TPR bio passage - Heme metabolism

[Monkeymaniac]

I've been having difficulty understanding one of the questions presented in "Heme Metabolism" passage of Metabolic Components chapter.

The passage talks about a genetic disease called Congenital Erythropoietic Porphyria (CEP). Basically a person with CEP produces some concentration non-functioning heme groups, which casues the degradation of red blood cells with these faulty heme groups.

One of the question asks:
Based on information in the passage, which of the following statements is FALSE?

The answer is:
Persons suffering from CEP exhibit a lowered arterial pO2 (that's partial pressure of O2).

It says that the reasoning behind is that

The partial pressure of oxygen is determined only by the amount of oxygen dissolved in the blood, not by the amount of oxygen bound to hemoglobin.

What's throwing me off is that I've always thought that although lung is filled with oxygen, oxygen in the blood is mostly carried by red blood cells, and thus oxygens dissolved in blood are mostly bound to hemoglobin. What exactly am I missing here? Thanks in advance.

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[RogueUnicorn]

you're using dissolved in 2 different contexts. when they are saying oxygen is dissolved in blood, they mean literally dissolved into the liquid of the solution, the way sugars are dissolved in solution. oxygen bound to hemoglobin is not considered 'dissolved,' it's considered 'bound'

 

[Charles_Carmichael]

you're using dissolved in 2 different contexts. when they are saying oxygen is dissolved in blood, they mean literally dissolved into the liquid of the solution, the way sugars are dissolved in solution. oxygen bound to hemoglobin is not considered 'dissolved,' it's considered 'bound'

Yup, this is true. Whenever you see mention of pO2 levels, etc, with regards to respiratory physio, they're talking about dissolved O2 (ie. the gas that's dissolved in blood, not bound to Hb).

 

[medking]

I've been having difficulty understanding one of the questions presented in "Heme Metabolism" passage of Metabolic Components chapter.

The passage talks about a genetic disease called Congenital Erythropoietic Porphyria (CEP). Basically a person with CEP produces some concentration non-functioning heme groups, which casues the degradation of red blood cells with these faulty heme groups.

One of the question asks:
Based on information in the passage, which of the following statements is FALSE?

The answer is:
Persons suffering from CEP exhibit a lowered arterial pO2 (that's partial pressure of O2).

It says that the reasoning behind is that

What's throwing me off is that I've always thought that although lung is filled with oxygen, oxygen in the blood is mostly carried by red blood cells, and thus oxygens dissolved in blood are mostly bound to hemoglobin. What exactly am I missing here? Thanks in advance.

One more thing to point out. Don't get confused with pO2 and O2 content of the blood. Two different things.

 

[Monkeymaniac]

Thank you guys for the help. After digger a bit more, I found out that only 98% of the oxygen in blood are bound to hemoglibin, and the rest are indeed dissolved in the blood.

One more thing to point out. Don't get confused with pO2 and O2 content of the blood. Two different things.

medking, in our body, aren't V and RT from the ideal gas law, P[V]=n[RT], pretty much constant? So the partial pressure of oxygen in our body is proportional to the concentration of the oxygen?

 

[TieuBachHo]

I am thinking that they mean the relative pO2 stays the same although the total O2 consumption decreases. The total pO2 accounts for both dissolved and bound oxygen in the blood. For example, although the ascended O2 consumption descreases, but the body's relative pO2 is the same.