A kidney is a pair of dark bean-shaped structure. The kidney is located on both sides of the vertebral column. Each kidney weighs about 150g an adult human. The kidney is about 10-12cm length, 5-7cm breadth, and 2-3cm in thickness.

The kidney is positioned behind the peritoneum of the abdominal cavity, they are said to be retroperitoneal organs. The outer surface of the kidney is convex and the inner is concave.

A depression called hilus is present on the concave side. The ureter originates from hilus and joins to the urinary bladder backward. The renal artery and renal vein pass in and out through the hilus.

Internally the kidney is distinguished into two zones an outer dark red part called the cortex and an inner pale red zone called the medulla. The ureter entering through the hilus called the pelvis. Pelvis has a number of cup-like cavities known as calyces.

4-14 pyramid-shaped structures are present in the medullary zone called renal pyramids. The narrow apex of each pyramid called the papilla. The papilla is fitted into small tube-like structures called calyx minor. Several Calyces join to form one major calyx.

A mass of cortical tissues is present between two renal pyramids called Column of Bertini. The outside of the kidney is covered by a layer of fibrous tissue known as a capsule.

A kidney consists of millions of nephrons. The nephron is the basic functional unit of the kidney. Each nephron consists of a Malpighian capsule, a nephric tubule, and a collecting duct. Nephrons are specialized excretion of Urine.

Urine is stored in the urinary bladder. The urinary bladder is surrounded by sphincters. Sphincters remain closed until the time of micturition. The average capacity of the urinary bladder varies from 150L to 300L.

The urethra is a membranous tissue. The urethra arises from the neck of the urinary bladder and extends up to the urethral orifice. The urethra serves as a passage of Urine.

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