How do valves in the heart and blood vessels work?

[scilearner]

Hello everyone,

 

How do valves in the body basically work. I can understand how blood flowing on either direction can close or open valves depending on the type of valve. But someone told me it is the elastic recoil of the veins that closes the valve. I thought it would blood that was going back that closed the valve. Also in the heart does the contraction of right ventricle close the mitral valve or the blood going back from the ventricle that closes the valve.

 

Also while we are at it. I read that aortic valve closes before pulmonary valve in a text book. The reason was this in the text book

 

"Aortic valve closes before the closure of pulmonary valve because of the lower impedance of the pulmonary vasculature"

 

I don't understand what they are saying could anyone explain. Thanks

[Mokele]

What most directly causes valves to shut is blood flowing in the "wrong" direction forcing the valve closed. The valves themselves are totally passive flaps of tissue.

 

Elasticity does play a role in the heart valves closing, but only as an indirect mechanism that causes backflow - when the heart pumps out blood, it not only pushes blood through the aorta, but causes the aorta to stretch and expand in diameter. When the heart contraction ends, the aorta recoils pushing blood both further through the body and back into the heart, but the backflow is stopped by the valve.

[scilearner]

Thanks Mokele Nice to see you back answering my questions.

 

Also I found the answer for 2nd question on another site. I'll post it here so it might be useful for someone else in the future.

 

First lets understand why is A2 before P2 ?

1.Both right & left ventricular systole ends at the same time .(ie, systolic muscle contraction of both ventricles ends at same time)

2.pulmonary arterial pressure is less than aortic pressure (i.e, pulmonary resistance to forward flow from ventricles is less than aortic resistance => therefore we can say that pulmonary impedance is less than aortic impedance.){impedance is nothing but resistance}

3.Therefore as pulmonary impedance is less, even after right ventricular systolic contraction blood continues to flow through valve until pulmonary arterial pressure increases more than right ventricle). But as aortic impedance is more ,it stops blood flow through the aortic valve before itself.

4.Due to the above reasons ,Right ventricular ejection begins prior to left ventricular ejection, has a slightly longer duration, and terminates after left ventricular ejection, resulting in P2 normally occurring after A2.