Explain how ADH affects the production and concentration of urine by the kidneys.

ADH (Anti-diuretic Hormone) is a key hormone in osmoregulation, the control of water balance in the body. The process is a negative feedback loop: 1. **Detection:** The hypothalamus in the brain monitors the water potential (concentration) of the blood. If the blood becomes too concentrated (e.g., due to dehydration from sweating), the hypothalamus detects this change. 2. **Hormone Release:** The hypothalamus stimulates the pituitary gland to release more ADH into the bloodstream. 3. **Action on Kidneys:** ADH travels to the kidneys, its target organ. It specifically acts on the walls of the collecting ducts and the distal convoluted tubules, making them more permeable to water. 4. **Water Reabsorption:** Because the tubule walls are now more permeable, more water moves by osmosis from the filtrate inside the tubule back into the concentrated blood in the surrounding capillaries. 5. **Urine Output:** Since more water has been returned to the blood, less water is left in the tubules to form urine. This results in the production of a small volume of highly concentrated (hypertonic) urine. This action helps the body to conserve water and return the blood concentration to normal.