25) THE PLASMA OSMOLALITY DECREASES AFTER INFUSION

[Editor]

a) isotonic saline solution
b) vasopressin
c) aldosterone
d) isotonic glucose solution
e) 20% albumin solution

[Editor]

FTFTF

Isotonic saline would not alter the osmolality as it is iso-osmotic. Vasopressin (ADH) causes peripheral vasoconstriction and water retention (via an increased cAMP and increased water permeability of the renal collecting ducts).This would cause a dilutional effect and hence the osmoloality would fall.
Aldosterone is a 21 carbon corticosteroid that has a mineral corticoid effect, t1/2 20 mins. This cause’s sodium reabsorption for potassium ions (counter-transport mechanism) in the distal convoluted tubule. This results in an increase in the osmolality.
Isotonic glucose is isotonic at the point of administration. However glucose uptake into cells and subsequent metabolism leaves a hypotonic solution.
Albumin in responsible for the oncotic pressure in starlings capillary. Any increase in this effect will lead to an increase in plasma volume due to reabsorption from the interstitial space. For fluid to move from one compartment to another it must move from a hypo-osmotic solution to a more concentrated one. hence at the point of administration the plasma osmolality must be increased.