BIOL 121 Lecture Notes - Lecture 32: Vascular Resistance, Mean Arterial Pressure, Vascular Smooth Muscle
Document Summary
Two other mechanisms, in addition to contraction of venous smooth muscle can increase venous pressure and facilitate venous return: (1) skeletal pump (2) respiratory pump: skeletal muscle pump: during skeletal muscle contraction, venous diameter decreases increasing venous pressure. This pressure increase in the abdominal cavity is transmitted passively to intra-abdominal veins. Simultaneously, pressure in the thorax decreases, thus decreasing pressure in intrathoracic veins and right atrium. Therefore, increasing inspiration increases venous pressure, increasing blood flow back to the heart. Venous return and cardiac output must be the same except for transient differences over brief periods of time. Mean arterial pressure (map) = cardiac output (co) * peripheral vascular resistance (pvr) Map is the steady-state component of blood pressure. Primary hypertension: most cases of hypertension; arises from genetic problems in homeostatic mechanisms that regulate map co is usually normal, typically there is a problem with an increase in total peripheral resistance (tpr): possibly decrease in no production.
