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Selective reabsorption

The filtererd substances which are useful to the body are selectively reabsorbed back into the bloodstream. This process requires energy and occurs in the renal tubules.

This animation shows how selective reabsorption occurs.

The kidney acts as an osmoregulator in two ways: It reabsorbs sodium chloride ions and water from the ultrafiltrate.

Reabsorption of sodium chloride ions from the ultrafiltrate.

This process occurs at the loop of henle by active transport. The process is regulated by a hormone called aldosterone. Low concentration of sodium ions in blood stimulates the adrenal gland to secrete aldosterone hormone. This hormone leads to increased reabsorption of sodium ions into the bloodstream.

Reabsorption of water

This is regulated by the antidiuretic hormone, also called vasopressin.

The animation shows the events that occur when the osmotic pressure of blood changes. When the osmotic pressure increases, this change is detected by the hypothalamus. The hypothalamus sends impulses to the pituitary gland causing it to secrete more antidiuretic hormone. The hormone causes the nephrons to become more permeable to reabsorption of water. More water is therefore reabsorbed back into the blood stream, hence lowering the osmotic pressure.

If the kidney fails an artificial machine called a dialysis machine can be used to clean the body of waste products and excess water. This video features a patient on a dialysis machine.