Excretory System - Notes, Biology Notes | Study General Science(Prelims) by IRS Divey Sethi - UPSC

Excretory System 

Removal of waste from the body

• Waste materials excreted in animals are of many kinds :
• Nitrogenous Substances, Carbon-Dioxide, Pigments, Excess Water, etc.

The Nitrogenous Waste can be excreted in the following forms :

• Ammonia : Highly Toxic, Soluble in Water and has to be immediately excreted.
• Urea : Far less toxic than ammonia. Less water required than ammonia. In Mammals, Alligators, Turtles (called Ureotelic).
• Uric Acid : In animals where conservation of water is needed. In Birds, Insects, Land Reptiles (called Uricotelic).

Excretory System of Mammals

Kidneys

• Left kidney is higher than the right kidney.
• A kidney is composed of 1.2 million microscopic structural and functional units called nephrons or uriniferous tubules.

Ureters

• Open into Urinary Bladder

Urinary Bladder

• Size depends upon the amount of urine in it (up to 700 – 800 ml).
• The lower part is guarded by 2 Sphinctors : inner involuntary and outer voluntary.

Urethra

• Leads to the exterior.
• In females, it carries only urine. Opens by urinary aperture in the vulva in front of vaginal aperture.
• In males it carries urine as well as spermatic fluid.

Nephron

Functional unit of kidney.

• It is a long tube differentiated into 4 regions.
• 1. Bowman’s Capsule
• 2. Proximal Convoluted Tubule (PCT)
• 3. Loop of Henle
• 4. Distal Convoluted Tubule (DCT)

1. Bowman’s Capsule

• Contains a globular bunch of capillaries, the glomerulus.
• The Bowman’s capsule and the glomerulus together form a globular body called Malpighian body.
• In glomerular filtrate : water (99%), inorganic salts, amino acids, fatty acids, glucose, urea, uric acid, hippuric acid, hormones, vitamins are present.

2. Proximal Convoluted Tubule (PCT)

• Starts from the neck of Bowman’s capsule and is highly twisted.
• Almost whole of the glucose and vitamins, about 75% of amino acids, about 70% of Na and K, a large amount of Ca and Mg and 75% water is absorbed.

3. Loop of Henle

• U – shaped.
• Consist of 2 straight limbs : descending and ascending.
• No water is absorbed in ascending limb.

4. Distal Convoluted Tubule (DCT)

• Greatly twisted.
• Reabsorbs some Na and Cl.
• Leads to Collecting Tubules which lead to ureters