Breathing regulation

[gabdolce]

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Hi all,

A quick question for you guys - I got a question regarding breathing regulation and I think this may be a wrong answer:

If a native of high mountains came down to sea level for the first time, what would be the net effect on his blood Pco2?

a) it would decrease
b) it would increase
c) it would increase and acidify the blood
d) there would be no net effect.

Solutions say D; I stick to my story with C - here's why:

If he is coming down from somewhere where he has biologically adapted to hypoxic environments, that means that once he comes down to sea level, these accommodations would overcompensate and make his body hypersaturated with O2. Thus, to compensate, his body would depress breathing rate and hypoventilation = acidosis [answer C].

Thoughts guys?

Thanks in advance.

 

[tendiw]

Firstly it is important to remember the body will ALWAYS act to maintain homeostasis. Due to living in a low oxygen environment, the individual would have a higher concetration of red blood cells in his system, at this point, the partial pressures of oxygen is "X%" and for CO2 its is "Y%", X+Y=100%.

When the environment is changed to one with more O2 as in that of lower sea levels, the body will try to maintain what it has (homeostasis) and the concentration of red blood cells in the body would drop accordingly, and less O2 would be taken up by the body. This is adaptation happening. The net result is the body maintains it X and Y partial pressure.

After a large meal, blood glucose levels rise, the body tries to maintain homeostasis by reducing it...which is why insulin is released to lower blood glucose to normal.

The initial effect would be the more oxygen is taken in BUT because more oxygen is available and you have more RBCs, and more CO2 is produced and released...so at the end of the day, the partial pressure would remain the same as both CO2 and O2 would increase...(before homeostasis balancing would occur).

If the question asked if CO2 levels would increase...then yes but partial pressure of CO2 and oxygen are constant

extremely high or extremely low partial pressures of oxygen and along with co2 would be harmful to the body...the body must maintain everything at and acceptable range

 

[gabdolce]

What is your distinction between Co2 "levels" and partial pressure of Co2? Those are the same things.

 

[tendiw]

What is your distinction between Co2 "levels" and partial pressure of Co2? Those are the same things.

PCO2 and CO2 are very different. PCO2 is basically the percentage or ratio composition of gas in the body that is composed of CO2...so basically if you had say 100mg of compounds in a jar and 55mg was compound A and 45mg was compound B, the partial ratio of compound A is 0.55 (found by 55mg/100mg). If you found a new jar of compound A and B, and there was 110mg of compound A and 90mg of compound B...the partial ratio of compound A is still 0.55 (found by 110mg/200mg) however the "level" of compound A is now higher, from 55mg to 110mg.

Thats the difference between "levels" and "partial ratios"

 

[gabdolce]

Ok, if I were to buy that explanation, then how do you account for the fact that in the opposite case, where the individual must acclimate to a higher altitude, his respiration increases due to hypoxia and consequently leads to alkalosis?

 

[tendiw]

The person movin from lower to higher sea levels has low hemoglobin and when they move up, they have to increase respiration to account for lower oxygen levels I. The atmosphere...the body needs to maintain homeostasis so when atmospheric oxygen drops, respiration must increase to collect more oxygen to maintain balance.

Eventually this person will adapt by getting more red blood cells (more hemoglobin)

 

[Phlame217]

Think about it as a weight lifter:

A strong man can carry a lot of weight, and therefore very little weight too. (moving from High atmosphere to low)

A weak man can carry little weight, but must work out and grow to carry heavy weight (moving from low to high atmosphere)

BTW, the immediate effects of going to low to high atmosphere is alkalosis due to low paO2 triggering hyperventilation to increase the paO2 levels (causes heavily left shift of O2 curve). The long term effect is the chronic resp alkalosis triggers the phosphofructtokinase shunt in glycolosis to produce more 2,3-BPG which aids in the right shift of the oxygen binding curve. Ultimately the kidney releases EPO triggering RBC density to increase and increasing overall oxygen carrying load.