60 Countercurrent & Secretion

60 Countercurrent & Secretion - PSL302: Lecture 60,...

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Countercurrent & Secretion Outline - Reabsorption - Countercurrent multiplier system - Secretion, excretion & clearance - Secretion of H + & K + - Excretion and clearance - Measurement of GFR - Clearance of (i) Inulin (ii) Urea (iii) Creatinine (iv) Para-aminohippuric Acid (PAH) (v) Glucose Reabsorption Medullary osmotic gradient Countercurrent multiplier system PSL302: Lecture 60, by Perumalla Wed. Mar. 16, 2011 1 of 9
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Cortex Medulla No osmotic gradient (mOsm) Fluid enters tubule Water moves out of descending limb by osmosis Active transport of Na + , Cl ± , K + ions into medullary interstitial fluid increases osmolarity Peritubular fluid Tubular fluid Fluid Iso-osmotic state in descending limb; osmotic difference between descending and ascending limbs More fluid enters tubule, pushing fluid through by bulk flow Active transport of Na + , Cl ± , K + ions into Medullary interstitial uid increases osmolarity 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 Na + Cl ± K + 300 400 200 300 300 300 300 400 200 400 200 400 200 300 300 H 2 O H 2 O 300 400 200 400 400 400 400 400 200 400 200 400 200 300 300 300 400 200 300 300 400 400 400 400 400 400 400 200 300 300 Na + Cl ± K + 1 2 3 4 1 2 3 4 Osmotic gradient established (mOsm) Water moves out of descending limb by osmosis Iso-osmotic state in descending limb; osmotic difference between descending and ascending limbs More water enters tubule and process continues System is in steady state 300 350 150 300 300 400 400 500 300 500 300 350 150 200 300 H 2 O H 2 O H 2 O 300 350 150 350 350 500 500 500 300 500 300 350 150 200 300 300 300 100 300 500 900 900 700 500 300 100 300 7 1200 1200 1100 1400 1400 5 5 6 7 Summary of counter-current multiplier 1. Fluid in proximal tubule = 300 mOsm 2. The osmolarity of the ±uid in descending limb as it descends, osmolarity of the ±uid in ascending limb as it ascends 3. The ±uid in distal tubule is hypo-osmotic (100mOsm), cortical interstitial ±uid is iso-osmotic , (300mOsm) and the medullar interstitial ±uid becomes ly hyper-osmotic from cortex to renal pelvis. 4. Length of the loops of Henle is related to concentration of the renal medulla (Kangaroo rats vs. Beavers) Vasa recta: countercurrent exchanger PSL302: Lecture 60, by Perumalla Wed. Mar. 16, 2011 2 of 9
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Result of counter-current multiplier - Fluid in proximal tubule = 300mOsm - Fluid in descending limb = osmolarity as it descends - Osmolarity = interstitial ±uid - Osmolarity > descending limb - Fluid in ascending limb = osmolarity
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60 Countercurrent & Secretion - PSL302: Lecture 60,...

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