Concept preview

What you will be able to do

1. 01Name the four organs of the urinary system and state the job of each.
2. 02Describe the gross anatomy of a kidney: cortex, medulla, renal pyramids and renal pelvis.
3. 03Identify the parts of a nephron from the glomerulus to the collecting duct.
4. 04Explain the blood supply of a nephron and why the nephron is called the kidney's functional unit.

Every second of your life the cells of your body burn fuel, build molecules and break others down, and like any busy chemical factory they leave behind a steady stream of waste. The most important of these wastes is urea, a nitrogen-containing compound made in the liver when surplus amino acids are broken apart. If urea and other wastes were allowed to build up in the blood they would quickly become poisonous. At the same time the body faces a second, quieter challenge: it must hold the amount of water and the concentration of dissolved salts in the blood within a narrow, safe band, whatever you happen to eat or drink. The organ system that solves both problems at once is the urinary system, and its work is a perfect example of homeostasis — the active keeping-steady of the body's internal environment.