Excretion

2.68a Understand how the kidney carries out it's roles of excretion and osmoregulation.

Note: Urea contains Nitrogen, which is toxic in the body and cannot be stored.

The original form of Nitrogen and potentially toxic to the body are amino acids (normally used for growth). When they are in excess, they are toxic and must be removed.
This is the role of both the liver and the kidneys.

Stage 1: blood circulates to the liver and the amino acids are broken down and converted into the molecule we call Urea, which then circulates to both kidneys.

Stage 2: The kidneys will filter the urea from the blood and the urea will be added to water to form urine which drains down the ureters and collects in the bladder

Stage 3: the Urea is now removed from the body as Urine (through the bladder)

Stage 4: The filtered blood returns to the circulation in the veins with the toxic amino acids removed.