Anatomy & Physiology

Anatomy & Physiology Study Guide 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. • At the capillaries, blood pressure transports water and solutes out of the plasma and across capillary walls. Water moves out of the capillaries, through the peripheral tissues, and returning to the bloodstream by way of the lymphatic system. Water movement across capillary walls is determined by the interplay between osmotic pressures and hydrostatic pressures. • Osmotic pressure (OP) is a measure of the pressure that must be applied to prevent osmotic movement across a membrane. Osmotic water movement continues until solute concentrations are equalized, or the movement is prevented by an opposing hydrostatic pressure. • The rates of filtration and reabsorption gradually change as blood passes along the length of a capillary, as determined by the net filtration pressure (the difference between the net hydrostatic pressure and the net osmotic pressure). Cardiovascular regulatory mechanisms involve autoregulation, neural mechanisms, and endocrine responses: • Homeostatic mechanisms guarantee that tissue perfusion (blood flow) conveys adequate oxygen and nutrients. • Autoregulation, neural mechanisms, and endocrine mechanisms affect the coordinated regulation of cardiovascular function. Autoregulation includes local factors altering the Achieve Page 276 of 368 ©2018