Anatomy & Physiology I and II

Anatomy & Physiology Study Guide • The arterial system includes the large elastic arteries, medium-sized muscular arteries, and smaller arterioles. As we move toward the capillaries, the quantity of vessels rises, but the diameters of the individual vessels lower, and the walls become thinner. • Atherosclerosis, a kind of arteriosclerosis, is linked with changes in the endothelial lining of arteries. Fatty masses of tissue, known as plaques, typically develop during atherosclerosis. • Capillaries are the only blood vessels with walls thin enough to allow an exchange between blood and interstitial fluid. Capillaries are continuous or fenestrated. Sinusoids have fenestrated walls and form elaborate networks that allow very slow blood flow. Sinusoids are located in the liver and in various endocrine organs. • Capillaries form interconnected networks called capillary beds (capillary plexuses). A precapillary sphincter, which is a band of smooth muscle, adjusts the blood flow into each capillary. Blood flow in a capillary will change as vasomotion happens. The whole capillary bed may be bypassed by blood flow through arteriovenous anastomoses. • Venules get blood from the capillaries and merge into medium-sized veins and then large veins. The arterial system is high-pressure; blood pressure in veins is lower. Valves in veins stop the backflow of blood. • Peripheral venoconstriction maintains adequate blood volume in the arterial system after a hemorrhage. The venous reserve normally accounts for 20 percent of total blood volume. Pressure and resistance determine blood flow and affect rates of capillary exchange: • Cardiovascular regulation involves the manipulation of blood pressure and resistance to control the rates of blood flow and capillary exchange. • Blood flow occurs from a place of higher pressure to one of lower pressure and is proportional to the pressure gradient. The circulatory pressure is the pressure gradient across the systemic circuit. It is published as three values: arterial blood pressure (BP), capillary hydrostatic pressure (CHP), and venous pressure. • The resistance (R) decides the rate of blood flow through the systemic circuit. The major determining factor of blood flow rate is the peripheral resistance—the resistance of the arterial system. Neural and hormonal control mechanisms regulate blood pressure and peripheral resistance. • Vascular resistance is the resistance of blood vessels. It is the largest component of peripheral resistance and depends on vessel length and vessel diameter. • Viscosity and turbulence also contribute to peripheral resistance. • The high arterial pressures overcome peripheral resistance and maintain blood flow through peripheral tissues. Capillary pressures are low; slight changes in capillary pressure determine the rate of fluid’s movement into or out of the bloodstream. Venous pressure, normally low, decides venous return and influences cardiac output and peripheral blood flow. • Arterial blood pressure increases during ventricular systole and declines during ventricular diastole. The difference between the two blood pressures is the pulse pressure. Blood pressure is calculated at the brachial artery with the use of a sphygmomanometer. • Valves, muscular compression, and the respiratory pump (thoracoabdominal pump) help the low venous pressures move blood toward the heart. ©2018 Achieve Test Prep Page 274 of 367