tonicity

Tonicity: is the ability of a solution to affect the fluid volume and pressure in a cell.

Hypotonic: has a lower concentration of nonpermeating solutes than the intracellular fluid. Cells in a hypotonic solution absorb water, swell and may lyse.

Isotonic: total concentration of nonpermeating solutes is the same as in intracellular cellular fluid.

Hypertonic: has a higher concentration of nonpermeating solutes than intracellular fluid. It causes cells to lose water and shrivel( crenate).

fluid deficiency
1. hypovolemia: total body water is reduced, isotonic
2. dehydration: total body water is reduced, hypertonic

Fluid excess
1. volume excess:total body water is elevated, isotonic
2. hypotonic hydration:total body water is elevated, hypotonic


















Fluid deficiency: output exceeds intake over a long enough period of time.

Hypovolemia: occurs when PROPORTIONATE amounts of water and sodium are lost without replacement. Total body water declines but osmolarity remain normal.
Occurs: haemorrhage, severe burns, chronic vomiting or diarrhea.

Dehydration: occurs when body eliminates significantly more water than sodium so ECF osmolarity rises.
Occurs: lack of drinking water, diabetes mellitus, ADH hyposecretion( diabetes insipidus), profuse sweating, overuse of diuretics


Fluid excess: less common than fluid deficiency because kidneys are highly effective at compensating for excessive intake by excreting more urine. Renal failure can cause this condition.

Volume excess: both sodium and water are retained and the ECF remains isotonic. This can result from aldosterone hypersecretion or renal failure.

Hypotonic hydration: more water than sodium is retained or ingested and the ECF becomes hypotonic.
Occurs: If you lose a large amount of water and salt through urine and sweat and you replace it by drinking plain water. Without proportionate intake of electrolytes, water dilutes the ECF, makes it hypotonic, and causes cellular swelling. ADH hypersecretion can cause hypotonic hydration by stimulating excessive water retention as sodium continues to be excreted. This can cause pulmonary and cerebral oedema.