How is the amount of urine produced regulated?
The amount of urine produced is regulated by the process of re-absorption in the kidney tubules. The purpose of making urine is to filter out waste products, specifically nitrogenous waste such as urea or uric acid, from the blood.
In a healthy adult, the initial filtrate in the kidneys is about 180 litres daily. However, the volume actually excreted is regulated to only a litre or two per day. This regulation occurs because the remaining filtrate is re-absorbed in the kidney tubules, ensuring the body retains necessary fluids while expelling waste.
Explanation
The provided context explains the regulation of urine amount through the mechanism of re-absorption. It highlights that while 180 litres of filtrate is produced daily, only 1-2 litres is excreted. The difference is attributed to re-absorption in the kidney tubules. The text also establishes that the purpose of urine production is the removal of nitrogenous waste like urea.