NextStep FL 4, B/B Q8 - Causes of low blood pH

[biancadoc]

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Which of the following could NOT explain a patient who presents with a blood pH of 7.0?
A.
Anaerobic respiration leading to lactic acid buildup
B.
Hypoventilation
C.
Carbonic anhydrase working only in the reverse direction
D.
Underproduction of bicarbonate

Answer is C.

This is confusing me a bit. I get why carbonic anhydrase working in reverse wouldn't lower the pH...less H+ produced means higher pH. But doesn't underproduction of bicarb basically have the same outcome?

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

Since H+ and bicarb are made in the same reaction, wouldn't less bicarb mean less H+ and higher pH too? Is this just a case of C being the best choice as opposed to the only choice?

 

[Neuroplasticity]

Underproduction of bicarbonate causes a right shift in the reaction: H2CO3 --> HCO3- + H+, producing more protons and lowering pH.

If carbonic anhydrase only works in the reverse direction, carbonic acid will be reduced, causing a left shift in: H2CO3 --> HCO3- + H+, reducing protons and raising pH.

 

[biancadoc]

Got it, perfect answer. Seems totally obvious now...I am so very tired.

 

[Neuroplasticity]

Just keep working hard and you'll make it!

 

[Spectar]

Underproduction of bicarbonate causes a right shift in the reaction: H2CO3 --> HCO3- + H+, producing more protons and lowering pH.

If carbonic anhydrase only works in the reverse direction, carbonic acid will be reduced, causing a left shift in: H2CO3 --> HCO3- + H+, reducing protons and raising pH.

Just a quick question... wouldn't the passage have to define what they count as "reverse?" Since the enzyme works in both directions (like all enzymes)?

 

[Neuroplasticity]

Just a quick question... wouldn't the passage have to define what they count as "reverse?" Since the enzyme works in both directions (like all enzymes)?

I believe you are correct.

 

[DaAlienist]

Just a quick question... wouldn't the passage have to define what they count as "reverse?" Since the enzyme works in both directions (like all enzymes)?

Would not the typical fwd reaction be the default "forward" and the reverse be the default "reverse?" For example we typically right the bicarb buffer as

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

This is also how they present it in the passage, I assume? So, haven't they given you what forward and reverse is? If the reaction is not given, would it be fair for the AAMC to expect me to assume the equation above is considered forward when read left to right?