The nephron: filtering and reabsorption

The nephron: filtering and reabsorptionSpec 7.19B

Each kidney contains many tiny tubes called nephrons. The nephron filters the blood and forms urine. Blood enters a knot of capillaries, the glomerulus, which sits inside a cup-shaped Bowman's capsule.

1. Filtration: blood in the glomerulus is at high pressure. Small molecules such as water, glucose, urea and ions are forced out into the Bowman's capsule. Large molecules such as proteins, and blood cells, stay in the blood.
2. Selective reabsorption of glucose: in the first part of the tubule, all the glucose is reabsorbed back into the blood by active transport, which uses energy from respiration.
3. Reabsorption of water: as the filtrate passes along the loop of Henle and the collecting duct, water is reabsorbed back into the blood. How much depends on the body's needs.
4. What is left, which is urea, excess ions and water, is urine. It passes to the ureter.

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