2.68 Excretion and Osmoroegulation

2.68 understand how the kidney carries out its roles of excretion and of osmoregulation

Excretion

Kidneys excrete Water, Salts, and Urea (contains nitrogen = toxic to the body \ cannot be stored)

1. Blood circulates to the liver and amino acids are broken down into Urea
2. Urea re-enters the blood stream and circulates to the kidneys (there are two)
3. The kidneys filter the Urea from the blood
4. Urea is diluted with water to form Urine
5. Drains down the Ureter and collects in the bladder.

Osmoregulation

Osmo – Osmosis
Regulation – to control

• The tissue fluid surrounding cells must be isotonic (equal amount of water entering and exiting cells) so that the cells maintain their size and shape and can function.
• Blood circulating in the tissue may be very concentrated (causing a hypertonic tissue fluid) or too dilute (causing a hypotonic tissue fluid)
• To keep an isotonic solution the composition of blood must be controlled, this is the job of the kidney.
• Excess water, and salts can be removed and excreted through the Ureter to control the contents of water and salts in the blood
• This means that the Tissue fluid can be kept isotonic with the cells cytoplasm.