ICSE Class 9 Biology Chapter 17 Aids to Health

Aids To Health

Syllabus: Aids to health: Active and passive immunity. Meaning of active and passive immunity. An understanding of the use and action of the following - vaccination, immunisation, antitoxin, serum, antiseptics, disinfectants and antibiotics.

An idea of the local defence system and its merits, difference between antiseptics and disinfectants.

To be healthy, we need personal care as well as community involvement. This chapter on Aids to Health is intended to familiarise you with various (natural and artificial) ways of protection from diseases. Apart from the importance of the topic for examination, the information given here is very helpful for leading a healthy life.

17.1 Need To Keep Healthy

Every individual wishes to keep healthy and disease-free. This requires several things - some at personal level and some at community level. At personal level, one has to keep his body clean by washing, bathing, brushing teeth, regular physical exercise, and proper diet and proper rest and sleep. At community level, our surroundings should be kept clean with no accumulation of garbage or stagnant water, etc., so that the disease-spreading insects and pests do not thrive.

World Health Day April, 7

This day is celebrated to create consciousness about keeping healthy and disseminate the message at all levels.

Teacher's Note

Good health requires both personal hygiene and clean surroundings; this is why we see sanitation workers in every community.

17.2 Immunity

Immunity means body's defence against disease. Our body is all the time invaded by various harmful substances like pollutants (poisonous chemicals) and germs. They may enter our body in the following four ways:

1. Directly through the skin.

2. Through mucous membranes of eyes, nose, urinary or genital tracts.

3. Through food or water intake.

4. Through the air we breathe in.

Our body system first tends to prevent their entry into the body. Secondly, if somehow they do enter, the body fights with them, so that they cause no harm (rendered harmless).

The defence system in our body works at two levels:

A. Local defence system (Prevention of entry of germs). This is a kind of barrier system which tackles the germs at their possible entry points. It includes:

(1) protective mechanical barriers

(2) thrown out, if entered

(3) germ-killing secretions, and

(4) germ-fighting WBCs.

B. Immune system. It deals with the germs after they have entered into the body tissues.

17.2.1 Local Defence System

1. Protective mechanical barriers. These include the skin, hair, mucus, etc.

(i) Skin - Skin has an outer tough layer made of a protein keratin and it is almost impermeable to germs. At any given time, there are lots of germs settled on the outer surface of the skin, which have come through the air or through direct contact with contaminated objects. Even a handshake or a kiss on the cheeks of a baby transfers germs from one individual to another. Washing with soap and water removes the germs. Any scratch or cut in the skin opens the way for germs to get in. Should there be any cut in the skin, the clotting of blood plugs the cut ends of blood vessels at the wound to prevent entry of germs.

(ii) Hairs - Hairs intercept the germ's journey inwards or upto the skin. Hairs inside the nostrils trap dust containing the germs.

(iii) Mucus - Mucus is a slimy secretion of the epithelial lining of various organs. For example:

the mucus secreted in the nasal passage and the wind pipe, traps many bacteria and prevents their entry into the body tissues.

Cilia of the wind-pipe throw out the bacteria trapped in the mucus.

2. Thrown out, if entered

Coughing, sneezing and vomiting are direct methods to throw out the germs or any foreign unwanted objects which get into the respiratory and digestive systems. Even diarrhoea (loose motions) helps in throwing out the germs if the infection persists in the digestive track.

3. Germ-killing secretions

(i) Saliva, sweat, tears and nasal secretions contain germ-killing substances.

(ii) Hydrochloric acid secreted by the stomach kills germs that gain entry along with the food.

4. Germ-fighting white blood cells (WBCs). Should any microbe enter the body systems, the white blood cells (phagocytes) are ready to fight them. They squeeze out of the walls of the blood capillaries (by diapedesis) and engulf the bacteria or the germs and destroy them (phagocytosis) (Figs. 17.1 and 17.2). Pus in a wound, for example, is a mixture of destroyed germs, killed WBCs and damaged tissue cells.

Merits Of Local Defence Systems

1. They start working instantaneously.

2. They are not dependent on previous exposure to infections.

3. They are effective against a wide range of potentially infectious agents.

Teacher's Note

Your skin is like a shield that protects you from germs every day - when you wash your hands, you're removing germs that landed on this shield.

17.2.2 Immune System

The local defence systems are not effective in all cases and circumstances. Certain microbes (germs) or their poisonous secretions (toxins) do enter the deeper tissues and various organ-systems, by their special mechanisms of entry or through any breaches in the protective barriers.

At this stage, the blood and other body fluids start fighting against the germs or any other unacceptable foreign substance. The body fluids contain special proteins called antibodies which react with the invading germs, and antitoxins which react with their poisons (toxins) to destroy them, and thus they provide protection against disease (immunity).

Immunity is the resistance to the onset of a disease after infection by harmful germs.

To define more elaborately - Immunity is the "capacity of our body to deal with foreign substances, e.g., bacteria, viruses, toxins, etc. that enter our body and to render them harmless." or simply, "it provides resistance against disease-causing germs."

Kinds Of Immunity

Immunity can be classified into two main categories - innate and acquired immunity and their different subcategories are as follows:

1. Innate Immunity, also called natural or native immunity. This immunity is by virtue of genetic constitutional make-up. It is there in the body without any external stimulation or a previous infection.

(a) Non-specific innate immunity. A degree of natural resistance to all infections in general. For example, humans do not suffer from the plants' highly infectious diseases, or even certain diseases of animals.

(b) Specific innate immunity. This is a natural resistance to a particular kind of germ only. Some races or some individuals do not suffer from certain infectious diseases. For example, human beings are immune to a highly infectious disease of dogs (known as 'Distemper'), which kills about 50% of all infested dogs.

2. Acquired Immunity - Resistance to a disease which an individual acquires during his life-time. It may be the result of:

Either

A previous infection (actively acquired immunity), e.g., a person having once suffered from "measles" will not normally suffer from it again.

Or

"Ready-made" antibodies supplied from outside (passively acquired immunity), e.g., a person bitten by a poisonous snake is given anti-venom injection (venom: poison) which contains antibodies for the poison that were produced in the body of a horse.

(a) Actively acquired immunity. This is the resistance developed by an individual due to a previous infection or antigen (chemical found on the surface of the disease-causing germ cell) which enters his body naturally leading to (i) naturally acquired active immunity) or is introduced artificially, as in vaccinations leading to (ii) artificially acquired active immunity). In either case, the body lymphocytes react in two ways:

- They produce antibodies which freely circulate in the blood & lymph, and which bind to the microorganism to kill it.

- They produce killer cells carrying specific receptors for foreign antigens found on invading germs.

The actively acquired immunities are usually long-lasting carried out through 'memory' lymphocytes.

(b) Passively acquired immunity. This is the immunity provided to an individual not by his own body but from an outside source in the form of "ready-made" antibodies. The passively acquired immunity again can be of two types:

(i) Naturally acquired passive immunity. In it, the ready-made or the "pre-prepared" mother's antibodies may reach the foetus (developing embryo) through the placenta.

(ii) Artificially acquired passive immunity. In this, the antibodies are produced in the blood of a horse or the other animal by injecting germs into its body. Antiserum injections are prepared from the serum (containing antibodies) of such animals' blood and are injected into the body of the patient, e.g. in the treatment of snake-bite by antivenim or that of a diphtheria patient by anti-diphtheria injections. Haffkine's Institute in Bombay and another institute at Kasauli are preparing several such anti-sera. Antivemme for treating snake-bite is also based on the same principle. For the sake of simplicity, let us just take the active and passive immunities and summarise the differences between them as given in table 17.1 at the bottom.

17.2.3 Antibodies

These are special chemicals found in the blood which act against the germs or their secretions.

Some of the characteristics of the antibodies are as follows:

1. The antibodies are proteins (they belong to the class of immunoglobulins).

2. Antibodies are produced by a type of specialised lymphocytes on exposure to antigens (chemical substances found on the germs' cells) (Fig. 17.3). These special lymphocytes particularly concentrate in the lymph nodes and spleen and also in the circulating blood and lymph.

3. Our body can make an unlimited variety of different antibodies.

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

5. An antibody recognises its particular antigen and binds to it rendering it harmless, which is subsequently destroyed and eliminated by the body.

6. Some antibodies are present in the blood of some people from the very birth. Such people having these particular antibodies in their blood do not suffer from those particular diseases even if the germs for them have crossed the barriers and escaped the phagocytes.

7. Immunity produced by the antibodies on exposure to antigens may be either for a short period (as in common cold, chiefly), or for a longer period (as in small pox, measles, etc.).

Teacher's Note

When you get a vaccine, your body learns to fight the disease on its own, similar to how you remember a friend's face after meeting them once.

A detailed account of AIDS, its germ, mode of infection, symptoms etc. have been given in Concise Biology Part I of Class IX.

Dec. 1 - World AIDS Day

(Awareness for its severity and protection)

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