AP Ch 32 Cardiovascular and Lymphatic Systems PDF

## Summary Review - Continued - Serially connected pump systems: The pulmonary circulation and the systemic circulation, plus the lymphatics. - The low-pressure pulmonary circulation is driven by the right side of the heart. The function of the pulmonary circulation is to deliver blood to the lung...

## Summary Review - Continued - Serially connected pump systems: The pulmonary circulation and the systemic circulation, plus the lymphatics. - The low-pressure pulmonary circulation is driven by the right side of the heart. The function of the pulmonary circulation is to deliver blood to the lungs for oxygenation. - The higher pressure systemic circulation is driven by the left side of the heart, and its function is to move oxygenated blood to body tissues and to deliver waste products to the lungs, kidneys, and liver. - The lymphatic vessels collect fluids from the interstitium and return the fluids to the circulatory system. Another important function of the lymphatic system is the movement of lymphocytes and leukocytes between different components of the immune system. ## The Heart 1. The heart consists of four chambers (two atria and two ventricles), four valves (two AV valves and two semilunar valves), a muscular wall, a fibrous skeleton, a conduction system, nerve fibers, systemic vessels (the coronary circulation), and openings where the great vessels enter the atria and ventricles. 2. The heart wall, which encloses the heart and divides it into chambers, is made up of three layers: the epicardium (outer layer), the myocardium (muscular layer), and the endocardium (inner lining). The heart is contained within the pericardium, a double-walled sac. 3. The myocardial layer of the two atria, which receive blood entering the heart, is thinner than the myocardial layer of the ventricles, which is stronger because it generates the pressure that causes the blood to circulate through the lungs or the systemic circulation. 4. The right and left sides of the heart are separated by portions of the heart wall called the interatrial septum and the interventricular septum. 5. Unoxygenated (venous) blood from the systemic circulation enters the right atrium through the superior and inferior venae cavae. From the right atrium the blood passes through the right AV (tricuspid) valve into the right ventricle. In the ventricle the blood flows from the inflow tract to the outflow tract and then through the pulmonic semilunar valve (pulmonary valve) into the pulmonary artery, which delivers it to the lungs for oxygenation. 6. Oxygenated blood from the lungs enters the left atrium through the four pulmonary veins (two from the left lung and two from the right lung). From the left atrium the blood passes through the left AV valve (mitral valve) into the left ventricle. In the ventricle the blood flows from the inflow tract to the outflow tract and then through the aortic semilunar valve (aortic valve) into the aorta, which delivers it to systemic arteries of the entire body. 7. The heart valves that ensure the one-way flow of blood from the atria to the ventricles are called the atrioventricular valves. The valves that ensure one-way flow from the ventricles to either the pulmonary artery or the aorta are called semilunar valves. 8. Oxygenated blood enters the coronary arteries through openings within the semilunar valves at the entrance to the aorta, and deoxygenated blood from the coronary veins enters the right atrium through the coronary sinus. 9. The pumping action of the heart consists of two phases: diastole, during which the myocardium relaxes and the chambers fill with blood; and systole, during which the myocardium contracts, forcing blood out of the ventricles. A cardiac cycle consists of one systolic contraction and the diastolic relaxation that follows it. Each cardiac cycle makes up one heartbeat. 10. The sinoatrial (SA) node generates electrical impulses, and the conduction system of the heart transmits these electrical impulses (cardiac action potentials) that stimulate systolic contraction. The autonomic nerves (sympathetic and parasympathetic fibers) can adjust heart rate and systolic force, but they do not stimulate the heart to beat. 11. Collateral arteries are connections between branches of the same coronary artery or connections of branches of the right coronary artery with branches of the left. New collateral vessels are formed through two processes: arteriogenesis and angiogenesis. This collateral growth is stimulated by shear stress, an increased blood flow speed near an area of stenosis, or narrowing, and the production of growth factors and cytokines. 12. The heart has an extensive capillary network. 13. The normal ECG is the sum of all cardiac action potentials. The P wave represents atrial depolarization; the QRS complex is the sum of all ventricular cell depolarizations. The ST interval occurs when the entire ventricular myocardium is depolarized. 14. Cardiac action potentials are generated by the SA node at the rate of between 60 and 100 impulses per minute. The impulses travel through the conduction system of the heart, stimulating myocardial contraction as they travel. 15. Cells of the cardiac conduction system possess the properties of automaticity and rhythmicity. Automatic cells return to threshold and depolarize rhythmically without an outside stimulus. The cells of the SA node depolarize faster than other automatic cells, making it the natural pacemaker of the heart. If the SA node is disabled, the next fastest pacemaker, the AV node, assumes control. 16. Each cardiac action potential travels from the SA node to the AV node to the bundle of His (AV bundle), through the bundle branches, and finally to the Purkinje fibers and the ventricular myocardium. There the impulse is stopped. It is prevented from reversing its path by the refractory period of cells that has just been polarized. The refractory period ensures that diastole (relaxation) will occur, thereby completing the cardiac cycle. 17. Adrenergic receptor number, type, and function govern autonomic (sympathetic) regulation of heart rate, contractile force, and dilation or constriction of coronary arteries. The presence of specific receptors (α1, α2, β1, β2, β3) in the myocardium and coronary vessels determines the effects of the neurotransmitters norepinephrine and epinephrine. 18. Unique features that distinguish myocardial cells from skeletal cells enable myocardial cells to transmit action potentials faster (through intercalated disks), synthesize more ATP (because of a large number of mitochondria), and have readier access to ions in the interstitium (because of an abundance of transverse tubules). These combined differences enable the myocardium to work constantly, which is not required of skeletal muscle. 19. Cross-bridges between actin and myosin enable contraction to occur. Calcium and its interaction with the troponin complex facilitate the contraction process. With troponin release of calcium, myocardial relaxation begins. 20. Cardiac performance is affected by preload, afterload, heart rate, and myocardial contractility. 21. Preload, or pressure generated in the ventricles at the end of diastole, depends on the amount of blood in the ventricle. Afterload is the resistance to ejection of the blood from the ventricle. Afterload depends on pressure in the aorta. 22. Contractility is the potential for myocardial fiber shortening during systole. It is determined by the amount of stretch during diastole (i.e., preload) and by sympathetic stimulation of the ventricles. - The Frank-Starling law of the heart states that the myocardial stretch determines the force of myocardial contraction (the greater the stretch, the stronger the contraction). - Laplace's law states that the amount of contractile force generated within a chamber depends on the radius of the chamber and the thickness of its wall (the smaller the radius and the thicker the wall, the greater the force of contraction). ## The Systemic Circulation 1. Blood flows from the left ventricle into the aorta and from the porta into arteries that eventually branch into arterioles and capillaries, the smallest of the arterial vessels. Oxygen, nutrients, and other substances needed for cellular metabolism pass from the capillaries into the interstitium, where they are available for uptake by the cells. Capillaries also absorb products of cellular metabolism from the interstitium. 2. Venules, the smallest veins, receive capillary blood. From the venules the venous blood flows into larger and larger veins until it reaches the venae cavae, through which it enters the right atrium. 3. Vessel walls consist of three layers: the tunica intima (inner layer), the tunica media (middle layer), and the tunica externa (outer layer). 4. Layers of the vessel wall differ in thickness and composition from vessel to vessel, depending on the vessel's size and location within the circulatory system. In general, the tunica media of arteries close to the heart contains a greater proportion of elastic fibers because these arteries must be able to distend during systole and recoil during diastole. Distributing arteries farther from the heart contain a greater proportion of smooth muscle fibers because these arteries must be able to constrict and dilate to control blood pressure and volume within specific capillary beds. 5. Blood flow into the capillary beds is controlled by the contraction and relaxation of smooth muscle bands (precapillary sphincters) at junctions between metarterioles and capillaries. The endothelium is probably a source of prostaglandins that control vasomotion. 6. Blood flow through the veins is assisted by the contraction of skeletal muscles (the muscle pump), and backwards flow in the lower body is prevented by one-way valves, particularly in the deep veins of the legs. 7. Blood flow is affected by blood pressure; resistance to flow within the vessels; blood consistency (which affects velocity); anatomic features that may cause turbulent or laminar flow; and compliance (distensibility) of the vessels. 8. Poiseuille's law describes the relationship of blood flow, pressure, and resistance as the difference between pressure at the inflow end of the vessel and pressure at the outflow end divided by resistance within the vessel. 9. Resistance to blood flow depends on vessel length and radius and on the viscosity of the blood. The greater a vessel's length and the blood's viscosity and the narrower the radius of the vessel's lumen, the greater the resistance within the vessel. 10. Total peripheral resistance, or the resistance to flow within the entire systemic circulatory system, depends on the combined lengths and radii of all the vessels within the system and on whether the vessels are arranged in series (greater resistance) or in parallel (lesser resistance). 11. Blood flow is influenced also by neural stimulation (of vasoconstriction or vasodilation) and by autonomic features that cause turbulence within the vascular lumen (e.g., protrusions from the vessel wall, twists and turns, bifurcations). 12. Arterial blood pressure is influenced and regulated by factors that affect cardiac output (heart rate and stroke volume), total resistance within the system, and blood volume. 13. Many hormones and other endothelial mediators alter vasomotion including epinephrine, norepinephrine, antidiuretic hormone, renin-angiotensin system, natriuretic peptides, adrenomedullin, nitric oxide, prostaglandins, and endothelium-derived relaxing factor. 14. Venous pressure is influenced by blood volume within the venous system and compliance of the venous walls. 15. Blood flow through the coronary circulation is governed not only by the same principles as flow through other vascular beds but also by two adaptations dictated by cardiac dynamics. First, blood flows into the coronary arteries during diastole rather than systole because during systole, the cusps of the aortic semilunar valve block the openings of the coronary arteries. Second, systolic contraction inhibits coronary artery flow by compressing the coronary arteries. 16. Autoregulation enables the coronary vessels to maintain optimal perfusion pressure despite systolic effects, and myoglobin in heart muscle stores oxygen for use during the systolic phase of the cardiac cycle. ## Lymphatic System - The vessels of the lymphatic system run in the same sheaths as those of the arteries and veins. - Lymph (interstitial fluid plus cells of the immune system) is absorbed by lymphatic venules in the capillary beds and travels through ever larger lymphatic veins until it empties into the right lymphatic duct and the thoracic duct, which drain into the right and left subclavian veins, respectively. - As lymph travels toward the thoracic ducts, it passes through lymph nodes clustered around the lymphatic vessels. The lymph nodes are sites of immune function and are ideally placed to sample fluid and cells moving from the periphery into the central circulation. ## Tests of Cardiovascular Function 1. The evaluation of an individual with known or suspected cardiovascular disease must include a careful history and physical examination including assessment of risk factors, symptoms, vital signs, level of consciousness, mucous membrane color, and cardiopulmonary functioning. 2. Important tests for cardiac disorders are ECG and Holter monitoring, which detect disturbances of impulse generation or conduction. 3. Stress tests elicit clinical manifestations of cardiovascular disease that might not be present at rest. 4. The sensitivity of stress testing is improved by the use of radiotracer imaging techniques such as SPECT. 5. Echocardiography detects structural and functional cardiac abnormalities over time. 6. Cardiac catheterization is used to measure the oxygen content and pressure of blood in the heart's chambers and to inject contrast media for x-ray examination of the size and shape of the chambers and valves. Injection of contrast medium into the coronary arteries (coronary angiography), on the other hand, permits visualization of the coronary circulation and every tissue perfused by the coronary arteries. 7. Evaluation of the systemic vascular system can include arterial pressure pulse waveform analysis, Doppler ultrasonography, venography, and arteriography. ## Aging and the Cardiovascular System 1. Cardiovascular disease is the most common cause of morbidity and mortality in older adults in Western society and in much of the rest of the world. In addition, age is a key driver of cardiovascular risk, which explains why it is the primary cause of death in persons older than age 65. 2. The most common cardiovascular disease condition is hypertension followed by coronary atherosclerosis, for which hypertension is a risk factor. 3. It is challenging to determine the normal physiologic changes in cardiac function with aging because many pathologic changes are usually present and physical fitness is variable in older people as well. 4. The most relevant age-associated physiologic changes in cardiovascular performance include myocardial and blood vessel stiffening, changes in neurogenic control over vascular tone, increased occurrence of atrial fibrillation, and loss of exercise capacity plus left ventricular hypertrophy and fibrosis. 5. With active risk reduction, physical activity, and disease management, older adults can have markedly improved cardiovascular health. ## Key Terms - a wave, 1021 - Actin, 1030 - Adrenomedullin (ADM), 1046 - Diastole, 1021 - Diastolic blood pressure, 1043 - Diastolic depolarization, 1028 - Nitric oxide (NO), 1046 - Node, 1025 - Norepinephrine, 1029