Water and osmotic polyuria?

Question

Can someone give me some info on both of them?

Answer 1

Get background here: http://en.wikipedia.org/wiki/Polyuria

Now water polyuria is caused by excess water in the body. If your body is holding too much water, your kidneys will kick into gear and get rid of it.

Osmotic polyuria is caused when your blood has a very high osmotic pressure, perhaps due to excess salts or ions in your blood. When the osmotic change is detected, your kidneys kick into gear and start releasing lots of water to try to balance the osmotic pressure between both barriers.

In essence, what happens in both situations is the same: it relates to pressure. Too much water or excess ions will create pressure on the kidney membranes, which activates renal activity and ergo, urine.

Answer 2

Kidneys regulate fluid volume. Assuming you start with a balanced volume where the net fluid/solute movement is zero:

1)Drink lots of water - This adds free water to the body and dilutes the proper electrolyte balance. (This also increases total body fluid.) The kidneys now excrete the free water as dilute urine.

2)Eat lots of salt/sugar/other osmotically active agent (if it does not cross the cell membrane readily, it is osmotically active). This concentrates the solute concentration in the body. The kidneys excrete this excess salt/sugar/etc. Water is necessary to dissolve these solutes, but the kidney does not want to excrete the water, so the urine is concentrated.

Example: In diabetes, the glucose concentration is high. Glucose is osmotically active. The kidney tries to excrete as much as possible, and water follows.

This might be a little bit over simplified, but I believe it explains the basics. There are of course numerous other factors that determine the concentration of the urine (hormones such as ADH, Aldosterone, Renin, etc.) but that would involve a LONG discussion.