Excretory System in Human

Human excretory system consists of –

(1) A pair of kidneys (2) A pair of ureters

(3) Urinary bladder (4) Urethra

1.0Kidney

Kidney is the primary excretory organ, its primary function is the removal of metabolic waste, thereby maintaining homeostasis of the body.

Colour – Reddish brown

Shape – Bean-shaped

Weight – 120 - 170 gms

Size – 10-12cm length, 5-7cm breadth, 2-3cm thickness.

Position – Located laterally on either side of vertebral column.

The human kidneys are not located at similar positions due to the presence of liver above right kidney, so that the right kidney get slightly lower position.

External structure

Each kidney is surrounded and covered by a tough, fibrous capsule of connective tissues. This capsule is called renal capsule. The lateral surface of kidney is convex while medial surface is concave.

Internal structure

The internal structure of kidneys can be divided into two parts. Its outer part is called cortex and inner part is called medulla. A kidney is composed of numerous microscopic, coiled tubules called nephrons or uriniferous tubules.

2.0Ureters

They are tubes which carry urine to urinary bladder. Each ureter originates from the hilum of kidney. The anterior part of the ureter is broad, like a funnel and called pelvis and its posterior part is in the form of a long tube.

3.0Urinary bladder

Each ureter opens into the urinary bladder. It is a muscular pear-shaped sac. It has thick distensible wall lined by transitional epithelium that allows expansion. The contraction of bladder muscles squirts urine out.

4.0Urethra

It is a tubular structure which extends from the urinary bladder to the outside. It carries the urine to the outside.

• The pale yellow colour of urine is due to the urochrome pigment. It is formed in the liver due to the breakdown of haemoglobin.

• Urea (main nitrogenous waste in our body) is formed in the liver through the ornithine cycle.

• Micturition is the term used for urination (Passing out of urine).

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