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OCR Biology A Exam Thread (Breadth - May 26, 2016 and Depth - June 7, 2016)

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I'm so confused going over cardiac cycle in the book and it says.. When both the atrium and ventricle are filled with blood the atrium contracts forcing all the blood into the right ventricle.

I thought the right atrium has to fill first and then when the pressure builds up the AV valve opens and the right ventricle fills up.

Could someone help clarify please?
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bp_22
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Yeah you're right. The atrium empties its contents when its full with blood and pressure in it has built up. SA node triggers this atrial contraction. Blood passes through the AV valve which opens causing the ventricle to fill up with blood.
Original post by Carrot_Cake_13
I'm so confused going over cardiac cycle in the book and it says.. When both the atrium and ventricle are filled with blood the atrium contracts forcing all the blood into the right ventricle.

I thought the right atrium has to fill first and then when the pressure builds up the AV valve opens and the right ventricle fills up.

Could someone help clarify please?
Original post by bp_22
Yeah you're right. The atrium empties its contents when its full with blood and pressure in it has built up. SA node triggers this atrial contraction. Blood passes through the AV valve which opens causing the ventricle to fill up with blood.


Ahhh so the textbook is incorrect. Thank you for clarifying! It was scaring me!! Is this systole btw?

What's the stuff with the delay? I'm going over this complete last minute :afraid:
Original post by Carrot_Cake_13
I'm so confused going over cardiac cycle in the book and it says.. When both the atrium and ventricle are filled with blood the atrium contracts forcing all the blood into the right ventricle.

I thought the right atrium has to fill first and then when the pressure builds up the AV valve opens and the right ventricle fills up.

Could someone help clarify please?


I remember my teacher saying that a small amount of blood enters the ventricle during diastole and then it goes atrial systole and then ventricular systole. I'm pretty sure the ventricle doesn't fill at the same time as the atrium.

Edit: I've just checked the revision guide and they said nothing about it so I'd just keep it simple and say what you initially though if it comes up on an
exam.

Second edit FFS:

During diastole:
As the ventricles continue to relax, the pressue falls below the pressure in the atria. This causes the AV valves to open and blood flows passively into the ventricles from the atria.
(edited 7 years ago)
Original post by Carrot_Cake_13
I'm so confused going over cardiac cycle in the book and it says.. When both the atrium and ventricle are filled with blood the atrium contracts forcing all the blood into the right ventricle.

I thought the right atrium has to fill first and then when the pressure builds up the AV valve opens and the right ventricle fills up.

Could someone help clarify please?


I think that atria fill with blood then AV valve opens and ventricles fill with blood, now both atria and ventricles are filled with blood. Then atria contract forcing the blood into the ventricles (pressure in ventricles has to be created by some force, like contraction of atria)
Original post by Internets
I remember my teacher saying that a small amount of blood enters the ventricle during diastole and then it goes atrial systole and then ventricular systole. I'm pretty sure the ventricle doesn't fill at the same time as the atrium.

Edit: I've just checked the revision guide and they said nothing about it so I'd just keep it simple and say what you initially though if it comes up on an exam.


Yeah the bits filling at the same time where just lines out of the textbook. Okai. Thank you I'll leave it to what I had previously. Errr is it okay to just say systole instead of atrial/ventricular systole?
Original post by Carrot_Cake_13
Yeah the bits filling at the same time where just lines out of the textbook. Okai. Thank you I'll leave it to what I had previously. Errr is it okay to just say systole instead of atrial/ventricular systole?


Just be safe and say atrial/ventricular systole because they are events that happen at different times.
Original post by Internets
Just be safe and say atrial/ventricular systole because they are events that happen at different times.


Oh okay yeah that makes sense. Thanks :smile: Also I remember hearing stuff about the delay at the AVN.. Do you know what that's about?

Wait is the AVN the same as the valve? Or just some electrical signal stuff?
Are we given the equations for t-test in the exam?
Original post by Carrot_Cake_13
Oh okay yeah that makes sense. Thanks :smile: Also I remember hearing stuff about the delay at the AVN.. Do you know what that's about?

Wait is the AVN the same as the valve? Or just some electrical signal stuff?


There are two nodes: the atrioventricular node (avn) and the sinoatrial node (SAN). They basically initiate and sets the rhythm of the contraction of the chambers via waves electrical activity.

There's a delay because you want the atria and ventricles to contract at different times.

SAN make atria contract and then the electrical signals are sent to the AVN where there is a delay and then electrical signals are sent down the bundle of his and to the Purkyne tissue which makes the heart contract from the apex up.
(edited 7 years ago)
Original post by Normy18
Are we given the equations for t-test in the exam?


I think we are given all of the formulae we need, correct me if I'm wrong.
(edited 7 years ago)
Anyone know how to work out the heart rate from a cardiac graph?
Original post by Carrot_Cake_13
I'm so confused going over cardiac cycle in the book and it says.. When both the atrium and ventricle are filled with blood the atrium contracts forcing all the blood into the right ventricle.

I thought the right atrium has to fill first and then when the pressure builds up the AV valve opens and the right ventricle fills up.

Could someone help clarify please?


Think of it like this. Blood is always moving.

So the atria fill during diastole, here the pressure is high enough to open the AV valves but not the semi-luna valves and so some blood also flows into the ventricles. During atrial systole the atria walls contract forcing all the blood to enter the ventricles. The atria then relax and the ventricle walls contract (ventricular systole) this causes the AV valves to close (lub sound) and opens the semi-lunar valves and blood flows into the arteries and out of the heart. The relaxing of the ventricles then causes the semi-lunar valves to close (dub sound).

Also when talking about this in the exam make sure you say 'the walls contract causing atrial systole/venricular systole' (this is usually worth a mark)
Original post by Desouza123
Anyone know how to work out the heart rate from a cardiac graph?


Measure the time for heart beat. on average its around 0.8(s)
So now you need to find out how many times 0.8 fits into 60 seconds as that is how many times it beats in one min 1 min. so 60/0.8=75
so the answer is 75 beats per minite OR 75bpm

If the graph showed more than one beat measure a few and work out an average heart beat length i guess
300/number of squares between qrs complex (peaks)
Original post by 4nonymous
Think of it like this. Blood is always moving.

So the atria fill during diastole, here the pressure is high enough to open the AV valves but not the semi-luna valves and so some blood also flows into the ventricles. During atrial systole the atria walls contract forcing all the blood to enter the ventricles. The atria then relax and the ventricle walls contract (ventricular systole) this causes the AV valves to close (lub sound) and opens the semi-lunar valves and blood flows into the arteries and out of the heart. The relaxing of the ventricles then causes the semi-lunar valves to close (dub sound).

Also when talking about this in the exam make sure you say 'the walls contract causing atrial systole/venricular systole' (this is usually worth a mark)


Wow this is explained so beautifully thank you :adore:
Original post by KappaRoss
Measure the time for heart beat. on average its around 0.8(s)
So now you need to find out how many times 0.8 fits into 60 seconds as that is how many times it beats in one min 1 min. so 60/0.8=75
so the answer is 75 beats per minite OR 75bpm

If the graph showed more than one beat measure a few and work out an average heart beat length i guess


Thank you :biggrin:
1460557816289.gif
Original post by Desouza123
Thank you :biggrin:


im so scared for this exam ;/
Original post by KappaRoss
1460557816289.gif

im so scared for this exam ;/


Ahh, I'm sure you will be fine. I hope they dont ask some stupid 6 marker about a biosensor or how to use colorimetry to find out how much glucose there is in a solution :frown:
@4nonymous Sorry to be more of a hassle.. Could you explain the blood flows into the arteries and out of the heart bit. I remember something on the pulmonary artery being the only vessel to carry deoxygenated blood? Idk whether that's true though..

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