urine osmolarity

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  • 1. URINE OSMOLARITY PBL TUTOR(Group-IV) Dr.Rupesh Shrestha Presenter Lalit karki

2. Case correlation Sudhir,13 years boy presents with puffy face,haematuria,frothy urine and his urine amount has markedly decresed. He was primarily confirmed as the case of acute on chronic renal failure. Dr. Anish wanted to do urine for osmolarity and fractional excretion of sodium. 3. Introduction Urine osmolarity is the number of dissolved particles per unit of water in the urine. Urine concentration An index of the concentration of osmotically active particles,particularly chloride, sodium, urea, glucose and potassium in the urine. Minimum urine concentration:50 - 70 mOsm / L Maximum urine concentration :1200 - 1400 mOsm / L 4. Excreting a dilute urine Decrease water reabsorption Continue electrolyte reabsorption Mechanism: decreased ADH release and reduced water permeability in distal and collecting tubules 5. Excreting a concentrated urine Continue electrolyte reabsorption Increase water reabsorption Mechanism: Increased ADH release which increases water permeability in distal and collecting tubules High osmolarity of renal medulla Countercurrent flow of tubular fluid 6. Role of ADH 7. Counter current multiplier system High permeability of thin descending limb to water. The active transport of Na and Cl out of thick ascending limb Inflow of tubular fluid from the proximal tubule with outflow into the distal tubule. 8. Vasa recta-counter current exchangers Supply medullary parts Prevents rapid dissipation of medullary hyperosmolarity On descending part Nacl and urea is reabsorbed.and water is secreted On ascending part NaCl and urea are secreted into the interstitium, while water is reabsorbed. 9. Urea concentrating medullary intestitium Contribution is about 40-50% 4 urea transporters (UT1-4) UT-A1 and UT-A3 is activated by presence of ADH Amount of urea in urine and medullary interstitium depends on filtration. 10. Concentrated urine 11. Concept of Free Water Cleareance To quantitate the gain or loss of water by excretion of a concentrated or dilute urine. C(H2O)=V-(Uosm x V)/Posm -ve for hypertonic urine +ve for hypotonic urine Osmotic diuresis Presence of unreabsorbed solutes increase the urine volume. Relation of urine concentration to GFR Decrease in GFR increase the urine concentration and vice-versa. 12. References Textbook of medical physiology, Guyton and Hall,12th edition Ganongs Review of medical physiology,23rd edition 13. Group members: -Aliza Hamal -Anup Bhatta -Bijay Shrestha -Bikash Sapkota -Lalit Karki -Prabesh Raghubansi -Prayash Panthi -Suchana Sharma -Sujata Pandey -Sunder Chapagain


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