1. Chapter 21: Anatomy of the Cardiovascular System
Anatomy & Physiology
Chapter 21:
Anatomy of the Cardiovascular System

2. Heart Location of the heart (Figure 21-2)
Lies in the mediastinum, behind the body of the sternum between the points of attachment of ribs two through six; approximately two thirds of its mass is to the left of the midline of the body, and one third is to the right
Posteriorly the heart rests on the bodies of thoracic vertebrae five through eight 2

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5. Heart Location of the heart (cont)
Apex lies on the diaphragm, pointing to the left
Base lies just below the second rib
Boundaries of the heart are clinically important as an aid in diagnosing heart disorders 5

6. Heart Size and shape of the heart (Figures 21-1 and 21-2)
At birth, the heart is transverse and appears large in proportion to the diameter of the chest cavity
Between puberty and 25 years of age, the heart attains its adult shape and weight
In adults, the shape of the heart tends to resemble that of the chest 6

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8. Heart Coverings of the heart Structure of the heart coverings
Pericardium (Figure 21-4)
Fibrous pericardium—tough, loose-fitting inextensible sac
Serous pericardium—parietal layer lies inside the fibrous pericardium, and visceral layer (epicardium) adheres to the outside of the heart
Pericardial space—lies between visceral and parietal layers and contains 10 to 15 ml of pericardial fluid
Function of the heart coverings—provides protection against friction 8

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10. Heart Structure of the heart
Wall of the heart—made up of three distinct layers (Figure 21-5)
Epicardium—outer layer of heart wall
Myocardium—thick, contractile middle layer of heart wall; compresses the heart cavities, and the blood within them, with great force
Endocardium—delicate inner layer of endothelial tissue 10

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12. Heart Structure of the heart (cont)
Chambers of the heart—divided into four cavities with the right and left chambers separated by the septum (Figures 21-6 and 21-7)
Atria
Two superior chambers known as “receiving chambers” because they receive blood from veins 12

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15. Heart Chambers of the heart (cont) Atria (cont)
Atria alternately relax to receive blood and then contract to push blood into ventricles
Myocardial wall of each atrium is not very thick, because little pressure is needed to move blood such a small distance
Auricle—earlike flap protruding from each atrium 15

16. Heart Chambers of the heart (cont) Ventricles
Two lower chambers known as “pumping chambers” because they push blood into the large network of vessels
Ventricular myocardium is thicker than the myocardium of the atria because great force must be generated to pump the blood a large distance; myocardium of left ventricle is thicker than the right, because it must push blood much further 16

17. Heart Structure of the heart (cont)
Valves of the heart—mechanical devices that permit the flow of blood in one direction only (Figure 21-8)
Atrioventricular (AV) valves—prevent blood from flowing back into the atria from the ventricles when the ventricles contract
Tricuspid valve (right AV valve)—guards the right atrioventricular orifice; free edges of three flaps of endocardium are attached to papillary muscles by chordae tendineae
Bicuspid, or mitral, valve (left AV valve)—similar in structure to tricuspid valve except has only two flaps 17

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19. Heart Valves of the heart (cont)
Semilunar (SL) valves—half-moon–shaped flaps growing out from the lining of the pulmonary trunk and aorta; prevent blood from flowing back into the ventricles from the aorta and pulmonary trunk
Pulmonary valve—at entrance of the pulmonary trunk
Aortic valve—at entrance of the aorta 19

20. Heart Valves of the heart (cont) Skeleton of the heart
Set of connected rings that serve as a semirigid support for the heart valves and for the attachment of cardiac muscle of the myocardium
Serves as an electrical barrier between the myocardium of the atria and that of the ventricles
Surface projection (review Figure 21-9)
Flow of blood through heart (review Figure 21- 7) 20

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22. Heart Structure of the heart (cont)
Coronary circulation—blood supply of heart tissue (Figures 21-10, 21-11, and )
Coronary arteries—myocardial cells receive blood from the right and left coronary arteries
First branches to come off the aorta
Ventricles receive blood from branches of both right and left coronary arteries 22

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26. Heart Coronary arteries (cont)
Each ventricle receives blood only from a small branch of the corresponding coronary artery
Most abundant blood supply goes to the myocardium of the left ventricle
Right coronary artery is dominant in approximately 50% of all hearts and the left in about 20%; in approximately 30%, neither coronary artery is dominant
Few anastomoses exist between the larger branches of the coronary arteries 26

27. Heart Coronary circulation (cont) Cardiac veins
As a rule, veins follow a course that closely parallels that of coronary arteries
After going through cardiac veins, blood enters the coronary sinus to drain into the right atrium
Several veins drain directly into the right atrium 27

28. Heart Structure of the heart (cont) Nerve supply of the heart
Conduction system of the heart—made up of modified cardiac muscle, it generates and distributes the heart’s own rhythmic contractions; can be regulated by afferent nerves
Cardiac plexuses—located near the arch of the aorta, made up of the combination of sympathetic and parasympathetic fibers 28

29. Heart Nerve supply of the heart (cont)
Fibers from the cardiac plexus accompany the right and left coronary arteries to enter the heart
Most fibers end in the SA node, but some end in the AV node and in the atrial myocardium; the SA node acts as the heart’s pacemaker (Chapter 22)
Sympathetic nerves—accelerator nerves
Vagus fibers—inhibitory, or depressor, nerves 29

30. Blood Vessel Types Types of blood vessels (Figures 21- 13 and 21-14)
Angiogenesis—formation of new blood vessels
Arteries
Carry blood away from heart—all arteries except pulmonary artery carry oxygenated blood 30

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33. Blood Vessel Types Arteries (cont)
Elastic (conducting) arteries—largest in body
Examples: aorta and its major branches
Able to stretch without injury
Accommodate surge of blood when heart contracts and able to recoil when ventricles relax
Muscular (distributing) arteries
Smaller in diameter than elastic arteries
Muscular layer is thick
Examples: brachial, gastric, superior mesenteric 33

34. Blood Vessel Types Arteries (cont) Arterioles (resistance vessels)
Smallest arteries
Important in regulating blood flow to end organs
Metarterioles
Short connecting vessel between true arteriole and 20 to 100 capillaries
Encircled by precapillary sphincters
Distal end called thoroughfare channel, which is free of precapillary sphincters 34

35. Blood Vessel Types Types of blood vessels (cont)
Capillaries—primary exchange vessels
Microscopic vessels
Carry blood from arterioles to venules—together, arterioles, capillaries, and venules constitute the microcirculation (Figure 21-15)
Not evenly distributed—highest numbers in tissues with high metabolic rate; may be absent in some “avascular” tissues, such as cartilage 35

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37. Blood Vessel Types Capillaries (cont)
Types of capillaries (Figure 21-16)
True capillaries—receive blood flowing from metarteriole with input regulated by precapillary sphincters
Continuous capillaries
Continuous lining of endothelial cells
Openings called intercellular clefts exist between adjacent endothelial cells 37

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39. Blood Vessel Types Types of capillaries (cont) Fenestrated capillaries
Have both intercellular clefts and “holes,” or fenestrations, through plasma membrane to facilitate exchange functions
Sinusoids
Large lumen and tortuous course
Absent or incomplete basement membrane
Very porous—permit migration of cells into or out of vessel lumen 39

40. Blood Vessel Types Types of blood vessels (cont) Veins
Carry blood toward the heart
Act as collectors and as reservoir vessels; called capacitance vessels 40

41. Blood Vessel Types
Structure of blood vessels (Figure and 21-14)
Components or “building blocks” commonly present
Lining endothelial tissue—one layer of squamous endothelial cells
Only lining found in capillary
Lines entire vascular tree 41

42. Blood Vessel Types
Lining endothelial tissue—one layer of squamous endothelial cells (cont)
Provides a smooth luminal surface— protects against intravascular coagulation
Intercellular clefts, cytoplasmic pores, and fenestrations in cells allow exchange to occur between blood and tissue fluid
Capable of secreting a number of substances
Capable of reproduction 42

43. Blood Vessel Types
Components or “building blocks” commonly present (cont)
Collagen fibers
Exhibit woven appearance
Formed from protein molecules that aggregate into fibers
Visible with light microscope
Have only a limited ability to stretch (2% to 3%) under physiological conditions
Function to strengthen and keep lumen of vessel open 43

44. Blood Vessel Types
Components or “building blocks” commonly present (cont)
Elastic fibers
Composed of insoluble protein called elastin
Form highly elastic networks
Wavy fibers can stretch more than 100% under physiological conditions
Play important role in creating passive tension to help regulate blood pressure throughout the cardiac cycle 44

45. Blood Vessel Types
Components or “building blocks” commonly present (cont)
Smooth muscle tissue
Present in all segments of vascular system except capillaries
Most abundant in elastic and muscular arteries
Exerts active tension in vessels when contracting 45

46. Blood Vessel Types Structure of blood vessels (cont) Layers
Tunica externa—found in arteries and veins (tunica adventitia)
Tunica media—found in arteries and veins
Tunica intima—found in all blood vessels; only layer present in capillaries 46

47. Major Blood Vessels Circulatory routes (Figure 21-17)
Systemic circulation—blood flows from the left ventricle of the heart through blood vessels to all parts of the body (except gas exchange tissues of lungs) and back to the right atrium
Pulmonary circulation—venous blood moves from right atrium to right ventricle to pulmonary artery to lung arterioles and capillaries, where gases are exchanged; oxygenated blood returns to left atrium by way of pulmonary veins; from left atrium, blood enters the left ventricle 47

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49. Major Blood Vessels Systemic circulation
Systemic arteries (review Table 21-2 and Figures to 21-26)
Main arteries give off branches, which continue to rebranch, forming arterioles and then capillaries
End-arteries—arteries that eventually diverge into capillaries
Arterial anastomosis—arteries that open into other branches of the same or other arteries; incidence of arterial anastomoses increases as distance from the heart increases
Arteriovenous anastomoses or shunts occur when blood flows from an artery directly into a vein 49

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59. Major Blood Vessels Systemic circulation (cont)
Systemic veins (review Table 21-3 and Figures to 21-34)
Veins are the ultimate extensions of capillaries; unite into vessels of increasing size to form venules and then veins
Large veins of the cranial cavity are called dural sinuses
Veins anastomose the same as arteries
Venous blood from the head, neck, upper extremities, and thoracic cavity (except lungs) drains into superior vena cava 59

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68. Major Blood Vessels Systemic veins (cont)
Venous blood from thoracic organs drains directly into superior vena cava or azygos vein
Hepatic portal circulation (Table 21-3 and Figures and )
Veins from the spleen, stomach, pancreas, gallbladder, and intestines send their blood to the liver by way of the hepatic portal vein
In the liver the venous blood mingles with arterial blood in the sinusoids and is eventually drained from the liver by hepatic veins that join the inferior vena cava
Venous blood from the lower extremities and abdomen drains into the inferior vena cava 68

69. Major Blood Vessels Fetal circulation
Basic plan of fetal circulation—additional vessels needed to allow fetal blood to secure oxygen and nutrients from maternal blood at the placenta (Figure )
Two umbilical arteries—extensions of the internal iliac arteries; carry fetal blood to the placenta
Placenta—attached to uterine wall; where exchange of oxygen and other substances between the separated maternal and fetal blood occurs (Figure 21-35) 69

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72. Major Blood Vessels Basic plan of fetal circulation (cont)
Umbilical vein—returns oxygenated blood from the placenta to the fetus; enters body through the umbilicus and goes to the undersurface of the liver where it gives off two or three branches and then continues as the ductus venosus
Ductus venosus—continuation of the umbilical vein and drains into inferior vena cava
Foramen ovale—opening in septum between the right and left atria
Ductus arteriosus—small vessel connecting the pulmonary trunk with the aortic arch 72

73. Major Blood Vessels Fetal circulation (cont)
Changes in circulation at birth (compare Figures and 21-37)
When umbilical cord is cut, the two umbilical arteries, the placenta and umbilical vein, no longer function
Umbilical vein within the baby’s body becomes the round ligament of the liver 73

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75. Major Blood Vessels Changes in circulation at birth (cont)
Ductus venosus becomes the ligamentum venosum of the liver
Foramen ovale—functionally closed shortly after a newborn’s first breath and pulmonary circulation is established; structural closure takes approximately 9 months
Ductus arteriosus—contracts with establishment of respiration, becomes ligamentum arteriosum 75

76. Cycle of Life: Cardiovascular Anatomy
Birth—change from placenta- dependent system
Heart and blood vessels maintain basic structure and function from childhood through adulthood 76

77. Cycle of Life: Cardiovascular Anatomy
Only apparent normal changes occur as a result of exercise
Exercise thickens myocardium
Exercise increases the supply of blood vessels in skeletal muscle tissue
Adulthood through later adulthood—degenerative changes
Atherosclerosis—blockage or weakening of critical arteries (Figure 21-43)
Heart valves and myocardial tissue degenerate— reduces pumping efficiency 77

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