BIO question

[elz787]

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when your blood concentration of CO2 increases, will your rate of breathing increase or decrease?

i'm a bit confused because I read somewhere that if you hyperventilate it increases the CO2 concentration in bllood

 

[sgdorfl90]

when the CO2 conc. increases in your body, the body senses this, and not the lack of O2 in the body. As a result, a message is sent to the respiratory center involving phrenic nerve(which increases diaphragm contraction), and as a result, it increases respiration. Hope that helps.

 

[dat_student]

when your blood concentration of CO2 increases, will your rate of breathing increase or decrease?

i'm a bit confused because I read somewhere that if you hyperventilate it increases the CO2 concentration in bllood

hyperventilation causes acidosis

 

[dat_student]

when the CO2 conc. increases in your body, the body senses this, and not the lack of O2 in the body. As a result, a message is sent to the respiratory center involving phrenic nerve(which increases diaphragm contraction), and as a result, it increases respiration. Hope that helps.

semi-correct

 

[mochafreak]

Hyperventilation causes alkalosis, it is the body's response to acidosis.

 

[elz787]

so, in one of kaplans answers it said that increasing hyperventilation increases the co2 concentration in blood, this is FALSE right?>

 

[mochafreak]

Hey guys, I asked ISU Steve to come on over...he's an RT and horribly overqualified to answer this question...I'm only a lowly EMT-B. 😉

 

[ISU_Steve]

OK.....As MochaFreak said, i'm a respiratory therapist....this is my area of expertise.

A few points:
1. pH is inverse to the CO2 level; increase the CO2, the pH drops (acidosis); decrease the CO2, the pH raises (alkalosis).
2. CO2 level (specifically PaCO2 in the clinical setting) is a inverse marker of ventilatory function (CO2 raises as ventilation decreases; ventilation increases and CO2 decreases), and the respiratory drive is (normally) based off of CO2 levels.
3. There are chemoreceptors in the brain that sense increased levels of [H+] ions in the CSF (an indirect measure of CO2 levels- hydrogen ion concentration increases (the pH drops (acidosis)) and increase the drive to breath by stimulating the dorsal respiratory groups and ventral respiratory groups in the medulla.
So, yes increased CO2 will normally cause hyperventilation.
But increased ventilation (hyperventilation) decreases CO2 levels. Here's a trick I used to teach my RT students:
Blow = low
(where blow is increased ventilation) (and low is low CO2)

By the way, get used to seeing more of me over here.....I've decided to push my DAT up to January of next year instead of waiting until closer to the time I apply.

 

[ISU_Steve]

MochaFreak, don't knock yourself for being "just" an EMT-B. I have a lot of respect for EMT's in general and especially for you in particular.

 

[dat_student]

Hyperventilation causes alkalosis, it is the body's response to acidosis.

you are absolutely right. Should have thought a bit more before posting a response. I should have said "hyperventilation is the response to acidosis" (as you mentioned). If I remember it correctly it's the drop in pH and NOT the change in [CO2] that causes hyperventillation. That was the part of the argument I didn't like.

 

[ISU_Steve]

It's a drop in the pH of the CSF that provokes it, if you want to get technical, but that's a secondary response to the raise in the CO2 in the blood for two reasons:
1. Acidosis is most commonly caused by one of two things: excessive CO2 (respiratory acidosis (i.e. hypoventilation/respiratory failure) or insufficient HCO3- (metabolic acidosis). In this cases, let's forget the metabolic variant because it will just confuse things even further.
2. because the blood-brain barrier is permeable to CO2, but not HCO3- or H+ ions. When the PaCO2 of the blood rises, CO2 rapidly crosses the blood-brain barrier (because of the concentration gradient). Once in the CSF, CO2 reacts with water to form HCO3 and H+ (via the breakdown of H2CO3 (carbonic acid):

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

The hydrogen ions generated in this way stimulate the chemoreceptors, not the CO2, but the rise in CO2 levels due to decreased ventilation is the indirect cause.

Does this clarify things?

 

[elz787]

Thanks!

 

[ISU_Steve]

No problem....anytime.

 

[dat_student]

It's a drop in the pH of the CSF that provokes it, if you want to get technical, but that's a secondary response to the raise in the CO2 in the blood for two reasons:
1. Acidosis is most commonly caused by one of two things: excessive CO2 (respiratory acidosis (i.e. hypoventilation/respiratory failure) or insufficient HCO3- (metabolic acidosis). In this cases, let's forget the metabolic variant because it will just confuse things even further.
2. because the blood-brain barrier is permeable to CO2, but not HCO3- or H+ ions. When the PaCO2 of the blood rises, CO2 rapidly crosses the blood-brain barrier (because of the concentration gradient). Once in the CSF, CO2 reacts with water to form HCO3 and H+ (via the breakdown of H2CO3 (carbonic acid):

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

The hydrogen ions generated in this way stimulate the chemoreceptors, not the CO2, but the rise in CO2 levels due to decreased ventilation is the indirect cause.

Does this clarify things?

Thanks so much. Everything is now clear. This post helped me learn so much about "mixed acidosis", "respiratory acidosis", "metabollic acidosis", "acid-base nomogram" etc. It's been a long time since I took my medical physiology class. Computer Science has erased most of my biology knowledge. ouch! Thanks again for everything.

 

[ISU_Steve]

If you need me to go over anything else, please let me know. I used to teach blood gas analysis and physiology to RT students and I really enjoy teaching so I am more than happy to go over anything you might need me to.

 

[dat_student]

If you need me to go over anything else, please let me know. I used to teach blood gas analysis and physiology to RT students and I really enjoy teaching so I am more than happy to go over anything you might need me to.

Thanks so much.