae. The fibers originate at the

papillary muscles, conical muscular proections that arise from the inner surface of the right

ventricle. The right A/ valve closes when the right ventricle contracts, preventing the

bacflow of blood into the right atrium. +ithout the chordae tendinae to anchor their free

edges, the cusps would be lie swinging doors that permitted blood flow in both directions.

The internal surface of the ventricle also contains a series of muscular ridges, the trabeculae

carnae. The moderator band is a muscular ridge that extends hori&ontally from the inferior

portion of the interventricular septum and connects to the anterior papillary muscle. This

ridge contains a portion of the conducting system, an internal networ that coordinates the

contraction of cardiac muscle cells. The moderator band delivers the stimulus for contraction


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to the papillary muscles, so that they begin tensing the chordate tendineae before the rest of

the ventricle contracts.

The superior end of the right ventricle tapers to the conus arteriosus, a conical pouch that

ends at the pulmonary valve, or pulmonary semilunar valve. The pulmonary valve consists of

three semilunar cusps of thic connective tissue. lood flowing from the right ventriclepasses through this valve to enter the pulmonary trun, the start of the pulmonary circuit.

The arrangement of cusps prevents bacflow as the right ventricle relaxes. 3nce in the

pulmonary trun, blood flows into the left pulmonary arteries and the right pulmonary

arteries. These vessels branch repeatedly within the lungs before supplying the capillaries,

where gas exchange occurs.

The Left Atrium

0rom the respiratory capillaries, blood collects into small veins that ultimately unite to form

the four pulmonary veins. The posterior wall of the left atrium receives blood from two left

and two right pulmonary veins. *ie the right atrium, the left atrium has an auricle. A valve,the left atrioventricular "A/# valve, or bicuspid valve, guards the entrance to the left ventricle.

As the name bicuspid implies, the left A/ valve contains a pair, not a trio, of cusps.

The Left Ventricle

The left ventricle has thic, muscular walls that enable it to develop pressure sufficient to

push blood through the large systemic circuit. The internal organi&ation of the left ventricle

generally resembles that of the right ventricle, except for the absence of a moderator band.

The trabeculae carneae are prominent, and a pair of large papillary muscles tense the

cordae tendineae that anchor the cusps of the A/ valve and prevent the bacflow of blood

into the left atrium.

lood leaves the left ventricle by passing through the aortic valve, or aortic semilunar valve,

into the ascending aorta. The arrangement of cusps in the aortic valve is the same as that in

the pulmonary valve. 3nce the blood has been pumped out of the heart and into the

systemic circuit, the aortic valve prevents bacflow into the left ventricle. 0rom the ascending

aorta, blood flows through the aortic arch and into the descending aorta. The pulmonary

trun is attached to the aortic arch by the ligamentum arteriosum, a fibrous band that is a

remnant of an important fetal blood vessel that once lined the pulmonary and systemic

circuits.

The Heart Valves

The Atrioventricular Valves

The atrioventricular "A/# valves prevent the bacflow of blood from the ventricles to the atria

when the ventricles are contracting. The chordae tendineae and papillary muscles play

important rules in the normal function of the A/ valves. +hen the ventricles are relaxed, the

chordate tendineae are loose, and the A/ valves offer no resistance of the flow of blood from

the atria into the ventricles. +hen the ventricles contract, blood moving bac toward the atria

swings the cusps together, closing the valves. At the same time, the contraction of the

papillary muscles tenses the chordate tendineae, stopping the cusps before they swing into

the atria.


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The Semilunar Valves

The pulmonary and aortic valves prevent the bacflow of blood from the pulmonary trun

and aorta into the right and left ventricles, respectively. 4nlie the A/ valves, the semilunar

valves do not re!uire muscular braces, because the arterial walls do not contract and the

relative positions of the cusps are stable. +hen the semilunar valves close, the three

symmetrical cusps support one another lie the legs of a tripod.

-aclie dilations of the base of the ascending aorta are adacent to each cusp of the aortic

valve. These sacs, called aortic sinuses, prevent the individual cusps from sticing to the

wall of the aorta when the valve opens. The right and left coronary arteries, which deliver

blood to the myocardium, originate at the aortic sinuses.


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onnective Tissues and the ardiac S!eleton

The connective tissues of the heart include large numbers of collagen and elastic fibers.ach cardiac muscle cell is wrapped in a strong, but elastic, sheath and adacent cells are

tied together by fibrous cross(lins. These fibers, are, in turn, interwoven into sheets that

separate the superficial and deep muscle layers. The connective tissue fibers provide

physical support for the cardiac muscle fibers, blood vessels, and nerves of the myocardium%

help distribute the forces of contraction% add strength and prevent overexpansion of the

heart% and provide elasticity that helps return the heart to its original si&e and shape after a

contraction.

The cardiac seleton "or fibrous seleton# of the heart consists of four dense bands of tough

elastic tissue that encircle the heart valves and the bases of the pulmonary trun and aorta.

These bands stabili&e the positions of the heart valves and ventricular muscle cells andelectrically insulate the ventricular cells from the atrial cells.

The "lood Supply to the Heart


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The oronary Arteries

The left and right coronary arteries originate at the base of the ascending aorta, at the aortic

sinuses. lood pressure here is the highest in the systemic circuit. ach time the left

ventricle contracts, it forces blood into the aorta. The arrival of additional blood at elevated

pressure stretches the elastic walls of the aorta. +hen the left ventricle relaxes, blood no

longer flows into the aorta, pressure declines, and the walls of the aorta recoil. The recoil,

called elastic rebound, pushes blood both forward, into the systemic circuits, and bacward,

through the aortic sinuses and then into the coronary arteries. Thus, the combination of

elevated blood pressure and elastic rebound ensures a continuous flow of blood to meet the

demands of active cardiac muscle tissue. owever, myocardial blood flow is not steady, it

peas while the heart muscle is relaxed, and almost ceases when it contracts.

The right coronary arteriy, which follows the coronary sulcus around the heart, supplies

blood to the right atrium, portions of both ventricles, and portions of the conducting system of

the heart, including the sinoatrial "-A# node and the atrioventricular "A/# node. The cells of

these nodes are essential to establishing the normal heart rate.

'nferior to the right atrium, the right coronary artery generally gives rise to one or more

marginal arteries, which extend across the surface of the right ventricle. The right coronary

artery then continues across the posterior surface of the heart, supplying the posterior

interventricular artery, or posterior descending artery, which runs towards the apex within the

posterior interventricular sulcus. The posterior interventricular artery supplies blood to the

interventricular septum and adacent portions of the ventricles.

The left coronary artery supplies blood to the left ventricle, left atrium, and interventricular

septum. As it reaches the anterior surface of the heart, it gives rise to a circumflex branch

and an anterior interventricular branch. The circumflex artery curves to the left around thecoronary sulcus, eventually meeting and fusing with small branches of the right coronary

artery. The much larger anterior interventricular artery, or left anterior descending artery,

swings around the pulmonary trun and runs along the surface within the anterior

interventricular sulcus.

The anterior interventricular artery supplies small tributaries continuous with those of

posterior interventricular artery. -uch interconnections between arteries are called arterial

anastomoses. ecause the arteries are interconnected in this way, the blood supply to the

cardiac muscles remains relatively constant despite pressure fluctuations in the left and right

coronary arteries as the heart beats.

The ardiac Veins

The great cardiac vein begins on the anterior surface of the ventricles. This vein drains blood

from the region supplied by the anterior interventricular artery, a branch of the left coronary

artery. The great cardiac vein reaches the level of the atria and then curves around the left

side of the heart within the coronary sulcus. The vein empties into the coronary sinus, which

lies in the posterior portion of the coronary sulcus. The coronary sinus opens into the right

atrium near the base of the inferior vena cava.

3ther cardiac veins that empty into the great cardiac vein or the coronary sinus include "1#

the posterior cardiac vein, draining the area served by the circumflex artery, "2# the middle

cardiac vein, draining the area supplied by the posterior interventricular artery, "$# the small


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cardiac vein which receives blood from the posterior surfaces of the right atrium and

ventricle. The anterior cardiac veins which drain the anterior surface of the right ventricle,

empty directly into the right atrium.

Anatomy of the "lood Vesselsii

The Systemic irculation

The Aorta and Its "ranches

The systemic circulation includes the arteries and arterioles that carry oxygenated blood

from the left ventricle to systemic capillaries, plus the veins and venules that return

deoxygenated blood to the right atrium. lood leaving the aorta and flowing through the

systemic arteries is a bright red color. As blood flows through capillaries, it loses some of its

oxygen and pics up carbon dioxide, becoming a dar red color. All systemic arteries branch

from the aorta. 6ompleting the circuit, all the veins of the systemic circulation drain into the

superior vena cava, the inferior vena cava, or the coronary sinus, which in turn empty into

the right atrium. The bronchial arteries, which carry nutrients to the lungs, also are part of the

systemic circulation.


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The aorta is the largest artery of the body, with a diameter of 2($ cm. 'ts four principal

divisions are the ascending aorta, arch of the aorta, thoracic aorta, and abdominal aorta. The

portion of the aorta that emerges from the left ventricle posterior to the pulmonary trun is

the ascending aorta. The beginning of the aorta contains the aortic valve. The ascending

aorta gives off two coronary artery branches that supply the myocardium of the heart. Then

the ascending aorta arches to the left, forming the arch of aorta, which descends and endsat the level of the intervertebral discs between the fourth and fifth thoracic vertebrae. As the

aorta continues to descend, it lies close to the vertebral bodies, passes through the aortic

hiatus of the diaphragm, and divides at the level of the fourth lumbal vertebra into two

common iliac arteries, which carry blood to the lower limbs. The section of the aorta between

the arch of the aorta and the diaphragm is called the thoracic aorta, the section between the

diaphragm and the common iliac arteries is the abdominal aorta. ach division of the aorta

gives off arteries that branch into distributing arteries that lead to various organs. +ithin the

organs, the arteries divide into arterioles and then into capillaries that service the systemic

tissues "all tissues except the alveoli of the lungs#.

Asce!di!g Aorta

The ascending aorta is about 5 cm in length and begins at the aortic valve. 't is directed

superiorly, slightly anteriorly, and to the right. 't ends at the level of the sternal angle, where

it becomes the arch of aorta. At its origin, the ascending aorta contains three dilations called

aortic sinuses. Two of these, the right and left sinuses, give rise to the right and left coronary

arteries, respectively.

The right and left coronary arteries arise from the ascending aorta ust superior to the aortic

valve. The posterior interventricular branch of the right coronary artery supplies both

ventricles, and the marginal branch supplies the right ventricle. The anterior interventricularbranch of the left coronary artery supplies both ventricles, and the circumflex branch

supplies the left atrium and left ventricle.

T"e Arc" o# t"e Aorta

The arch of the aorta is (5 cm in length and is the continuation of the ascending aorta. 't

emerges from the pericardium posterior to the sternum at the level of the sternal angle. The

arch of the aorta is directed superiorly and posteriorly to the left and then inferiorly% it ends at

the intervertebral discs between the fourth and fifth thoracic vertebrae, where it becomes the

thoracic aorta. Three maor arteries branch from the superior aspect of the arch of the aorta%

the brachiocephalic trun, the left common carotid, and the left subclavian. The first andlargest branch from the arch of the aorta is the brachiocephalic trun. 't extends superiorly,

bending slightly to the right, and divides at the right sternoclavicular oint to orm the right

subclavian artery and right common carotid artery. The second branch from the arch of the

aorta is the left common carotid artery. The third branch from the arch of aorta is the left

subclavian artery, which distributes blood to the left vertebral artery and vessels of the left

upper limb.

T"oracic Aorta

The thoracic aorta is about 2) cm in long and is a continuation of the arch of the aorta. 't

begins at the level of the intervertebral disc between the fourth and fifth thoracic vertebrae,where it lies to the left of the vertebral column. As it descends, it moves closer to the midline


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and extends through an opening in the diaphragm "aortic hiatus#, which is located anterior to

the vertebral column at the level of the intervertebral disc between the twelfth thoracic and

first lumbar vertebrae. Along its course, the thoracic aorta sends off numerous small arteries,

visceral branches to viscera, and parietal branches to body wall structures.

A$domi!al AortaThe abdominal aorta is the continuation of the thoracic aorta. 't begins at the aortic hiatus in

the diaphragm and ends at about the level of the fourth lumbal vertebra, where it divides into

the right and left common iliac arteries. The abdominal aorta lies anterior to the vertebral

column.

As with the thoracic aorta, the abdominal aorta gives off visceral and parietal branches. The

unpaired visceral branches arise from the anterior surface of the aorta and include the celiac

trun and the superior mesenteric and inferior mesenteric arteries.

The paired visceral brances arise from the lateral surfaces of the aorta and include thesuprarenal, renal, and gonadal arteries. The unpaired parietal branch is the median sacral

artery. The paired parietal branches arise from the posterior surfaces of the aorta and

include the inferior phrenic and lumbar arteries.

Arteries of the #elvis and Lo$er Lim%s

The abdominal aorta ends by dividing into the right and left common iliac arteries. These, in

turn, divide into the internal and external iliac arteries. 'n se!uence, the external illiacs

become the femoral arteries in the thighs, the popliteal arteries posterior to the nee, and the

anterior and posterior tibial arteries in the legs.


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Veins of the Systemic irculation

Although only one systemic artery, the aorta, taes oxygenated blood away from the heart

"left ventricle#, three systemic veins, the coronary sinus, superior vena cava, and inferior

vena cava, return deoxygenated blood to the heart "right atrium#. The coronary sinus

receives blood from the cardiac veins% the superior vena cava receives blood from other

veins superior to the diaphragm, except the air sacs "alveoli# of the lungs% the inferior vena

cava receives blood from the veins inferior to the diaphragm.

Veins of the Head and &ec!

8ost blood draining from the head passes into three pairs of veins% the internal ugular,

external ugular, and vertebral veins. +ithin the brain, all veins drain into dural venous

sinuses and then into the internal ugular veins. 9ural venous sinuses are endothelial(lined

venous channels between layers of the cranial dura mater.

Veins of the 'pper Lim%s

oth superficial and deep veins return blood from the upper limbs to the heart. -uperficial

veins are located ust deep to the sin and often visible. They anastomose extensively with

one another and with deep veins% and they do not accompany arteries. -uperficial veins are

larger than deep veins and return most of the blood from the upper limbs. 9eep veins are


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located deep in the body. They usually accompany arteries and have the same names as

the corresponding arteries. oth superficial and deep veins have valves, but valves are more

numerous in the deep veins.

Veins of the Thora(

Although the brachiocephalic veins drain some portion of the thorax, most thoracic structures

are drained by a networ of veins, valled the a&ygos system, that runs on either side of the

vertebral column. The system consists of three veins : the a&ygos, hemia&ygos, and

accessory hemia&ygos veins, that show considerable variation in origin, course, tributaries,

anastomoses, and termination. 4ltimately they empty into the superior vena cava.

Veins of the A%domen and #elvis

lood from the abdominal and pelvic viscera and abdominal wall returns to the heart via the

inferior vena cava. 8any small veins enter the inferior vena cava. 8ost carry return flow from

parietal branches of the abdominal aorta, and their names correspond to the names of the

arteries. The inferior vena cava does not receive veins directly from the gastrointestinal

trac, spleen, pancreas, and gallbladder. These organs pass their blood into a common vein,

the hepatic portal vein, which delivers the blood to the liver. The superior mesenteric and

splenic veins unite to form the hepatic portal vein. After passing through the liver for

processing, blood drains into the hepatic veins, which empty to the inferior vena cava.

Veins of the Lo$er Lim%s

As with the upper limbs, blood from the lower limbs is drained by both superficial and deep

veins. The superficial veins often anastomose with one another and with deep veins along

their length. 9eep veins, for the most part, have the same names as corresponding arteries.

All veins of the lower limbs have valves, which are more numerous in the veins of the upper

limbs.

Histology of the ardiac )uscleiii

6ardiac muscle "heart muscle# is found only in the heart and in pulmonary veins where they

oin the heart. 6ardiac muscle is derived from a strictly defined mass of splanchinic

mesenchyme, the myoepicardial mantle, whose cells give rise to the epicardium and

myocardium.

The adult myocardium consists of an anastomosing networ of branching cardiac musclecells arranged in layers "laminae#. *aminae are separated from one another by slender

connective tissue sheets that convey blood vessels, nerves, and the conducting system of

the heart. 6apillaries, derived from these branches, invade the intercellular connective

tissue, forming a rich, dense networ of capillary beds surrounding every cardiac muscle

cells.

Almost half the volume of the cardiac muscle cell is occupied by mitochondria, attesting to its

great energy consumption. ;lycogen, to a certain extent, but mostly triglycerides form the

energy supply of the heart. ecause the oxygen re!uirement of cardiac muscle cells is high,

they contain an abundant supply of myoglobin.


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Although the resting lengths of individual cardiac muscle cells vary, on average they are 15

micrometer in diameter and


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of a second#. 9uring this time, a tremendous number of sodium and calcium ions enter the

cardiac muscle cell cytoplasm, thus increasing the calcium ion concentration supplied by the

T tubule and the sarcoplasmic reticulum. An additional difference between the movement of

ions in seletal and cardiac muscle cells is that potassium ions can leave the seletal muscle

cells extremely !uicly, thus reestablishing the resting membrane potential% in cardiac

muscle cells, the egress of potassium ions is retarded thus contributed to the protractedaction potential.

Histology of The "lood Vesselsiv

The whole circulatory system has a common basic structure. 't has tunica intima, which is an

inner lining comprising a single layer of endothelium supported by a basement membrane

and delicate collagenous tissue% tunica media, which is an intermediate predominantlymuscular layer% and tunica adventitia% which is an outer principally supporting tissue layer.

The tissue of the thic walls of large vessels "e.g.# aorta cannot be sustained by diffusion of

oxygen and nutrients from their lumina, and are supplied by small arteries "vasa vasorum#

which run in the tunica adventitia and sends arterioles and capillaries into the tunica media.

The muscular content exhibits the greatest variation from one part of the system to another.

0or example, it is totally absent in capillaries but comprises almost the whole mass of the

heart. lood flow is predominantly influenced by variation in activity of the muscular tissue.


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References


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i8artini 0, >ath ?*. 0undamentals of anatomy and physiology. < thed. >ew ?ersey @earson

enamin 6ummings% 2)). pB

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Anatomy and Histology of the Cardiovascular System