Maintaining Body's Water Balance

What happens if the blood becomes too concentrated (low water level)?

Pituitary gland releases hormone ADH into the bloodstream.

What does ADH do?

Travels to the kidneys and causes kidney tubules to become more permeable to water. i.e. more water can now pass out of the kidney tubules.

This means more water is absorbed from the tubules back into the blood.

What happens as the water level in the blood returns to normal?

The pituitary gland stops releasing ADH.

What happens if the blood water concentration is dilute?

Pituitary gland does not produce ADH. Kidneys reabsorb less water into the blood.

More urine is produced and concentration of water in the blood returns to normal.

What happens if the kidneys fail?

The level of water, ions and urea need to be adjusted using a machine. This is kidney dialysis.

What happens to a persons blood if they have kidney failure?

Their blood will contain a higher concentration of water, ions and urea than it should.

What happens in kidney dialysis?

The patients blood passes over a semi-permeable membrane.

What does the semi-permeable membrane in kidney dialysis do?

Allows water, urea and ions through, but not larger molecules such as proteins and blood cells.

What is on the other side of the semi permeable membrane in kidney dialysis?

Dialysis fluid which contains the normal concentrations of water and ions, but does not contain any urea.

What happens to blood during kidney dialysis?

Urea diffuses from the blood into dialysis fluid.

Dialysis fluid is constantly refreshed, ensuring there is always a large concentration gradient for urea.

What happens to ions and water in the blood during kidney dialysis?

Some of the ions and some of the water will diffuse from the blood into the dialysis fluid.

Concentrations of water and ions in patients blood will return to normal.

What is the control of water and mineral salts within the body called?

Osmoregulation.

Why is it important that water and mineral salts are regulated?

To prevent the cells from bursting or shrivelling and so that they continue to function efficiently.

What happens if the concentration inside the cell is in equilibrium to outside the cell?

Then water and salts move in and out of the cell at equal rates.

What happens if the concentration of salts inside the cells becomes greater than the concentration outside the cell?

The solution outside is more dilute (hypotonic). This means that water moves into the cell by osmosis. This causes the cell to swell and it can burst open.

What happens if concentration of salts inside the cell becomes lower than outside?

Then the solution outside is more concentrated (hypertonic). Water moves out of the cell by osmosis.

Causes cell to shrivel and cannot function properly.