Thus NH3 is converted to NH4 ion that doesnt get absorbed very well more water

Thus nh3 is converted to nh4 ion that doesnt get

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Thus NH 3 is converted to NH 4 ion that doesn’t get absorbed very well (more water soluble than ammonia which is lipid soluble) so it gets excreted. SCFA present in abundance will cause the NH 3 that is generated to go more towards NH 4 ion and will get excreted out. However, survival mechanism to retain that N in body ensues: the bloodstream will secrete HCO 3 - at the surface of the colonocyte in the lumen, which will take up H + being generated by production of the SCFAs and push NH 4 back to NH 3 This would be important for people on low N diets where they want to recycle as much N waste products as they can. I f in normal protein intake, you don’t need to hold on to all the N that you ingest
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1/30/2014 19 N SOURCES IN THE LI - In addition to the 3 primary N waste products (see pg.16) there are other sources of N that enter the LI: o Undigested dietary proteins (especially plant proteins) o Undigested digestive secretions (mucins, enterocytes etc) o Turnover over epithelial cells o NH 3 from the foods we eat The terminal N on Gln is very susceptible to hydrolysis in the gut and frees up that NH 3 ROLE THAT BACTERIA PLAY IN N ECONOMY - In the LI the bacteria play a role in the N economy: o Bacteria produce urease Urease converts urea to NH 3 which diffuses to the mucosal surface of the colonocyte That NH 3 is freely absorbed through the colonocyte back to the liver where it can be turned again into urea or N recycled back to AAs if the body needs it o Bacteria produce uricase Most of the uric acid that the body produces is filtered out by the kidney and ends up in urine but a portion of it diffuses into the LI where bacterial uricase can convert it to 1) NH 3 which can diffuse across or 2) creatinine of which most is cleared in urine Estimated that ¼ - 1/5 of total urea produced everyday gets recycled through the gut. Normal individuals produce ~30g urea/d - Clinical conditions resulting in elevated tissue NH 3 or elevated blood N in the brain shuts down mitochondrial respiration o When you combine α -KG with lots of NH 3 you make glutamate. This depletes α -KG from the TCA cycle to make ATP can cause coma Combination tx: Low protein diet Broad spectrum antibiotic to wipe out the bacteria in the LI so that they can’t recycle the N waste products back into NH 3 Lactulose SCFA PRODUCTION IN THE LI = pH - Bacteria thrive on NRG and N - SCFAs are produced from digestion of certain nutrients ( i.e.- water-soluble fibers & resistant starches) by bacteria.
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1/30/2014 20 o Resistant starch: substrate for bacteria, type of CHO ( e.g.- green bananas and raw potatoes) o Fermentable fibers ( i.e.- pectin, guar gum, gum arabic) - SCFAs acidify the colon which favors the conversion of NH 3 to NH 4 + which doesn’t easily diffuse across the colonocyte membrane and thus doesn’t get recycled o To remedy this, HCO 3 - is secreted at the surface of the brush border to bring the pH back up to keep the ammonia in NH 3 form where it is more easily taken up HOW BACTERIA RECYCLE N VIA LACTULOSE -
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  • Spring '14
  • Knutson,MitchellD
  • Trp

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