Urine Composition and Osmoregulation
Follow the ADH loop on a hot day.
Step through what happens to your urine on a hot summer day, and then after you drink a large glass of water.
Normal urine is about 95 per cent water and 5 per cent dissolved solid wastes, chiefly urea, creatinine, uric acid and sodium chloride, coloured clear yellow by the pigment urochrome.
Free play — step through the process at your own pace, and move the slider to see what changes. Switch to when you're ready to test yourself.
What this lesson covers
Challenges to clear
- Reach the stage where the hormone is actually released.
- Run the whole loop from summer sweat to a glass of water.
The task
Step through what happens to your urine on a hot summer day, and then after you drink a large glass of water.
What this lesson covers
- Urine leaves the collecting ducts — Normal urine is about 95 per cent water and 5 per cent dissolved solid wastes, chiefly urea, creatinine, uric acid and sodium chloride, coloured clear yellow by the pigment urochrome.
- Sweating concentrates the blood — On a hot day the skin loses around 500 mL of water as sweat, so the water content of the blood falls and its osmotic pressure rises.
- The pituitary releases ADH — The posterior lobe of the pituitary gland secretes antidiuretic hormone into the blood in response to the shortage of water.
- Tubules reabsorb more water — ADH makes the kidney tubules take back more water from the glomerular filtrate and return it to the surrounding capillaries.
- Urine becomes thicker — Less water leaves the body, so in summer you urinate fewer times than in winter and the urine passed is more concentrated. Blood composition is restored, and this regulation of the osmotic pressure of the blood is called osmoregulation.
- Drink water and ADH falls — With less ADH, less water is reabsorbed and urine output climbs. This increased production of urine is called diuresis, and tea, coffee and alcohol act as diuretics.
Hint
Two very different diseases sound alike. Sweet urine means glucose is escaping because reabsorption failed for want of insulin, which is diabetes mellitus. Tasteless watery urine means too little ADH, which is diabetes insipidus.