Question on the Respiratory System

[premedmind]

During intense physical exercise, wouldn't the increased respiration rate promote the expulsion of CO2 from the body, ultimately acting to increase the pH of the blood?

HOWEVER; cellular respiration is also occurring of course, and the tissues of the body are releasing CO2 into the blood, ultimately decreasing the pH of the blood.

I've read in EK Bio Lecture 7 that they state "sustained physical excercise results in lowered pH of the blood chemistry"

Would the two factors balance each other out?

Take acidosis of the blood for example. The body increases the respiratory rate to expel CO2 and thus increase the blood pH. I would assume the same occurs during physical exercise.

[mosquitoman]

i think vigorous exercise implies the muscles are about to produce lactic acid - that is the body is not respirating fast enough to provide O2 for the muscles and thereby not expelling CO2 fast enough (thus lowering the ph)

[gleek]

The increased respiratory rate is effected much more by the high CO2 than by the low O2. The increased respiratory rate is in response to the rising CO2, and helps normalize the blood pH.

The decreased pH after sustained activity is, as was said, likely due to the accumulation of lactic acid.

[DrJosephKim]

Remember that when we exercise, our muscles transition from aerobic to anaerobic respiration. Hence, the production of lactic acid occurs during anaerobic respiration.

[Vihsadas]

You guys should think about which forms of ATP production are in use during exercise and otherwise.

You have glycolysis and the TCA (to simplify).

So under conditions of rest, what happens with regards to these two cycles?

Under conditions of exercise, what changes?

Think about where the majority of the CO2 is coming from, and how that would be affected based on a change in where the ATP is coming when we start exercising intensely.


Moving to Study Q&A forum

[premedmind]

Originally Posted by Vihsadas

You guys should think about which forms of ATP production are in use during exercise and otherwise.

You have glycolysis and the TCA (to simplify).

So under conditions of rest, what happens with regards to these two cycles?

Under conditions of exercise, what changes?

Think about where the majority of the CO2 is coming from, and how that would be affected based on a change in where the ATP is coming when we start exercising intensely.


Moving to Study Q&A forum

I would assume under conditions of exercise, more CO2 is produced by TCA, as opposed to rest, where less CO2 is produced by TCA. Because Pyruvate is needed for TCA glycolysis is also heightened??

The majority of the CO2 is coming from TCA (more turns of TCA would produce more CO2)...am I right?

[Vihsadas]

Originally Posted by premedmind

I would assume under conditions of exercise, more CO2 is produced by TCA, as opposed to rest, where less CO2 is produced by TCA. Because Pyruvate is needed for TCA glycolysis is also heightened??

The majority of the CO2 is coming from TCA (more turns of TCA would produce more CO2)...am I right?

Well if it happens like the way you say it does, then why do we get a build up of lactic acid during exercise? Where does lactic acid comes from?

I'll give you a piece of information that will probably be hard for you to find on google, etc.

Glycolysis produces ATP much faster than the TCA, but the TCA is much more efficient (more ATP per glucose) in producing ATP. During exercise, which do you think is more important, producing ATP faster, or more efficiently?

[spyderracing32]

Originally Posted by premedmind

I would assume under conditions of exercise, more CO2 is produced by TCA, as opposed to rest, where less CO2 is produced by TCA. Because Pyruvate is needed for TCA glycolysis is also heightened??

The majority of the CO2 is coming from TCA (more turns of TCA would produce more CO2)...am I right?

To a point but then glycolysis takes over and lactic acid fermentation begins when insufficient oxygen is delivered to the cells to sustain muscular contraction.

[Vihsadas]

Originally Posted by spyderracing32

To a point but then glycolysis takes over and lactic acid fermentation begins when insufficient oxygen is delivered to the cells to sustain muscular contraction.

Exactly. And for MCAT purposes, the majority of energy for intense exercise comes from Glycolysis. Okay, knowing that and knowing what you already know about how CO2 is produced, you can probably figure out your original question, and know why.

[premedmind]

Originally Posted by Vihsadas

Exactly. And for MCAT purposes, the majority of energy for intense exercise comes from Glycolysis. Okay, knowing that and knowing what you already know about how CO2 is produced, you can probably figure out your original question, and know why.

Well then to sum it up..

Because glycolysis operates anaerobically or aerobically, glycolysis predominates over TCA during intense exercise because insufficient oxygen is reaching the cells of the tissues. Fermentation produces lactic acid in the muscle cells. The lactic acid, along with CO2, are expelled from the cell as waste products thereby lowering blood pH.

How does that sound? Cellular respiration is my weak spot...

[Vihsadas]

I'm going to be nitpicky with what you've posted, but you're more or les son the right track.

Originally Posted by premedmind

Well then to sum it up..

Because glycolysis operates anaerobically or aerobically (Technically, glycolysis, as a process, is only anaerobic as no O2 is needed for glycolysis. Glycolysis occurs, however, both in conditions where there is oxygen and conditions where there is not much oxygen, which is what I think you meant), glycolysis predominates over TCA during intense exercise because insufficient oxygen is reaching the cells of the tissues (Glycolysis predominates over the TCA because the TCA cannot produce ATP fast enough to meet to muscular demand. If the TCA could churn out ATP much much quicker, then we wouldn't need glycolysis to predominate during exercise. I *think* that it's not the amount of oxygen that is limiting, but rather the amount of ATP that can be produced). Fermentation produces lactic acid in the muscle cells. The lactic acid, along with CO2, are expelled from the cell as waste products thereby lowering blood pH.(Yes and no. During sub-maximal exercise, the breathing rate increases to match the increased proudction of CO2 from the TCA. This is because a faster ventilatory rate serves to remove CO2 from the blood. Now, yes its true the TCA is more active during exercise, but glycolysis still predominates!! But, in sub-maximal exercise, lactic acid production doesn't cause acidosis because the CO2 buffering system can still handle the extra acid. Now, in very intense exercise, glycolysis ramps up and you have a large production of lactic acid which causes acidosis overcoming the CO2/H2CO3 buffering system. So in this case, you're respirator rate goes up severely but cannot remove enough CO2 from the blood to compensate for the increase in lactic acid.)

How does that sound? Cellular respiration is my weak spot...

So to sum up:

pH is buffered by CO2 via the carbonic anhydrase mediated CO2 <=> H2CO3 <=> HCO3 equilibrium. So an increase in CO2 is an effective increase in blood acidity. Similarly, the body works to maintain blood pH by increasing or decreasing the rate of respiration. An increased rate of respiration causes more CO2 to be removed from the blood, serving to raise blood pH.

Now,

At rest: TCA produces CO2, rest breathing rate is enough to remove enough CO2 from the body, maintaining blood pH

Sub-maximal exercise: Glycolysis ramps up slightly, TCA works slightly more, body produces more CO2, and some lactic acid, breathing rate increases to remove CO2 (thereby removing the acid effect of BOTH increase TCA CO2, and increased lactic acid).

Maximal exercise: Glycolysis overtakes TCA in terms of ATP production per time, and produces massive quantities of lactic acid. TCA is still producing CO2, but this contributes very little to acidity when compared to the lactic acid. Your breathing rate can no longer serves to remove enough CO2 from the body to buffer the pH decrease from an increased lactic acid production, and you get blood acidosis.

Hope this helps.