Precapillary sphincter

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Precapillary sphincter
2105 Capillary Bed.jpg
Illustration of a capillary system with precapillary sphincters
Anatomical terminology

A precapillary sphincter is a band of smooth muscle that adjusts blood flow into capillaries mainly in the mesenteric microcirculation.[1][2] At the point where each of the capillaries originates from an arteriole, a smooth muscle fiber encircles the capillary. This is called the precapillary sphincter. The sphincter can open and close the entrance to the capillary, by which contraction causes blood flow in a capillary to change as vasomotion occurs.[3] The entire capillary bed may be bypassed by blood flow through arteriovenous anastomoses or through preferential flow through metarterioles.[2] If the sphincter is damaged or can not contract, blood can flow into the capillary bed at high pressures. When capillary pressures are high (as per gravity etc.), fluid passes out of the capillaries into the interstitial space, and edema or fluid swelling is the result.[citation needed]

Dispute over concept[edit]

Precapillary sphincters as well as metarterioles were discovered in the mesenteric circulation in the 1950s. Medical and physiological text-books such as Guyton, Boron and Fulton etc. were quick to claim the existence of said sphincters and metarterioles all over the body, despite lack of evidence.[2] At least since 1976 there has been considerable debate about the existence of precapillary sphincters and metarterioles.[4] Today it is held that they are unique to the mesenteric circulation and some researchers have suggested the term precapillary resistance instead.[2]

References[edit]

  1. ^ Precapillary Sphincter definition. The Free Dictionary by Farlex. Medical Dictionary
  2. ^ a b c d Sakai T, Hosoyamada Y (September 2013). "Are the precapillary sphincters and metarterioles universal components of the microcirculation? An historical review". The Journal of Physiological Sciences 63 (5): 319–31. doi:10.1007/s12576-013-0274-7. PMC 3751330. PMID 23824465. 
  3. ^ Autoregulation and Capillary Dynamics. PDF Autoregulation and Capillary DynamicsPearson Education Inc., publishing as Benjamin Cummings[unreliable source?]
  4. ^ Wiedeman MP, Tuma RF, Mayrovitz HN (July 1976). "Defining the precapillary sphincter". Microvascular Research 12 (1): 71–5. PMID 967027. 

Further reading[edit]