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AS edexcel biololgy cardiac cycle help

Hi,
I understand the cardiac cycle, but i have real difficulties in working out which stage the heart is in based on the volume of blood in each chamber. Can anyone explain to me how to do this quickly and easily?

An example of the question type is here:

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Reply 1

coolgamer

Valve 2 is closed valve one open..,?

Reply 2

hibzmourad

Original post by GGLFC

hi there,

ok, i'm going to give you a quick walk through on how this works because just giving you the answer won't do a great deal of a help.
in stages 1 to 3, the pressure in the aortic valve remains constant, which suggests that it has been closed the whole time, otherwise it would have increased when the aortic valve opens which will have allowed blood to enter and cause the aortic valve to contract hence increasing the pressure. so if the aortic valve was closed, the atrioventricular valve must be open. other evidence to support this is that in stage 2, the pressure in the left atrium is greater than in the left ventricle. we know that pressure tends to move from an area of high pressure to an area with lower pressure so the AV valve must be open to allow the blood to be forced out of the left atrium into the left ventricle. and sure enough, you can see that in stage 3, the pressure in the LV is greater than in the LA (and just before the aortic valve opens)
in stage 4, the ventricle will contract increasing its pressure so that it moves into the aorta where there is a lower pressure.
so to conclude, the answer is valve 1 is open !!!
hope that helped :cool: