Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 1 Chapter 18 Anatomy of the Cardiovascular System

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 2 Heart  Location of the heart (Figure 18-1)  Lies in the mediastinum, behind the body of the sternum between the points of attachment of ribs 2 through 6; approximately two thirds of its mass is to the left of the midline of the body and one third to the right  Posteriorly the heart rests on the bodies of thoracic vertebrae 5 through 8  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

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 3 Heart  Size and shape of the heart (Figures 18-1 and 18-2)  At birth, is transverse and appears large in proportion to diameter of chest cavity  Between puberty and 25 years of age the heart attains its adult shape and weight  In adult, shape of the heart tends to resemble that of the chest

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 4 Heart  Coverings of the heart  Structure of the heart coverings Pericardium (Figure 18-4) Pericardium (Figure 18-4)  Fibrous pericardium—tough, loose-fitting inextensible sac  Serous pericardium—parietal layer lies inside fibrous pericardium, and visceral layer (epicardium) adheres to outside of the heart; pericardial space with pericardial fluid separates the two layers  Function of the heart coverings—provides protection against friction

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 5 Heart  Structure of the heart  Wall of the heart—made up of three distinct layers (Figure 18-5): Epicardium—outer layer of heart wall 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 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 Endocardium—delicate inner layer of endothelial tissue

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 6 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 18-6 and 18-7): Atria Atria  Two superior chambers, known as “receiving chambers,” because they receive blood from veins  Atria alternately contract and relax to receive blood and then push it 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 Ventricles Ventricles  Two lower chambers, known as “pumping chambers,” because they push blood into the large network of vessels  Ventricular myocardium is thicker than myocardium of the atria, because great force must be generated to pump blood a large distance; myocardium of left ventricle is thicker than the right, because it must push blood much further

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 7 Heart  Structure of the heart (cont.)  Valves of the heart—mechanical devices that permit the flow of blood in one direction only (Figure 18-8) Atrioventricular (AV) valves—prevent blood from flowing back into the atria from the ventricles when the ventricles contract 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 only two flaps present

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 8 Heart  Valves of the heart (cont.) Semilunar (SL) valves—half moon–shaped flaps growing out from the lining of the pulmonary artery and aorta; prevent blood from flowing back into ventricles from aorta and pulmonary artery Semilunar (SL) valves—half moon–shaped flaps growing out from the lining of the pulmonary artery and aorta; prevent blood from flowing back into ventricles from aorta and pulmonary artery  Pulmonary semilunar valve—at entrance of pulmonary artery  Aortic semilunar valve—at entrance of aorta Skeleton of the heart Skeleton of the heart  Set of connected rings that serve as a semirigid support for the heart valves and for 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 18-9) Surface projection (review Figure 18-9) Flow of blood through heart (review Figure 18-7) Flow of blood through heart (review Figure 18-7)

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 9 Heart  Structure of the heart (cont.)  Blood supply of heart tissue (Figures and 18-11) Coronary arteries—myocardial cells receive blood from right and left coronary arteries Coronary arteries—myocardial cells receive blood from right and left coronary arteries  First branches to come off aorta  Ventricles receive blood from branches of both right and left coronary arteries  Each ventricle receives blood only from a small branch of corresponding coronary artery  Most abundant blood supply goes to myocardium of left ventricle  The 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

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 10 Heart  Blood supply of heart tissue (cont.) Veins of the coronary circulation Veins of the coronary circulation  As a rule, veins follow a course that closely parallels that of coronary arteries  After going through cardiac veins, blood enters coronary sinus to drain into right atrium  Several veins drain directly into right atrium

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 11 Heart  Structure of the heart (cont.)  Conduction system of the heart—comprising the sinoatrial (SA) node, atrioventricular (AV) node, AV bundle, and Purkinje fibers; made up of modified cardiac muscle (Figure 18-11) Sinoatrial node (SA node or pacemaker)— hundreds of cells in right atrial wall near opening of superior vena cava Sinoatrial node (SA node or pacemaker)— hundreds of cells in right atrial wall near opening of superior vena cava Atrioventricular node (AV node)—small mass of special cardiac muscle in right atrium along lower part of interatrial septum Atrioventricular node (AV node)—small mass of special cardiac muscle in right atrium along lower part of interatrial septum Atrioventricular bundle (AV bundle or bundle of His) and Purkinje fibers Atrioventricular bundle (AV bundle or bundle of His) and Purkinje fibers  AV bundle originates in AV node, extends by two branches down the two sides of the interventricular septum, and continues as Purkinje fibers  Purkinje fibers extend out to papillary muscles and lateral walls of ventricles

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 12 Heart  Structure of the heart (cont.)  Nerve supply of the heart Cardiac plexuses—located near arch of aorta, made up of the combination of sympathetic and parasympathetic fibers Cardiac plexuses—located near arch of aorta, made up of the combination of sympathetic and parasympathetic fibers Fibers from cardiac plexus accompany right and left coronary arteries to enter the heart Fibers from cardiac plexus accompany 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 Most fibers end in the SA node, but some end in the AV node and in the atrial myocardium Sympathetic nerves—accelerator nerves Sympathetic nerves—accelerator nerves Vagus fibers—inhibitory, or depressor, nerves Vagus fibers—inhibitory, or depressor, nerves

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 13 Blood Vessels  Types of blood vessels  Arteries Carry blood away from heart—all arteries except pulmonary artery carry oxygenated blood Carry blood away from heart—all arteries except pulmonary artery carry oxygenated blood Elastic arteries—largest in body Elastic 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

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 14 Blood Vessels  Arteries (cont.) Muscular (distributing) arteries Muscular (distributing) arteries  Smaller in diameter than elastic arteries  Muscular layer is thick  Examples: brachial, gastric, superior mesenteric Arterioles (resistance vessels) Arterioles (resistance vessels)  Smallest arteries  Important in regulating blood flow to end-organs Metarterioles 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

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 15 Blood Vessels  Types of blood vessels (cont.)  Capillaries—primary exchange vessels Microscopic vessels Microscopic vessels Carry blood from arterioles to venules—together, arterioles, capillaries and venules constitute the microcirculation (Figure 18-15) Carry blood from arterioles to venules—together, arterioles, capillaries and venules constitute the microcirculation (Figure 18-15) Not evenly distributed—highest numbers in tissues with high metabolic rate; may be absent in some “avascular” tissues such as cartilage Not evenly distributed—highest numbers in tissues with high metabolic rate; may be absent in some “avascular” tissues such as cartilage

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 16 Blood Vessels Types of capillaries (Figure 18-16) Types of capillaries (Figure 18-16)  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  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

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 17 Blood Vessels  Types of blood vessels (cont.)  Veins Carry blood toward the heart Carry blood toward the heart Act as collectors and as reservoir vessels; called capacitance vessels Act as collectors and as reservoir vessels; called capacitance vessels

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 18 Blood Vessels  Structure of blood vessels (Figure 18-14)  Layers Tunica adventitia—found in arteries and veins Tunica adventitia—found in arteries and veins Tunica media—found in arteries and veins Tunica media—found in arteries and veins Tunica intima—found in all blood vessels; only layer present in capillaries Tunica intima—found in all blood vessels; only layer present in capillaries

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 19 Blood Vessels  Structure of blood vessels (cont.)  “Building blocks” commonly present Lining endothelial cells Lining endothelial cells  Only lining found in capillary  Line entire vascular tree  Provide a smooth luminal surface—protects against intravascular coagulation  Intercellular clefts, cytoplasmic pores, and fenestrations allow exchange to occur between blood and tissue fluid  Capable of secreting a number of substances  Capable of reproduction

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 20 Blood Vessels  “Building blocks” commonly present (cont.) Collagen fibers 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

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 21 Blood Vessels  “Building blocks” commonly present (cont.) Elastic fibers Elastic fibers  Composed of insoluble protein called elastin  Form highly elastic networks  Fibers can stretch over 100% under physiological conditions  Play important role in creating passive tension to help regulate blood pressure throughout cardiac cycle Smooth muscle fibers Smooth muscle fibers  Present in all segments of vascular system except capillaries  Most numerous in elastic and muscular arteries  Exert active tension in vessels when contracting

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 22 Major Blood Vessels  Circulatory routes (Figure 18-13)  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 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 via pulmonary veins; from left atrium, blood enters left ventricle

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 23 Major Blood Vessels  Systemic circulation  Systemic arteries (review Tables 18-2 to 18-6; Figures to 18-22) Main arteries give off branches, which continue to rebranch, forming arterioles and then capillaries Main arteries give off branches, which continue to rebranch, forming arterioles and then capillaries End-arteries—arteries that eventually diverge into 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 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 Arteriovenous anastomoses or shunts occur when blood flows from an artery directly into a vein

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 24 Major Blood Vessels  Systemic circulation (cont.)  Systemic veins (review Figures to 18-29) Veins are the ultimate extensions of capillaries; unite into vessels of increasing size to form venules and then veins 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 Large veins of the cranial cavity are called dural sinuses Veins anastomose as do arteries Veins anastomose as do arteries Venous blood from the head, neck, upper extremities, and thoracic cavity (except lungs) drains into superior vena cava Venous blood from the head, neck, upper extremities, and thoracic cavity (except lungs) drains into superior vena cava Venous blood from thoracic organs drains directly into superior vena cava or azygos vein Venous blood from thoracic organs drains directly into superior vena cava or azygos vein Hepatic portal circulation (Figure 18-28) Hepatic portal circulation (Figure 18-28)  Veins from the spleen, stomach, pancreas, gallbladder, and intestines send their blood to the liver via the hepatic portal vein  In the liver, venous blood mingles with arterial blood in the capillaries and is eventually drained from liver by hepatic veins that join the inferior vena cava Venous blood from lower extremities and abdomen drains into inferior vena cava Venous blood from lower extremities and abdomen drains into inferior vena cava

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 25 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 18-31) Two umbilical arteries—extensions of internal iliac arteries; carry fetal blood to placenta Two umbilical arteries—extensions of internal iliac arteries; carry fetal blood to placenta Placenta—attached to uterine wall, where exchange of oxygen and other substances between the separated maternal and fetal blood occurs (Figure 18-30) Placenta—attached to uterine wall, where exchange of oxygen and other substances between the separated maternal and fetal blood occurs (Figure 18-30) Umbilical vein—returns oxygenated blood from placenta to fetus; enters body through umbilicus and goes to undersurface of liver, where it gives off two or three branches and then continues as ductus venosus Umbilical vein—returns oxygenated blood from placenta to fetus; enters body through umbilicus and goes to undersurface of liver, where it gives off two or three branches and then continues as ductus venosus Ductus venosus—continuation of umbilical vein, drains into inferior vena cava Ductus venosus—continuation of umbilical vein, drains into inferior vena cava Foramen ovale—opening in septum between right and left atria Foramen ovale—opening in septum between right and left atria Ductus arteriosus—small vessel connecting pulmonary artery with descending thoracic aorta Ductus arteriosus—small vessel connecting pulmonary artery with descending thoracic aorta

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 26 Major Blood Vessels  Fetal circulation (cont.)  Changes in circulation at birth (compare Figures and 18-32) When umbilical cord is cut, the two umbilical arteries, the placenta and the umbilical vein no longer function When umbilical cord is cut, the two umbilical arteries, the placenta and the umbilical vein no longer function Umbilical vein within the baby’s body becomes the round ligament of the liver Umbilical vein within the baby’s body becomes the round ligament of the liver Ductus venosus becomes the ligamentum venosum of the liver 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 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 Ductus arteriosus—contracts with establishment of respiration, becomes ligamentum arteriosum

Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 27 Cycle of Life: Cardiovascular Anatomy  Birth—change from placenta-dependent system  Heart and blood vessels maintain basic structure and function from childhood through adulthood  Exercise thickens myocardium and increases supply of blood vessels in skeletal muscle tissue  Adulthood through later adulthood—degenerative changes  Atherosclerosis—blockage or weakening of critical arteries  Heart valves and myocardial tissue degenerate—reduces pumping efficiency