英和和英

出典:『Wikipedia』 (2011/04/21 20:34 UTC 版)

英語による解説

引用

Pulsatile blood flow in the body is a response to periodic variations in velocity. These pulsating characteristics have been shown to be a result of two pumps. As the primary pump, the heart causes the blood flow and velocity to oscillate from zero to very high rates as the valves at the entrances and exits to the ventricles intermittently close and open with each beat of the heart. The second pump is a result of the respiratory and skeletal systems, which exert their greatest action on venous flow. Specifically pulsation that result from the release of blood from the left ventricle show that they exhibit non-liner, transient pulsations in pressure and flow. These create complex pulse patterns which are further propagated through the rest of the network. This results in variations in the applied shear stress to the layer of enodthelial cells which separate blood flow from the vessel wall. Depending upon the amount of force, the ECs will release chemicals that either induce dilation or constriction of the smooth muscle surrounding the vessel.