Cardiovascular System 9256
Anatomy and Physiology
The cardiovascular (CV) system, also called the circulatory system, circulates blood to all parts of
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body by the action of the heart. This process provides the body’s cells with oxygen and nutritive elements and removes waste materials and carbon dioxide. The heart, a muscular pump, is the central
organ of the system. It beats approximately 100,000 times each day, pumping roughly 8,000 liters of
blood, enough to fill about 8,500 quart-sized milk cartons. Arteries, veins, and capillaries comprise
the network of vessels that transport blood (fluid consisting of blood cells and plasma) throughout the
body. Blood flows through the heart, to the lungs, back to the heart, and on to the various body parts.
Table 9.1 provides an at-a-glance look at the cardiovascular system. Figure 9.1 shows a schematic
overview of the cardiovascular system.
Heart
The heart is the center of the cardiovascular system from which the various blood
vessels originate and later return. It is slightly larger than a person’s fist and weighs
approximately 300 g in the average adult. It lies slightly to the left of the midline of the
body, behind the sternum (see Figure 9.2). The heart has three layers or linings.
• Endocardium. The inner lining of the heart.
• Myocardium. The muscular middle layer of the heart.
• Pericardium. The outer membranous sac surrounding the heart.
Circulation of Blood through the Chambers of the Heart
The heart is a pump and is divided into the right and left heart by a partition called
the septum. Each side contains an upper and lower chamber. See Figure 9.3. The atria,
or upper chambers, are separated by the interatrial septum. The ventricles, or lower
chambers, are separated by the interventricular septum. The atria receive blood from
the various parts of the body. The ventricles pump blood to body parts. Valves control
the intake and outflow of blood in the heart chambers. Figure 9.4 shows the functioning of the heart valves and flow of blood through the heart.
Table 9.1 Cardiovascular System at-a-Glance
Organ/Structure Primary Functions/Description
Heart The muscular pump that circulates blood through the heart, the lungs (pulmonary
circulation), and the rest of the body (systemic circulation)
Arteries Branching system of vessels that transports blood from the right and left ventricles of the
heart to all body parts; transports blood away from the heart
Veins Vessels that transport blood from peripheral tissues back to the heart
Capillaries Microscopic blood vessels that connect arterioles with venules; facilitate passage of
life-sustaining fluids containing oxygen and nutrients to cell bodies and the removal of
accumulated waste and carbon dioxide
Blood Fluid consisting of formed elements (erythrocytes, thrombocytes, leukocytes) and plasma. It
is a specialized bodily fluid that delivers necessary substances to the body’s cells (oxygen,
foods, salts, hormones) and transports waste products (carbon dioxide, urea, lactic acid)
away from those same cells. Blood is circulated around the body through blood vessels
by the pumping action of the heart. See Chapter 10, Blood and Lymphatic System, for a
further discussion of blood.Cardiovascular System • 257
Figure 9.1 Schematic overview of the cardiovascular system.
AIR (OXYGEN)
Lung capillaries
Trachea
Left pulmonary artery
Lung capillaries
Left pulmonary vein
Heart
(blood)
Veins
Right
pulmonary
vein
Arteries
Venules
Arterioles
BODY CAPILLARIES
Right lung Left lung
Right
pulmonary artery
Blood high in oxygen and low in carbon
dioxide (oxygenated)
= =
Blood low in oxygen and high in carbon
dioxide (deoxygenated)
Figure 9.2 Location of the heart in the chest cavity.
Midsternal line
Second rib
Sternum
Diaphragm
Mediastinum
(contains the organs
between the pleural cavities)
Superior vena cava
Pericardium
Diaphragm
Apex of heart
Aorta
Pulmonary trunk
Left lung258 • Chapter Nine
Figure 9.3 Interior view of the heart chambers
with tissues of the heart (endocardium, myocardium,
and pericardium).
Left ventricle
Endocardium
Myocardium
Pericardium
Superior vena cava
Aorta
Pulmonary trunk
Right atrium
Right ventricle
Inferior vena cava
Left atrium
Pulmonary valve
Tricuspid valve
Aortic valve
Mitral (Bicuspid) valve
Figure 9.4 The functioning of the heart
valves and blood flow.
To lung
Left pulmonary artery
(branches)
To lung
Right pulmonary
artery (branches)
From body
From body
To body
Right atrium
Tricuspid valve
Right ventricle
Inferior vena cava
From lung
Right pulmonary
vein (branches)
Aorta
Left ventricle
Interventricular
septum
Myocardium
(heart muscle)
Apex
Left atrium
Aortic valve
Mitral (bicuspid) valve
Descending aorta
From lung
Left pulmonary vein
(branches)
1
2 3
4 5
6
Superior vena cava
Pulmonary valveCardiovascular System • 259
right atrium
The right upper portion of the heart is called the right atrium (RA). It is a thin-walled
space that receives blood from the upper and lower parts of the body (except the
lungs). Two large veins, the superior vena cava and inferior vena cava, bring deoxygenated blood into the right atrium. Deoxygenated blood fills the right atrium
before passing through the tricuspid (atrioventricular) valve and into the right
ventricle.
right ventricle
The right lower portion of the heart is called the right ventricle (RV). It receives blood
from the right atrium through the tricuspid valve. When filled, the RV contracts. This
creates pressure, closing the right atrium and forcing open the pulmonary (semilunar)
valve, sending blood into the left and right pulmonary arteries, which carry it to the
lungs. The pulmonary artery is the only artery in the body that carries blood deficient
in oxygen. In the lungs, the blood gives up wastes and takes on oxygen as it passes
through capillary beds into veins. Oxygenated blood leaves the lungs through the left
and right pulmonary veins, which carry it to the heart’s left atrium. The pulmonary
veins are the only veins in the body that carry oxygen-rich (oxygenated) blood. The
circulation of blood through the vessels from the heart to the lungs and then back to
the heart again is the pulmonary circulation.
left atrium
The left upper portion of the heart is called the left atrium (LA). It receives blood rich in
oxygen as it returns from the lungs via the left and right pulmonary veins. As oxygenated blood fills the LA, it creates pressure that forces open the mitral (bicuspid) valve
and allows the blood to fill the left ventricle.
left ventricle
The left lower portion of the heart is called the left ventricle (LV). It receives blood from
the left atrium through the mitral valve. When filled, the LV contracts. This creates
pressure closing the mitral valve and forcing open the aortic valve. The oxygenated
blood from the LV flows through the aortic valve and into a large artery known as the
aorta and from there to all parts of the body (except the lungs) via a branching system
of arteries and capillaries.
fyi Pediatric cardiologists have recognized more than 50 congenital heart defects. If the left side of the heart is not completely separated from the right side, various septal defects develop. If the four
chambers of the heart do not develop normally, complex anomalies form, such as tetralogy of Fallot
(TOF), a congenital heart condition involving four defects: pulmonary artery stenosis, ventricular septal
defect (VSD), displacement of the aorta to the right, and hypertrophy of the right ventricle.
Heart Valves
The valves of the heart are located at the entrance and exit of each ventricle and, as
you learned in the preceding section, control the flow of blood within the heart. See
Figure 9.5.260 • Chapter Nine
tricuspid valve
The tricuspid or right atrioventricular valve guards the opening between the right atrium
and the right ventricle. In a normal state, the tricuspid valve opens to allow the flow of
blood into the ventricle and then closes to prevent any backflow of blood.
pulmonary (semilunar) valve
The exit point for blood leaving the right ventricle is called the pulmonary (semilunar)
valve. Located between the right ventricle and the pulmonary artery, it allows blood to
flow from the right ventricle through the pulmonary artery to the lungs.
mitral (bicuspid) valve
The left atrioventricular valve between the left atrium and the left ventricle is called
the mitral valve (MV) or bicuspid valve. It allows blood to flow to the left ventricle and
closes to prevent its return to the left atrium.
aortic (semilunar) valve
Blood exits from the left ventricle through the aortic (semilunar) valve. Located between
the left ventricle and the aorta, it allows blood to flow into the aorta and prevents its
backflow to the ventricle.
Vascular System of the Heart
Due to the membranous lining of the heart (endocardium) and the thickness of the
myocardium, the heart has its own vascular system to meet its high oxygen demand.
The coronary arteries supply the heart with oxygen-rich blood, and the cardiac veins,
draining into the coronary sinus, collect the blood (oxygen poor) and return it to the
right atrium. See Figure 9.6.
Figure 9.5 Valves of the heart.
Anterior
Posterior
Aortic valve
(left semilunar valve)
Tricuspid valve
(right atrioventricular valve)
Mitral valve
(left atrioventricular valve)
Pulmonary valve
(right semilunar valve)Cardiovascular System • 261
Conduction System of the Heart
The autonomic nervous system controls the rate and rhythm of the heartbeat. It is
normally generated by specialized neuromuscular tissue of the heart that is capable of
causing cardiac muscle to contract rhythmically. This tissue of the heart comprises the
sinoatrial node, the atrioventricular node, and the atrioventricular bundle. See Figure 9.7.
Figure 9.6 Coronary circulation. (A) Coronary vessels portraying the complexity and extent of the coronary circulation.
(B) Coronary vessels that supply the posterior surface of the heart.
Anterior interventricular
artery (descending
branch)
Right coronary
artery
Small cardiac
vein
Anterior cardiac veins
Marginal branch
A
Great
cardiac
vein
Circumflex
branch
Coronary sinus
Posterior cardiac vein
Right coronary
artery
Small cardiac
vein
Marginal branch
Posterior interventricular vein
Middle cardiac vein (descending branch)
B
Pulmonary trunk
Left coronary artery
Great cardiac vein
Aortic arch
Sinoatrial node
(pacemaker)
Internodal pathway
Atrioventricular node
Atrioventricular bundle
(Bundle of His)
Bundle branches
Purkinje fibers
Aorta
Purkinje fibers
Interventricular
septum
Superior vena cava
Left atrium
1.
2.
3.
4.
5.
Figure 9.7 Conduction system of the heart.262 • Chapter Nine
sinoatrial node (sa node)
Called the pacemaker of the heart, the SA node is located in the upper wall of the right
atrium, just below the opening of the superior vena cava. It consists of a dense network
of Purkinje fibers (atypical muscle fibers) considered to be the source of impulses initiating the heartbeat. Electrical impulses discharged by the SA node are distributed to the
right and left atria and cause them to contract.
atrioventricular node (av node)
Located beneath the endocardium of the right atrium, the AV node transmits electrical
impulses to the bundle of His (atrioventricular bundle).
atrioventricular bundle (bundle of his)
The atrioventricular bundle or bundle of His forms a part of the conduction system of
the heart. It is a collection of heart muscle cells specialized for electrical conduction
that transmits the electrical impulses from the AV node to the point of the apex of
the fascicular branches. The bundle of His branches into the two bundle branches
that run along the interventricular septum. The bundles give rise to thin filaments
known as Purkinje fibers. These fibers distribute the impulse to the ventricular muscle. Together, the bundle branches and Purkinje network comprise the ventricular
conduction system.
The average adult heartbeat (pulse) is between 60 and 90 beats per minute. The rate
of the heartbeat can be affected by emotions, smoking, disease, body size, age, stress,
the environment, and many other factors.
The heart’s electrical activity can be recorded by an electrocardiogram (ECG, EKG),
which provides valuable information in diagnosing cardiac abnormalities, such as
myocardial damage and arrhythmias (see the section Diagnostic and Laboratory Tests
and Figure 9.38).
Blood Vessels
There are three main types of blood vessels: arteries, veins, and capillaries. Blood circulates throughout the body through their pathways.
Arteries
The arteries constitute a branching system of vessels that transports blood away from
the heart to all body parts. See Figure 9.8. In a normal state, arteries are elastic tubes
that recoil and carry blood in pulsating waves. All arteries have a pulse, reflecting the
rhythmical beating of the heart; however, certain points are commonly used to check
the rate, rhythm, and condition of the arterial wall.
A person’s pulse can be felt in a place that allows for an artery to be compressed
against a bone. The most commonly used sites for taking a pulse are the radial artery,
the brachial artery, and the carotid artery. See Table 9.2 and Figure 9.9. The pulse rate
can also be measured by using a stethoscope (auscultation) and counting the heartbeat
for 1 full minute. This is known as the apical pulse and is taken over the heart itself. In
contrast with other pulse sites, the apical pulse site is unilateral and is located at the
apex of the heart or at the fifth intercostal space, just to the left of the midclavicular line.
It is commonly used to check pulse rate in infants and children, and when the radial
pulse is difficult to palpate (to feel by touch).Cardiovascular System • 263
Figure 9.8 Major arteries of the systemic circulation.
Left common carotid artery
Left subclavian artery
Aortic arch
Renal artery
Abdominal aorta
Radial artery
Ulnar artery
Popliteal artery
Peroneal artery
Right common carotid artery
Right subclavian artery
Ascending aorta
Brachial artery
Common iliac artery
Internal iliac artery
External iliac artery
Femoral artery
Anterior tibial artery
Posterior tibial artery264 • Chapter Nine
Table 9.2 Pulse Checkpoints
Carotid
Brachial
Radial
Femoral
Popliteal
Dorsalis pedis
Temporal
Figure 9.9 Primary pulse points of the body.
Checkpoint Site/Use
Temporal Temple area of the head. Used to control bleeding from the head and scalp and to monitor
circulation.
Carotid Neck. In an emergency (cardiac arrest), most readily accessible site.
Brachial Antecubital space of the elbow. Most common site used to check blood pressure.
Radial Radial (thumb side) of the wrist. Most common site for taking a pulse.
Femoral Groin area. Monitor circulation.
Popliteal Behind the knee. Monitor circulation.
Dorsalis pedis Dorsal surface of the foot. Assess for peripheral artery disease (PAD).
Veins
Veins are the vessels that transport blood from peripheral tissues back to the heart. In
a normal state, veins have thin walls and valves that prevent the backflow of blood.
The great saphenous vein is the most important superficial vein of the lower limb. The
pulmonary veins carry oxygenated blood from the lungs to the heart. The superior and
inferior venae cavae carry deoxygenated blood from the upper and lower systemic
circulation. See Figure 9.10.
Capillaries
The capillaries are microscopic blood vessels with single-celled walls that connect arterioles (small arteries) with venules (small veins). See Figure 9.11. Blood passing through capillaries gives up the oxygen and nutrients carried to this point by the arteries and picks up
waste and carbon dioxide as it enters veins. Veins lead away from the capillaries as tiny
vessels and increase in size until they join the superior and inferior venae cavae as they
return to the heart. The extremely thin walls of capillaries facilitate passage of oxygen
and nutrients to cell bodies and the removal of accumulated waste and carbon dioxide.Cardiovascular System • 265
Figure 9.10 Major veins of the systemic circulation.
Superior vena cava
Hepatic portal vein
Superior mesenteric vein
Inferior vena cava
Ulnar vein
Radial vein
Common iliac vein
External iliac vein
Internal iliac vein
Digital veins
Subclavian vein
Right and left brachiocephalic veins
Cephalic vein
Brachial vein
Basilic vein
Median cubital vein
Renal vein
External jugular vein
Internal jugular vein
Femoral vein
Great saphenous vein
Popliteal vein
Posterior tibial vein
Anterior tibial vein
Fibular vein266 • Chapter Nine
Figure 9.11 Capillaries.
Capillary
network
Lumen
Venule
Valve
Tunica interna:
• Endothelium
• Subendothelial layer
• Internal elastic lamina
Tunica media
Tunica externa
Artery Vein
Arteriole
fyi The newborn’s pulse rate is irregular and rapid, varying from 120 to 140 beats/minute. Blood pressure pulse (P), blood pressure (BP), and respiration (R) vary according to a child’s age. A
is low and can vary with the size of the cuff used. The average blood pressure at birth is 80/46. The
respirations are approximately 35–50 per minute.
Blood Pressure
Blood pressure (BP) is the pressure exerted by the blood on the walls of the arteries. It
results from two forces. One is created by the heart as it pumps blood into the arteries and through the circulatory system. The other is the force of the arteries as they
resist the blood flow. The higher (systolic) number represents the pressure while the
heart contracts to pump blood to the body. The lower (diastolic) number represents
the pressure when the heart relaxes between beats. Blood pressure is reported in
millimeters of mercury (mmHg) and is measured with a sphygmomanometer. See
Figure 9.12.
The systolic pressure is always stated first. For example, 116/74 (116 over 74);
systolic = 116, diastolic = 74. Blood pressure below 120 over 80 mmHg is considered
optimal for adults. A systolic pressure of 120–139 mmHg or a diastolic pressure of
80–89 mmHg is considered to be prehypertension and needs to be monitored on a regular basis. A blood pressure reading of 140 over 90 or higher is considered elevated
(hypertension). [Show Less]