IMMUNITY

Immunity means body's defence against diseases.

Germs may enter our body through-

1. Skin

2. Mucous membranes of eyes, nose, genital tracks, etc.

3. Food or water

4. Air we breathe

Defense system has 2 levels-

• Local defense system- tackle the germs at their possible entry points. It includes-

1. Protective mechanical barriers

2. Thrown out if entered

3. Germ killing decretions

4. Germ fighting WBCs

• Immune system- it deals with germs after they have entered into the body tissues

LOCAL DEFENSE SYSTEM-

• Protective mechanical barriers

Skin- it is the outer tough layer is made up of keratin and it is impermeable to germs. Clotting of blood plugs the cut ends of blood vessels so it would prevent germs.

Hair- intercept the germs journey inwards or upto the skin. Inside the nostrils trap dust containing germs.

Mucus- slimy secretion of epithelial lining of various organs like nose, etc.

• Thrown out if entered

Coughing, vomiting and sneezing are direct methods to throw out germs. Even diarrhea helps in throwing out the germs in digestive tract.

• Germ killing secretions

Saliva sweat, tears and nasal secretions contain germ killing substances.

HCl secreted by stomach kills germs that enter with food.

• WBCs - phagocytes

They fight the any germ or microbe which enters the body. They are squeezed out of capillaries and engulf bacteria and destroy them.

Merits of local defense system-

1. Start working instantaneously

2. Not dependent on previous exposure to infections

3. Effective against wide range of potentially infectious agents.

IMMUNE SYSTEM-

Immunity is the resistance to the onset of a disease after the infection by the harmful germs. Or capacity of our body to deal with foriegn substances.

Kinds of immunity-

1. Innate- virtue of genetic constitutional makeup. In body without any external stimulation or previous infection. Types-

Non specific- a degree of natural resistance to all the infections.

Specific- a natural resistance to a particular kind of germ only. Some individuals do not suffer from certain infectious diseases.

2. Acquired- resistance to a disease which an individual acquires during his lifetime. It may result of-

Actively acquired immunity- infection developed by an individual due to previous disease or antigen which enter naturally leading to- naturally acquired or introduced artificially- artificially acquired. In either case lymphocytes or WBCs in the body react in 2 ways-

• They produce antibodies which freely circulates and binds microorganism.

• They produce killer cells carrying specific receptors for antigens found invading germs.

It is long lasting carried out through memory lymphocytes.

Passively acquired- immunity provided by outside in form of ready made antibodies. Types-

Naturally- readymade or prepared mothers antibodies may reach the foetus through placenta.

Artificially- antibodies produced in the blood of a horse or some other animal by injecting germs into its body. Antiserum injection are prepared.

Antibodies-

They are special chemicals found in the blood which act against the germs or their secretions. Characteristics-

1. They are proteins

2. Produced by a type of specialized lymphocytes on exposure to antigens. Concentrate in the lymph nodes.

3. Our body can make unlimited variety of different antibodies

4. They are specific which means that one kind of antibody acts against one particular type of antigen only.

5. Recognises its particular antigen and binds to rendering it harmless which is destroyed by the body.

6. Some antibodies are present in blood of few people from the birth

7. Immunity produced on exposure of antigen may be short period or long period.