--- title: "Osmoregulation and the Action of ADH" description: "The water potential of blood is held steady by changing how much water the collecting duct takes back. ADH is the signal and the permeability of one tubule wall is the effector." canonical: https://lightmysky.com/learn/science/osmoregulation-and-the-action-of-adh-mt_Rz_MmL-Pa- source: https://lightmysky.com/learn/science/osmoregulation-and-the-action-of-adh-mt_Rz_MmL-Pa-.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Osmoregulation and the Action of ADH The water potential of blood is held steady by changing how much water the collecting duct takes back. ADH is the signal and the permeability of one tubule wall is the effector. Subject: Science · Area: The Human Body · Ages 17 to 18 Page: https://lightmysky.com/learn/science/osmoregulation-and-the-action-of-adh-mt_Rz_MmL-Pa- ## Ready when they can - Traces the loop from a fall in blood water potential through to a change in urine volume. - Explains what ADH does to the collecting duct rather than to the kidney as a whole. - Predicts what happens to urine concentration after a large drink of water. ## Lesson: How ADH tunes your urine Your blood must stay at the right wateriness all day. When you lose water by sweating, or eat a salty meal, your blood grows more concentrated and its water potential falls. Your brain notices the change and releases a hormone called ADH, short for antidiuretic hormone. Anti means against and diuretic means making lots of urine, so the name already tells you its job. ADH travels in the blood to the kidneys and works on one specific part: the collecting duct, the last stretch where urine finishes forming. There it makes the duct wall more permeable to water, so more water is pulled back into the blood instead of leaving in the urine. Notice the precision: ADH changes the permeability of one tubule wall, not the whole kidney. The result is a smaller volume of darker, more concentrated urine, and the loop then closes on itself. As rescued water dilutes the blood back toward normal, ADH release fades. That is negative feedback: a change in one direction triggers a response that brings things back to normal. **Example.** Run the loop backwards after a large drink of water. Your blood grows dilute, so the brain releases less ADH. The collecting duct wall stays less permeable, water stays behind in the tubule, and you produce a larger volume of pale, watery urine. Dehydration means too little body water; diuresis means making an unusually large volume of urine. **Recap.** ADH makes the collecting duct leak water back into blood, so urine volume falls and concentration rises. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Hormones and Negative Feedback](https://lightmysky.com/learn/science/hormones-and-negative-feedback-mt_OBa6BHmW29) - [Ultrafiltration and Selective Reabsorption in the Nephron](https://lightmysky.com/learn/science/ultrafiltration-and-selective-reabsorption-in-the-nephron-mt_vSKfoJN6zh) ## Opens up - [Transamination, Ammonia and the Urea Cycle](https://lightmysky.com/learn/science/transamination-ammonia-and-the-urea-cycle-mt_MFu5uQKyFL)