Because of its close anatomical relationship, the urinary and reproductive organs are as Urogenital system. The urinary system proper is an excretory system, removing water and waste products of metabolism from the body as urine. Other organs of excretion are the skin, lungs, and rectum. The urinary system includes the kidneys, bladder, ureters, and urethra.

The Urinary Tract

Kidneys: These are pair of bean-shaped organs (Fig.) weighing about 16.86 g. (6 oz) each, located deep in the small of the back, one on each side of the spinal column. Each kidney contains a million or more tiny filtering units, called nephrons. Each nephrons is enclosed in a cup-like capsule in which are meshed kidney tubules and a network of tiny blood vessels (glomeruli). Blood enters the glomeruli from branches of the renal artery. The cells of the kidney tubule selectively extract from the blood the water and waste products in solution that make up the urine.
Ureters: They are a pair of 40 to 45 cm.(about 16 to 18 inches) long tubes with the diameter about the thickness of a pencil, that convey urine from the kidneys to the bladder. They originate in the kidney and terminate at the base of the bladder. Urine trickles down them at the rate of about a drop every 30 seconds.
Bladder: This is a collapsible balloon-like sac composed of smooth muscle and lined with a smooth membrane. It is a urine tank, situated in the forward part of the pelvic cavity. In the female it lies behind and above the uterus. The relaxation of the sphincter muscle guarding the bladder, allows urine to escape.
Urethra: This mucous-membrane-lined tube or canal conveys urine the neck of the bladder to the outside world. The male urethra is about 20 to 22 inches) long and terminates in the tip of the penis. It is also the passage-way through which semen is ejaculated, the ejaculatory ducts, being a part of the reproductive system, open into it. The female urethra is short, measuring about 3.8 cm. (11/2 inches) Its external opening is located just in front of the opening of the vagina.