BIOLOGY 151 Lecture Notes - Lecture 33: Heart Valve, Venae Cavae, Red Blood Cell
Document Summary
Diffusion only works well over short distances. So nutrients need to be delivered close to where they are needed. No cell in tissues is further than 2 or 3 cell diameters from a capillary: only a few rare exceptions. So lots of capillaries needed: average human statistics. So all blood pumped through body in a minute. During exercise multiplies by over factor of 3: blood supply to heart and muscle increases, blood supply to brain stays the same, blood supply to everything else decreases. 62,000 miles of vessels within each of us. Enough to circle the earth twice: capillaries. Some fluid forced out: called lymph, motile cells like macrophages can crawl out in it, lymph later collected by lymphatic system and returned to the heart. Precapillary sphincters: control which capillaries blood flows though, 2 pumps. Sends oxygenated blood to the body: aorta, arterioles, capillaries, join into venules, veins, vena cava. Atrium: thin walls, low pressure pump, pumps blood into ventricle.
