Excretory System Icse Class 9

THE EXCRETORY SYSTEM

* Excretion plays an important role in maintaining homeostatic (steady state) of the body.

* Organs concerned with formation , storage and elimination of urea constitute the excretory system.(or better ‘Urinary System’ in humans)

* The list of substances eliminated are:

1. Carbon dioxide and water vapour: Every living cell releases energy by oxidation of glucose to release carbon dioxide and water vapour. Carbon dioxide is eliminated through lungs and water vapour is stored as normal water in the body.

2. Nitrogenous metabolic wastes: These include uric acid, urea and ammonia. These are dead protein remains of tissues that are brought to it. Excess amino acids are harmful. The liver breakdown forms usable glucose while the urea is eliminated.

3. Excess salts: These include common salt NaCl and excess water soluble vitamins (B and C).Salts are removed through kidneys.

4. Water: It is taken in through food and beverages in large quantities. Excess water serves as a medium for removal of harmful wastes by dissolving.

5. Bile pigments are breakdown products of haemoglobin of dead RBCs. Liver cells extract it from circulation and secrete it into the bile juice poured into duodenum by common bile duct. These pigments (when modified by intestinal juices) give faeces a yellowish brown colour and are excreted through urine.

* Excretion is the removal of all harmful and unwanted products from the body. (especially nitrogenous wastes)

* THE EXCRETORY ORGANS

KIDNEYS: These are primary excretory organs eliminating excretory products (mainly urea) in form of urine.

SWEAT GLANDS: These glands are actually concerned with cooling. Sweat secretion is only incidental. Very little urea is excreted.

LUNGS: CO2 by expired air is the form of excretion by lungs.

* Kidneys are two bean-shaped organs (10cm long and 6cm wide) are located on either side of the backbone and are protected by the last two ribs. The right...