The fundamental filtration unit in the kidneys is a cluster of blood capillaries with very thin walls. The cup-shaped end of a coiled tube called Bowman’s capsule that collects the filtrate is related with each capillary cluster in the kidney. The filtration units known as nephrons are found in enormous numbers in each kidney.

As the urine passes along the tube, several substances in the initial filtrate, such as glucose, amino acids, salts, and a significant amount of water, are selectively reabsorbed. The amount of water reabsorbed is determined by the amount of excess water in the body as well as the amount of dissolved waste to be expelled. Each kidney’s urine eventually reaches the ureter, a lengthy tube that connects the kidneys to the urinary bladder.

Urine is kept in the urinary bladder until it is pushed out via the urethra by the pressure of the inflated bladder. Because the bladder is muscular, it is controlled by the neurological system.