Nephron

The nephrons remove urea, excess mineral salts and excess water from the blood to make urine.

![[../assets/nephron.png]]

Urine Formation

• Involves two processes:
  • Ultra-filtration
  • Selective reabsorption

Sequence

1. Blood from renal artery brings metabolic wastes and useful substances to the kidney tubule
2. Blood enters the Glomerulus through an afferent arteriole. The diameter of afferent arteriole is wider than efferent arteriole. This creates a high hydrostatic blood pressure
3. All small molecules are forced into the Bowman's capsule by the high blood pressure
4. Blood cells, platelets and protein are large molecules so they remain in the blood
5. At the proximal convoluted kidney tubule, all glucose and amino acids, most mineral salts are reabsorbed into blood capillaries
6. Solutes are selectively reabsorbed into the blood capillaries by active transport. Most of the water is reabsorbed by osmosis
7. Unwanted materials remain in kidney tubule which flows out of the kidney tubule into the ureter
8. Blood that flows away from the kidney tubule contains very little urea and less excess water