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Immune System

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Human diseases can be split into two categories: -

· Those that happen before or during birth
· And, those that happen afterwards.


Damage to the body caused by injury or disease is repaired naturally by the growth and spread of new tissue to replace damaged ones. The precise way in which the replace process works varies according to the type of tissue and the size and nature of the damage.

The first step in healing is the formation of a blood clot, sealing the cut and stopping the bleeding. A scar of dried blood forms on the surface of the skin and protects the new tissue forming beneath it. Fibrous tissue builds up in the wound, new cells and blood vessels grow in the gap, and a week later there is no visible indication of the injury. However this is not the case in all injuries, in more complicated cases the wound is replaced by fibrous scar tissue. Eg. Lungs, Kidneys etc.

HOW THE BODY FIGHTS INFECTION Viruses, bacteria, fungi, worms and other parasites, which enter the body through the skin, nose, mouth or other openings of the body, cause infectious diseases. The body has various barriers against such invasions and they are as follows:-

1. ADENOIDS & TONSILS: - are made of lymphoid tissue, located at the entrances to the throat, they act as barriers to bacteria & viruses.

2. LACHRYMAL GLANDS: - located above the outer corner of each eye, secrete tears, which wash dust and dirt from the eyes. Tears also contain Lysozyme, a substance that combats bacteria.

3. SALIVARY GLANDS: - are found in the cheeks and under the tongue. The salvia they secrete contains substances, which help to resist infection.

4. MUCOUS MEMBRANE: - is a soft moist tissue lining the body openings and passages, such as the nose & the throat. It secretes mucus, a sticky fluid, which provides protection against some bacteria. In the nasal cavity the mucous membrane also traps germs and dust.

5. LYMPH NODES: - Are small lumpy structures scattered along the course of the lymphatic system. The neck, armpits and groins have the greatest numbers where they act as traps for bacteria & other invaders. The nodes also produce white blood cells, which attack foreign matter.

6. SPLEEN: - which has lymphoid tissue, helps to form white blood cells and remove used ones.

7. STOMACH: - has digestive juices including hydrochloric acid which helps to sterilize the food intake.

8. LIVER: - produces two substances, fibrinogen and prothrombin, which make the blood clot and so help in wound healing. This large gland also destroys many parasites and poisons which are carried to it in the blood stream.

9. INTESTINES: - contains bacteria which usually remain there and are harmless. Some intestinal bacteria, such as bacillus, cause disease if they get into other areas of the body.

10. LYMPHATIC SYSTEM: - is a second circulation, which is intertwined with the network of blood vessels, the lymph stream contains white blood cells, which helps to stop the spread of infection by producing antibodies.

11. SKIN: - provides the body’s main protection against disease. Because it is dry and slightly acid, and its surface in constantly being replaced, invaders rarely colonize the skin, except in the case of injury. Beneficial bacteria live on the skin, but they can be a cause of illness if they penetrate below the surface.

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