Question Regarding Heart! Who can answer?

[dataman]

Hi,

I was studying cardiology and this question poped up in mind...

Why does the heart have 4 part... I mean the Atriums are extra...
why heart couldn't be just ventricles...? Blood comes in to Right Ventricle and pumps to lungs and from lungs to left ventricle and out to aorta?

what am I missing here?

maybe it is a dumb question Im not understanding what is the point of atriums

I would appreciate your replies...

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[Firebird]

Hi,

I was studying cardiology and this question poped up in mind...

Why does the heart have 4 part... I mean the Atriums are extra...
why heart couldn't be just ventricles...? Blood comes in to Right Ventricle and pumps to lungs and from lungs to left ventricle and out to aorta?

what am I missing here?

maybe it is a dumb question Im not understanding what is the point of atriums

I would appreciate your replies...

The atria "top off" the ventricles so that they are at a maximal volume just before systole. Dyastole alone does not create enough negative pressure to fill the ventricles, nor does the venous pressure. If you consider that the heart beats between 60 and 80 times per minute, a small decrease in left ventricular end-diastolic volume would cause a significant decrease in cardiac output.

 

[dataman]

Thank you.. make sense.

 

[ucla2usc]

Hi,

I was studying cardiology and this question poped up in mind...

Why does the heart have 4 part... I mean the Atriums are extra...
why heart couldn't be just ventricles...? Blood comes in to Right Ventricle and pumps to lungs and from lungs to left ventricle and out to aorta?

what am I missing here?

maybe it is a dumb question Im not understanding what is the point of atriums

I would appreciate your replies...

Not really a dumb question...in fact, in afib the atria seem to be only useful for keeping coag clinics busy! On the contrary...could you imagine what a disaster mitral stenosis or regurg would be if their was not LA to enlarge?

 

[dataman]

Not really a dumb question...in fact, in afib the atria seem to be only useful for keeping coag clinics busy! On the contrary...could you imagine what a disaster mitral stenosis or regurg would be if their was not LA to enlarge?

That made me feel good.. thanks. I'm sure our body has the best engineer up there... it takes us thousands of years to understand it!

But again lets say if we only had ventricles.. like if we joined the atrium and ventricles and end up with a bigger ventricles heart could have beat slower and have a longer diastoly and more time to fill up the ventricles...

More blood each beat less beat per minute!

 

[cardsurgguy]

That made me feel good.. thanks. I'm sure our body has the best engineer up there... it takes us thousands of years to understand it!

But again lets say if we only had ventricles.. like if we joined the atrium and ventricles and end up with a bigger ventricles heart could have beat slower and have a longer diastoly and more time to fill up the ventricles...

More blood each beat less beat per minute!

Bigger isn't always better.

In many forms of cardiomyopathy, the heart (specifically the ventricles) gets bigger in terms of space (dilated cardiomyopathy) or the heart muscle itself (hypertrophic cardiomyopathy).

This leads into the vicious cycle of heart failure and ultimately heart transplant. The heart gets bigger and it actually has to pump harder to achieve the same cardiac output. Because it needs to pump harder, it gets even bigger, which again makes it weaker and so on...

I see what you're saying in theory, if the ventricles were bigger, they should be able to pump out more blood since they are bigger. I would suspect in reality they would have to work harder than what would be proportional.
In other words, the heart may be 30 percent bigger in size, but each cell in the heart might have to work 50 percent harder.

I guess you could consider it this way with a little analogy (which is kinda weird, so I may be the only one who actually gets what I'm trying to say here...)
I believe ants are the species on Earth who are the strongest for their weight. Look at their size-they are also one of the smallest.
If you were to make a graph of size on the Y axis and ease/ability of work on the X axis for the heart or strength, whatever, it would probably increase at a decreasing rate.
So you could do more work overall with just ventricles for the larger size but the heart is working harder per unit (out of its economies of scale so to speak).


Does that make any sense whatsoever? Or am I the only one who understands what I mean by that (even if it is barely)

 

[dataman]

Cardsurgguy...I think I know where you are comming from...

If you are concerned that due to the higher pressure per beat of heart the muscels get bigger... then look at it this way: the amount of muscels and tissues between Atria and Ventricles are taking up space... so take them off and add them to the walls of heart and make stronger walls to creat stronger ventricles... I dont see why when heart gets bigger it should get weaker, as you said?

like when you work harder with your arm muscle it gets bigger and stronger... it adjusts to the amount of work it does.


Did any one work with an artificial heart? how does that work? is it the 4 pump system like a real heart or a 2 pump (2 artificial ventricles) like our theory?

 

[P Diddy]

Not really a dumb question...in fact, in afib the atria seem to be only useful for keeping coag clinics busy! On the contrary...could you imagine what a disaster mitral stenosis or regurg would be if their was not LA to enlarge?

if there were no atria, there wouldn't be a mitral valve to stenose/regurg.

i don't know if there's a good physiologic explanation out there. the way I justify atria is the 'bucket' phenomenon. you know when there's a fire and people stand in a line and pass the bucket of water to the guy who finally throws it on the fire? that way there's always a bucket of water ready for the fire, there's less of a wait period.

in the same way, atria serve as a reservoir of blood for the next cardiac cycle. after the ventricle contracts, there's already a bolus ready for the ventricles to fill again. granted, if there were no atria the bolus would come from the IVC and SVC, but this would be a continuous drip and completely passive. it would take a long time for the ventricles to fill. at low heart rates this would not be a problem and perhaps more efficient (no AV valves, etc).

at high heart rates, however, i would think that the atria are more efficient at transferring blood to the ventricle, especially since the atria contract. at normal heart rates the atrial kick contributes 25% of blood volume that the ventricle receives, but this proportion is higher at high heart rates. also, consider a noncompliant ventricle with increased end diastolic pressure. a person would go into heart failure earlier if not for atria, which can squeeze blood into the ventricle when the gradient is unfavorable for passive ventricular filling.

this begs the question of why we don't have 6 or 8 chamber hearts. i think probably there are diminishing returns. for another set of heart chambers to develop, the physiologic advantage would have to be great enough to overcome the disadvantages of more valves (clots, malfunction) and the increased size of the heart, which would leave less room in the chest cavity for other organs like the lungs, which are also important.

p diddy

 

[dataman]

Well Explained P Diddy

thank you!

 

[Firebird]

I have a gut feeling, dataman, that increasing the wall thickness would decrease efficiency. Also, there would be that much more myocardium to infarct during an ischemic episode. The most susceptible region of the myocardium to ischemia is the subendocardium, right? So if you thicken the wall, that will essentially thicken the subendocardium. Ischemia would result in a larger area of infarction.

P diddy said:

in the same way, atria serve as a reservoir of blood for the next cardiac cycle. after the ventricle contracts, there's already a bolus ready for the ventricles to fill again. granted, if there were no atria the bolus would come from the IVC and SVC, but this would be a continuous drip and completely passive.

Does blood drip into the atria? If you think about it, the atria are essentially the same thing as a two chambered heart as far as where the blood enters first is concerned. Diastole "sucks" blood into the atria, just as it would if the ventricles were the first aspect of the circuit. The pressure in the IVC/SVC would not provide enough blood to fill the atria to any significant degree. So I don't think the bucket brigade idea is exactly right, because even if nothing was pushing blood into the ventricles, they would pull a blood bolus into themselves.

As I said in my first post, I really think the purpose of the atria is to fill the ventricles to an efficiency maximum, which I think is what you were getting at when you mentioned the atrial kick providing 25% of the blood. And as we both were saying, at higher heart rates, this becomes even more significant.

 

[dataman]

Looks like the conclusion is:
The purpose of Atria is to make sure ventricles have enough blood even in higher heart rate.

 

[burton117]

That made me feel good.. thanks. I'm sure our body has the best engineer up there... it takes us thousands of years to understand it!

Ditto!!

 

[P Diddy]

Does blood drip into the atria? If you think about it, the atria are essentially the same thing as a two chambered heart as far as where the blood enters first is concerned. Diastole "sucks" blood into the atria, just as it would if the ventricles were the first aspect of the circuit. The pressure in the IVC/SVC would not provide enough blood to fill the atria to any significant degree. So I don't think the bucket brigade idea is exactly right, because even if nothing was pushing blood into the ventricles, they would pull a blood bolus into themselves.

blood does drip into the atria along a pressure differential. I invoked the bucket brigade to illustrate the point that active transfer (ie bucket brigade, atrial kick) can speed this process, making it more efficient. in the heart's case there's only one bucket, don't know if you can call that a brigade. nevertheless, i'm going to write a book about the atria called bucket brigade. it will sell like hotcakes, which I hear are quite popular among the young whippersnappers these days.

p diddy

 

[dataman]

i'm going to write a book about the atria called bucket brigade. it will sell like hotcakes, which I hear are quite popular among the young whippersnappers these days.
p diddy

Would you put my name in it too!!!

 

[Firebird]

blood does drip into the atria along a pressure differential. I invoked the bucket brigade to illustrate the point that active transfer (ie bucket brigade, atrial kick) can speed this process, making it more efficient. in the heart's case there's only one bucket, don't know if you can call that a brigade. nevertheless, i'm going to write a book about the atria called bucket brigade. it will sell like hotcakes, which I hear are quite popular among the young whippersnappers these days.

p diddy

Are you sure that blood doesn't rush into the atria during diastole rather than a constant drip?

 

[P Diddy]

Are you sure that blood doesn't rush into the atria during diastole rather than a constant drip?

sure, blood drips into the atria during diastole. constantly.

p diddy

 

[Firebird]

I stand corrected. After referencing my physiology text, I read that there is no negative pressure created during diastole and that diastolic filling is due solely to the pressure from the veins. I don't know if I missed this in physiology class, or if it wasn't mentioned, but I would never have thought the meager pressure in the venous system would ever fill the right heart adequately. Guess I should just give in to medical school and stop trying to think independently.

 

[P Diddy]

I stand corrected. After referencing my physiology text, I read that there is no negative pressure created during diastole and that diastolic filling is due solely to the pressure from the veins. I don't know if I missed this in physiology class, or if it wasn't mentioned, but I would never have thought the meager pressure in the venous system would ever fill the right heart adequately. Guess I should just give in to medical school and stop trying to think independently.

oh, it's no big deal. the heart will keep filling even if you and I disagree on the exact mechanism. however, you definitely should try to keep thinking independently, WITHOUT reference to physiology texts, every once in a while. that's how discoveries are made, when you juxtapose how things ought to be with how they actually are.

p diddy