5.3.3 - Maintaining Water & Nitrogen Balance in the Body

What is osmosis?

The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane.

In what ways is water lost from the body?

• During exhalation via the lungs.

• Sweating.

• Urine (some reabsorbed in the kidney).

In what ways are ions lost from the body?

• Sweating.

• Urine (some reabsorbed in the kidney).

How are excess amino acids excreted from the body?

• Excess amino acids are deaminated in the liver to form ammonia.

• Ammonia is toxic, therefore it’s converted into urea.

• Urea is excreted from the body via sweat and urine.

How do the kidneys maintain the balance of water and other substances in the body?

• Filter blood in order to remove waste products e.g. urea.

• Selectively reabsorb useful molecules e.g. glucose, water, ions.

What is the full name of the hormone ADH?

Anti-diuretic hormone.

Where is ADH secreted in the body?

The pituitary gland of the brain.

How does ADH affect the reabsorption of water in the kidneys?

• When the blood is too concentrated, the pituitary gland secretes more ADH.

• ADH travels in the bloodstream to the kidney and increases the permeability of kidney tubules to water.

• More water is reabsorbed in the kidneys, resulting in a smaller volume of more concentrated urine.

Why is kidney failure dangerous?

When the kidneys are damaged, they may be unable to filter the blood properly. This may lead to:

• A build-up of toxic molecules (e.g. urea) in the body.

• An uncontrolled ion and water balance and cells being damaged as a result of osmosis.

What are the two main ways of treating kidney failure?

• Dialysis

• Transplant

What is kidney dialysis?

• The use of a specialist machine to carry out the function of kidneys.

• Dialysis fluid contains the same concentration of glucose and ions as healthy blood.

• As a result, only excess and waste molecules are lost from the blood, and glucose and ions remain.