11 The Cardiovascular System

WHAT The cardiovascular system delivers oxygen and HOW nutrients to the body tissues The heart pumps and carries away wastes blood throughout the body such as carbon dioxide in blood vessels. Blood flow via blood. requires both the pumping action of the heart and changes in blood pressure.

WHY If the cardiovascular system cannot perform its functions, wastes build up in tissues. INSTRUCTORS Body organs fail to function properly, New Building Vocabulary and then, once oxygen becomes Coaching Activities for this depleted, they will die. chapter are assignable in

hen most people hear the term cardio- only with the interstitial fluid in their immediate Wvascular system, they immediately think vicinity. Thus, some means of changing and of the heart. We have all felt our own “refreshing” these fluids is necessary to renew the heart “pound” from time to time when we are ner- nutrients and prevent pollution caused by vous. The crucial importance of the heart has been the buildup of wastes. Like a bustling factory, the recognized for ages. However, the cardiovascular body must have a transportation system to carry system is much more than just the heart, and its various “cargoes” back and forth. Instead of from a scientific and medical standpoint, it is roads, railway tracks, and subways, the body’s important to understand why this system is so vital delivery routes are its hollow blood vessels. to life. Most simply stated, the major function of the Night and day, minute after minute, our tril- cardiovascular system is transportation. Using lions of cells take up nutrients and excrete wastes. blood as the transport vehicle, the system carries Although the pace of these exchanges slows dur- oxygen, nutrients, cell wastes, hormones, and ing sleep, they must go on continuously: when many other substances vital for body homeostasis they stop, we die. Cells can make such exchanges to and from the cells. The force to move the blood

356 Chapter 11: The Cardiovascular System 357

Superior Aorta vena cava Parietal pleura (cut) Pulmonary Left lung trunk

Pericardium (cut)

Apex of heart Diaphragm

(a) Figure 11.1 Location of the heart within the thorax. (a) Relationship of the JGCTV|CPFITGCVXGUUGNUVQVJGNWPIU (Figure continues on page 358.) around the body is provided by the beating heart flanked on each side by the lungs (Figure 11.1). Its and by blood pressure. pointed apex is directed toward the left hip and The cardiovascular system includes a muscular rests on the diaphragm, approximately at the level pump equipped with one-way valves and a system of the fifth intercostal space. (This is exactly where of large and small “plumbing” tubes within which one would place a stethoscope to count the heart the blood travels. (We discussed blood, the sub- rate for an apical pulse.) Its broad posterosuperior stance transported, in Chapter 10.) Here we will aspect, or base, from which the great vessels of the consider the heart (the pump) and the blood ves- body emerge, points toward the right shoulder and sels (the “plumbing”). lies beneath the second rib. 11 Coverings and Walls of the Heart The Heart The heart is enclosed by a sac called the pericar- Anatomy of the Heart dium (per″i-kar′de-um) that is made up of three layers: an outer fibrous layer and an inner serous ➔ Learning Objective membrane pair. The loosely fitting superficial part □ Describe the location of the heart in the body, of this sac is referred to as the fibrous pericar- CPF|KFGPVKH[KVUOCLQTCPCVQOKECNCTGCUQPCP dium. This fibrous layer helps protect the heart appropriate model or diagram. and anchors it to surrounding structures, such as Size, Location, and Orientation the diaphragm and sternum. Deep to the fibrous pericardium is the slippery, two-layered serous The modest size and weight of the heart give few pericardium. The parietal layer of the serous peri- hints of its incredible strength. Approximately the cardium, or parietal pericardium, lines the inte- size of a person’s fist, the hollow, cone-shaped heart rior of the fibrous pericardium. At the superior weighs less than a pound. Snugly enclosed within aspect of the heart, this parietal layer attaches to the inferior mediastinum (me″de-as-ti′num), the the large arteries leaving the heart and then makes medial section of the thoracic cavity, the heart is 358 Essentials of Human Anatomy and Physiology

Mediastinum Midsternal line

2nd rib Heart Sternum Right lung

Diaphragm Point of maximal intensity (PMI) Posterior (b) (c) Figure 11.1 (continued) Location of the heart within the thorax. (b)|4GNCVKQPUJKRQHVJGJGCTVVQVJGUVGTPWOCPFTKDU (c) Cross-sectional XKGY|UJQYKPITGNCVKXGRQUKVKQPQHVJGJGCTVKPVJGVJQTCZ a U-turn and continues inferiorly over the heart myocardium is reinforced internally by a network of surface. The visceral layer of the serous pericar- dense fibrous connective tissue called the “skeleton dium, or visceral pericardium, also called the of the heart.” The endocardium (en″do-kar′de-um) epicardium, is part of the heart wall (Figure 11.2). is a thin, glistening sheet of endothelium that lines In other words, the epicardium is the innermost the heart chambers. It is continuous with the linings layer of the pericardium and the outermost layer of of the blood vessels leaving and entering the heart. the heart wall. Lubricating serous fluid is produced (Figure 11.3 shows two views of the heart—an exter- by the serous pericardial membranes and collects nal anterior view and a frontal section. As the ana- in the pericardial cavity between these serous lay- tomical areas of the heart are described in the next ers. This fluid allows the heart to beat easily in a section, keep referring to Figure 11.3 to locate each relatively frictionless environment as the serous of the heart structures or regions.) pericardial layers slide smoothly across each other. Chambers and Associated Great Homeostatic Imbalance 11.1 Vessels ➔ Learning Objectives Inflammation of the pericardium, pericarditis □ ″ ′ Trace the pathway of blood through the heart. (per ˘ı-kar-di tis), often results in a decrease in the □ already small amount of serous fluid. This causes Compare the pulmonary and systemic circuits. the pericardial layers to rub, bind, and stick to The heart has four hollow cavities, or chambers— each other, forming painful adhesions that inter- two atria (a′tre-ah; singular atrium) and two ven- fere with heart movements. ______✚ tricles (ven′tr˘ı-kulz). Each of these chambers is The heart walls are composed of three layers: the lined with endocardium, which helps blood flow outer epicardium (the visceral pericardium just smoothly through the heart. The superior atria are described), the myocardium, and the innermost primarily receiving chambers. As a rule, they are endocardium (see Figure 11.2). The myocardium not important in the pumping activity of the heart. (mi″o-kar′de-um) consists of thick bundles of cardiac Instead, they assist with filling the ventricles. Blood muscle twisted and whorled into ringlike arrange- flows into the atria under low pressure from the ments (see Figure 6.2b, p. 184). It is the layer that veins of the body and then continues on to fill actually contracts. Myocardial cells are linked together the ventricles. The inferior, thick-walled ventricles by intercalated discs, which contain both desmo- are the discharging chambers, or actual pumps of somes and gap junctions. The gap junctions at the the heart. When they contract, blood is propelled intercalated discs allow ions to flow from cell to cell, out of the heart and into circulation. The right ven- carrying a wave of excitement across the heart. The tricle forms most of the heart’s anterior surface; the left ventricle forms its apex (Figure 11.3a). The Chapter 11: The Cardiovascular System 359

Pulmonary Fibrous trunk pericardium Parietal layer of serous pericardium Pericardium Pericardial cavity Visceral layer of serous pericardium

Epicardium Myocardium Heart wall Endocardium

Heart chamber

Figure 11.2 Heart wall and coverings.0QVGVJCVVJGXKUEGTCNNC[GTQHVJG RGTKECTFKWOCPFVJGGRKECTFKWOQHVJGJGCTVYCNNCTGVJGUCOGUVTWEVWTG

Brachiocephalic trunk Left common carotid artery Superior vena cava Left subclavian artery

Right pulmonary artery Aortic arch Ligamentum arteriosum Ascending aorta Left pulmonary artery Pulmonary trunk Left pulmonary veins

Right pulmonary Left atrium veins

Right atrium Circumflex artery Right coronary artery 11 in coronary sulcus (right Left coronary artery in atrioventricular groove) coronary sulcus (left atrioventricular groove) Anterior cardiac vein Left ventricle Right ventricle Great cardiac vein Marginal artery Anterior interventricular Small cardiac vein artery (in anterior interventricular sulcus) Inferior vena cava Apex (a) Anterior view of heart showing major vessels Figure 11.3 Gross anatomy of the heart. (Figure continues on page 360.) 360 Essentials of Human Anatomy and Physiology

Superior vena cava Aorta

Left pulmonary artery Right pulmonary artery Left atrium

Right atrium Left pulmonary veins

Right pulmonary veins Pulmonary semilunar valve Left atrioventricular valve Fossa ovalis (bicuspid valve) Aortic semilunar valve Right atrioventricular valve (tricuspid valve) Left ventricle Right ventricle

Chordae tendineae Interventricular septum Inferior vena cava Myocardium

Visceral pericardium (epicardium) (b) Frontal section showing interior chambers and valves Figure 11.3 (continued) Gross anatomy of the heart. septum that divides the heart longitudinally is (oxygen enters the blood and carbon dioxide enters referred to as the interatrial septum where it the lungs) and then return it to the heart. divides the atria and the interventricular septum Oxygen-rich blood returned to the left atrium where it divides the ventricles. flows into the left ventricle and is pumped out into Although it is a single organ, the heart functions the aorta (a-or′tah), from which the systemic arter- as a double pump, with arteries carrying blood away ies branch to supply essentially all body tissues. from and veins carrying blood toward the heart. The After oxygen is delivered to tissues, oxygen-poor right side works as the pulmonary circuit pump. It blood circulates from the tissues back to the right receives oxygen-poor blood from the veins of the atrium via the systemic veins, which finally empty body through the large superior vena cava and their cargo into either the superior or inferior vena inferior vena cava (plural venae cavae; ka′ve) and cava. This second circuit, from the left ventricle pumps it out through the pulmonary trunk. The through the body tissues and back to the right pulmonary trunk splits into the right and left pulmo- atrium, is called the systemic circulation (see nary arteries, which carry blood to the lungs, Figure 11.4). It supplies oxygen- and nutrient-rich where oxygen is picked up and carbon dioxide is blood to all body organs. Because the left ventricle unloaded. Oxygen-rich blood drains from the lungs pumps blood over the much longer systemic path- and is returned to the left side of the heart through way through the body, its walls are substantially the four pulmonary veins. This circuit, from the thicker than those of the right ventricle (Figure 11.5), right ventricle (the pump) to the lungs and back to and it is a much more powerful pump. the left atrium (receiving chamber), is called the pul- monary circulation (Figure 11.4). Its only function Did You Get It? is to carry blood to the lungs for gas exchange 1. 9JCVKUVJGNQECVKQPQHVJGJGCTVKPVJGVJQTCZ! Chapter 11: The Cardiovascular System 361

Capillary beds of lungs where gas exchange occurs

Pulmonary Circuit Pulmonary arteries Pulmonary Left veins ventricle Venae Aorta and cavae branches Right ventricle

Left Muscular atrium interventricular septum

Left Figure 11.5 Anatomical differences in right and left ventricles.6JGNGHVXGPVTKENGJCUCVJKEMGTYCNNCPF Right ventricle KVUECXKV[KUDCUKECNN[EKTEWNCT6JGTKIJVXGPVTKENGECXKV[KU atrium Heart Right ETGUEGPVUJCRGFCPFYTCRUCTQWPFVJGNGHVXGPVTKENG ventricle Systemic Circuit Heart Valves ➔ Learning Objective □ Explain the operation of the heart valves. The heart is equipped with four valves, which allow blood to flow in only one direction through the heart chambers—from the atria through the Capillary ventricles and out the great arteries leaving the beds of all heart (see Figure 11.3b). The atrioventricular body tissues (AV) valves (a″tre-o-ven-trik′u-lar) are located where gas between the atria and ventricles on each side. exchange These valves prevent backflow into the atria when occurs the ventricles contract. The left AV valve—the 11 KEY: bicuspid valve, also called the mitral (mi′tral) Oxygen-rich, CO2-poor blood valve—consists of two flaps, or cusps, of endocar- Oxygen-poor, CO2-rich blood dium. The right AV valve, the tricuspid valve, has three cusps. Tiny white cords, the chordae ten- Figure 11.4 The systemic and pulmonary dineae (kor′de ten-din′e)—literally, “tendinous circulations.6JGNGHVUKFGQHVJGJGCTVKUVJGU[UVGOKE cords” (think of them as “heart strings”)—anchor RWORVJGTKIJVUKFGKUVJGRWNOQPCT[EKTEWKVRWOR the cusps to the walls of the ventricles. When the #NVJQWIJVJGTGCTGVYQRWNOQPCT[CTVGTKGUQPGGCEJVQ VJGTKIJVCPFNGHVNWPIHQTUKORNKEKV[QPN[QPGKUUJQYP heart is relaxed and blood is passively filling its chambers, the AV valve cusps hang limply into the ventricles (Figure 11. 6a, p. 362). 2. 9JKEJJGCTVEJCODGTJCUVJGVJKEMGUVYCNNU!9JCV As the ventricles contract, they press on the KU|VJGHWPEVKQPCNUKIPKHKECPEGQHVJKUUVTWEVWTCN blood in their chambers, and the pressure inside FKHHGTGPEG! 3. *QYFQGUVJGHWPEVKQPQHVJGU[UVGOKEEKTEWNCVKQP the ventricles (intraventricular pressure) begins to FKHHGTHTQOVJCVQHVJGRWNOQPCT[EKTEWNCVKQP! rise. This forces the AV valve cusps upward, clos- ing the valves. At this point the chordae tendineae For answers, see Appendix A. tighten and anchor the cusps in a closed position. 362 Essentials of Human Anatomy and Physiology

(a) Operation of the AV valves

1 Blood returning 4 Ventricles contract, to the atria puts forcing blood against pressure against AV valve cusps. AV valves; the AV valves are forced open. 5 AV valves close.

2 As the ventricles 6 Chordae tendineae fill, AV valve cusps tighten, preventing hang limply into valve cusps from ventricles. everting into atria. 3 Atria contract, Ventricles forcing additional blood into ventricles.

AV valves open; AV valves closed; atrial pressure atrial pressure greater than less than ventricular pressure ventricular pressure

(b) Operation of the semilunar valves

Pulmonary trunk Aorta

1 As ventricles 2 As ventricles relax contract and and intraventricular intraventricular pressure falls, blood pressure rises, blood flows back from is pushed up against arteries, filling the semilunar valves, cusps of semilunar forcing them open. valves and forcing them to close.

Semilunar valves open Semilunar valves closed

Figure 11.6 Operation of the heart valves. (a)#VTKQXGPVTKEWNCT #8 XCNXGU (b)|5GOKNWPCTXCNXGU Chapter 11: The Cardiovascular System 363

If the cusps were unanchored, they would blow upward into the atria like an umbrella being turned inside out by a gusty wind. In this manner, the AV valves prevent backflow into the atria when the ventricles are contracting. The second set of valves, the semilunar (sem″˘ı-lu′nar) valves, guards the bases of the two large arteries leaving the ventricular chambers. Thus, they are known as the pulmonary semilu- nar valve and aortic semilunar valve (see 2TQUVJGVKECQTVKEJGCTVXCNXG Figure 11.3b). Each semilunar valve has three ______✚ cusps that fit tightly together when the valves are closed. When the ventricles are contracting and Cardiac Circulation forcing blood out of the heart, the cusps are ➔ Learning Objective forced open and flattened against the walls of the □ Name the functional blood supply of the heart. arteries by the tremendous force of rushing blood (Figure 11.6b). Then, when the ventricles relax, Although the heart chambers are bathed with blood the blood begins to flow backward toward the almost continuously, the blood contained in the heart, and the cusps fill with blood like a para- heart does not nourish the myocardium. The func- chute filling with air, closing the valves. This pre- tional blood supply that oxygenates and nourishes vents arterial blood from reentering the heart. the myocardium is provided by the right and left Each set of valves operates at a different time. coronary arteries. The coronary arteries branch The AV valves are open during heart relaxation from the base of the aorta and encircle the heart in and closed when the ventricles are contracting. the coronary sulcus (atrioventricular groove) The semilunar valves are closed during heart at the junction of the atria and ventricles (see relaxation and are forced open when the ventri- Figure 11.3a). The coronary arteries and their major cles contract. The valves force blood to continually branches (the anterior interventricular artery move forward through the heart by opening and and circumflex artery on the left, and the poste- closing in response to pressure changes in the rior interventricular artery and marginal artery heart. on the right) are compressed (flow is inhibited, not stopped completely) when the ventricles are con- Homeostatic Imbalance 11.2 tracting and fill when the heart is relaxed. The myo- cardium is drained by several cardiac veins, which Heart valves are simple devices, and the heart— empty into an enlarged vessel on the posterior of the heart called the coronary sinus. The coronary like any mechanical pump—can function with 11 “leaky” valves as long as the damage is not too sinus, in turn, empties into the right atrium. great. However, severely deformed valves can seri- ously hamper cardiac function. For example, an Homeostatic Imbalance 11.3 incompetent valve forces the heart to pump and repump the same blood because the valve does When the heart beats at a very rapid rate, the not close properly, so blood backflows. In valvu- myocardium may receive an inadequate blood lar stenosis, the valve cusps become stiff, often supply because the relaxation periods (when the because of repeated bacterial infection of the blood is able to flow to the heart tissue) are short- endocardium (endocarditis). This forces the heart ened. Situations in which the myocardium is to contract more vigorously than normal to create deprived of oxygen often result in crushing chest enough pressure to drive blood through the nar- pain called angina pectoris (an-ji′nah pek′tor-is). rowed valve. In each case, the heart’s workload This pain is a warning that should never be increases, and ultimately the heart weakens and ignored, because if angina is prolonged, the oxygen- may fail. Under such conditions, the faulty valve is deprived heart cells may die, forming an area replaced with a synthetic valve (see photo), a called an infarct. The resulting myocardial cryopreserved human valve, or a chemically infarction (in-fark′shun), or MI, is commonly treated valve taken from a pig heart. called a “heart attack” or a “coronary.” ______✚ 364 Essentials of Human Anatomy and Physiology

Figure 11.7 The intrinsic conduction system of the heart.6JGFGRQNCTK\CVKQP Superior YCXGKPKVKCVGFD[VJGUKPQCVTKCN vena cava 5# PQFGRCUUGUUWEEGUUKXGN[ VJTQWIJVJGCVTKCNO[QECTFKWO Sinoatrial (SA) VQVJGCVTKQXGPVTKEWNCT #8  node (pacemaker) Left atrium PQFGVJG#8DWPFNGVJGTKIJV CPFNGHVDWPFNGDTCPEJGUCPF Atrioventricular (AV) node VJG2WTMKPLGHKDGTUKPVJGXGP- VTKEWNCTYCNNU Right atrium Atrioventricular (AV) bundle (bundle of His) Bundle branches Purkinje fibers

Purkinje fibers Interventricular septum

Did You Get It? before they will contract, cardiac muscle cells can 4. 9J[CTGVJGJGCTVXCNXGUKORQTVCPV! and do contract spontaneously and independently, 5. 9J[OKIJVCVJTQODWUKPCEQTQPCT[CTVGT[ECWUG even if all nervous connections are severed. UWFFGPFGCVJ! Moreover, these spontaneous contractions occur in For answers, see Appendix A. a regular and continuous way. Although cardiac muscle can beat independently, the muscle cells Physiology of the Heart in different areas of the heart have different As the heart beats, or contracts, the blood makes rhythms. Atrial cells beat about 60 times per min- continuous round-trips—into and out of the heart, ute, but ventricular cells contract more slowly through the rest of the body, and then back to the (20–40 times per minute). Therefore, without some heart—only to be sent out again. The amount of type of unifying control system, the heart would work that a heart does is almost too incredible to be an uncoordinated and inefficient pump. believe. In one day it pushes the body’s supply of Two systems act to regulate heart activity. 6 quarts or so of blood (6 liters [L]) through One of these involves the nerves of the auto- the blood vessels over 1,000 times, meaning that nomic nervous system, which act like brakes and it actually pumps about 6,000 quarts of blood gas pedals to decrease or increase the heart rate, (1500 gallons) in a single day! depending on which division is activated. We consider this topic later (see p. 368). The second Intrinsic Conduction System of the Heart: system is the intrinsic conduction system, or Setting the Basic Rhythm nodal system, that is built into the heart tissue ➔ Learning Objectives (Figure 11.7) and sets its basic rhythm like a drummer sets the beat for a rock band playing a □ Name the elements of the intrinsic conduction system of the heart, and describe the pathway of song. The intrinsic conduction system is com- impulses through this system. posed of a special tissue found nowhere else in □ Explain what information can be gained from an the body; it is much like a cross between muscle electrocardiogram. and nervous tissue. This system causes heart muscle depolarization in only one direction— What makes the heart beat? Unlike skeletal muscle from the atria to the ventricles. cells, which must be stimulated by nerve impulses Chapter 11: The Cardiovascular System 365

CONCEPTLINK There are other conditions that can interfere 6JKU KU XGT[ UKOKNCT VQ VJG QPGYC[ IGPGTCVKQP QH CP with the regular conduction of impulses across the CEVKQPRQVGPVKCNCUKVVTCXGNUFQYPVJGCZQPQHCPGWTQP heart—for example, damage to the SA node results NKMGCYCXG %JCRVGTRRs 6JGUKIPCNUVJCV in a slower heart rate. When this is a problem, arti- UVKOWNCVG ECTFKCE OWUENG EQPVTCEVKQP CNUQ VTCXGN QPG ficial pacemakers are usually installed surgically. YC[VJTQWIJQWVVJGKPVTKPUKEEQPFWEVKQPU[UVGO ➔ Ischemia (is-ke′me-ah), or lack of an ade- quate blood supply to the heart muscle, may lead In addition, the intrinsic conduction system to fibrillation—a rapid, uncoordinated quivering enforces a contraction rate of approximately 75 of the ventricles (it looks like a bag of wiggling beats per minute on the heart; thus, the heart worms). Fibrillation makes the heart unable to beats as a coordinated unit. pump any blood and so is a major cause of death One of the most important parts of the intrin- from heart attacks in adults. Many businesses train sic conduction system is a crescent-shaped node their employees in the use of AEDs (automatic of tissue called the sinoatrial (si″no-a′tre-al) (SA) external defibrillators), which has proven to be node, located in the right atrium. Other compo- lifesaving in many cases. ______✚ nents include the atrioventricular (AV) node at ″ ′ the junction of the atria and ventricles, the atrio- Tachycardia (tak e-kar de-ah) is a rapid heart rate (over 100 beats per minute). Bradycardia ventricular (AV) bundle (bundle of His) and ″ ′ the right and left bundle branches located in the (brad e-kar de-ah) is a heart rate that is substan- interventricular septum, and finally the Purkinje tially slower than normal (less than 60 beats per (pur-kin′je) fibers, which spread within the myo- minute). Neither condition is pathological, but cardium of the ventricle walls. prolonged tachycardia may progress to fibrillation. The SA node is a tiny cell mass with a mammoth Cardiac Cycle and Heart Sounds job. Because it has the highest rate of depolarization ➔ in the whole system, it starts each heartbeat and sets Learning Objective the pace for the whole heart. Consequently, the SA □ Define systole, diastole, stroke volume, cardiac node is often called the pacemaker. From the SA cycle, heart sounds, and murmur. node, the impulse spreads through the atria to the In a healthy heart, the atria contract simultaneously. AV node, and then the atria contract. At the AV Then, as they start to relax, the ventricles begin to node, the impulse is delayed briefly to give the atria contract. Systole (sis′to-le) and diastole (di-as′to-le) time to finish contracting. It then passes rapidly mean heart contraction and relaxation, respectively. through the AV bundle, the bundle branches, and Because most of the pumping work is done by the the Purkinje fibers, resulting in a “wringing” contrac- ventricles, these terms refer to the contraction and tion of the ventricles that begins at the heart apex relaxation of the ventricles unless otherwise stated. and moves toward the atria. This contraction effec- The term cardiac cycle refers to the events of 11 tively ejects blood superiorly into the large arteries one complete heartbeat, during which both atria leaving the heart. “A Closer Look” (on p. 367) and ventricles contract and then relax. The aver- describes electrocardiography, the clinical proce- age heart beats approximately 75 times per min- dure for mapping the electrical activity of the heart. ute, so the length of the cardiac cycle is normally about 0.8 second. We will consider the cardiac Homeostatic Imbalance 11.4 cycle in terms of events occurring during five peri- ods (Figure 11.8, p. 366). Because the atria and ventricles are separated from 1 one another by “insulating” connective tissue, Atrial diastole (ventricular filling). Our dis- which is part of the fibrous skeleton of the heart, cussion begins with the heart completely depolarization waves can reach the ventricles only relaxed. Pressure in the heart is low, the AV by traveling through the AV node. Thus, any dam- valves are open, and blood is flowing pas- age to the AV node can partially or totally block sively through the atria into the ventricles. The the ventricles from the control of the SA node. semilunar valves are closed. When this occurs, the ventricles begin to beat at 2 Atrial systole. The ventricles remain in dias- their own rate, which is much slower, some or all tole as the atria contract, forcing blood into the of the time. This condition is called heart block. ventricles to complete ventricular filling. 366 Essentials of Human Anatomy and Physiology

Are the ventricular cardiac cells contracting isometrically Q: or isotonically during phase 3?

Left atrium Right atrium

Left ventricle Right ventricle 1 Atrial diastole 2 Atrial 3 Isovolumetric 4 Ventricular 5 Isovolumetric (ventricular filling) systole contraction systole (ejection relaxation phase) Figure 11.8 Summary of events EQPVTCEVKPIVJKEMTGFCPFDNWG OGCUWTGOGPVq RJCUGUKPRGTKQFU occurring during the cardiac CTTQYUKPFKECVGFKTGEVKQPQHDNQQF CPFVJGXGPVTKENGUCTGENQUGF cycle.5OCNNDNCEMCTTQYUKPFKECVG HNQY&WTKPIVJGisovolumetric EJCODGTUCPFVJGXQNWOGQHDNQQF VJGTGIKQPUQHVJGJGCTVVJCVCTG NKVGTCNN[pUCOGXQNWOG VJG[EQPVCKPKUWPEJCPIKPI

3 Isovolumetric contraction. Atrial systole dup, pause, lub-dup, pause, and so on. The first ends, and ventricular systole begins. The initial heart sound (lub) is caused by the closing of the rise in intraventricular pressure closes the AV AV valves. The second heart sound (dup) occurs valves, preventing backflow of blood into the when the semilunar valves close at the end of ven- atria. For a moment, the ventricles are com- tricular systole. The first heart sound is longer and pletely closed chambers. louder than the second heart sound, which tends 4 Ventricular systole (ejection phase). The ven- to be short and sharp. tricles continue to contract, causing the intra- ventricular pressure to surpass the pressure in Homeostatic Imbalance 11.5 the major arteries leaving the heart. This causes the semilunar valves to open and blood to be Abnormal or unusual heart sounds are called ejected from the ventricles. During this phase, heart murmurs. Blood flows silently as long as the atria are again relaxed and filling with blood. the flow is smooth and uninterrupted. If it strikes obstructions, its flow becomes turbulent and gen- 5 Isovolumetric relaxation. As ventricular dias- erates sounds that can be heard with a stetho- tole begins, the pressure in the ventricles falls scope. Heart murmurs are fairly common in young below that in the major arteries, and the semi- children (and some elderly people) with perfectly lunar valves close to prevent backflow into the healthy hearts, probably because their heart walls ventricles. For another moment, the ventricles are relatively thin and vibrate with rushing blood. are completely closed chambers and intraven- However, murmurs in patients who do not fall into tricular pressure continues to decrease. either of these groups most often indicate valve Meanwhile, the atria have been in diastole, fill- problems. For example, if a valve does not close ing with blood. When atrial pressure increases tightly (is incompetent), a swishing sound will be above intraventricular pressure, the AV valves heard after that valve has (supposedly) closed, as open, and the cycle repeats. the blood flows back through the partially open When using a stethoscope, you can hear two valve. Distinct sounds also can be heard when distinct sounds during each cardiac cycle. These blood flows turbulently through stenosed (nar- heart sounds are often described by the two rowed) valves. ______✚ syllables “lub” and “dup,” and the sequence is lub-

Did You Get It?

their contraction becomes isotonic. becomes contraction their

blood against the semilunar valves, at which point point which at valves, semilunar the against blood 6. 9JCVKUVJGHWPEVKQPQHVJGKPVTKPUKEEQPFWEVKQP

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8. &WTKPIKUQXQNWOGVTKEEQPVTCEVKQPQHVJGECTFKCE heart rate (HR) and the stroke volume (SV). 11 E[ENG|YJKEJEJCODGTUCTGTGNCZKPICPFYJKEJCTG Stroke volume is the volume of blood pumped out EQPVTCEVKPI! by a ventricle with each heartbeat. In general, 9. 9JCVECWUGUVJGNWDFWRUQWPFUJGCTFYKVJC stroke volume increases as the force of ventricular UVGVJQUEQRG! contraction increases. If we use the normal resting For answers, see Appendix A. values for heart rate (75 beats per minute) and stroke volume (70 ml per beat), the average adult Cardiac Output cardiac output can be easily calculated: ➔ Learning Objective CO = HR (75 beats/min) × SV (70 ml/beat) □ Describe the effect of each of the following on CO = 5250 ml/min = 5.25 L/min heart rate: stimulation by the vagus nerve, exercise, epinephrine, and various ions. The normal adult blood volume is about 6,000 ml, so nearly the entire blood supply passes Cardiac output (CO) is the amount of blood through the body once each minute. Cardiac out- pumped out by each side of the heart (actually put varies with the demands of the body. It rises each ventricle) in 1 minute. It is the product of the

367 368 Essentials of Human Anatomy and Physiology when the stroke volume is increased or the heart 1. Neural (ANS) controls. During times of beats faster or both; it drops when either or both physical or emotional stress, the nerves of of these factors decrease. Let’s take a look at how the sympathetic division of the autonomic stroke volume and heart rate are regulated. nervous system more strongly stimulate the SA and AV nodes and the cardiac muscle Regulation of Stroke Volume A healthy heart itself. As a result, the heart beats more rap- pumps out about 60 percent of the blood present idly. This is a familiar phenomenon to any- in its ventricles. As noted previously, this is approx- one who has ever been frightened or has imately 70 ml (about 2 ounces) with each heart- had to run to catch a bus. As fast as the heart beat. According to Starling’s law of the heart, the pumps under ordinary conditions, it really critical factor controlling stroke volume is how speeds up when special demands are placed much the cardiac muscle cells are stretched by the on it. Because a faster blood flow increases filling of the chambers just before they contract. the rate at which fresh blood reaches body The more they are stretched, the stronger the con- cells, more oxygen and glucose are made traction will be. The important factor stretching available to them during periods of stress. the heart muscle is venous return, the amount of When demand declines, the heart adjusts blood entering the heart and distending its ventri- accordingly. Parasympathetic nerves, primar- cles. If one side of the heart suddenly begins to ily vagus nerve fibers, slow and steady the pump more blood than the other, the increased heart, giving it more time to rest during non- venous return to the opposite ventricle will force it crisis times. to pump out an equal amount, thus preventing 2. Hormones and ions. Various hormones and backup of blood in the circulation. ions can have a dramatic effect on heart activ- Anything that increases the volume or speed ity. Both epinephrine, which mimics sympa- of venous return also increases stroke volume and thetic nerves and is released in response to force of contraction (Figure 11.9). For example, a sympathetic nerve stimulation, and thyroxine, slow heartbeat allows more time for the ventricles a thyroid hormone, increase heart rate. to fill. Exercise speeds venous return because it Electrolyte imbalances pose a real threat to results in increased heart rate and force; the the heart. For example, recall that calcium enhanced squeezing action of active skeletal mus- ions are required for muscle contraction. A cles on the veins helps return blood to the heart. reduced level of ionic calcium in the blood This so-called muscular pump also plays a major depresses the heartbeat, whereas an excessive role in increasing the venous return. In contrast, level of blood calcium ions causes such pro- low venous return, such as might result from longed contractions that the heart may stop severe blood loss or an abnormally rapid heart entirely. Either excess or lack of needed ions rate, decreases stroke volume, causing the heart to such as sodium and potassium also modifies beat less forcefully. heart activity. A deficit of potassium ions in the blood, for example, causes the heart to Factors Modifying Basic Heart Rate In healthy beat feebly, and abnormal heart rhythms people, stroke volume tends to be relatively con- appear. stant. However, when blood volume drops sud- 3. Physical factors. A number of physical fac- denly or when the heart has been seriously tors, including age, gender, exercise, and body weakened, stroke volume declines, and cardiac temperature, influence heart rate. Resting output is maintained by a faster heartbeat. heart rate is fastest in the fetus (140–160 beats Although heart contraction does not depend on per minute) and then gradually decreases the nervous system, its rate can be changed tem- throughout life. The average adult heart rate is porarily by the autonomic nerves. Indeed, the faster in females (72–80 beats per minute) most important external influence on heart rate is than in males (64–72 beats per minute). Heat the activity of the autonomic nervous system. increases heart rate by boosting the metabolic Several chemicals, hormones, and ions also mod- rate of heart cells. This explains the rapid, ify heart rate. Some of these factors are discussed pounding heartbeat you feel when you have a next (see also Figure 11.9). Chapter 11: The Cardiovascular System 369

Crisis stressors Low blood High blood Exercise Decreased (physical or emotional pressure pressure blood volume trauma; increased body or blood (hemorrhage) temperature; exercise) volume

Activation of Sympathetic nervous system activity skeletal muscle and respiratory “pumps”

Crisis has Hormones: Increased Decreased passed epinephrine, venous venous thyroxine return return

Parasympathetic nervous system Increased contractile controls (via force of cardiac muscle vagus nerves)

KEY: Heart rate (beats/min) Stroke volume (ml/beat) Increases, stimulates Reduces, inhibits Initial stimulus Physiological response End result Cardiac output (ml/min)

Figure 11.9 Influence of selected factors on cardiac output.0QVGVJCVCP[ FGETGCUGKPJGCTVTCVGQTUVTQMGXQNWOGYKNNTGUWNVKPCEQTTGURQPFKPIFGETGCUGKP ECTFKCEQWVRWV

high fever and accounts in part for the effect progressive condition that reflects weakening of of exercise on heart rate (remember, working the heart by coronary atherosclerosis (clogging of muscles generate heat). Cold has the opposite the coronary vessels with fatty buildup), hyperten- 11 effect; it directly decreases heart rate. As sive heart disease, or multiple myocardial infarc- noted previously, exercise acts through ner- tions (repaired with noncontracting scar tissue). In vous system controls (sympathetic division) to these patients, the heart pumps weakly and is increase heart rate (and also, through the nearly “worn out.” The weak contractions of a action of the muscular pump, to increase heart in CHF result in a lower stroke volume. For stroke volume). those patients, the drug digitalis is routinely pre- scribed. It enhances contractile force and stroke Homeostatic Imbalance 11.6 volume of the heart, resulting in greater cardiac output. The pumping action of the healthy heart maintains Because the heart is a double pump, each side a balance between cardiac output and venous can fail independently of the other. If the left heart return. But when the pumping efficiency of the fails, pulmonary congestion occurs. The right side heart is reduced so that circulation is inadequate of the heart continues to propel blood to the to meet tissue needs, congestive heart failure lungs, but the left side is unable to eject the (CHF) occurs. Congestive heart failure is usually a returning blood into the systemic circulation. As 370 Essentials of Human Anatomy and Physiology blood “backs up” in the lungs, they become swol- which carry blood away from the heart, and veins, len with blood, the pressure within them increases, which drain the tissues and return the blood to the and fluid leaks into the lung tissue, causing pul- heart, are simply conducting vessels—the free- monary edema. If untreated, the person “drowns” ways and secondary roads. Only the tiny hairlike in these fluids. capillaries, which extend and branch through the If the right side of the heart fails, peripheral tissues and connect the smallest arteries (arteri- congestion occurs as blood backs up in the sys- oles) to the smallest veins (venules), directly serve temic circulation. Edema is most noticeable in the the needs of the body cells. The capillaries are the distal parts of the body: The feet, ankles, and fin- side streets or alleys that intimately intertwine gers become swollen and puffy. Failure of one among the body cells and provide access to side of the heart puts a greater strain on the individual “homes.” It is only through their walls opposite side, and eventually the whole heart that exchanges between tissue cells and the blood fails. ______✚ can occur. Notice that we routinely depict arteries in red Did You Get It? and veins in blue. By convention, red indicates 10. 9JCVFQGUVJGVGTOcardiac outputOGCP! oxygen-rich blood, the normal status of blood in 11. 9JCVYQWNF[QWGZRGEVVQJCRRGPVQVJGJGCTVTCVG most of the body’s arteries, and blue indicates rela- QHCPKPFKXKFWCNYKVJCHGXGT!9J[! tively oxygen-depleted, carbon dioxide–rich blood, 12. 9JCVKUVJGOQUVKORQTVCPVHCEVQTCHHGEVKPIUVTQMG the normal status of blood in most of the veins. XQNWOG! However, there are exceptions. For instance, we For answers, see Appendix A. have seen that oxygen-poor blood is carried in the pulmonary trunk, an artery, while oxygen- Blood Vessels rich blood is transported back to the heart in pulmonary veins. An easy way to remember this ➔ Learning Objective difference is the following: Arteries are red □ Compare and contrast the structure and function of and veins are blue, but for the lungs there’s an arteries, veins, and capillaries. exception of two. Blood circulates inside the blood vessels, which Microscopic Anatomy form a closed transport system called the vascu- of Blood Vessels lar system. The idea that blood circulates, or “makes rounds,” through the body is only about Tunics 300 years old. The ancient Greeks believed that Except for the microscopic capillaries (which have blood moved through the body like an ocean only one layer), the walls of blood vessels have tide, first moving out from the heart and then three layers, or tunics (Figure 11.10). The tunica ebbing back to it in the same vessels to get rid of intima (tu′n˘ı-kah in-tim′ah), which lines the lumen, its impurities in the lungs. It was not until the sev- or interior, of the vessels, is a thin layer of endo- enteenth century that William Harvey, an English thelium (squamous epithelial cells) resting on a physician, proved that blood did, in fact, move in basement membrane. Its cells fit closely together circles. and form a slick surface that decreases friction as Like a system of roads, the vascular system has blood flows through the vessel lumen. its freeways, secondary roads, and alleys. As the The tunica media (me′de-ah) is the bulky heart beats, it propels blood into the large arter- middle layer, made up mostly of smooth muscle ies leaving the heart. As the large arteries branch, and elastic fibers. Some of the larger arteries have blood moves into successively smaller and smaller elastic laminae, sheets of elastic tissue, in addi- arteries and then into the arterioles (ar-ter′e-ˉolz), tion to the scattered elastic fibers. The smooth which feed the capillary (kap′˘ı-lar″e) beds in the muscle, which is controlled by the sympathetic tissues. Capillary beds are drained by venules nervous system, is active in changing the diame- (ven′ulz), which in turn empty into veins that ter of the vessels. As the vessels constrict or merge and finally empty into the great veins dilate, blood pressure increases or decreases, (venae cavae) entering the heart. Thus arteries, respectively. Chapter 11: The Cardiovascular System 371

Figure 11.10 Structure of blood vessels. (a).KIJVRJQVQOKETQITCRJQHCOWUEWNCTCTVGT[CPFVJG EQTTGURQPFKPIXGKPKPETQUUUGEVKQP * (b)6JGYCNNUQH CTVGTKGUCPFXGKPUCTGEQORQUGFQHVJTGGVWPKEUVJGVWPKEC KPVKOCVWPKECOGFKCCPFVWPKECGZVGTPC%CRKNNCTKGUt DGVYGGPCTVGTKGUCPFXGKPUKPVJGEKTEWNCVQT[RCVJYC[tCTG EQORQUGFQPN[QHVJGVWPKECKPVKOC0QVKEGVJCVVJGVWPKEC OGFKCKUVJKEMKPCTVGTKGUCPFTGNCVKXGN[VJKPKPXGKPU

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The tunica externa (eks′tern-ah) is the outer- particular, tends to be much heavier. This struc- most tunic. This layer is composed largely of tural difference is related to a difference in func- fibrous connective tissue, and its function is to tion of these two types of vessels. Arteries, which support and protect the vessels. carry blood away from the heart, must be able to expand as blood is forced into them and then Structural Differences in Arteries, recoil passively as the blood flows off into the cir- Veins, and Capillaries culation during diastole. Their walls must be strong The walls of arteries are usually much thicker and stretchy enough to take these continuous than those of veins. The arterial tunica media, in 372 Essentials of Human Anatomy and Physiology

• To see the effect of venous valves, perform the following simple experiment on yourself: Allow one hand to hang by your side for a minute or Valve (open) two, until the blood vessels on its dorsal aspect become distended (swollen) with blood. Place two fingertips side by side on top of and per- Contracted pendicular to one of the distended veins. Then, skeletal pressing firmly, move your proximal finger muscle along the vein toward your heart. Now release that finger. As you can see, the vein remains collapsed in spite of gravity because your prox- imal finger pushed the blood past a valve. Now Valve (closed) remove your distal finger, and watch the vein fill rapidly with blood. Skeletal muscle activity, known as the mus- cular pump, also enhances venous return. As the muscles surrounding the veins contract Vein and relax, the blood is squeezed, or “milked,” through the veins toward the heart (Figure 11.11). Finally, the drop in pressure that occurs in the thorax just before we inhale causes the Direction of large veins near the heart to fill. Thus, the respi- blood flow ratory pump also helps return blood to the heart (see Figure 11.9). The transparent walls of the capillaries are Figure 11.11 Operation of the muscular pump. only one cell layer thick—just the tunica intima. 9JGPUMGNGVCNOWUENGUEQPVTCEVCPFRTGUUCICKPUVVJG Because of this exceptional thinness, substances HNGZKDNGXGKPUVJGXCNXGURTQZKOCNVQVJGCTGCQH are exchanged easily between the blood and the EQPVTCEVKQPCTGHQTEGFQRGPCPFDNQQFKUUSWGG\GF tissue cells. The tiny capillaries tend to form inter- VQYCTFVJGJGCTVNKMGVQQVJRCUVGHTQOCVWDG6JGXCNXGU weaving capillary beds. The flow of blood from an FKUVCNVQVJGRQKPVQHEQPVTCEVKQPCTGENQUGFD[VJG arteriole to a venule—that is, through a capillary DCEMHNQYKPIDNQQF bed—is called microcirculation. In most body regions, a capillary bed consists of two types of changes in pressure without stretching out perma- vessels: (1) a vascular shunt, a vessel that directly nently (see Figure 11.19). connects the arteriole and venule at opposite ends Veins, in contrast, carry blood back toward the of the bed, and (2) true capillaries, the actual heart, and the pressure in them tends to be low all exchange vessels (Figure 11.12). the time. Thus veins have thinner walls. However, The true capillaries number 10 to 100 per cap- because the blood pressure in veins is usually too illary bed, depending on the organ or tissues low to force the blood back to the heart, and served. They usually branch off the proximal end because blood returning to the heart often flows of the shunt and return to the distal end, but occa- against gravity (up the legs, for example), veins sionally they spring from the terminal arteriole are modified to ensure that the amount of blood and empty directly into the postcapillary venule. returning to the heart (venous return) equals the A cuff of smooth muscle fibers, called a precapil- amount being pumped out of the heart (cardiac lary sphincter, surrounds the root of each true output) at any time. The lumens of veins tend to capillary and acts as a valve to regulate the flow of be much larger than those of corresponding arter- blood into the capillary. Blood flowing through a ies, and they tend to have a thinner tunica media terminal arteriole may take one of two routes: but a thicker tunica externa. The larger veins have through the true capillaries or through the shunt. valves that prevent backflow of blood like those When the precapillary sphincters are relaxed in the heart (see Figure 11.10). (open), blood flows through the true capillaries Chapter 11: The Cardiovascular System 373 and takes part in exchanges with tissue cells. When the sphincters are contracted (closed), Assume the capillary bed depicted here is in the Q: biceps brachii muscle of your arm. What condition blood flows through the shunts and bypasses the would the capillary bed be in, (a) or (b), if you were tissue cells in that region. doing push-ups at the gym? Vascular shunt Homeostatic Imbalance 11.7 Precapillary sphincters Varicose veins are common in people who stand for long periods of time (for example, cashiers and hairdressers) and in obese (or pregnant) individu- als. The common factors are the pooling of blood in the feet and legs and inefficient venous return resulting from inactivity or pressure on the veins. In any case, the overworked valves give way, and the veins become twisted and dilated. A serious complication of varicose veins is thrombophlebi- Tr ue tis (throm″bo-fl˘e-bi′tis), inflammation of a vein capillaries that results when a clot forms in a vessel with Terminal arteriole Postcapillary poor circulation. Because all venous blood must venule pass through the pulmonary circulation before traveling through the body tissues again, a com- (a) Sphincters open; blood flows through true capillaries. mon consequence of thrombophlebitis is clot detachment and pulmonary embolism, which is a life-threatening condition in which the embolism lodges in a vessel in the lung. ______✚

Did You Get It? 13. #UUWOG[QWCTGXKGYKPICDNQQFXGUUGNWPFGTVJG OKETQUEQRG+VJCUCNCTIGNQRUKFGFNWOGPTGNCVKXGN[ VJKEMVWPKECGZVGTPCCPFCTGNCVKXGN[VJKPVWPKEC OGFKC9JKEJMKPFQHDNQQFXGUUGNKUVJKU! 14. #TVGTKGUNCEMXCNXGUDWVXGKPUJCXGVJGO*QYKUVJKU UVTWEVWTCNFKHHGTGPEGTGNCVGFVQDNQQFRTGUUWTG! 15. *QYKUVJGUVTWEVWTGQHECRKNNCTKGUTGNCVGFVQVJGKT Terminal arteriole Postcapillary HWPEVKQPKPVJGDQF[! venule For answers, see Appendix A. (b) Sphincters closed; blood flows through 11 vascular shunt. Gross Anatomy of Blood Vessels Figure 11.12 Anatomy of a capillary bed. The ➔ Learning Objective XCUEWNCTUJWPVD[RCUUGUVJGVTWGECRKNNCTKGUYJGP □ +FGPVKH[VJGDQF[oUOCLQTCTVGTKGUCPFXGKPUCPF RTGECRKNNCT[URJKPEVGTUEQPVTQNNKPIDNQQFGPVT[KPVQVJG name the body region supplied by each. VTWGECRKNNCTKGUCTGEQPUVTKEVGF

/CLQT#TVGTKGUQHVJG5[UVGOKE%KTEWNCVKQP heart as the ascending aorta, arches to the left as The aorta is the largest artery of the body, and it the aortic arch, and then plunges downward is a truly splendid vessel. In adults, the aorta is through the thorax, following the spine (thoracic about the size of a garden hose (with an internal aorta) finally to pass through the diaphragm into diameter about equal to the diameter of your the abdominopelvic cavity, where it becomes the thumb) where it leaves the left ventricle of the abdominal aorta (Figure 11.13, p. 375). heart. It decreases only slightly in diameter as it

runs to its terminus. Different parts of the aorta are with blood to serve the working muscle cells. muscle working the serve to blood with named for either their location or their shape. The flushed be would capillaries true The (a). Condition aorta springs upward from the left ventricle of the A: 374 Essentials of Human Anatomy and Physiology

The major branches of the aorta and the three branches: the L. gastric artery, which organs they serve are listed next in sequence from supplies the stomach; the splenic artery, which the heart. (Figure 11.13 shows the course of the supplies the spleen; and the common hepatic aorta and its major branches.) As you locate the artery, which supplies the liver. arteries on the figure, use what you already know • The unpaired superior mesenteric (mes″en- to make your learning easier. In many cases the ter′ik) artery supplies most of the small intes- name of the artery tells you the body region or tine and the first half of the large intestine, or organs served (for example, renal artery, brachial colon. artery, and coronary artery) or the bone followed • The renal (R. and L.) arteries serve the (femoral artery and ulnar artery). kidneys. Arterial Branches of the Ascending Aorta • The gonadal (R. and L.) arteries supply the • The only branches of the ascending aorta are gonads. They are called the ovarian arteries in the right (R.) coronary artery and left (L.) females (serving the ovaries) and the testicular coronary artery, which serve the heart. arteries in males (serving the testes). • The lumbar arteries (not illustrated in Figure Arterial Branches of the Aortic Arch 11.13) are several pairs of arteries serving the • The brachiocephalic (bra″ke-o-s˘e-fal′ik) heavy muscles of the abdomen and trunk walls. trunk (the first branch off the aortic arch) • The inferior mesenteric artery is a small, splits into the R. common carotid (kah- unpaired artery supplying the second half of ′ r˘o tid) artery, which further branches into the the large intestine. R. internal and R. external carotid arteries, and • The common iliac (R. and L.) arteries are the the R. subclavian (sub-kla′ve-an) artery. final branches of the abdominal aorta. Each di- (See same-named vessels on the left side vides into an internal iliac artery, which sup- of the body for organs served.) plies the pelvic organs (bladder, rectum, and so • The L. common carotid artery is the second on), and an external iliac artery, which enters branch off the aortic arch. It divides, forming the thigh, where it becomes the femoral ar- the L. internal carotid, which serves the brain, tery. The femoral artery and its branch, the and the L. external carotid, which serves the deep artery of the thigh, serve the thigh. At skin and muscles of the head and neck. the knee, the femoral artery becomes the popli- • The third branch of the aortic arch, the teal artery, which then splits into the anterior L. subclavian artery, gives off an important tibial artery and posterior tibial artery, branch—the vertebral artery, which serves which supply the leg and foot. The anterior tib- part of the brain. In the axilla, the subclavian ial artery terminates in the dorsalis pedis ar- artery becomes the axillary artery and then tery, which via the arcuate artery supplies the continues into the arm as the brachial artery, dorsum of the foot. (The dorsalis pedis is often which supplies the arm. At the elbow, the bra- palpated in patients with circulatory problems chial artery splits to form the radial artery of the legs to determine whether the distal part and ulnar artery, which serve the forearm. of the leg has adequate circulation.)

Arterial Branches of the Thoracic Aorta /CLQT8GKPUQHVJG5[UVGOKE%KTEWNCVKQP • The intercostal arteries (10 pairs) supply the Although arteries are generally located in deep, muscles of the thorax wall. Other branches of well-protected body areas, many veins are more the thoracic aorta supply the lungs (bronchial superficial, and some are easily seen and palpated arteries), the esophagus (esophageal arteries), on the body surface. Most deep veins follow the and the diaphragm (phrenic arteries). (These course of the major arteries, and with a few excep- arteries are not illustrated in Figure 11.13.) tions, the naming of these veins is identical to that of their companion arteries. Major systemic arteries Arterial Branches of the Abdominal Aorta branch off the aorta, whereas the veins converge • The celiac trunk is the first branch of the ab- on the venae cavae, which enter the right atrium of dominal aorta. It is a single vessel that has the heart. Veins draining the head and arms empty Chapter 11: The Cardiovascular System 375

Figure 11.13 /CLQTCTVGTKGUQHVJG U[UVGOKE|EKTEWNCVKQPCPVGTKQTXKGY All CTVGTKGU|CTGDKNCVGTCNWPNGUUQVJGTYKUG Arteries of the head and trunk UVCVGFKPVJGVGZVCNVJQWIJDQVJOC[PQVDG Internal carotid artery TGRTGUGPVGFKPVJKUHKIWTG External carotid artery Common carotid arteries Vertebral artery Arteries that supply the upper limb Subclavian artery Subclavian artery Brachiocephalic trunk Aortic arch Axillary artery Ascending aorta Coronary artery Thoracic aorta (above diaphragm) Brachial artery Celiac trunk Abdominal aorta

Superior mesenteric Radial artery artery Ulnar artery Renal artery Gonadal artery

Deep palmar arch

Superficial palmar arch Digital arteries

Inferior mesenteric artery Arteries that supply the lower limb Common iliac artery External iliac artery Femoral artery 11 Popliteal artery Internal iliac artery

Anterior tibial artery Posterior tibial artery

Dorsalis pedis artery

Arcuate artery 376 Essentials of Human Anatomy and Physiology into the superior vena cava, and those draining As before, we will trace the venous drainage in a the lower body empty into the inferior vena cava. distal-to-proximal direction. (These veins are described next and shown in • The anterior tibial vein and posterior tibial Figure 11.14. As before, locate the veins on the fig- vein and the fibular vein drain the leg (calf ure as you read their descriptions.) and foot). (The fibular vein is not shown in Figure 11.14.) The posterior tibial vein be- Veins Draining into the Superior Vena Cava comes the popliteal vein at the knee and Veins draining into the superior vena cava are then the femoral vein in the thigh. The femo- listed in a distal-to-proximal direction; that is, in ral vein becomes the external iliac vein as it the same direction the blood flows into the supe- enters the pelvis. rior vena cava. • The great saphenous (sah-fe′nus) veins are • The radial vein and ulnar vein are deep veins the longest veins in the body. They receive the draining the forearm. They unite to form the deep superficial drainage of the leg. They begin at brachial vein, which drains the arm and empties the dorsal venous arch in the foot and travel into the axillary vein in the axillary region. up the medial aspect of the leg to empty into • The cephalic (se-fal′ik) vein provides for the the femoral vein in the thigh. superficial drainage of the lateral aspect of the • Each common iliac (R. and L.) vein is formed arm and empties into the axillary vein. by the union of the external iliac vein and • The basilic (bah-sil′ik) vein is a superficial the internal iliac vein (which drains the pel- vein that drains the medial aspect of the arm vis) on its own side. The common iliac veins and empties into the brachial vein proximally. join to form the inferior vena cava, which then The basilic and cephalic veins are joined at the ascends superiorly in the abdominal cavity. anterior aspect of the elbow by the median • The R. gonadal vein drains the right ovary in cubital vein. (The median cubital vein is often females and the right testicle in males. (The chosen as the site for withdrawing blood for L. gonadal vein empties into the left renal the purpose of blood testing.) vein superiorly.) (The gonadal veins are not • The subclavian vein receives venous blood illustrated in Figure 11.14.) from the arm through the axillary vein and • The renal (R. and L.) veins drain the kidneys. from the skin and muscles of the head through • The hepatic portal vein is a single vein that the external jugular vein. drains the digestive tract organs and carries • The vertebral vein drains the posterior part this blood through the liver before it enters the of the head. systemic circulation. (We discuss the hepatic • The internal jugular vein drains the dural si- portal circulation in the next section.) nuses of the brain. • The hepatic (R. and L.) veins drain the liver. • The brachiocephalic (R. and L.) veins are large veins that receive venous drainage from Did You Get It? the subclavian, vertebral, and internal jugular 16. +PYJCVRCTVQHVJGDQF[CTGVJGHGOQTCNRQRNKVGCN veins on their respective sides. The brachioce- CPFCTEWCVGCTVGTKGUHQWPF! phalic veins join to form the superior vena 17. +PYJCVRCTVQHVJGDQF[CTGVJGCZKNNCT[EGRJCNKE cava, which enters the heart. CPF|DCUKNKEXGKPUNQECVGF! • The azygos (ˉaz′ˉ-gos)ı vein is a single vein that For answers, see Appendix A. drains the thorax and enters the superior vena Special Circulations cava just before it joins the heart. (This vein is not illustrated in Figure 11.14.) ➔ Learning Objective □ Discuss the unique features of the arterial circulation Veins Draining into the Inferior Vena Cava The of the brain, and hepatic portal circulation. inferior vena cava, which is much longer than the superior vena cava, returns blood to the heart Arterial Supply of the Brain and the Circle of from all body regions inferior to the diaphragm. Willis Because a lack of blood for even a few minutes Chapter 11: The Cardiovascular System 377

Figure 11.14 /CLQTXGKPUQHVJGU[UVGOKE circulation, anterior view.6JGXGUUGNUQHVJG Veins of the head and trunk RWNOQPCT[EKTEWNCVKQPCTGPQVKNNWUVTCVGF Dural venous sinuses CEEQWPVKPIHQTVJGKPEQORNGVGCRRGCTCPEGQH VJGEKTEWNCVKQPHTQOVJGJGCTV#NNXGKPUCTG DKNCVGTCNWPNGUUURGEKHKECNN[UVCVGFKPVJGVGZV External jugular vein Vertebral vein Internal jugular vein Veins that drain the upper limb Subclavian vein Right and left brachiocephalic veins Axillary vein Superior vena cava Cephalic vein Brachial vein Great cardiac vein Basilic vein

Hepatic veins Splenic vein Hepatic portal vein Renal vein Median cubital vein

Superior Ulnar vein mesenteric vein Radial vein

Inferior mesenteric vein Digital veins

Veins that drain the lower limb External iliac vein Inferior vena cava Femoral vein Common iliac vein Great saphenous vein 11 Popliteal vein Internal iliac vein

Posterior tibial vein Anterior tibial vein Small saphenous vein

Dorsal venous arch Dorsal metatarsal veins 378 Essentials of Human Anatomy and Physiology

Anterior Cerebral arterial circle Frontal lobe (circle of Willis) Optic chiasma r#PVGTKQT communicating Middle artery cerebral artery r#PVGTKQT cerebral artery Internal r2QUVGTKQT carotid communicating artery artery Mammillary r2QUVGTKQT body cerebral artery Temporal Basilar artery lobe Vertebral artery 2QPU Occipital lobe Cerebellum

(a) Posterior

(b) Figure 11.15 Arterial supply of the brain. (a)/CLQTCTVGTKGUQHVJGDTCKP 6JGHQWTCTVGTKGUEQORQUKPIVJGEKTENGQH9KNNKUCTGKPFKECVGFD[DWNNGVRQKPVU 6JG EGTGDGNNWOKUUJQYPQPN[QPVJGNGHVUKFGQHVJGDTCKP (b)%QNQTK\GFCTVGTKQITCRJ QHVJGDTCKPoUCTVGTKGU causes the delicate brain cells to die, a continuous The paired vertebral arteries pass upward blood supply to the brain is crucial. The brain is from the subclavian arteries at the base of the supplied by two pairs of arteries, the internal carotid neck. Within the skull, the vertebral arteries join arteries and the vertebral arteries (Figure 11.15). to form the single basilar artery. This artery The internal carotid arteries, branches of serves the brain stem and cerebellum as it travels the common carotid arteries, run through the neck upward. At the base of the cerebrum, the basilar and enter the skull through the temporal bone. artery divides to form the posterior cerebral Once inside the cranium, each divides into the arteries, which supply the posterior part of the anterior cerebral artery and middle cerebral cerebrum. artery, which supply most of the cerebrum. Chapter 11: The Cardiovascular System 379

Arterial Venous blood blood Inferior vena cava Stomach and intestine Liver Nutrients and Liver cells (hepatocytes) toxins absorbed Nutrients and toxins leave

Hepatic portal vein

First capillary bed Second capillary bed (liver sinusoids) Hepatic vein

Hepatic portal system Figure 11.16 The basic scheme 0WVTKGPVUCPFVQZKPURKEMGFWR UKPWUQKFUVJGDNQQFEQPVKPWGUKPVQ of the hepatic portal system. HTQO|ECRKNNCTKGUKPVJGUVQOCEJCPF VJGJGRCVKEXGKPUCPFKPHGTKQTXGPC 0QVGVJGRTGUGPEGQHVYQECRKNNCT[ KPVGUVKPGCTGVTCPURQTVGFVQVJGNKXGT ECXC DGFUYKVJKPVJGRQTVCNU[UVGO HQTRTQEGUUKPI(TQOVJGNKXGT

The anterior and posterior blood supplies of stored or processed in various ways for later release the brain are united by small communicating arte- to the blood. The liver is drained by the hepatic rial branches. The result is a complete circle of veins that enter the inferior vena cava. connecting blood vessels called the cerebral arte- rial circle or the circle of Willis, which sur- CONCEPTLINK rounds the base of the brain. The cerebral arterial .KMG VJG RQTVCN EKTEWNCVKQP VJCV NKPMU VJG J[RQVJCNC- circle protects the brain by providing more than OWU| QH VJG DTCKP CPF VJG CPVGTKQT RKVWKVCT[ INCPF one route for blood to reach brain tissue in case %JCRVGTR VJGJGRCVKERQTVCNEKTEWNCVKQPKUC of a clot or impaired blood flow anywhere in the WPKSWGCPFWPWUWCNEKTEWNCVKQP0QTOCNN[CTVGTKGUHGGF system. ECRKNNCT[ DGFU YJKEJ KP VWTP FTCKP KPVQ XGKPU +P VJG JGRCVKERQTVCNEKTEWNCVKQPveinsHGGFVJGNKXGTEKTEWNC- 11 Hepatic Portal Circulation The veins of the VKQP (KIWTG  ➔ hepatic portal circulation drain the digestive organs, spleen, and pancreas and deliver this blood The major vessels composing the hepatic por- to the liver through the hepatic portal vein (Figure tal circulation (Figure 11.17, p. 380) include the 11.16). When you have just eaten, the hepatic portal inferior and superior mesenteric veins, the splenic blood contains large amounts of nutrients. Because vein, and the left gastric vein. The inferior mes- the liver is a key body organ involved in maintain- enteric vein, draining the terminal part of the ing the proper glucose, fat, and protein concentra- large intestine, drains into the splenic vein, which tions in the blood, this system allows blood to “take itself drains the spleen, pancreas, and the left side a detour” to ensure that the liver processes these of the stomach. The splenic vein and superior substances before they enter the systemic circula- mesenteric vein (which drains the small intestine tion. The liver also helps detoxify blood by remov- and the first part of the colon) join to form the ing and processing toxins absorbed by the stomach hepatic portal vein. The L. gastric vein, which and intestines. As blood flows slowly through the drains the right side of the stomach, drains directly liver, some of the nutrients are removed to be into the hepatic portal vein. 380 Essentials of Human Anatomy and Physiology

Inferior vena cava (not part of hepatic portal system)

Gastric veins Liver Spleen Stomach Hepatic portal vein Splenic vein

Pancreas

Inferior mesenteric vein

Superior mesenteric vein

Small intestine Large intestine

Figure 11.17 The hepatic portal circulation.

Did You Get It? Arterial Pulse 18. 9JKEJXGUUGNtVJGJGRCVKERQTVCNXGKPJGRCVKEXGKPQT The alternating expansion and recoil of an artery JGRCVKECTVGT[tJCUVJGJKIJGUVEQPVGPVQHPWVTKGPVU that occurs with each beat of the left ventricle cre- CHVGTCOGCN! ates a pressure wave—a pulse—that travels 19. +PYJCVVYQKORQTVCPVYC[UKUVJGRWNOQPCT[ through the entire arterial system. Normally the EKTEWNCVKQPFKHHGTGPVHTQOVJGU[UVGOKEEKTEWNCVKQP! pulse rate (pressure surges per minute) equals the For answers, see Appendix A. heart rate (beats per minute). The pulse averages Physiology of Circulation 70 to 76 beats per minute in a healthy resting per- son. It is influenced by activity, postural changes, ➔ Learning Objective and emotions. □ Define pulse, and name several pulse points. You can feel a pulse in any artery lying close to the body surface by compressing the artery A fairly good indication of the efficiency of a per- against firm tissue; this provides an easy way of son’s circulatory system can be obtained by taking counting heart rate. Because it is so accessible, the arterial pulse and blood pressure measurements. point where the radial artery surfaces at the wrist These measurements, along with those of respira- (the radial pulse) is routinely used to take a pulse tory rate and body temperature, are referred to measurement, but there are several other clinically collectively as vital signs in clinical settings. important arterial pulse points (Figure 11.18). Chapter 11: The Cardiovascular System 381

Because these same points are compressed to stop blood flow into distal tissues during significant Superficial temporal artery blood loss or hemorrhage, they are also called pressure points. For example, if you seriously Facial artery cut your hand, you can stop the bleeding some- what by compressing the brachial artery. Common carotid artery • Palpate each of the pulse points shown in Figure 11.18 by placing the tips of your first two or three fingers of one hand over the Brachial artery artery at the site indicated. Do not use your thumb, because it has its own pulse. Compress the artery firmly as you begin and then imme- Radial artery diately ease up on your pressure slightly. In each case, notice the regularity and relative Femoral artery strength of the pulse. Popliteal artery Did You Get It? 20. 9JKEJCTVGT[KURCNRCVGFCVVJGYTKUV!#VVJGITQKP! #VVJGUKFGQHVJGPGEM! Posterior tibial For the answer, see Appendix A. artery

Blood Pressure Dorsalis pedis artery ➔ Learning Objectives □ Define blood pressure, and list factors affecting Figure 11.18 Body sites where the pulse is most and/or determining blood pressure. easily palpated. (Most of the specific arteries □ Define hypertension and atherosclerosis, and KPFKECVGFCTGFKUEWUUGFQPR describe possible health consequences of these conditions. The high pressure in these elastic arteries Any system equipped with a pump that forces forces the blood to continuously move into areas fluid through a one-way network of closed tubes where the pressure is lower. The pressure is high- operates under pressure. Blood pressure is the est in the large arteries closest to the heart and pressure the blood exerts against the inner walls continues to drop throughout the systemic path- of the blood vessels, and it is the force that keeps way, reaching zero at the right atrium (KIWTG|11.19). blood circulating continuously even between Recall that the blood flows into the smaller arter- heartbeats. Unless stated otherwise, the term blood ies, then arterioles, capillaries, venules, veins, and 11 pressure in this discussion is understood to mean finally back to the large venae cavae entering the the pressure within the large systemic arteries near right atrium of the heart. It flows continuously the heart. along a pressure gradient (from high to low pres- sure) as it makes its circuit, day in and day out. Blood Pressure Gradient When the ventricles The valves in the large veins, the milking activity contract, they force blood into large, thick-walled of the skeletal muscles, and pressure changes in elastic arteries close to the heart that expand as the thorax are so important because together they the blood is pushed into them. ensure blood flows back to the heart to be pumped out to the body again. The pressure dif- CONCEPTLINK ferences between arteries and veins become very #U[QWTGOGODGTKPVJGRCUUKXGRTQEGUUQHHKNVTCVKQP clear when these vessels are cut. If a vein is cut, UWDUVCPEGUOQXGHTQOCTGCUQHJKIJRTGUUWTGVQCTGCU the blood flows evenly from the wound; a lacer- QH NQY RTGUUWTG VJTQWIJ C HKNVGT %JCRVGT  R   ated artery produces rapid spurts of blood. A simi- $NQQFHNQYKUFTKXGPD[VJGUGUCOGFKHHGTGPEGUKPRTGU- lar pressure drop occurs as blood flows through UWTGDWVYKVJQWVCHKNVGT ➔ the pulmonary pathway. 382 Essentials of Human Anatomy and Physiology

the higher systolic pressure written first—120/80

120 (read “120 over 80”) translates to a systolic pres- Systolic pressure sure of 120 mm Hg and a diastolic pressure of 80 100 mm Hg. Most often, systemic arterial blood pres-

80 sure is measured indirectly by the auscultatory (os-kul′tuh-tor-e) method. This procedure is used 60 to measure blood pressure in the brachial artery of Diastolic the arm (Figure 11.20). 40 pressure Blood pressure (mm Hg) 20 Effects of Various Factors on Blood Pressure

0 Arterial blood pressure (BP) is directly related to cardiac output (CO; the amount of blood Aorta Veins pumped out of the left ventricle per minute) and Arteries Venules Arterioles Capillaries peripheral resistance (PR). This relationship is Venae cavae expressed by the equation BP = CO × PR. We Figure 11.19 Blood pressure in the systemic have already considered regulation of cardiac circuit of the cardiovascular system. output, so we will concentrate on peripheral resistance here. Continuous blood flow absolutely depends on Peripheral resistance is the amount of fric- the stretchiness of the larger arteries and their abil- tion the blood encounters as it flows through the ity to recoil and keep exerting pressure on the blood vessels. Many factors increase peripheral blood as it flows into the rest of the vascular sys- resistance, but probably the most important is the tem. Think of a garden hose with relatively hard constriction, or narrowing, of blood vessels, espe- walls. When the water is turned on, the water cially arterioles, as a result of either sympathetic spurts out under high pressure because the hose nervous system activity or atherosclerosis. walls don’t expand. However, when the water fau- Increased blood volume or increased blood vis- cet is suddenly turned off, the flow of water stops cosity (thickness) also raises peripheral resistance. just as abruptly. The reason is that the walls of the Any factor that increases either cardiac output or hose cannot recoil to keep pressure on the water; peripheral resistance causes an almost immediate therefore, the pressure drops, and the flow of rise in blood pressure. Many factors can alter water stops. The importance of the elasticity of the blood pressure—age, weight, time of day, exer- arteries is best appreciated when it is lost, as hap- cise, body position, emotional state, and various pens in arteriosclerosis. Arteriosclerosis is also drugs, to name a few. The influence of a few of called “hardening of the arteries” (see “A Closer these factors is discussed next. Look” on pp. 386–387). • Neural factors: the autonomic nervous system. The parasympathetic division of the Did You Get It? autonomic nervous system has little or no ef- 21. *QYFQGUDNQQFRTGUUWTGEJCPIGVJTQWIJQWVVJG fect on blood pressure, but the sympathetic U[UVGOKEEKTEWNCVQT[RCVJYC[! division is important. The major action of the For the answer, see Appendix A. sympathetic nerves on the vascular system is to cause vasoconstriction (vˉas″o-kon- Measuring Blood Pressure The off-and-on flow strik′shun), or narrowing of the blood vessels, of blood into the arteries as the heart alternately which increases the blood pressure. The sym- contracts and relaxes causes the blood pressure to pathetic center in the medulla of the brain is rise and fall during each beat. Thus, two arterial activated to cause vasoconstriction in many blood pressures are usually measured: systolic different circumstances (Figure 11.21, p. 384). (sis-t˘o′lik) pressure, the pressure in the arteries at For example, when we stand up suddenly af- the peak of ventricular contraction, and diastolic ter lying down, gravity causes blood to pool (di″us-t˘o′lik) pressure, the pressure when the very briefly in the vessels of the legs and ventricles are relaxing. Blood pressures are feet, and blood pressure drops. This activates reported in millimeters of mercury (mm Hg), with pressoreceptors, also called baroreceptors Chapter 11: The Cardiovascular System 383

Blood pressure Pressure Pressure Pressure 120 systolic in cuff in cuff in cuff 70 diastolic above 120; below 120, below 70; (to be measured) no sounds but above 70 no sounds audible audible

120 mm Hg 120 mm Hg Rubber cuff inflated with 70 mm Hg 70 mm Hg air

Sounds audible in Brachial Brachial stethoscope artery artery closed

(a)The course of the (b)The blood pressure (c)The pressure in the (d) As the pressure is brachial artery of the cuff is wrapped snugly cuff is gradually reduced still further, arm. Assume a blood around the arm just reduced while the the sounds become pressure of 120/70 in above the elbow and examiner listens louder and more a young, healthy inflated until the cuff (auscultates) for distinct; when the person. pressure exceeds the sounds in the brachial artery is no longer systolic blood artery with a constricted and blood pressure. At this point, stethoscope. The flows freely, the blood flow into the arm pressure read as the sounds can no longer is stopped, and a first soft tapping be heard. The brachial pulse cannot sounds are heard (the pressure at which the be felt or heard. first point at which a sounds disappear is small amount of blood recorded as the is spurting through the diastolic pressure. constricted artery) is recorded as the systolic pressure. Figure 11.20 Measuring blood pressure.

(baro = pressure), in the large arteries of The final example concerns sympathetic 11 the neck and chest. They send off warning nervous system activity when we exercise signals that result in reflexive vasoconstric- vigorously or are frightened and have to tion, quickly increasing blood pressure back make a hasty escape. Under these conditions, to the homeostatic level. generalized vasoconstriction occurs except When blood volume suddenly decreases, in the skeletal muscles. The vessels of the as in hemorrhage, blood pressure drops, and skeletal muscles dilate to increase the blood the heart begins to beat more rapidly as it tries flow to the working muscles. (However, note to compensate. However, because blood loss that the sympathetic nerves never cause vaso- reduces venous return, the heart also beats constriction of blood vessels of the heart or weakly and inefficiently. In such cases, the brain.) sympathetic nervous system causes vasocon- • Renal factors: the kidneys. The kidneys striction to increase the blood pressure so that play a major role in regulating arterial blood (it is hoped) venous return increases and cir- pressure by altering blood volume. As blood culation can continue. This phenomenon also pressure (and/or blood volume) increases happens during severe dehydration. above normal, the kidneys allow more water 384 Essentials of Human Anatomy and Physiology

Decreased blood volume Exercise Postural changes Chemicals Increased (renin, nicotine blood and others) viscosity

Sympathetic nervous system centers

Kidney conserves water and salt

Increased Increased Vasoconstriction stroke volume heart rate

Increased cardiac output Increased peripheral resistance

KEY: Increases, stimulates Increased arterial blood pressure Initial stimulus Physiological response End result

Figure 11.21 Summary of factors that increase arterial blood pressure.

to leave the body in the urine. Because the the blood, water follows. Thus, blood volume source of this water is the bloodstream, and blood pressure both rise in response to blood volume decreases, which in turn de- aldosterone. creases blood pressure. However, when arte- • Temperature. In general, cold has a vaso- rial blood pressure falls, the kidneys retain constricting effect. This is why your exposed body water, maintaining blood volume and skin feels cold to the touch on a winter day blood pressure (see Figure 11.21). In order to and why cold compresses are recommended increase blood volume and blood pressure, to prevent swelling of a bruised area. Heat fluids must be ingested or administered intra- has a vasodilating effect. This explains why venously. skin reddens during exercise as body temper- In addition, when arterial blood pressure ature increases and why warm compresses is low, certain kidney cells release the enzyme are used to speed the circulation into an in- renin into the blood. Renin triggers a series flamed area. of chemical reactions that result in the forma- • Chemicals. The effects of chemical sub- tion of angiotensin II, a potent vasoconstric- stances, many of which are drugs, on blood tor chemical. Angiotensin also stimulates the pressure are widespread and well known in adrenal cortex to release aldosterone, a hor- many cases. We will give just a few examples mone that enhances sodium ion reabsorption here. Epinephrine increases both heart rate by the kidneys. As sodium ions move into and blood pressure. Chapter 11: The Cardiovascular System 385

CONCEPTLINK tion called orthostatic hypotension. Because an Recall that epinephrine KU VJG pHKIJVQTHNKIJVq JQT- aging sympathetic nervous system reacts more OQPGYJKEJKURTQFWEGFD[VJGCFTGPCNOGFWNNCCPF slowly to postural changes, blood pools briefly in JGNRU WU FGCN YKVJ UJQTVVGTO UVTGUU %JCRVGT  the lower limbs, reducing blood pressure and, R|  ➔ consequently, blood delivery to the brain. Making postural changes more slowly to give the nervous Nicotine increases blood pressure by caus- system time to make the necessary adjustments ing vasoconstriction. Both alcohol and hista- usually prevents this problem. ______✚ mine cause vasodilation and decrease blood Chronic hypotension (not explained by physi- pressure. The reason a person who has “one cal conditioning) may hint at poor nutrition and too many” becomes flushed is that alcohol di- inadequate levels of blood proteins. Because lates the skin vessels. blood viscosity is low, blood pressure is also lower • Diet. Although medical opinions tend to than normal. Acute hypotension is one of the most change and are at odds from time to time, it is important warnings of circulatory shock, a con- generally thought that a diet low in salt, satu- dition in which the blood vessels are inadequately rated fats, and cholesterol helps to prevent hy- filled and blood cannot circulate normally. The pertension, or high blood pressure. most common cause is blood loss. Did You Get It? A brief elevation in blood pressure is a normal response to fever, physical exertion, and emo- 22. 9JCVKUVJGGHHGEVQHJGOQTTJCIGQPDNQQFRTGUUWTG! tional upset, such as anger or fear. Persistent 9J[! hypertension (high blood pressure), is patho- For the answer, see Appendix A. logical and is defined as a condition of sustained elevated arterial pressure of 140/90 or higher. Variations in Blood Pressure In normal adults at rest, systolic blood pressure varies between 110 Homeostatic Imbalance 11.9 and 140 mm Hg, and diastolic pressure between 70 and 80 mm Hg—but blood pressure varies Chronic hypertension is a common and danger- considerably from one person to another and ous disease that warns of increased peripheral cycles over a 24-hour period, peaking in the resistance. Although it progresses without symp- morning. What is normal for you may not be nor- toms for the first 10 to 20 years, it slowly and mal for your grandfather or your neighbor. Blood surely strains the heart and damages the arteries. pressure varies with age, weight, race, mood, For this reason, hypertension is often called the physical activity, and posture. Nearly all these “silent killer.” Because the heart is forced to pump variations can be explained in terms of the factors against increased resistance, it must work harder, affecting blood pressure that we have already and in time, the myocardium enlarges. When 11 discussed. finally strained beyond its capacity to respond, Hypotension, or low blood pressure, is gen- the heart weakens and its walls become flabby. erally considered to be a systolic blood pressure Hypertension also ravages blood vessels, causing below 100 mm Hg. In many cases, it simply small tears in the endothelium that accelerate the reflects individual differences and is no cause for progress of atherosclerosis (the early stage of arte- concern. In fact, low blood pressure is an riosclerosis). expected result of physical conditioning and is Although hypertension and atherosclerosis are often associated with long life and an old age free often linked, it is difficult to blame hypertension on of illness. any distinct anatomical pathology. In fact, about 90 percent of hypertensive people have primary Homeostatic Imbalance 11.8 (essential) hypertension, which cannot be attrib- uted to any specific organic cause. However, factors Elderly people may experience temporary low such as diet, obesity, heredity, race, and stress appear blood pressure and dizziness when they rise sud- to be involved. For instance, more women than men denly from a reclining or sitting position—a condi- and more blacks than whites are hypertensive. A CLOSER Atherosclerosis? LOOK )GV1WVVJG%CTFKQXCUEWNCT&TÞPQ

hen arteries are narrowed by summons the immune system to Watherosclerosis, the clogging repair the damage. Most plaques process begins on the inside: the walls grow slowly, through a series of inju- of the vessels thicken and then pro- ries that heal, only to be ruptured trude into the vessel lumen. Once this again and again. As the plaque grows, happens, a roaming blood clot or the injured endothelial cells release arterial spasms can close the vessel chemicals that make the endothelium completely. All blood vessels are sus- more permeable, allowing fats and ceptible to atherosclerosis, but for cholesterol to take up residence just some unknown reason the aorta and deep to the tunica intima. Monocytes the coronary arteries are most often attracted to the area migrate beneath affected. the endothelium, where they become Atherosclerotic plaques nearly macrophages that gorge themselves close a human artery. Onset and Stages on the fat in particular. These cells can QH|#VJGTQUENGTQUKU become so filled with oxidized mounds of muscle begin to protrude What triggers this scourge of blood HCVU|VJCVVJG[CTGVTCPUHQTOGFKPVQ into the vessel wall (and ultimately the vessels that indirectly causes half of the “foam cells” that lose their ability to vessel lumen), the condition is called deaths in the Western world? The ini- function. Soon they are joined by atherosclerosis (see photo). tial event is damage to the tunica smooth muscle cells migrating from Arteriosclerosis is the end stage intima caused by bloodborne chemi- the tunica media of the blood vessel of the disease. As enlarging plaques cals such as carbon monoxide (present wall. These cells deposit collagen and hinder diffusion of nutrients from the in cigarette smoke or auto exhaust); by elastin fibers in the area and also take blood to the deeper tissues of the bacteria or viruses; or by physical fac- in fat, becoming foam cells. The result artery wall, smooth muscle cells in the tors such as a blow or persistent hyper- is the erroneously named fatty streak tunica media die, and the elastic fibers tension. Once a break has occurred, stage, characterized by thickening of deteriorate and are gradually replaced blood platelets cling to the injured site the tunica intima by lesions called by nonelastic scar tissue. Then, cal- and initiate clotting to prevent blood fibrous plaques or atherosclerotic cium salts are deposited in the loss. The injured endothelium plaques9JGPVJGUGUOCNN|HCVV[

Hypertension runs in families. The child of a hyper- Capillaries form an intricate network among the tensive parent is twice as likely to develop high body’s cells, and no substance has to diffuse very blood pressure as is a child of parents with normal far to enter or leave a cell. The substances to be blood pressure. High blood pressure is common in exchanged diffuse through the interstitial fluid obese people because the total length of their blood (tissue fluid) between cells. vessels is greater than that in thinner individuals. For Substances tend to move to and from body each pound of fat, miles of additional blood vessels cells according to their concentration gradients. are required, making the heart work harder to pump Thus, oxygen and nutrients leave the blood and blood over longer distances. ______✚ move into the tissue cells, and carbon dioxide and other wastes exit the tissue cells and enter Capillary Exchange of Gases and Nutrients the blood. Basically, substances entering or leav- ➔ Learning Objective ing the blood may take one of four routes across □ Describe the exchanges that occur across capillary the plasma membranes of the single layer of walls. endothelial cells forming the capillary wall (KIWTG|11.22).

386 NGUKQPU|HQTOKPIcomplicated statins, cholesterol-reducing drugs, Sometimes after angioplasty, a metal- plaques. Collectively, these events show promise. Even the humble aspi- mesh tube called a stent is placed in cause the arterial wall to fray and rin is gaining new respect, and many the artery to keep it open. ulcerate, conditions that encourage cardiologists recommend that people When a blood clot is trapped by thrombus formation. The increased at high risk take one “baby aspirin” the diseased vessel walls, the answer rigidity of the vessels leads to hyper- (81 mg) daily. may be a clot-dissolving agent, for tension. Together, these events So what can help when the dam- example, tissue plasminogen activator increase the risk of myocardial infarc- age is done and the heart is at risk (tPA), a naturally occurring substance tions, strokes, and aneurysms. because of atherosclerotic coronary now being produced by genetic engi- The popular view that most heart vessels? In the past, the only choice neering techniques. Intravenously attacks are the consequence of severe has been coronary artery bypass sur- injecting tPA can restore blood flow vessel narrowing and hardening is gery, in which vessels removed from quickly and put an early end to a now being challenged. It appears that the legs or thoracic cavity are heart attack in progress. the body’s defense system betrays it. implanted in the heart to restore cir- There is little doubt that lifestyle The inflammatory process that occurs culation. A more recently developed factors—emotional stress, smoking, in the still soft, unstable, cholesterol- technique, balloon angioplasty, uses a obesity, high-fat and high-cholesterol rich plaques changes the biology of catheter with a balloon packed into its diets, and lack of exercise—contribute the vessel wall and makes the plaques tip. When the catheter reaches the to both atherosclerosis and hyperten- susceptible to rupture, exploding off blockage, the balloon is inflated, and sion. With these changeable risk fac- fragments that trigger massive clots the fatty mass is compressed against tors, why not just have patients that can cause lethal heart attacks. the vessel wall. However, this proce- change their lifestyle? This is easier dure is useful to clear only very local- said than done. Although taking anti- Treatment and Prevention ized obstructions. A newer catheter oxidants (vitamins C and E and beta Some medical centers test heart device uses a laser beam to vaporize carotene) and exercising more may patients for elevated levels of choles- the arterial clogs. Although these “undo” some of the damage, old terol and C-reactive protein, a marker intravascular devices are faster, habits die hard, and North Americans of inflammation. Electron beam CT cheaper, and less risky than bypass like their burgers and butter. If athero- scans may be able to identify people surgery, they carry with them the sclerosis could be reversed to give the CVTKUMD[|FGVGEVKPIECNEKWOFGRQUKVU same major shortcoming: they do heart a longer and healthier life, many in their coronary arteries. Antibiotics nothing to stop the underlying dis- more people with diseased arteries and anti-inflammatory drugs are being ease, and in time new blockages may be more willing to trade lifelong tested as preventive measures, and occur in 30 to 50 percent of cases. habits for a healthy old age!

11 1. Direct diffusion through membrane. As fenestrated capillaries. These unique capil- with all cells, substances can diffuse directly laries are found where absorption is a priority through (cross) their plasma membranes if the (intestinal capillaries or capillaries serving substances are lipid-soluble (such as the respi- endocrine glands) or where filtration occurs ratory gases oxygen and carbon dioxide). (the kidney). A fenestra is an oval pore, or 2. Diffusion through intercellular clefts. opening (fenestra = window), and is usu- Limited passage of fluid and small solutes is ally covered by a delicate membrane (see allowed by intercellular clefts (gaps between Figure 11.22). Even so, a fenestra is much cells in the capillary wall). Most of our capillar- more permeable than other regions of the ies have intercellular clefts, except for brain plasma membrane. capillaries, which are entirely secured together 4. Transport via vesicles. Certain lipid- by tight junctions (the basis of the blood-brain insoluble substances may enter or leave the barrier, described in Chapter 7). blood and/or pass through the plasma mem- 3. Diffusion through pores. Very free passage branes of endothelial cells within vesicles, that of small solutes and fluids is allowed by is, by endocytosis or exocytosis.

387 388 Essentials of Human Anatomy and Physiology

Lumen of Assume there is a bacterial infection in the capillary Q: interstitial fluid. How would this affect bulk fluid Vesicles flow across the capillary walls in the area? Tissue cell Interstitial fluid Intercellular Fenestra cleft (pore)

4 Transport via vesicles Net fluid Net fluid movement movement out in Blo od fl ow 3 ow fl Diffusion od lo through pore B

2 Diffusion through 1 Direct intercellular cleft Arterial Venule diffusion end of end of through capillary capillary membrane Interstitial fluid

Figure 11.22 Capillary transport mechanisms. The At the arterial end of a At the venule end of HQWTRQUUKDNGRCVJYC[UQTTQWVGUQHVTCPURQTVCETQUUVJG capillary, blood the capillary, blood YCNNQHCPGPFQVJGNKCNEGNNQHCECRKNNCT[ 6JGGPFQVJGNKCN pressure is more than pressure is less than EGNNKUKNNWUVTCVGFCUKHEWVKPETQUUUGEVKQP osmotic pressure, and osmotic pressure, and fluid flows out of the fluid flows from the capillary and into the interstitial fluid into the Only substances unable to pass by one of these interstitial fluid. capillary. routes are prevented from leaving (or entering) the capillaries. These include protein molecules (in plasma or interstitial fluid) and blood cells. Blood pressure is Fluid Movements at Capillary Beds higher than osmotic pressure In addition to the exchanges made via passive dif- Osmotic pressure remains steady fusion through capillary endothelial cell plasma in capillary bed membranes, clefts, or fenestrations, and via vesi- cles, there are active forces operating at capillary beds. Because of their intercellular clefts and fenes- trations, some capillaries are leaky, and bulk fluid Blood pressure is flow (fluid moving all at once) occurs across their lower than osmotic plasma membranes. Hence, blood pressure tends pressure to force fluid (and solutes) out of the capillaries, and osmotic pressure tends to draw fluid into them Figure 11.23 Bulk fluid flow across capillary walls. because blood has a higher solute concentration (NWKFHNQYFGRGPFUNCTIGN[QPVJGFKHHGTGPEG DGVYGGPVJGDNQQFRTGUUWTGCPFVJGQUOQVKERTGUUWTGCV (due to its plasma proteins) than does interstitial FKHHGTGPVTGIKQPUQHVJGECRKNNCT[DGF fluid. Whether fluid moves out of or into a capillary depends on the difference between the two pres-

sures. As a rule, blood pressure is higher than area. the in accumulated rise as inflammatory molecules and debris debris and molecules inflammatory as rise osmotic pressure at the arterial end of the capillary would fluid interstitial the of pressure osmotic the

bed, and lower than osmotic pressure at the venous A: because flow fluid increase would infection Bacterial end. Consequently, fluid moves out of the capillar- ies at the beginning of the bed and is reclaimed at the opposite (venule) end (Figure 11.23). However, Chapter 11: The Cardiovascular System 389 not quite all of the fluid forced out of the blood is directly into the left atrium through the foramen reclaimed at the venule end. Returning fluid left in ovale (fo-ra′men o-val′e), a flaplike opening in tissues to the blood is the chore of the lymphatic the interatrial septum. Blood that does manage to system (discussed in Chapter 12). enter the right ventricle is pumped out to the pul- monary trunk, where it meets a second shunt, the Did You Get It? ductus arteriosus (ar-ter″e-o′sus), a short vessel 23. 9QWNF[QWGZRGEVHNWKFVQDGGPVGTKPIQTNGCXKPIVJG that connects the aorta and the pulmonary trunk. ECRKNNCTKGUCVVJGXGPQWUGPFQHCECRKNNCT[DGF! Because the collapsed lungs are a high-pressure For the answer, see Appendix A. area, blood tends to enter the systemic circulation through the ductus arteriosus. The aorta carries blood to the tissues of the fetal body and ulti- Developmental Aspects of mately back to the placenta through the umbilical the Cardiovascular System arteries. At birth, or shortly after, the foramen ovale ➔ Learning Objectives closes. Its remnant, the fossa ovalis, is visible in □ Briefly describe the development of the the right atrium (see Figure 11.3b). The ductus cardiovascular system. arteriosus collapses and is converted to the fibrous □ Name the fetal vascular modifications, or “fetal ligamentum arteriosum (lig″ah-men′tum ar- shunts,” and describe their function before birth. ter″e-o′sum) (see Figure 11.3a). As blood stops □ Describe changes in the cardiovascular system that flowing through the umbilical vessels, they col- occur with aging, and list several factors that help lapse, and the circulatory pattern converts to that maintain cardiovascular health. of an adult. The heart begins as a simple tube in the embryo. It is beating and busily pumping blood by the Homeostatic Imbalance 11.10 fourth week of pregnancy. During the next 3 weeks, the heart continues to change and mature, Congenital heart defects account for about half of finally becoming a four-chambered structure capa- infant deaths resulting from all congenital defects. ble of acting as a double pump—all without miss- Environmental interferences, such as maternal infec- ing a beat! tion and drugs ingested during the first 3 months of Because the lungs and digestive system are pregnancy (when the embryonic heart is forming), immature and not functioning in a fetus, all nutri- seem to be the major causes of such problems. ent, excretory, and gas exchanges occur through Congenital heart defects may include a ductus arte- the placenta. Nutrients and oxygen move from the riosus that does not close, septal openings, and mother’s blood into the fetal blood, and fetal other structural abnormalities of the heart. Such ✚ wastes move in the opposite direction. The umbil- problems can usually be corrected surgically. ____ 11 ical cord contains three blood vessels: one large In the absence of congenital heart problems, umbilical vein and two smaller umbilical arter- the heart usually functions smoothly throughout a ies (Figure 11.24, p. 390). The umbilical vein car- long lifetime for most people. Homeostatic mecha- ries blood rich in nutrients and oxygen to the nisms are so effective that we rarely are aware of fetus. The umbilical arteries carry blood laden when the heart is working harder. The heart will with carbon dioxide and metabolic waste products hypertrophy and its cardiac output will increase from the fetus to the placenta. As blood flows substantially if we exercise regularly and aerobi- superiorly toward the heart of the fetus, most of it cally (that is, vigorously enough to force it to beat bypasses the immature liver through the ductus ′ ′ at a higher-than-normal rate for extended periods venosus (duk tus ve-no sus) and enters the infe- of time). The heart becomes not only a more pow- rior vena cava, which carries the blood to the right erful pump but also a more efficient one: pulse atrium of the heart. rate and blood pressure decrease. An added ben- Because the nonfunctional fetal lungs are col- efit of aerobic exercise is that it clears fatty depos- lapsed, two shunts (diverting vessels) make sure its from the blood vessel walls, helping to slow the that they are almost entirely bypassed. Some of progress of atherosclerosis. However, let’s raise a the blood entering the right atrium is shunted (Text continues on page 392.) 390 Essentials of Human Anatomy and Physiology

Superior vena cava Ductus arteriosus

Pulmonary trunk Pulmonary artery Foramen ovale Pulmonary veins

Inferior vena cava Hepatic vein Ductus venosus

Inferior vena cava

Hepatic portal vein

Umbilical vein Fetal umbilicus Aorta

Common iliac artery Umbilical cord

External iliac artery

Internal iliac artery Umbilical arteries Urinary bladder

KEY: High oxygenation Moderate oxygenation Low oxygenation Very low oxygenation Placenta

Right Pulmonary Ductus ventricle trunk arteriosus Placenta Umbilical Ductus Inferior Right Aorta Umbilical vein venosus vena atrium arteries cava Foramen Left Left ovale atrium ventricle

Figure 11.24 Schematic of the fetal circulation. *QOGQUVCVKE4GNCVKQPUJKRUDGVYGGPVJG SYSTEMS Cardiovascular SystemCPF1VJGT IN SYNC $QF[|5[UVGOU

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391 392 Essentials of Human Anatomy and Physiology caution flag here: The once-a-month or once-a- hypertensive heart disease. The insidious filling of year tennis player or snow shoveler has not built the blood vessels with fatty, calcified deposits up this type of heart endurance and strength. leads most commonly to coronary artery dis- When such an individual pushes his or her heart ease. Also, the roughening of the vessel walls too much, it may not be able to cope with the sud- encourages thrombus formation (see Chapter 10). den demand. This is why many “weekend ath- At least 30 percent of the population in the United letes” are myocardial infarction (heart attack) States has hypertension by the age of 50, and car- victims. diovascular disease causes more than one-half of As we get older, more and more signs of car- the deaths in people over age 65. Although the diovascular system disturbances start to appear. In aging process itself contributes to changes in the some people, the venous valves weaken, and pur- walls of the blood vessels that can lead to strokes ple, snakelike varicose veins appear. Not everyone or myocardial infarctions, most researchers feel has varicose veins, but we all have progressive that diet, not aging, is the single most important atherosclerosis. Some say the process begins at contributing factor to cardiovascular diseases. birth, and even children’s arteries show atheroscle- There is some agreement that the risk is lowered if rotic plaques. There’s an old saying, “You are people eat less animal fat, cholesterol, and salt. only as old as your arteries,” referring to this Other recommendations include avoiding stress, degenerative process. The gradual loss in elasticity eliminating cigarette smoking, and taking part in a of the blood vessels leads to hypertension and regular, moderate exercise program.

Summary

The Heart (pp. 357–370) of the right and left coronary arteries and their branches, and is drained by the cardiac veins and 1. The heart, located in the thorax, is flanked laterally the coronary sinus. by the lungs and enclosed in a multi-layered peri- cardium. 6. Cardiac muscle is able to initiate its own contrac- tion in a regular way, but its rate is influenced by 2. The bulk of the heart wall (myocardium) is com- both intrinsic and extrinsic factors. The intrinsic posed of cardiac muscle. The heart has four hollow conduction system increases the rate of heart chambers—two atria (receiving chambers) and two contraction and ensures that the heart beats as a ventricles (discharging chambers), each lined with unit. The SA node is the heart’s pacemaker. endocardium. (The heart is divided longitudinally Extrinsic factors include neural and hormonal by a septum.) stimuli. 3. The heart functions as a double pump. The right ventricle is the pulmonary pump (right ventricle to Complete an interactive tutorial: > lungs to left atrium). The left ventricle is the systemic Study Area > Interactive Physiology > Cardiovascular System > Electrical Activity of the Heart pump (left ventricle to body tissues to right atrium). 4. Four valves prevent backflow of blood in the 7. The time and events occurring from one heartbeat heart. The AV valves (mitral, or bicuspid, and tri- to the next are the cardiac cycle. cuspid) prevent backflow into the atria when the 8. As the heart beats, sounds resulting from the clos- ventricles are contracting. The semilunar valves ing of the valves (“lub-dup”) can be heard. Faulty (pulmonary and aortic) prevent backflow into the valves reduce the efficiency of the heart as a pump ventricles when the heart is relaxing. The valves and result in abnormal heart sounds (murmurs). open and close in response to pressure changes in the heart. Complete an interactive tutorial: > 5. The myocardium is nourished by the coronary cir- Study Area > Interactive Physiology > Cardiovascular System > Cardiac Cycle culation, which branches off the aorta and consists Chapter 11: The Cardiovascular System 393

9. Cardiac output, the amount of blood pumped out by veins superior to the diaphragm drain into the each ventricle in one minute, is the product of heart superior vena cava, and those inferior to the rate (HR) × stroke volume (SV). SV is the amount of diaphragm drain into the inferior vena cava. Both blood ejected by a ventricle with each beat. venae cavae enter the right atrium of the heart. (See pp. 374–377 for the names and locations of the sys- Complete an interactive tutorial: > temic veins.) Study Area > Interactive Physiology > Cardiovascular System > Cardiac Output 8. The arterial circulation of the brain is formed by branches of paired vertebral and internal carotid 10. SV rises or falls with the volume of venous return. arteries. The cerebral arterial circle provides alter- HR is influenced by the nerves of the autonomic nate routes for blood flow in case of a blockage in nervous system, drugs (and other chemicals), and the brain’s arterial supply. ion levels in the blood. 9. The hepatic portal circulation is formed by veins draining the digestive organs, which empty into the Blood Vessels (pp. 370–389) hepatic portal vein. The hepatic portal vein carries 1. Arteries, which transport blood away from the the nutrient-rich blood to the liver, where it is pro- heart, and veins, which carry blood back to the cessed before the blood is allowed to enter the heart, are conducting vessels. Only capillaries play systemic circulation. a role in actual exchanges with tissue cells. 10. The pulse is the alternating expansion and recoil of 2. Except for capillaries, blood vessels are composed a blood vessel wall (the pressure wave) that occurs of three tunics: The tunica intima forms a friction- as the heart beats. It may be felt easily over any reducing lining for the vessel. The tunica media is superficial artery; such sites are called pressure the bulky middle layer of muscle and elastic tissue. points. The tunica externa is the protective, outermost con- 11. Blood pressure is the pressure that blood exerts on nective tissue layer. Capillary walls are formed of the walls of the blood vessels. It is the force that the tunica intima only. causes blood to flow down its pressure gradient in 3. Artery walls are thick and strong to withstand the blood vessels. It is high in the arteries, lower in blood pressure fluctuations. They expand and the capillaries, and lowest in the right atrium. Both recoil as the heart beats. Vein walls are thinner, systolic and diastolic pressures are recorded when their lumens are larger, and they are equipped with measuring blood pressure. valves. These modifications reflect the low pressure 12. Arterial blood pressure is directly influenced by of the blood flowing in veins. heart activity (increased heart rate leads to 4. Capillary beds have two types of vessels—a vascu- increased blood pressure) and by resistance to lar shunt and true capillaries. Blood flow into true blood flow. The most important factors increasing capillaries is controlled by precapillary sphincters. the peripheral resistance are a decrease in the Exchanges with tissue cells occur across the walls diameter or stretchiness of the arteries and arteri- of the true capillaries. When the precapillary oles and an increase in blood viscosity. 11 sphincters are closed, blood flows directly through 13. Many factors influence blood pressure, including the vascular shunt. the activity of the sympathetic nerves and kidneys, 5. Varicose veins, a structural defect due to incompe- drugs, and diet. tent valves, is a common vascular problem, espe- Complete an interactive tutorial: > cially in people who are obese or who stand for Study Area > Interactive Physiology > Cardiovascular long hours. It is a predisposing factor for thrombo- System > Factors that Affect Blood Pressure phlebitis. 6. All the major arteries of the systemic circulation are 14. Hypertension, which reflects an increase in periph- branches of the aorta, which leaves the left ventri- eral resistance, strains the heart and damages blood cle. They branch into smaller arteries and then into vessels. In most cases, the precise cause is the arterioles, which feed the capillary beds of the unknown. body tissues. (For the names and locations of the 15. Substances move to and from the blood and tissue systemic arteries, see pp. 373–375.) cells through capillary walls. Some substances 7. The major veins of the systemic circulation ulti- are transported in vesicles, but most move by mately converge on one of the venae cavae. All diffusion—directly through the endothelial cell 394 Essentials of Human Anatomy and Physiology

plasma membranes, through intercellular clefts, or the fetus to the placenta. Shunts bypassing the through fenestrations. Fluid is forced from the lungs and liver are also present. bloodstream by blood pressure and drawn back 3. Congenital heart defects account for half of all into the blood by osmotic pressure. infant deaths resulting from congenital problems. Developmental Aspects of the Cardiovascular 4. Arteriosclerosis is an expected consequence of System (pp. 389–392) aging. Gradual loss of elasticity in the arteries leads to hypertension and hypertensive heart disease, 1. The heart begins as a tubelike structure that is beat- and clogging of the vessels with fatty substances ing and pumping blood by the fourth week of leads to coronary artery disease and stroke. embryonic development. Cardiovascular disease is an important cause of 2. The fetal circulation is a temporary circulation death in individuals over age 65. seen only in the fetus. It consists primarily of three 5. A healthy diet low in fat, cholesterol, and salt; stop- special vessels: the single umbilical vein that carries ping smoking; and regular aerobic exercise may nutrient- and oxygen-laden blood to the fetus from help to reverse the atherosclerotic process and pro- the placenta, and the two umbilical arteries that long life. carry carbon dioxide and waste-laden blood from

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Multiple Choice 4. During atrial systole, More than one choice may apply. a. the atrial pressure exceeds ventricular pressure. b. 70 percent of ventricular filling occurs. 1. Pulmonary veins deliver freshly oxygenated blood from the lungs to the c. the AV valves are open. a. right ventricle. d. valves prevent backflow into the great veins. b. left ventricle. 5. Atrial repolarization coincides in time with the c. right atrium. a. P wave. d. left atrium. b. T wave. 2. Given a volume of 150 ml at the end of diastole, a c. QRS wave. volume of 50 ml at the end of systole, and a heart d. P-Q interval. rate of 60 bpm, the cardiac output is 6. Soon after the onset of ventricular systole, the a. 600 ml/min. a. AV valves close. b. 6 liters/min. b. semilunar valves open. c. 1200 ml/min. c. first heart sound is heard. d. 3 liters/min. d. aortic pressure increases. 3. Which of the following depolarizes next after the 7. The base of the heart is its ______surface. AV node? a. diaphragmatic a. Atrial myocardium b. superior b. Ventricular myocardium c. anterior c. Bundle branches d. inferior d. AV bundle Chapter 11: The Cardiovascular System 395

8. In comparing a parallel artery and vein, you would 15. The most external part of the pericardium is the find that a. parietal layer of serous pericardium. a. the artery wall is thicker. b. fibrous pericardium. b. the artery diameter is greater. c. visceral layer of serous pericardium. c. the artery lumen is smaller. d. epicardium. d. the artery endothelium is thicker. 16. Which heart chamber pumps blood with the 9. Which of these vessels is bilaterally symmetrical greatest amount of force? (i.e., one vessel of the pair occurs on each side of a. Right atrium the body)? b. Right ventricle a. Internal carotid artery c. Left atrium b. Brachiocephalic trunk d. Left ventricle c. Azygos vein 17. How many cusps does the right atrioventricular d. Renal vein valve have? 10. A stroke that occludes a posterior cerebral artery a. Two will most likely affect b. Three a. hearing. c. Four b. vision. d. Six c. smell. 18. Which layer of the heart wall is an endothelium? d. higher thought processes. a. Endocardium 11. Vessels involved in the circulatory pathway to and/ b. Myocardium or from the brain are the c. Epicardium a. brachiocephalic trunk. d. Pericardium b. subclavian artery. c. internal jugular vein. Short Answer Essay d. internal carotid artery. 19. Draw a diagram of the heart showing the three 12. Which layer of the artery wall thickens most in layers composing its wall and its four chambers. atherosclerosis? Label each. Show where the AV and semilunar a. Tunica media valves are, and name them. Show and label all blood vessels entering and leaving the heart b. Tunica intima chambers. c. Tunica adventitia 20. Trace one drop of blood from the time it enters the d. Tunica externa right atrium of the heart until it enters the left 11 13. Which of the following are associated with aging? atrium. What is this circuit called? a. Increasing blood pressure 21. What is the function of the fluid that fills the b. Weakening of venous valves pericardial sac? c. Arteriosclerosis 22. Define systole and diastole. d. Collapse of the ductus arteriosus 23. Define stroke volume and cardiac cycle. 14. An increase in BP would be caused by all of the 24. How does the heart’s ability to contract differ from following except that of other muscles of the body? a. increase in SV. 25. Name the elements of the intrinsic conduction b. increase in heart rate. system, in order, beginning with the pacemaker. c. hemorrhage. 26. Name three different factors that increase heart d. vasoconstriction of the arterioles. rate. 396 Essentials of Human Anatomy and Physiology

27. Name and describe, from the inside out, the three 36. Which artery is palpated at the front of the ear? At tunics making up the walls of arteries and veins, the back of the knee? and give the most important function of each layer. 37. Define systolic pressure and diastolic pressure. 28. Describe the structure of capillary walls. 38. Two elements determine blood pressure—the 29. Why are artery walls so much thicker than those of cardiac output of the heart and the peripheral corresponding veins? resistance, or friction, in the blood vessels. Name two factors that increase cardiac output. Name two 30. Name three factors that are important in promoting factors that increase peripheral resistance. venous return. 39. In which position—sitting, lying down, or standing— 31. Arteries are often described as vessels that carry is the blood pressure normally highest? Lowest? oxygen-rich blood, and veins are said to carry Explain why. oxygen-poor (carbon dioxide–rich) blood. Name two sets of exceptions to this rule that were 40. What is different about the capillary exchanges discussed in this chapter. seen in a capillary with fenestrations and in- tercellular clefts and the exchanges seen in a cap- 32. Trace a drop of blood from the left ventricle of the illary lacking those modifications? heart to the wrist of the right hand and back to the heart. Now trace it to the dorsum of the right foot 41. What are varicose veins? What factors seem to and back to the right heart. promote their formation? 33. What is the function of the hepatic portal 42. Explain why blood flow in arteries is pulsatile and circulation? In what way is a portal circulation a blood flow in veins is not. “strange” circulation? 43. What is the relationship between cross-sectional 34. In a fetus, the liver and lungs are almost entirely area of a blood vessel and velocity (speed) of bypassed by blood. Why is this? Name the vessel blood flow in that vessel? that bypasses the liver. Name two lung bypasses. 44. Which type of blood vessel is most important in Three vessels travel in the umbilical cord; which of regulating vascular resistance, and how does it these carries oxygen- and nutrient-rich blood? achieve this? 35. Define pulse. Palpate your pulse. Which pulse point 45. What is the ductus venosus, and what is its did you use? function?

Critical Thinking and Clinical Application Questions

46. John is a 30-year-old man who is overweight and 48. Hannah, a 14-year-old girl undergoing a physical smokes. He has been diagnosed with hypertension examination before being admitted to summer and arteriosclerosis. Define each of these conditions. camp, was found to have a loud heart murmur at How are they often related? Why is hypertension the second intercostal space on the left side of the called the “silent killer”? Name three changes in sternum. The murmur takes the form of a swishing your lifestyle that might help prevent cardiovascular sound with no high-pitched whistle. What, exactly, disease in your old age. is producing the murmur? 47. Mrs. Hamad, a middle-aged woman, is admitted to 49. Mrs. Rees is brought to the emergency room after the coronary care unit with a diagnosis of left being involved in an auto accident. She is ventricular failure resulting from a myocardial hemorrhaging and has a rapid pulse that can barely infarction. Her chart indicates that she was be felt, but her blood pressure is still within normal awakened in the middle of the night by severe limits. Describe the compensatory mechanisms that chest pain. Her skin is pale and cold, and moist are maintaining her blood pressure in the face of sounds of pulmonary edema are heard over the blood loss. lower regions of both lungs. Explain how failure of 50. During a lethal heart attack, a blood clot lodges in the left ventricle might cause these signs and the first part of the circumflex branch of the left symptoms. Chapter 11: The Cardiovascular System 397

coronary artery, blocking blood flow through this 52. Grandma tells Hailey not to swim for 30 minutes vessel. What parts of the heart will become after eating. Explain why taking a vigorous swim ischemic and die? immediately after lunch is more likely to cause indigestion than cramping of your muscles. 51. Mr. Grimaldi was previously diagnosed as having a posterior pituitary tumor that causes hypersecretion 53. The guards at the royal palace in London stand at of ADH. He comes to the clinic regularly to have attention while on duty. On a very hot day, it is not his blood pressure checked. Would you expect his unusual for one (or more) to become lightheaded blood pressure to be chronically elevated or and faint. Explain this phenomenon. depressed? Why?

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