Kidney 2 - Mammalian kidney function (continued) The...

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Mammalian kidney function (continued) The proximal tubule site of reabsorption of about 70% of the filtered urine via transport of Na andCl (most important solute) virtually all amino acids and sugars are reabsorbed, but their osmotic effect is negligible. reabsorption is isotonic (because the PT membrane is so permeable to water), so volume but not osmotic concentration changes also the site of secretion of various organic acids (e.g., bile salts), hormones (e.g., epinephrine, acetylcholine, histamine) and drugs (penicillin, salicylate, morphine)--molecules that are too large to be filtered H + is also secreted into the urine--especially when you are acidotic Net result: Recovery of 70% of filtered water and NaCl Recovery of all filtered sugars (glucose) and amino acid Adjustment of pH Excretion of poisons No change in osmolarity of urine! The loop of Henle this segment is found for the first time in the birds and mammals produces the conditions that allow the production of a urine that is hypertonic to the blood for the first time in the vertebrates--important, but not vital, to terrestriality because the reptiles don't have one
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consists of three segments of very different morphology and permeability descending limb has a very high water permeability , low NaCl permeability because the extra-tubular fluids are hypertonic (see below), water is reabsorbed from the urine as it descends through the descending limb thus, the urine volume is reduced and its osmotic concentration increases before the urine enters the next segment of the loop thin ascending limb this tubule has a very high NaCl permeability and low water permeability because the NaCl concentration of the urine is greater than that the extra-tubular fluids (see below), NaCl diffuses out of the thin limb , so the urine starts to be diluted again, but the extra-tubular fluids become saltier thick ascending limb this tubule has a very low NaCl and water permeability , but active reabsorption of NaCl takes place produces an even more dilute urine by the time it enters the distal tubule so. ...the net result of passage through the loop of Henle is reduction in the volume of the urine and also a reduction in its osmotic concentration--thus, urine entering the distal tubule is hypotonic to the urine that left the proximal tubule so. ...how does the loop of Henle produce the conditions that
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This note was uploaded on 03/30/2010 for the course BSC BSC2011 taught by Professor Evans during the Spring '10 term at École Normale Supérieure.

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Kidney 2 - Mammalian kidney function (continued) The...

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