acid and respiratory rate

[happyfellow]

I came across this question and got it correct but I'm not sure if my reasoning is sound.

What effect does lactic acid have on respiratory rate?

Answer: it increases it.

Whenever I see a question like this should I be thinking that the acid is ultimately coming from too much CO2 and therefore I need to blow it off by increasing my respiratory rate? That was my reasoning and I'm unsure about it

thanks in advance

-happy

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[PhilIvey]

I came across this question and got it correct but I'm not sure if my reasoning is sound.

What effect does lactic acid have on respiratory rate?

Answer: it increases it.

Whenever I see a question like this should I be thinking that the acid is ultimately coming from too much CO2 and therefore I need to blow it off by increasing my respiratory rate? That was my reasoning and I'm unsure about it

thanks in advance

-happy

No. Too much lactic acid is a sign that there isn't enough O2 being delivered to the cells. Consequently, they resort to anaerobic respiration. The body's response is to increase the respiratory rate in order to supply sufficient O2 to these cells. Now, the acid from from lactic acid comes from fermentation. Do not mistake this with the increase in H+ concentration in the blood due to increased CO2 levels. Both effects contribute. If you have decreased O2 or increased CO2 the respiration rate will increase. However, it's more sensitive to CO2 change.

 

[RogueUnicorn]

No. Too much lactic acid is a sign that there isn't enough O2 being delivered to the cells. Consequently, they resort to anaerobic respiration. The body's response is to increase the respiratory rate in order to supply sufficient O2 to these cells. Now, the acid from from lactic acid comes from fermentation. Do not mistake this with the increase in H+ concentration in the blood due to increased CO2 levels. Both effects contribute. If you have decreased O2 or increased CO2 the respiration rate will increase. However, it's more sensitive to CO2 change.

no the body will respond to a drop in pH before it ever responds to a drop in O2. the compensatory mechanism is to blow off CO2 to reduce the over H+ concentration

 

[PhilIvey]

no the body will respond to a drop in pH before it ever responds to a drop in O2. the compensatory mechanism is to blow off CO2 to reduce the over H+ concentration

I didn't say it was equally, I said the body is more sensitive, hence it responds to H+. However, he thought the H+ produced by lactic acid is what the body is responding to. This is incorrect. The increase in respiration is due to a build up of CO2 which drops the pH and that's what the body responds to. However, a secondary effect is that the lack of O2 drives it. I never said it responded to O2 primarily. OP thought the H+ from lactic acid drives the respiration but it's the H+ from CO2 build up. The body does respond to O2 drops, just not as fast. There are O2 sensors, however, the CO2 sensors are more sensitive and what is activated directly as I'm sure you already know.

 

[RogueUnicorn]

I didn't say it was equally, I said the body is more sensitive, hence it responds to H+. However, he thought the H+ produced by lactic acid is what the body is responding to. This is incorrect. The increase in respiration is due to a build up of CO2 which drops the pH and that's what the body responds to. However, a secondary effect is that the lack of O2 drives it. I never said it responded to O2 primarily. OP thought the H+ from lactic acid drives the respiration but it's the H+ from CO2 build up. The body does respond to O2 drops, just not as fast. There are O2 sensors, however, the CO2 sensors are more sensitive and what is activated directly as I'm sure you already know.

edit: guess i should have read this more closely

 

[Charles_Carmichael]

Think of it via the carbonic anhydrase reaction:

H+ + HCO3- <-> H2CO3 <-> CO2 + H2O

In lactic acidosis, the increase in H+ will push the reaction to the right, generating more CO2. The acidity is not coming from excessive CO2 levels; rather, the excessive CO2 levels are a result of acidosis. The body's compensatory mechanism for this is to increase ventilation rate to get rid of the excess CO2. By doing this, you're constantly depleting CO2 and pushing the reaction even further to the right. All of these things work together to get rid of the acidosis (ie. bring the H+ levels back to normal).

Don't even think about O2 when answering this question.

Hope this helps.

 

[PhilIvey]

Think of it via the carbonic anhydrase reaction:

H+ + HCO3- <-> H2CO3 <-> CO2 + H2O

In lactic acidosis, the increase in H+ will push the reaction to the right, generating more CO2. The acidity is not coming from excessive CO2 levels; rather, the excessive CO2 levels are a result of acidosis. The body's compensatory mechanism for this is to increase ventilation rate to get rid of the excess CO2. By doing this, you're constantly depleting CO2 and pushing the reaction even further to the right. All of these things work together to get rid of the acidosis (ie. bring the H+ levels back to normal).

Don't even think about O2 when answering this question.

Hope this helps.

Yep, I guess I wanted him to have an overall understanding. However, for MCAT purposes, you're right in saying it is unnecessary.