i. Kidney: 

A pair of bean shaped kidneys are present on either side of the backbone from 12^th thoracic to 3^rd lumbar vertebra. Kidneys are present behind peritoneum. Hence are called retroperitoneal. Dimensions of each kidney are 10 × 5 × 4 cms. Average weight is 150 g in males and 135 g in females. Outer surface is convex and inner is concave. Notch on the inner concave surface is called hilum. Renal artery enters and renal vein as well as ureter leave the kidney through hilus. Each kidney has almost 1 million functional units called nephron.

ii. Ureters: 

A pair of ureters arise from hilum of each kidney. Each ureter is a long muscular tube 25 – 30 cm in length. Ureters open into urinary bladder by separate openings, which are not guarded by valves. They pass obliquely through the wall of urinary bladder. This helps in prevention of backward flow of urine due to compression of ureters while bladder is filled.

iii. Urinary bladder: 

It is a median pear-shaped sac. A hollow muscular organ, the bladder is situated in pelvic cavity posterior to pubic symphysis. At the base of the urinary bladder there is a small inverted triangular area called trigone. At the apex of this triangle is opening of urethra. At the two points of the base of the triangle are openings of ureters. Urinary bladder is covered externally by peritoneum.

Inner to peritoneum is muscular layer. It is formed by detrusor muscles which consist of three layers of smooth muscles. Longitudinal – circular – longitudinal respectively. Innermost layer is made up of transitional epithelial tissue. It helps bladder to stretch.

iv. Urethra: 

It is a fibromuscular tube-like structure arising from urinary bladder and opening to the exterior of the body. 

There are two urethral sphincters between urinary bladder and urethra. 

a. Internal sphincter:

Made up of detrusor muscles, involuntary in nature. 

b. External sphincter: 

Made up of striated muscles, voluntary in nature. If this valve is not functioning properly during inflammation of bladder, it can lead to kidney infection.

iv. Urethra: 

It is a fibromuscular tube-like structure arising from urinary bladder and opening to the exterior of the body. There are two urethral sphincters between urinary bladder and urethra. 

a. Internal sphincter: 

Made up of detrusor muscles, involuntary in nature. 

b. External sphincter: 

Made up of striated muscles, voluntary in nature. If this valve is not functioning properly during inflammation of bladder, it can lead to kidney infection.