BIOL 3070 Study Guide - Midterm Guide: Porphyrin, Motor Neuron, Sodium Chloride
1 Apr 2015
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Document Summary
2 main functions of venous system: 1) acts as a passageway for the return of blood from the capillaries to the heart. Under resting condition, mammalian veins contain more than 60% of total blood volume. Venous blood flow is enhanced by : 1) compression of veins in limbs by contraction of skeletal muscle surrounding veins 2) one-way valve which permit blood movement towards the heart but not backwards. Rete mirabile: many arterial capillaries surrounded by many venous capillaries. Capillaries: have a single layer of endothelial cells surrounded by a basement membrane ( or basal lamina). Lack smooth muscle, elastic or connective tissue layers. Precapillary sphincters: rings of smooth muscle between arterioles and capillaries that control blood flow through a capillary network. Constriction of the sphincters by contraction of muscles closes the capillary bed. Metarteriole: when precapillary spincter is constricted, the blood moves to an area where gas exchange is needed bypassing via a throughfare channel, called the metarteriole.
