Lecture 07 - Concentration and Dilution of Urine

Lecture 07 - Concentration and Dilution of Urine -...

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Concentration and Dilution of Urine Urine dilution and concentration Kidneys can elaborate a urine with osmolality varying from 50-1200 mOsm/L (with normal concentrating ability) Wide range of osmolality and many other species can concentrate more urine then we can Urine dilution occurs because solute is extracted in excess of water in the thick ascending limb and the distal tubule Taking away the Na and Cl (in the thick ascending limb) In the distal convoluted tubule also taking the Na and Cl and keeping water in the lumen AND because the dilute tubular fluid thus generated is excreted, meaning that ADH is suppressed So you DO NOT insert aquaporins into the apical membrane (to NOT allow water to move into the hypotonic medullary interstitium) Requirements for dilution THE STEPS Filtration (GFR) They have to have filter to have something to dilute Delivery of filtrate to diluting segments (thick ascending limb, distal tubule) Ascending limb loop diuretics (Na and Cl pulled out, water left there) Distal tubule thiazide diuretics Where the filter is delivered to be diluted Functional diluting segments You need the sites the filtrate delivered to function Any patient who take the diuretics patient cannot dilute urine maximumly ADH suppressed After creating a dilute in the tubular fluid, not reabsorb the liquid again Disorders of osmoregulation ( hyponatremia ) develop when urine cannot be diluted - many patients cannot dilute their urine and you’ll need to o When water is ingest because when the take in urine but they still cannot dilute their urine electrolyte - if patient cannot dilute their urine it would have to be a problem with one of these steps Urine dilution and concentration (2) Urine concentration occurs when, following the dilution of the filtrate by the thick ascending limb and the distal tubule, the tubular fluid is concentrated by the reabsorption of water in the collecting duct (with ADH present) Uosm > Posm = concentration Uosm < Posm = dilution (over) Posm = 290, Uosm = 340 it is not maximum concentration The water is reabsorbed into a hypertonic medullary interstitium Medullary gradient How is the medullary gradient established? Active NaCl transport by the thick ascending limb epithelial cells Unusual arrangement of blood vessels/nephron segments in the medulla (looped structures) Urea recycling between medullary collecting ducts and the deep portions of the loops of Henle To double the number of Osmo in the medulla for the gradient urea recycling Thick ascending limb (need to be functional) Development of medullary gradient requires deposition of solute in the absence of water solute out of the lumen without water Thick ascending limbs run from the junction between inner and outer medulla back to Bowman’s capsule (for the superficial loops there is some in the cortex, but this is less than the cortex and doesn’t contribute to the medullary gradient)
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This note was uploaded on 09/14/2011 for the course PHARM rs taught by Professor Staff during the Spring '11 term at UCSD.

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Lecture 07 - Concentration and Dilution of Urine -...

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