Urine is formed through three processes that occur in the kidney:
- Ultrafiltration, where almost all the blood components are filtered by the kidneys except for the blood cells and the plasma proteins, e.g. urea, water, sodium, glucose, potassium, ...etc.
- Selective reabsorption, where the essential components are reabsorbed back into the blood vessels, e.g. glucose, water, sodium, ...etc.
- Secretion, where, e.g. potassium is secreted by cells in exchange for another useful component, e.g. sodium in that case.
- Then the water reabosprtion content is further regulated before exiting the kidney through a hormone known as ADH.
- Urine is then formed, collected in the bladder and excreted outside the body later on
