Osmoregulation and the Kidney

This lesson covers osmoregulation and the role of the kidney in maintaining water balance as required by the Edexcel A-Level Biology specification (9BI0), Topic 9 -- Control Systems. You need to understand the structure of the nephron, the process of urine formation, and how ADH controls water reabsorption.

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What is Osmoregulation?

Osmoregulation is the control of the water potential of the blood and body fluids. It ensures that cells are bathed in fluid with a water potential that prevents them from gaining or losing excessive water by osmosis.

If the water potential of the blood becomes:

• Too low (too concentrated): cells lose water by osmosis → they shrink → metabolic processes are disrupted
• Too high (too dilute): cells gain water by osmosis → they swell and may lyse → tissue damage

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Structure of the Kidney

Each kidney contains approximately 1 million nephrons -- the functional units responsible for filtering the blood and producing urine.

Gross Structure