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A '''precapillary sphincter''' is a band of [[smooth muscle]] that adjusts [[blood]] flow into [[capillary|capillaries]] mainly in the [[mesenteric]] [[microcirculation]].<ref>[http://medical-dictionary.thefreedictionary.com/Precapillary+sphincter Precapillary Sphincter definition]. The Free Dictionary by Farlex. Medical Dictionary</ref><ref name="Precapillary sphincters and metarterioles historical ">{{cite journal | url=http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3751330/ | title=Are the precapillary sphincters and metarterioles universal components of the microcirculation? An historical review | author=Sakai et. al | journal=J Physiol Sci. 2013; 63: 319–331. | year=2013}}</ref> 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.<ref>{{PDF|[http://www.aw-bc.com/info/ip/assignmentfiles/cardiovascular/Autoreg_Cap_Dynamics.pdf Autoregulation and Capillary Dynamics.]}} Autoregulation and Capillary DynamicsPearson Education Inc., publishing as Benjamin Cummings</ref> The entire [[capillary bed]] may be bypassed by blood flow through [[arteriovenous anastomoses]] or through preferential flow through [[metarterioles]].<ref name="Precapillary sphincters and metarterioles historical " /> 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 [[Fluid compartments|interstitial space]], and [[edema]] or fluid swelling is the result.{{citation needed|date=November 2013}}
A '''precapillary sphincter''' is a band of [[smooth muscle]] that adjusts [[blood]] flow into [[capillary|capillaries]] mainly in the [[mesenteric]] [[microcirculation]].<ref>[http://medical-dictionary.thefreedictionary.com/Precapillary+sphincter Precapillary Sphincter definition]. The Free Dictionary by Farlex. Medical Dictionary</ref><ref name="Precapillary sphincters and metarterioles historical ">{{cite journal |author=Sakai T, Hosoyamada Y |title=Are the precapillary sphincters and metarterioles universal components of the microcirculation? An historical review |journal=The Journal of Physiological Sciences |volume=63 |issue=5 |pages=319–31 |year=2013 |month=September |pmid=23824465 |pmc=3751330 |doi=10.1007/s12576-013-0274-7}}</ref> 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.<ref>{{PDF|[http://www.aw-bc.com/info/ip/assignmentfiles/cardiovascular/Autoreg_Cap_Dynamics.pdf Autoregulation and Capillary Dynamics.]}} Autoregulation and Capillary DynamicsPearson Education Inc., publishing as Benjamin Cummings{{rs}}</ref> The entire [[capillary bed]] may be bypassed by blood flow through [[arteriovenous anastomoses]] or through preferential flow through [[metarterioles]].<ref name="Precapillary sphincters and metarterioles historical " /> 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 [[Fluid compartments|interstitial space]], and [[edema]] or fluid swelling is the result.{{citation needed|date=November 2013}}


==Dispute over concept==
==Dispute over concept==
Precapillary sphincters as well as [[metarterioles]] were discovered in the mesenteric circulation in the 1950s. Medical and physiological text-books such as ''[[Arthur Guyton|Guyton]]'', ''[[Walter Boron|Boron]]'' and ''Fulton'' etc. were quick to claim the existence of said sphincters and metarterioles all over the body, despite lack of evidence.<ref name="Precapillary sphincters and metarterioles historical " /> At least since 1976 there has been considerable debate about the existence of precapillary sphincters and metarterioles.<ref>{{cite journal | url=https://www.ncbi.nlm.nih.gov/pubmed/967027 | title=Defining the Precapillary Sphincter | author=Wiedeman et. al | journal=Molecular Research | year=1976}}</ref> Today it is held that they are unique to the mesenteric circulation and some researchers have suggested the term ''[[precapillary resistance]]'' instead.<ref name="Precapillary sphincters and metarterioles historical " />
Precapillary sphincters as well as [[metarterioles]] were discovered in the mesenteric circulation in the 1950s. Medical and physiological text-books such as ''[[Arthur Guyton|Guyton]]'', ''[[Walter Boron|Boron]]'' and ''Fulton'' etc. were quick to claim the existence of said sphincters and metarterioles all over the body, despite lack of evidence.<ref name="Precapillary sphincters and metarterioles historical " /> At least since 1976 there has been considerable debate about the existence of precapillary sphincters and metarterioles.<ref>{{cite journal |author=Wiedeman MP, Tuma RF, Mayrovitz HN |title=Defining the precapillary sphincter |journal=Microvascular Research |volume=12 |issue=1 |pages=71–5 |year=1976 |month=July |pmid=967027}}</ref> Today it is held that they are unique to the mesenteric circulation and some researchers have suggested the term ''[[precapillary resistance]]'' instead.<ref name="Precapillary sphincters and metarterioles historical " />


==References==
==References==
{{Reflist}}
{{Reflist}}


==Further reading==
*''Fundamentals of Anatomy & Physiology: seventh edition'', Frederic H. Martini
*''Fundamentals of Anatomy & Physiology: seventh edition'', Frederic H. Martini{{pn}}
*Dzulfitree B. Ahmad, Cyberjaya University College of Medical Sciences 07/08
* Guyton and Hall, Textbook of Medical Physiology
* Guyton and Hall, Textbook of Medical Physiology{{pn}}
*{{cite journal |author=Baez S, Feldman SM, Gootman PM |title=Central neural influence on precapillary microvessels and sphincter |journal=The American Journal of Physiology |volume=233 |issue=1 |pages=H141–7 |year=1977 |month=July |pmid=141891 |url=http://ajpheart.physiology.org/cgi/pmidlookup?view=long&pmid=141891}}

== External links ==
* [http://www.ncbi.nlm.nih.gov/pubmed/141891 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.


{{cardiovascular_system}}
{{cardiovascular_system}}

Revision as of 23:31, 6 April 2014

Precapillary sphincter
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

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

  1. ^ Precapillary Sphincter definition. The Free Dictionary by Farlex. Medical Dictionary
  2. ^ a b c d Sakai T, Hosoyamada Y (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. {{cite journal}}: Unknown parameter |month= ignored (help)
  3. ^ Template:PDF Autoregulation and Capillary DynamicsPearson Education Inc., publishing as Benjamin Cummings[unreliable source?]
  4. ^ Wiedeman MP, Tuma RF, Mayrovitz HN (1976). "Defining the precapillary sphincter". Microvascular Research. 12 (1): 71–5. PMID 967027. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)

Further reading


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