QS Study

Diuresis means excretion of a large volume of urine. It is a condition in which the kidneys filter too much bodily fluid. This means that your kidneys will create an increased volume of urine to be excreted from the body that might coincide with increases in lost ions and salts, in the name of preserving the usual fluid balance of the body.

Classification: 3 types.

  1. Water diuresis.
  2. Osmotic diuresis.
  3. Pressure diuresis.

Symptoms of diuresis go beyond frequent urination. They also can include:

  • thirst, due to loss of fluids
  • poor sleep from the frequent need to urinate
  • fatigue, caused by loss of essential minerals and electrolytes in urine

Water diuresis: It refers to the excretion of a large volume of hypotonic urine due to the excessive intake of H2O.


  • Excessive intake of H2O
  • ↓ Osmolarity of Extracellular Fluid (ECF)
  • Inhibition of osmoreceptor in the hypothalamus
  • ↓ ADH secretion
  • ↓ H2O reabsorption from DCT, CT, and CD.
  • A large volume of hypotonic urine
  • Water diuresis.

Osmotic diuresis: The presence of large quantities of unreabsorbed solutes in the renal tubules causes a ↑ in urine volume. It is called osmotic diuresis.

Mechanism: Solutes that are not reabsorbed in the proximal tubules exert an appreciable osmotic effect as the volume of tubular fluid decreases and concentration rises. Then they hold water in tubules.

Example –

  • Uncontrolled diabetes mellitus: ↑ Plasma glucose →↑ tubular load of glucose crosses TmG → Osmotic diuresis → Polyurea.
  • Use of diuretics in therapeutic measure eg., Lasix. Lasix prevents NaCl reabsorption from tubule.
  • Use of mannitol.

Pressure diuresis:

Pressure diuresis refers to the effect of increased BP to raise urinary volume excretion. It is the most powerful mechanism for control of blood volume and ECF volume. Pressure diuresis is coupled with pressure natriuresis.