strive01

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Jan 13, 2007
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I was just wondering if someone could take the time to explain to me to a somethings i am confused about on respiration. So I get the reaction that is happening in hemoglobin co2 + h2o <==> hc03- + H+, now what i dont understand are some critical thinking questions about it like how does increased repirtory rate be the negative feedback for both a decrease in pH and a decrease in pO2. if you have increased pc02 concentration why the pH decreases (is that just lechat principle that will move the equation to the right?) is that the same reasoning for why when co2 is exhaled by the lungs, the amount of carbonic acid int he blood is decreased and the pH of the blood increases and becomes more alkaline?
 

rocuronium

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May 11, 2008
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Respiratory rate is primarily controlled by carbon dioxide levels (i.e. PaCO2). Chemoreceptors sense the level of carbon dioxide and attempt to maintain it at a constant level. If the level is too high, respiratory rate increases and more carbon dioxide is expired. If the level is too low, respiratory rate decreases and the the blood CO2 levels rise.

Oxygen will only affect the respiratory rate if the PaO2 is very low. In healthy people, respiratory rate is influenced primarily by PaCO2.

Higher levels of carbon dioxide do cause a right shift in the formula as you mentioned.
 

vandyam

Vulnera Sanentur
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Jun 17, 2009
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I understand this concept pretty well (after having missed a couple questions on it during a practice test), but I just wanted to clarify: If your respiratory rate increases, this means you are getting rid of CO2 at a faster rate. Therefore, PH increases (becomes more basic) b/c the equation is shifting to the left, right? (no pun intended)
 

stockraider

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Oct 5, 2008
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I was just wondering if someone could take the time to explain to me to a somethings i am confused about on respiration. So I get the reaction that is happening in hemoglobin co2 + h2o <==> hc03- + H+, now what i dont understand are some critical thinking questions about it like how does increased repirtory rate be the negative feedback for both a decrease in pH and a decrease in pO2. if you have increased pc02 concentration why the pH decreases (is that just lechat principle that will move the equation to the right?) is that the same reasoning for why when co2 is exhaled by the lungs, the amount of carbonic acid int he blood is decreased and the pH of the blood increases and becomes more alkaline?
ok let's work backward here, remember hyperventilation is IN RESPONSE to an acidic ph, so it works to increase ph....this is probably what you mean by negative feedback--->low ph causes hyperventilation which in turn causes the ph to increase. ok now the equation co2 + h2o <==> hc03- + H+ can be seen to shift to the left when co2 dissapears due to hyperventilation. when the equation shifts to the left, you get away from H+ (on the right) hence increasing blood ph, when you have a lot of co2 in the blood, the same principle applies and the equation shifts to the right, decreasing blood ph. also remember for MCAT puproses a decrease in pO2 almost always implies an increase in pCO2, which means the blood becomes more acidic. this can be illustrated with blood vessels: a high pCO2 in the blood makes the body believe there is low oxygen in blood, so blood vessels DILATE to expand the surface area that for oxygen to get into the tissues. when CO2 is low, blood vessels constrict because the body assumes low CO2 means an adequate supply of oxygen is in the blood. this is why when we get rid of too much CO2 with hyperventilation we feel light headed and dizzy almost immediately, our blood vessels in the brain are constricting which occludes vital cerebrovascular supply of oxygen to the brain.

just remember this: hi co2, low ph and hi o2, hi ph..this is how your aortic and central chemoreceptors regulate things.
 

vandyam

Vulnera Sanentur
5+ Year Member
Jun 17, 2009
483
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ok let's work backward here, remember hyperventilation is IN RESPONSE to an acidic ph, so it works to increase ph....this is probably what you mean by negative feedback--->low ph causes hyperventilation which in turn causes the ph to increase. ok now the equation co2 + h2o <==> hc03- + H+ can be seen to shift to the left when co2 dissapears due to hyperventilation. when the equation shifts to the left, you get away from H+ (on the right) hence increasing blood ph, when you have a lot of co2 in the blood, the same principle applies and the equation shifts to the right, decreasing blood ph. also remember for MCAT puproses a decrease in pO2 almost always implies an increase in pCO2, which means the blood becomes more acidic. this can be illustrated with blood vessels: a high pCO2 in the blood makes the body believe there is low oxygen in blood, so blood vessels DILATE to expand the surface area that for oxygen to get into the tissues. when CO2 is low, blood vessels constrict because the body assumes low CO2 means an adequate supply of oxygen is in the blood. this is why when we get rid of too much CO2 with hyperventilation we feel light headed and dizzy almost immediately, our blood vessels in the brain are constricting which occludes vital cerebrovascular supply of oxygen to the brain.

just remember this: hi co2, low ph and hi o2, hi ph..this is how your aortic and central chemoreceptors regulate things.
This was a kick*ss explanation.