Expand the role of the kidneys in maintaining the constancy of the internal environment of the body.

The kidneys are an important organ for excreting and maintaining homeostasis of the human body. They do their job thanks to a complex structure – a network of tubules and glomeruli, which are essentially filters of different sizes. With an excess of fluid in the body, the kidneys increase urine output, urine becomes more diluted. With a lack of fluid, urine becomes more concentrated, until the complete cessation of diuresis. The kidneys also regulate the electrolyte composition of the blood – with an excess of potassium or sodium ions, they increase the amount of ions in the urine and vice versa.