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Offline qazibasit

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increased heart rate
« on: 01/07/2004 17:44:52 »
During muscular exersise why the heart beat increases and why the venous return is high is it because :
The more pumping of blood is required to fulfil the oxygen requirment or Is it due to the dilation of blood vessels.

I am a bit confused in it.


 

Offline DrN

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Re: increased heart rate
« Reply #1 on: 02/07/2004 13:46:34 »
when you do exercise your muscles use up more oxygen and produce more carbon dioxide, this sends messages to the brain telling it to provide more oxygen and get rid of the carbon dioxide at a faster rate. Hence the brain relays signals to the heart to increase its capacity, which it does by beating faster and to the veins to dilate them so they can carry more deoxygenated blood away from the muscles. so everything works together rather than as separate entities.
This is quite basic, but I can't get any more detailed than this!
 

Offline qazibasit

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Re: increased heart rate
« Reply #2 on: 02/07/2004 17:14:33 »
so you think that it is due to the increase oxygen requirement.
 

Offline DrN

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Re: increased heart rate
« Reply #3 on: 02/07/2004 21:52:35 »
yes, because thats the bit that comes first, you don't start your heart beating faster to prepare yourself for exercise - your body responds to the fact that you are doing exercise. i think it is actually the increased CO2 levels that initiate the chemical signals though, which lead to these responses, although i might be wrong there. something to do with carbolic acid production? might be going off on a tangent though.

although having said that, stress can cause much the same response - faster heart beat, more oxygen pumping round the body, which increases respiration rate, and all that is caused by adrenaline - fight or flight - and this can prepare you for exercise. but i think it all comes down to those chemical signals that stimulate the symapthetic and parasympathetic nervous systems, whether they're caused physiologically by increased O2 consumption or by adrenaline secretion.
 

Offline nilmot

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Re: increased heart rate
« Reply #4 on: 03/07/2004 10:20:22 »
This topic I think has already been discussed, I'll put the sort of detail expaination if anyone don't want to search but I think there are more detail ones if you do a search on the topic "Muscle and lactic acid" or words to do with respiration...etc in it, it's all related.

That is correct fishytails, production of CO2 will decrease the pH level of the blood because it is converted to carbonic acid, it act as a stimulant. The change in pH is detected by the carotid, aortic bodies situated in the carotid arteries and the aorta.

Impulse is sent to the medulla oblongata (not sure of the spelling) of the brain where the cardio-acceleratory centre receive the impulse and send another impulse down the sympathetic nerve to the SAN(sino-atrial node) to release noradrenaline at the end of the nerve to increase the number of output made by the SAN. Therefore the heart rate increase mainly to decrease the level of CO2, and also to provide other things needed for aerobic respiration to occur.

With the dilation of the vessel,

The stimulant this time is the blood pressure, because there are more frequent heart contractions and usually harder, this change is detected by pressure receptor. Impulse is sent to the vasomotor centre in the medulla and sending impulse to dilate the vessel to allow more blood to flow through for obvious reasons.

The two described above work independently, might be similar and seem one happen because of another but it's not because of that.

The increase in ventilation rate during exercise is also affected by the same stimulant as the heart rate.

Tom
 

Offline qazibasit

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Re: increased heart rate
« Reply #5 on: 03/07/2004 16:19:24 »
so this means that decrease ph will cause acidosis and that acidosis cause vasodilation and hence the heart rate is increased so this means that both heartrate is increased by increased CO2 level and also by the vassodilation.
 

Offline HanMit

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Re: increased heart rate
« Reply #6 on: 15/08/2004 21:05:53 »
In response to:'During muscular exersise why the heart beat increases and why the venous return is high is it because:The more pumping of blood is required to fulfil the oxygen requirment or Is it due to the dilation of blood vessels.
I am a bit confused in it...' from Gazibasit posted 1st July 2004.
and
‘…so this means that decrease ph will cause acidosis and that acidosis cause vasodilation and hence the heart rate is increased so this means that both heart rate is increased by increased CO2 level and also by the vassodilation…', from Gazibasit posted 3rd July 2004


Dear Gazibasit,
I am new to this site having registered to post a message in another forum . I do find a lot of the questions and answers posted by other members in the various forums very interesting and informative.
It appears to me that you ask not one question but several questions in your two postings. I should like to make an attempt as a humble physiologist to respond to them but I should like to clarify whether the core of your queries is: ‘what is the cause of increased heart rate during exercise?’. As I understand it, you wish to know whether the response is due to the baroreceptor reflex or the chemoreceptor reflex…
(‘… so this means that both heart rate is increased by increased CO2 level and also by the vassodilation…’ Gazibasit).Am I correct in this assumption?
I can see clearly (I humbly believe) where you are coming from and should like to respond to this, but firstly let me know if my interpretation is correct. I do not wish to waste your time, Gazibasit.
In the meantime, I should like to respond to your query in relation to the increase in venous return during exercise:
Venous return to the heart is increased during exercise due to:

(a) sympathetically mediated venoconstriction (capacitance vessels/ veins) in both exercising and non-exercising parts of the body -this counteracts pooling of blood

(b) The intermittent contraction of the skeletal muscles act as a pump due to the intermittent compression of the veins that course through them (that is why guards on duty for long periods of time, need to move around a little in order to avoid fainting-I know that you know this already), this again counteracts venous pooling and moves (pushes) the blood along to the right atrium

(c) the increase in the pressure gradient due to a more negative intrathoracic pressure produced by faster and deeper rates of breathing, this sort of sucks the blood towards the right atrium

Venous return is also augmented if you lie down .

That’s all for your dime for now.
Best Regards,
HanMit:)
 

Offline chris

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Re: increased heart rate
« Reply #7 on: 16/08/2004 11:28:13 »
Nice summary Hanmit, the only one you forgot was vis-a-fronte !

Chris

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Re: increased heart rate
« Reply #7 on: 16/08/2004 11:28:13 »

 

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