PGY300 renal lec 5

PGY300 renal lec 5 - REGULATION OF WATER BALANCE PHYSIOLOGY...

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REGULATION OF WATER BALANCE PHYSIOLOGY 300 DR. JOHN A. KRASNEY
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READING Chapter 20, pages 642-651 Animations: Urinary System, Early Filtrate Processing pages 16-23, Late Filtrate Processing. Fluid and Electrolytes, Water Homeostasis pages 1-28 http://www.cellphys.ubc.ca/undergrad_files/30 Univ British Columbia
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Reabsorption of Water Water reabsorption is passive and follows osmotic gradients. 80% of reabsorption of water and electrolytes occurs in proximal tubule (Obligatory). Remaining ~ 20% is reabsorbed in distal parts of the nephron according to the needs of the body (Facultative).
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Facultative Reabsorption of Water by the Kidney Loop of Henle Distal Tubule Collecting Duct
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Obligatory Excretion of Osmoles In order to maintain ECF osmolarity the kidneys must excrete 600 mOsm/day depending on solute intake. If urine were always isoosmotic to plasma (300 mOsm/L) then we would have to excrete 2 L of urine per day. The kidneys concentrate the urine so we only excrete 1.5 L/day (450 mosm/L). Uosm is higher than P osm if the kidneys are concentrating the urine (Uosm/Posm).
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How can the Kidney produce a urine with such a wide range of osmolarities?
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relative medulla percentage maximal species thickness long loops urine mOsm beaver 1.3 0 495-770 pig 1.6 3 1100 human 3.0 14 1400-1480 cat 4.8 100 2100-3250 porpoise --- --- 1833 jerboa 9.3 33 >6000 desert mouse 10.7 100 5700-6400 Sea water = 1100-1150 mOsm vs Posm=300 mosm/l Renal Concentrating Ability depends upon the Thickness of the Medulla
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Interaction between the flow of filtrate through the loop of Henle (countercurrent multiplier)
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PGY300 renal lec 5 - REGULATION OF WATER BALANCE PHYSIOLOGY...

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