NBME 22 Absorption of nitrogenous products from the gastrointestinal tract (NBME Answers)

NBME 22 Answers

nbme22/Block 3/Question#31 (reveal difficulty score)
A 35-year-old man is admitted to the hospital ...
Absorption of nitrogenous products from the gastrointestinal tract 🔍 / 📺 / 🌳 / 📖
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submitted by ∗yotsubato(1208)

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What do you use to treat Hepatic Encephalopathy? Lactulose. What does that do, it acidifies NH3 in the GI tract into NH4+ and promotes loss of the nitrogenous products that cause encephalopathy. This is how you remember this process.

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carmustine FA 2019 pg 385 "Triggers --> increased NH3 production & absorption (due to GI bleed, constipation, infection)." +4

drzed To add, you can also use rifaximin which will act as a antibiotic decreasing the production of NH3 from gut flora. Same concept. +3

nevergoingtopost Lactulose is the correct treatment for hepatic encephalopathy, but it actually acidifies the GI tract (colonic metabolism of lactose → lactate). This favors the NH3 form and decreases NH4+. NH3 is then additionally pulled from the blood into the gut. +2

abhishek021196 @nevergoingtopost - lactulose actually increases NH4+ generation : Pg 401 FA 2021. +

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submitted by dolphinpanda(3)

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Increased bleeding in the GI tract also delivers hemoglobin and other proteins to the tract which are broken down to nitrogenous products and then absorbed

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submitted by ∗dr.xx(176)

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The most important waste product is ammonia (NH3). This small molecule crosses the blood–brain barrier and is absorbed and metabolised by the astrocytes, a population of cells in the brain that constitutes 30% of the cerebral cortex. Astrocytes use ammonia when synthesising glutamine from glutamate. The increased levels of glutamine lead to an increase in osmotic pressure in the astrocytes, which become swollen. There is increased activity of the inhibitory γ-aminobutyric acid (GABA) system, and the energy supply to other brain cells is decreased. This can be thought of as an example of brain edema of the "cytotoxic" type.

https://en.wikipedia.org/wiki/Hepatic_encephalopathy#Causes

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submitted by ∗d_holles(218)

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Can portal HTN contribute to hepatic encephalopathy?

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djtallahassee Sorry for the late add. Portal system does contribute to hepatic enceph ESPECIALLY when there is a TIPS or shunt that bypasses the liver. However before, it won't directly contribute to more NH3+ +2

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