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Precapillary sphincter

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Title: Precapillary sphincter  
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Subject: Capillary
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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.



  • Fundamentals of Anatomy & Physiology: seventh edition, Frederic H. Martini
  • Dzulfitree B. Ahmad, Cyberjaya University College of Medical Sciences 07/08
  • Guyton and Hall, Textbook of Medical Physiology

External links

  • American Journal of Physiology, 1977 Jul;233(1):H141-7. Baez S, Feldman SM, Gootman PM.

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