Username6000
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An arteriole has muscle fibres. Explain how these muscle fibres reduce blood flow to capillaries.
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macpatgh-Sheldon
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Hi, the arteriole has muscle fibres that are circular in cross-section i.e. they run around the circumference of the cross-sectional view. So if these muscles contract i.e. shorten in length, they will obviously make a smaller circle hence narrowing the diameter of the arteriole. This is called arteriolar vasoconstriction and it reduces blood flow to vessels further down the circulation = in capillaries.

If you are aiming for A*, also try to remember that these muscles are not like the biceps of Arnold Shwarzeneger () i.e. they are not voluntary or striated muscles BUT RATHER involuntary or smooth muscles, and the usual mechanism that makes them contract is the action of the neurotransmitter, noradrenaline, acting on alpha adrenergic (sympathetic type) receptors.

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Username6000
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Thank you!!
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