how is the plasma osmolarity maintained?

Question

factors that effect the body's osmolarity

Answer 1

Osmolarity measures the effective gradient for water assuming that all the osmotic solute is completely impermeant. It is simply a count of the number of dissolved particles. Therefore a 300 millimolar solution of glucose, a 300 millimolar solution of urea, and a 150 millimolar solution of NaCl each have the same osmolarity.

A cell, placed in each of these solutions, would behave very differently, however. In a 150 mM NaCl solution, there would be equal osmotic strengths on both sides (NaCl is impermeant), and the cell would maintain the same volume.

Urea is very permeable through most cell membranes. It exerts little osmotic force against a real cell and its membrane. A cell placed in 300 mM urea would rapidly swell as both urea and water entered the cell down their activity gradients.

Tonicity is a functional term that describes the tendency of a solution to resist expansion of the intracellular volume.

Two solutions are isosmotic when they have the same number of dissolved particles, regardless of how much water would flow across a given membrane barrier. In contrast, two solutions are isotonic when they would cause no water movement across a membrane barrier, regardless of how many particles are dissolved.

In the example given above, a 150 mM NaCl solution would be isosmotic to the inside of a cell, and it would also be isotonic--the cell would not swell or shrink when placed in this solution. On the other hand, a 300 mM urea solution, while still isosmotic would cause the cell to swell and burst (due to its permeability). This isosmotic ureas solution is not isotonic. Instead it has a lower tonicity (called hypotonic).

Answer 2

Skin , Kidneys and Liver do the work mostly. Skin continuously sweats. If one is aware of sweating it`s called "sensible" perspiration. If one is unaware of it it`s "insensible" perspiration. Quantity and concentration of sweat is determined by osmolarity of blood , temperature of the atmosphere and intake of fluid, salt fat and muscular exercise.. Kidney also functions somewhat similarly. Dilute blood increases urinary output and concentrated blood decreases it. Kidney also excretes urea, salts and metabolites. Liver metabolises all food contents including water. Excess is secreted as intestinal secetion to be passed in stool. In these processes Hormones like Antidiuretic hormone,Glucocorticoids and mineralo corticoids play a very important role.

Answer 3

Please see the webpage for more details on Plasma osmolarity.