Cherry 發問於 科學及數學生物學 · 1 十年前

biology q~~~pls help

vasoconstriction occurs only in arteriole but not capillary and artery.

更新:

But, from my biology book ,

the function of thick smooth muscle in artery is to regulate the distribution of blood flow to various tissue for metabolic demand by altering the resistance of blood flow by altering the diameter of lumen.

Is is vasoconstriction?

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  • 1 十年前
    最愛解答

    I suppose you want an explaination as why vasoconstriction occurs in arteriole only.

    Vasoconstriction is the narrowing of blood vessels so that blood flow will be reduced to certain part of the body. One example is when you feel cold, the blood vessels near your skin will constrict so that warm blood will be kept inside the internal organs to keep them warm longer. Your skin then look pale (without blood colour) and feels cold too.

    Arteries usually carry large amounts of blood to many vital organs and many other body parts, and constricting them will reduce blood flow to vital organs and may cause big trouble. Besides, arteries are thick and narrowing it to control blood flow is not practical. It is better to narrow arterioles that is connected to this artery, to create a higher back-pressure (resistance) to slow down the blood in the arteries.

    On the contrary, narrowing arterioles can control blood flow to some particular organ and not affecting the rest of the area. You can achieve the fine tuning effect. Taking the "feeling cold" example, skin gets it blood supply from many different arteries. Constricting those arterioles supplying to skin surface will create a back-pressure for more blood to stay close to internal organs supplied by the same artery. The total supply from the artery remain the same.

    About the capillary, the blood in it is not pressurised as in arteries and arterioles. It is more of a distribution and drainage network than a mains supply. The capillaries are already very thin and if vasoconstrictions occurs here, the blood cannot reach the cells at all, leaving cells out of oxygen supply and may be tissue death. Also, a constricted capillary cannot drain blood properly back in to the veins. Deoxygenated blood is stuck in the body tissue and you can imagine the edema -浮腫;水腫- it will result.

    Hope this is what you needed.

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