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

6. 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

7. Role of ADH

8. 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.

9. 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.

10. 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.

11. Concentrated urine

13. 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.

14. References
• Textbook of medical physiology, Guyton and Hall,12th
edition
• Ganong’s Review of medical physiology,23rd
edition

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