Lesson Video 4-3, slide 4

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Lesson Video 4-3, slide 4

Post by ArielM » Wed Dec 13, 2017 8:59 pm

This question is from Lesson Video 4-3, slide 4.

If a person donates blood on January 1, on which day are they most likely to have elevated amounts of erythropoietin in circulation?

A. Feburary 6
B. March 4
C. May 2
D. July 1
The answer is C, May 2.

Under normal circumstances, I would understand how this answer is true. If this was a normal case where a person describes the normal 120 day life cycle of their red blood cells, then naturally, the red blood cells would die off then be naturally replenished, over a 120 day timeframe. So this is a process. This process is also further elucidated in a wikipedia article about Erythropoietin. The article states, "Erythropoietin levels in blood are quite low in the absence of anemia, at around 10 mU/mL. However, in hypoxic stress, EPO production may increase up to 1000-fold, reaching 10 000 mU/mL of blood". Furthermore, the passage states, "typical Red blood cells will circulate for about 120 days, after which time they undergo apoptosis." -the conditions described in the passages are under normal circumstances.

However, the question states, "If a person donates blood"- donation of blood is not considered a normal circumstance. The natural process of red blood cell production has been interrupted. The Red Blood Cells were prematurely taken away from the body, interrupting the natural 120 day lifespan, the blood count is now low- this condition (post blood donation) can be considered as a state of artificial hypoxia.

Therefore, under these hypoxic conditions, Erythropoietin levels would increase to compensate for the lack of O2 in the Human body. I don't understand how a person could go for four months without oxygen in these hypoxic conditions. The person loses blood and they continue along with low red blood cell count representative of and equivalent to the normal EPO levels, like nothing happened? It does not make sense for the body to work that way- to continue operating normally in abnormal conditions, like hypoxia. Wouldn't the Erythropoietin levels adjust to abnormal hypoxic circumstances? I would understand the answer to this question if the question were asking, "at which point in time would the blood levels be replenished."- But again, these are not normal circumstances, and the question is asking about the EPO levels, not the time when red blood cells will be replenished.

So when a person donates blood, wouldn't their Erythropoietin levels be significantly higher than normal- post blood donation- in order to compensate for the hypoxic circumstances? Would you not see high Epo levels if you tested a person's blood immediately after their blood donation?
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Re: Lesson Video 4-3, slide 4

Post by NS_Tutor_Andrew » Thu Dec 14, 2017 1:59 pm

Hi Ariel,

Thanks for the excellent question! You're absolutely right that we would expect an EPO surge right after blood donation, and that actually has been documented in research (here's one study, and here's another). However, this question has no answer choice for sometime in January, so it must be getting at something else. The idea is that there will be a surge of blood cell production (corresponding to an EPO surge) immediately after donation, and then another surge 120 days later when those blood cells are themselves replaced. Eventually, of course, we'd expect this process to be attenuated because everything in biology is noisy.

Hope this clarifies things, and if not, please feel free to follow up!
Andrew D.
Content Manager, Next Step Test Prep.
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Joined: Mon Oct 02, 2017 9:15 pm

Re: Lesson Video 4-3, slide 4

Post by ArielM » Thu Dec 14, 2017 6:01 pm

Hi Andrew,

You gave a wonderful explanation, I clearly understand now. The question is looking for the second Epo surge- 120 days later. 120 days after Jan 1 should be approximately May 2- and this would be where we would expect to see the second Epo surge. Thank you very much.

-Ariel Morrow
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