The kidneys remove toxic waste like urea as well as adjusting the amount of dissolved ions and water in the blood.
Step one: Ultrafiltration.
- A high pressure is built up which squeezes water, urea, ions and sugar out of the blood and into the Bowman's capsule.
- The membranes between the blood vessels and the Bowman's capsule act like filters, so big molecules like proteins and blood cells are not squeezed out. they stay in the blood.
Step two: Reabsorption.
- All the sugar is reabsorbed. This involves the process of active transport against the concentration gradient.
- Sufficient ions are reabsorbed. Excess ions are not. Active transport is needed.
- Sufficient water is reabsorbed.
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