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## Body's Defences Against Disease ### 17.2.1 Local Defence System * **Protective mechanical barriers:** These include the skin, hair, mucus etc. * **Skin:** Skin has an outer, tough layer made of a protein called keratin and is almost impermeable to germs. * **Hairs:** Hairs intercept...

## Body's Defences Against Disease ### 17.2.1 Local Defence System * **Protective mechanical barriers:** These include the skin, hair, mucus etc. * **Skin:** Skin has an outer, tough layer made of a protein called keratin and is almost impermeable to germs. * **Hairs:** Hairs intercept the germ's journey inwards or upto the skin. Hairs inside the nostrils trap dust containing germs. * **Mucus:** Mucus is a slimy secretion of the epithelial lining of various organs. For example, the mucus secreted in the nasal passage and windpipe, traps many bacteria and prevents their entry into the tissues. Cilia of the windpipe then throw out the bacteria trapped in the mucus. ### 2. Thrown out if entered Coughing, sneezing and vomiting are direct methods to throw out germs or any foreign unwanted objects which get into the respiratory and digestive systems. Even diarrhoea, or loose motions, helps in throwing out the germs if the infection persists in the digestive tract. ### 3. Germ-killing secretions * **Saliva, sweat, tears and nasal secretions:** contain germ-killing substances * **Hydrochloric acid:** secreted by the stomach kills germs that gain entry along with food. ### 4. Germ-fighting white blood cells (WBCs) Should any microbe enter the body, the white blood cells (phagocytes) are ready to fight them. * **Fig 17.1:** Shows the engulfing of bacteria (phagocytosis). A - Cell forcing its way (diapedesis); B - White cell attracted; C - Bacteria. * **Fig 17.2:** Shows two white blood cells patrolling the alveoli in a human lung. The spherical one is in its normal shape. Below it is an elongated white cell, about to engulf the round particle on the left. (Scanning electron microscopic view, highly magnified about 5,000.) **Aids to Health** * **April 7th:** is **World Health Day**. This day is celebrated to create consciousness regarding health, at all levels, and to disseminate information on health issues. * **MITY** means a body's defence against all the invaders and pollutants which entered the body. These invaders may enter the body by: * **The skin** * **Mucous membranes of eyes, nose, mouth and genital tracts** * **Food and water intake** * **Air we breathe in** * **Prevention of entry** * The body has two different defence systems: * **Local Defence System:** This system is the first line of defence, which prevents the entry of harmful micro-organisms. * **Internal Defence System:** It deals with the germs after they have entered the body tissues.