U1 M2 Excretion

Excretion

Key terms:

Excretion: the removal of metabolic waste from the body (removal of by-products or unwanted substances from normal cell processes)

metabolic waste: consists of waste substances that may be toxic or are produced in excess by the reactions inside cells

deamination: the removal of the amine group from an amino acid to produce ammonia

Main substances to be excreted:

although there are many substances that need to be excreted, there are two products that are produed in very large amounts

• carbon dioxide from respiration - produced by every living cell in the body
• nitrogen-containing compounds such as urea - produced in the liver from excess amino acids

Where are these eubstances excreted?

• carbon dioxide is passed from cells of respiring tissues into the bloodstream. It is transported in the blood (mostly in the form of hydrogencarbonate ions) to the lungs. In the lungs the carbon dioxide diffuses into the alveoli to be excreted as we breathe out.
• urea produced by breaking sown excess amino acids in liver (deammination). Urea then passed into bloodstream to be transported to kidneys. It is transported in solution - dissolved in plasma. In kidneys, urea is removed from blood to become a part of urine. urine is stored in the bladder before being excreted via the urethra.

Why must these sunstances be removed?

carbon dioxide:

• majority of carbon dioxide carried in blood as hydrogencarbonate ions (also form hdrogen ions). this occurs…