Precapillary sphincter
The precapillary sphincter is a band of smooth muscle that adjusts the blood flow into each capillary.[1] At the point where each true capillary originates from a metarteriole, a smooth muscle fiber usually encircles the capillary. This is called the precapillary sphincter. This sphincter can open and close the entrance to the capillary. Blood flow in a capillary changes as vasomotion occurs.[2] The entire capillary bed may be bypassed by blood flow through arteriovenous anastomoses. A precapillary sphincter encircles each capillary branch at the point where it branches from the arteriole. Contraction of the precapillary sphincter can close the branches off to blood flow. If the sphincter is damaged or can not contract, blood can flow into the capillary bed at high pressures. When capillary pressures are high (and this can be the result of gravity), fluid passes out of the capillaries into the interstitial space, and edema or fluid swelling is the result.
[edit] External links
- Central neural influence on precapillary microvessels and sphincter. PubMed Abstract, American Journal of Physiology, 1977 Jul;233(1):H141-7. Baez S, Feldman SM, Gootman PM.
[edit] References
- ^ Precapillary Sphincter definition. The Free Dictionary by Farlex. Medical Dictionary
- ^ PDF Autoregulation and Capillary Dynamics.PDF Autoregulation and Capillary DynamicsPearson Education Inc., publishing as Benjamin Cummings
- Fundamentals of Anatomy & Physiology: seventh edition, Frederic H. Martini
- Dzulfitree B. Ahmad, Cyberjaya University College of Medical Sciences 07/08
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