PHGY 210 Lecture Notes - Lecture 15: Vascular Resistance, Fibrous Cap, Arteriovenous Oxygen Difference
25 Feb 2013
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The mean blood pressure does not change, thus allowing for the person not to faint when standing up. When standing up, the blood flows out of the chest, which then allows for the right atrial pressure to drop. The baroreceptor effect makes it so that the contractility increases and the constriction of the arteries. During extended period of standing, pumping the calf muscles allows for the blood to be forced back into the heart, to restore the blood pressure. Venous valves and muscle pumps shifting blood and preventing them from back flowing. Venous pressure while standing is about 80mmhg at the bottom of the foot. Plasma volume is pumped out from the cell junctions, the longer one stands, the more the fluid leaks out. As such, 15 minutes of standing would lead to nearly 700ml of volume lost. The muscle pumps also lower the venous pressure in the veins and capillaries. Heart rates maxed out at 220 minus age.
