Nephron
The working unit of the kidney. Blood is filtered in the glomerulus, then the tubule takes back useful substances (water, glucose, salts) and leaves wastes such as urea in urine. Antidiuretic hormone (ADH) controls how much water is taken back.
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Analogy
A sieve followed by a recycling sorter.
In practice
On a hot day, more ADH is released, more water is retained and urine becomes small in volume and dark.
Practice
Flashcards
- What does ADH do in the kidney?It makes the tubule take back more water, so urine is more concentrated.
Questions people ask
Why is there glucose in the filtrate but not in urine?
The glomerulus filters small molecules, including glucose, out of the blood. The tubule then takes back all the glucose using transport proteins. If blood glucose is very high, as in untreated diabetes, the transporters are overloaded and some glucose stays in the urine.
What is urea and where does it come from?
Urea is a waste made in the liver when excess amino acids are broken down. The nitrogen is turned into urea, which is less toxic than ammonia. It travels in the blood to the kidneys and leaves the body in urine.