How and why does the volume and composition of urine change?

Hint: Urine is known to be a liquid by product produced as a result of metabolism which consists of harmful substances and thus needs to be expelled out of the body. Urine is produced by humans as well as many other animals.

Complete answer:
Urine is formed in the nephrons of the kidney by the following three steps- glomerular filtration, reabsorption and secretion. Glomerular filtration is the filtration of blood which occurs in the glomerulus that is surrounded by the bowman’s capsule. After filtration of the blood all the plasma constituents reach the bowman’s capsule and it is known as the filtrate.

Around ninety nine percent of the filtrate constituents which includes water and ions are reabsorbed by the renal tubules, this is known as reabsorption. The final step is secretion where tubular cells secrete potassium ions, hydrogen ions, etc. into the filtrate which maintains the balance of body fluids. These ions then combine with the filtrate to form urine which then reaches the urinary bladder through the collecting tubule.

The composition and volume of urine changes during certain conditions such as during excessive drinking of water the urine becomes diluted and more volume of it is released in contrast when water intake is reduced it becomes more concentrated and volume decreases as well.

It also changes in summer where most water is reabsorbed making the urine concentrated with less volume whereas in water it is more diluted with more volume. The urine composition is different for diabetic people as their urine is seen to comprise sugar along with other components.

Note: Urine production is an important physiological process as it helps in osmoregulation, which is maintenance of composition and volume of body fluids and thus in turn helps in maintaining homeostasis.