PS%206_solutions

PS%206_solutions - BIOE 322/BIOS 332 Fundamentals of...

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Page 1 of 4 BIOE 322/BIOS 332 Fundamentals of Systems Physiology Spring 2008 Problem Set #6 Solutions 1. While this athlete is relaxing, the sympathetic stimulation of the arteries in her skeletal muscles, the arteries in her digestive system, and the large veins decreases. As a result, vasoconstriction increases in the arteries of her muscles, and vasodilation occurs in the blood vessels of her digestive system and in the large veins. Blood flow decreases to her skeletal muscles, and blood flow increases to her digestive system. In addition, more blood accumulates in the large veins due to decreased skeletal muscle pump. Consequently, venous return to the heart decreases, which is consistent with the reduced cardiac output. 2. 1) Vasoconstriction of blood vessels in the skin in response to exposure to cold results in a decreased flow of blood through the skin and in a dramatic increase in resistance (Poiseuille’s Law). Vasoconstriction makes the skin appear pale. 2) Vasodilation of blood vessels in the skin results in increased blood flow through the skin. Vasodilation makes the skin appear flushed or red in color. 3) In a patient with erythrocytosis, the hematocrit increases dramatically. As a result, the viscosity of the blood increases, which increases resistance to flow. Consequently, flow decreases or a greater pressure is needed to maintain the same flow. 3. 3.1 Systemic arterial pressure is not a single value because arterial pressure varies over the course of each cardiac cycle. Its highest value is systolic pressure, which is measured just after blood is ejected from the left ventricle into the aorta (systole). Its lowest value is diastolic pressure, which is measured as blood flows from the arteries into the veins and back to the heart (diastole). Mean arterial pressure cannot be calculated as the simple average of systolic and diastolic pressures because averaging does not take into account the fact that a greater fraction of each cardiac cycle is spent in diastole (approx. 2/3) than in systole (approx. 1/3). Thus, mean arterial pressure is closer to diastolic pressure than to systolic pressure. Mean arterial pressure = diastolic pressure + 1/3 pulse pressure where pulse pressure = systolic pressure – diastolic pressure thus, Mean arterial pressure = (82 mmHg) + (1/3) (124 – 82 mmHg) = 96 mm Hg 3.2 Stroke volume (SV) is the blood volume ejected by the ventricle during systole. SV = left ventricular end-diastolic volume – left ventricular end-systolic volume = 140 – 70 mL = 70 mL Cardiac output is the blood volume ejected by the ventricle per minute. CO = SV * heart rate
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PS%206_solutions - BIOE 322/BIOS 332 Fundamentals of...

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