What is the normal osmolarity of blood?

Osmolality is the measure of the osmotic concentration of
a solution or fluid, a measure of the ionic concentration of dissolved substances per
unit of solvent. Osmolality can be measured in fecal material, serum, plasma, or
urine.

The plasma (blood) osmotic concentration is normally
between 275-295 mOsm/kg. If plasma osmolality increases above normal, ADH/antidiuretic
hormone is released from the posterior pituitary gland (neurohypophysis). ADH conserves
fluid in the renal system (prevents the loss) this will decrease the plasma
osmolality.

When you are thirsty the osmolality of your
plasma is increased, when you drink fluids this decreases the plasma osmolality. The
cells of your body maintain osmotic balance by selectively allowing water and ions,
specifically bicarbonate and chloride, into and out of the
cell.

Hematology/Rodack/p. 100,101