Regulation of Water Balance ( Osmolarity )

normal
1. osmolarity (285-300 mOsm/L) of ECF
2. blood pressure of 120/80 mmHg
3. Na+ content is NOT EQUAL to osmolarity. E.g. intravenous drip (isotonic saline)  ↑ Na+ content, but no change in osmolarity, so ECF volume ↑, but no change in ICF volume
Regulation of (a) blood osmolarity and (b) blood pressure
hypovolaemia and hypervolaemia
Regulatory components of ECF volume and osmolarity
Regulation of water intake
Locations of water reabsorption
Factors that maintain body water balance
production of concentrated urine
1. hyperosmotic urine
2. there is LESS water in urine
systems that generate the medullary osmotic gradient
1. The countercurrent multiplier system
2. The urea recycling
3. The countercurrent exchanger system
Free-water clearance (CH2O)
1. ability to concentrate or dilute urine
2. CH2O = V – Cosm
  1. CH2O = free-water clearance (mL/min)
  2. V = urine flow rate (mL/min)
  3. Cosm = osmolar clearance (UosmV/Posm) mL/min
3. When CH2O is zero
  1. Urine is isoosmotic to plasma
  2. loop diuretic
4. When CH2O is positive
  1. hypoosomotic to plasma (low ADH).
  2. high water intake
  3. central diabetes insipidus
  4. nephrogenic diabetes insipidus
5. When CH2O is negative:
  1. Urine that is hyperosmotic to plasma (high ADH).
  2. water deprivation
  3. SIADH.

Resource summary

	Created by Zulhilmi Zainal over 10 years ago