Pre-capillary sphincters | Circulatory system physiology | NCLEX-RN | Khan Academy

Find out how the body controls how much blood flows through a capillary bed. Rishi is a pediatric infectious disease physician and works at Khan Academy. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Rishi Desai.

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[RebecaArellano]

wow this was beyond helpful and much more cleaner drawing than my professor's, i understand everything much clearly :)

[cierabellamy]

Blood flow through a capillary bed is controlled by the capillary sphincters that direct blood to a particular tissue depending on their nutrient needs; precapillary sphincters are controlled by the pH of the tissue. When a tissue needs blood, the change in pH due to high levels of CO2 will cause the sphincter to open. When the tissue no longer needs freshly oxygenated blood and the balance is returned, the sphincter closes to allow other tissues to receive blood. (I'm pretty sure)

[labba]

your videos have been helping me so much. THANK YOU!

[lindasoto]

Thanks! finally understand the capillary bed blood flow more easily. 

[chagallzhang]

This is soooo clear! Thank you very much! I love all your videos Rishi!

[maicho]

Ciera Bellamy the precapillary sphincters are also highly sensitive to catecholamines (ie. epi and nEpi) and thats when they squeeze down, especially during episodes of shock for blood redistribution.

[ivisflores]

is there any way you could create a video on heart failure?

[DianahernandezV]

Can someone explain the following question for me?? I had it in a exam and I can't seem to understand it: I posted the exam's explanation as a reply comment, its A LOT to read. lol

Which of the following is an abnormal physiologic process that occurs at the capillary level during shock?

A. Minimal capillary blood flow, which results in aerobic metabolism
B: Sustained pre- and postcapillary constriction in response to hypoxia
C: Precapillary sphincter relaxation in response to lactic acid buildup
D: Postcapillary sphincter relaxation that causes capillary fluid depletion

the answer was C.. but if I am correct, I thought C was is the only normal, not abnormal. And where are the post capillaries located?

[hijamahijam]

Hi Rishi. If a pre-capillary sphincter muscle is contracted, and blood flow is ceased to a particular region, what happens to the cells of that region? If muscles do not relax, will the cells die eventually? thanks!

[saumyasandakelum]

thanks!!! awesome simple video. easy to understand.

[hasanani]

Very big Thanks from iraqi pharmacists

[AlDanMusic]

Is it also true that it can be used to squeeze blood and increase the velocity of blood going to the tissue?

[luckssj]

Are the lined with Glycocalyx Structure and Mucosa lining?

[lishannon]

The lecture is amazing! But I have a quick question: Does this smooth muscle exist in skeletal muscle capillaries? I just read on wiki, say, that "s of 2013 it is held that they are unique to the mesenteric circulation and some researchers have suggested the term precapillary resistance instead.[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.]" I feel confused...

[MartinUckermann]

How could muscle ever open or close? Surely, it contracts constricting the lumen of the metarterioles so that the blood do not flow where it is not needed, and it relaxes whenever it wants to allow the blood flow into that region.

[ZuziCardet]

so basically pre-capillary sphincters are made up of smooth muscles and they regulate where the blood is flowing.. but how they do this? they relax and contract?? open and close? thanks so much :)

[cierabellamy]

...yes the pH is determined by the CO2. Carbon dioxide in the blood isn't simply carried as carbon dioxide, the majority is converted by carbonic anhydrase into bicarbonate and hydrogen ions. pH is simply a measure of the concentration of hydrogen ions in a material base on a log scale. The more hydrogen ions, the more acidic the material is. Therefore, if the tissue has a greater concentration of carbon dioxide, it will have more hydrogen ions and have a lower pH, causing the sphincters to relax and blood to enter perfuse the tissue.

[maicho]

@hijama hijam if the precap sphincters do not relax, and for some reason they do not open up, due to hypoxia from the lack of blood flow to the tissues in that region, vasodilators (such as histamine from mast cells) will loosen up the smooth muscle as well as the true caps, and there will be blood flow again.  But if the hypoxia persists for too long, when the sphincter opens up, a lot of RBC with poor ability to change conformation enters, coagulates, along with WBC and platelet adhesion, plasma viscosity increases, endothelial cells damaged, clot would then form, DIC then follows, and you are pretty much dead.  This is in the case of shock.

[paywandd]

i got it
metarteriole has smooth muscles
thoroughfare has not smooth muscles

[damlala]

Can u translate your videos 4 arabics also plz