Key learning points

1. The kidneys are organs of the human excretory system; blood passes through the kidneys and is filtered.
2. Water and urea diffuse out of the blood plasma into kidney tubules to be excreted as urine, including nephron structure.
3. The kidneys reabsorb as much water as needed from the urine into the blood plasma to maintain water balance in the body.
4. Having too much water in the body leads to dilute urine, and vice versa.

Keywords

• Urea - a waste product created in the process of breaking down excess proteins and amino acids

• Blood plasma - the liquid part of the blood which contains dissolved nutrients and waste products

• Kidney - the organ in the excretory system which filters waste products from blood plasma and controls water balance

• Excretory system - the organ system responsible for removing waste from blood plasma

• Urine - a combination of waste urea, water and other substances which is stored in the bladder until urinated

Common misconception