BIOL 2420 Lecture 9: Lecture 9

• School: University of Manitoba
• Department: Biological Sciences
• Course: BIOL 2420
• Professor: W.G.Anderson

Document Summary

Co is determines by the rate of venous return (vr) Problem: gravitational forces act on the blood and lymph vessel columns between he heart and extremities while upright. Standing up after laying down can make us dizzy at rst - due to orthostatic hypotension. Stand up too quickly and the gravity changes - not enough blood is going to the brain. Below heart level, veins & lymph vessels will tend to ll and be distended. Major site of venous volume changes are the smaller veins located outside of the thorax. Small increase in p results in a big increase in volume. Leads to edema and eventually to fainting (via decreased map induced by decreased vr) if venous pooling occurs and persists. Blood often pools in bedridden individuals as well as people in wheelchairs. Pooling usually occurs in legs - most commonly in claves. Walls of veins contain sm innervated by sympathetic neurons. Ne binds to alpha1 - adrenergic receptors.