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
- 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.
- Open into 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.
- 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.
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