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  • IMAT 2014 Q38 Biology

  • Nicolas Sanchez

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    June 22, 2021 at 1:45 am
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    One set of semi-­lunar valves in the human heart closes when:

    A. the blood pressure in the aorta is greater than in the vena cava.

    B. the oxygen level in blood decreases at the respiring tissues.

    C. the blood pressure in the right ventricle is less than in the pulmonary artery.

    D. the blood pressure is greater in the left ventricle than in the aorta.

    E. another set of semi-­lunar valves opens.

  • Ari Horesh

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    June 22, 2021 at 12:26 pm
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    The following question is talking about the human heart. Before we answer this question, we should remember the flow of blood and the pressure in the different segments of the heart.

    Blood is returning through the Vena cava, into the right atrium, then, the ventricular valve opens up, and the blood enters the right ventricle, the heart “beats” causing a very high pressure in the ventricles until the pressure is high enough to open up the semilunar valves, when the diastolic phase of the pressure is lowered, and the semilunar valves are closed, the ventricular set is open.

    the semilunar valves closes when the blood pressure in the aorta and the pulmonery artery are greater than the ventricles, why? because the blood wants to “flow back” to the ventricles, the back flow is closing the semilunar valves. it opens back up when the pressure in the ventricles is hitting a points when it is larger than the aaorta and pulmonary valve

    The valves are never open together, but they can be closed together until the pressure in the ventricle is high enough to bypass the pressure of the aorta to open up the semilunar valves.

    Let’s check our statement:

    the blood pressure in the aorta is greater than in the vena cava. The vena cava has nothing to do with the aorta.

    The oxygen level in blood decreases at the respiring tissues – the oxygen level of blood always falls in certain places; it doesn’t matter if the valve is open or closed.

    The blood pressure in the right ventricle is less than in the pulmonary artery. – As we said above, the only way to open the semilunar valves is to bypass the pressure of the pulmonary trunk and the aorta.

    The blood pressure is greater in the left ventricle than in the aorta. – opens, not closes..

    Another set of semi­lunar valves opens. – we only have one set of semi-lunar valves!

    The answer is C.

    Ari Horesh voted up
    • Isha Aggarwal

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      July 29, 2021 at 9:29 am
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      I would also like to mention a point here

      that semilunar valve are of 2 type

      1- aortic valve (aorta which will take oxygenated blood out of heart)

      2- pulmonary valve( pulmonary artery which will take blood from RV to lungs for oxygenation)

      Ari Horesh voted up
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