URINE OSMOLARITY

PBL TUTOR(Group-IV)Dr.Rupesh Shrestha

PresenterLalit karki

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.

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

Excreting a dilute urine

• Decrease water reabsorption

• Continue electrolyte reabsorption

Mechanism:•decreased ADH release and reduced water permeability in distal and collecting tubules

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

Role of ADH

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.

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.

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.

Concentrated urine

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.

References

• Textbook of medical physiology, Guyton and Hall,12th edition

• Ganong’s Review of medical physiology,23rd edition

Group members:-Aliza Hamal-Anup Bhatta-Bijay Shrestha-Bikash Sapkota-Lalit Karki-Prabesh Raghubansi-Prayash Panthi-Suchana Sharma-Sujata Pandey-Sunder Chapagain