NBME 20 Failure of the Na+–K+ pump (NBME Answers)

Retired NBME 20 Answers

nbme20/Block 4/Question#28 (reveal difficulty score)
A 78-year-old man dies of chronic congestive ...
Failure of the Na+–K+ pump 🔍 / 📺 / 🌳 / 📖
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submitted by ∗nwinkelmann(366)

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This explains it really well with a picture: https://www.med.illinois.edu/m2/pathology/PathAtlasf/Atlas01.html.

Hydropic change = one of the early signs of cellular degeneration in response to injury that results in accumulation of water in the cell. Hypoxia/ischemia leads to decease in aerobic respiration in the mitochondria and decreased ATP production due to failure of the Na+/K+ ATPase leading to Na+ and water diffusion into the cell. Individual tubule cells appear swollen and "empty" with almost occluded lumen, glomerulus is hypercellular.

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dickass it's basically from pathoma chapter 1: cellular injury causes swelling +7

md_caffeiner @dickass you why arent you on every q stem? +2

mangotango do you mean "causing failure of the Na+/K+ ATPase" instead of "due to failure of Na+/K+ ATPase..." ? The low ATP is due to dec aerobic respiration, I believe. +2

fatboyslim @Mangotango yes exactly. Na/K ATPase stops working due to the lack of ATP. I think nwinkelmann mixed it up +1

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submitted by ∗xxabi(293)

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Swelling of the cell (e.g., hydropic degeneration): tissue ischemia → decreased ATP production → decreased Na+/K+ ATPase and Ca2+pump activity → diffusion of Na+ and water into the cell → cellular swelling

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endochondral1 can someone explain how to cross out the other choices> +1

endochondral1 what is hydropic degneration and where do i learn about it? why is it not the loss of plasma membrane integrity? +1

shaeking Endochondral1, I had the same question. I tried figuring it out and this is what I came up with. The CHF and congestion of the lungs is reducing the amount of oxygen getting to the renal cells. With hypoxia there is decreased aerobic resp in mitochondria with decreased ATP. Without ATPase Na builds up and water follows. As far as the loss of membrane integrity. I think it would cause cellular destruction not just hydropic changes. This is my best guess. +2

charcot_bouchard Membrane damage is irreversible stage of cellular injury. if membrane is damaged cell is dying & it will shrink. or totally destroyed by inflammation. they are specifically asking hydropic changes ie cellular swelling. which is the 1st sign of reversible cell injury due to failure of Na/K pump +2

winelover777 @endochondral1 Chapter 1 of Pathoma. Also FA 2019 p207 describes hydropic degeneration without saying those exact words in the first bullet under reversible cell injury. +1

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submitted by ∗qfever(67)

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Pathoma 2018 edition page 4 chapter 1 - Cellular Injury - III. Reversible & irreversible cellular injury - B.1.

I had difficulty trying to figure out what hydropic change means though...

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bharatpillai i swear i've done the same question before on uworld/ one of the previous NBMEs and the answer to that was intracellular Ca accumulation. +2

mangotango @bharatpillai that's also true! Dec ATP >> dec activity of Ca2+ and Na+/K+ pumps >> cellular swelling (earliest morphologic manifestation of reversible cell injury), mitochondrial swelling --- FA, pg 207 Na+/K+ ATPase inhibited >> inc intracellular Na+ >> dec activity of Ca2+/3Na+ exchange pump >> inc intracellular Ca2+ --- this is the same way digoxin works in the heart! +1

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submitted by andremosq(9)

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Question about cellular injury:

Hydropic change means swelling. Patient has a hypoxic change too.

Reversible cell injury: Decrease ATP --> Decrease activity of Ca2+ and Na+/K+ pump -->cellular swelling (earliest morphologic manifestation), mitochondrial swelling.

FA2020. pag 207

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