Why Do We Fall Ill ? - Class 9 Science notes PDF Download

Importance Of Health:

Health is an important part of all living organisms. Good health is essential for the performance of various activities as well as for mental development. Good food habits lead to good health. A healthy person can perform all the activities with full capacity.

Health

According to WHO health may be defined as, a state of compete physical, mental and social well-being and not merely the absence of disease or infirmity. Health is influenced by many factors like genetic, environmental, social, economical and physical. Here are some advantages of good health: -

(i) Good health makes living a joyful experience.
(ii) Good health permits us to perform various day-to-day tasks at our best.
(iii) Good health makes a human being healthy and cheerful.

 Personal Health And Community Health

Personal Health

Personal health includes all those factors which influence the health and well being of an individual. Personal health comprises of broad range of day-to-day activities like: -

(i) Care of body regarding bathing and washing.
(ii) Care of clothing.
(iii) Care of teeth.
(iv) Care of hair, feet and nails.
(v) Care of posture.
(vi) Cultivation of good habits regarding eating clean food, diet, exercise, sleep, no smoking and no drinking of alcohol etc. and good attitude towards life.

Unhygienic or dirty habits of individual persons can create problems for the whole community.

Community Health

Community health means all such activities, which contributed to the improvement and well being of the health of people in community. The factors responsible for community health are: 

(a) Provision of clean, safe drinking water.
(b) Provision of good and efficient sewage disposal system.
(c) Provision of a lot of clean air to people by development of   green open spaces.
(d) Prevention of the development of breeding sites of harmful insects.
(e) Maintenance of an effective garbage disposal system.
(f) Provision of medical aid to people and vaccination to children.
(g) Management of environmental pollution.
(h) Provision of family planning advises and services.
(i) Prevention of food adulteration. 
(j) Educating the people to take care of various diseases.
(k) Provision of nutritious food and milk to malnutrition children.

Conditions Essential For Good Health

1. Nutrition (Proper Diet)

Nutritional requirements depend on individual’s age and special need so each person should take a balanced and proper diet in his food so that he should not suffer malnutrition.

2. Personal And Domestic Hygiene

For keeping good health one should maintain personal hygiene. Such as taking bath with soap and water regularly and washing hands before taking meals. Brushing of teeth, cleaning of tongue daily etc. For keeping good health one should also take care of the domestic hygiene. i.e., we should have good habits of cooking and storing food and keeping the house neat and clean etc.

3.  Proper Habits

For keeping good health, we should avoid bad habits like chewing tobacco, smoking, cigarette, beedi and hooka. Drinking alcohol in the form of wine whisky, beer or country liquor and taking narcotic drugs.

4. Exercise And Relaxation

Regular exercise such as yoga, morning walk or jogging, cycling etc. is necessary to keep one’s body and mind fit. Proper relaxation or recreation is also necessary to get relief from strain and it keeps good mental health. Relaxation improves the capacity to do work. It provides a relief or diversion from the work or effort.

Disease

Disease means dis-ease, without ease, discomfort or disorder in the body. We can say that disease is a malfunctioning of the normal state of the living organism.

Sources Of Diseases

Diseases can be caused by the following factors: -

(i) Internal Factors
(ii) External Factors

Internal Factors

The factors, which exist within the human body, are called internal factors. These are: -

(i)    Improper functioning of various body parts
(ii)   Genetic disorders
(iii)  Hormonal imbalance
(iv) Improper functioning of immune system 

Example Of Diseases

Heart failure, Kidney failure, Arthritis, Cancer, Dwarfism, Myopia, Diabetes, Asthma.

External Factors

(i)    Imbalanced Diet
(ii)  Disease Causing Microorganisms
(iii) Environmental Pollutants
(iv) Tobacco, Alcohol And Narcotic Drugs

Examples Of Diseases

Night Blindness, Kwashiorkor, Marasmus, Obesity, Rickets, Pellagra, Beriberi, Malaria, Measles, Chickenpox, Diarrhea, AIDS, Leprosy, Cholera, Dengue, Jaundice etc.

Types Of Diseases

1.   Congenital Diseases
2.   Acquired Diseases

Congenital Diseases

The diseases, which are present since birth, are called congenital diseases. These are caused due to genetic disorder or metabolic disorder.

 Acquired Diseases

The diseases that develop after birth are called acquired diseases. These are further of two types: -

(i) Communicable Diseases (Infectious)
(ii) Non-communicable Diseases (Non-Infectious)

Communicable Diseases

Also called infectious diseases are caused by biological agents such as viruses, bacteria, protozoas, fungi and helminthes (worms) etc. These diseases rapidly spread from one person to another by many ways like water, air, physical contact and insects etc.

Non-Communicable Diseases

The non-communicable diseases do not spread from one person to another. These are caused from various means: -

(i)    Due to lack of certain essential substances.
(ii)   Degeneration of tissues.
(iii)  Uncontrolled growth of tissues or cells.
(iv)  Metabolic Disorders.
(v)   Injury or damage to any part of the body.

 Why Do We Say That Not Being Diseased Is Not The Same As Being Healthy?

We tend to think that if we are free of diseases we are healthy. But this is not so. Health is something more than absence of a disease, as health is a state of physical, mental and social well being. Depending upon requirement the meaning of health may vary from person to person. For example,

(i)    Good health for a dancer may means being able to stretch his body into difficult positions.
(ii)   Good health for a racer may means having enough breathing capacity in his/her lungs.
(iii)  There will be poor health if one is not energetic and not able to perform as per requirement.

From here we can conclude that we can be in a poor health without any cause of an identifiable disease.

What Does A Disease Look Like?

When there is a disease there is inflammation. It causes symptoms and signs to form which gives an indication that the body is not well. 

Inflammation

The process in which an active immune system appoints many cells to the affected tissues to kill the disease causing microbes is called inflammation. As a part of this process there are local effects such as swelling or pain and general effects such as fever.

Diseases are diagnosed with the help of symptoms and signs which are the characteristic effects of the diseases on the body and are readily apparent to the patient. These can be defined as follows: -

Symptoms

Symptoms indicate that there is something wrong in the body but do not give any exact clue of a particular disease. For example: - Fever, Headache, Fatigue, Body aches, Dizziness, Nausea, Rashes, Pain, Cough.

Signs

Signs provide definite indication of a particular disease. Signs are different for different diseases. For example: -

(i)    Headache, nausea, muscular pain, higher fever, feeling very cold and shivering are the signs of malaria.

(ii)   Sneezing, fever, headache, coughing, sudden onset of chills, discharge from the nose are the signs of influenza.

Note

Sometimes in order to pin point a particular disease the doctors rely on medical tests such as blood and urine test or X- rays etc.

On What Factors Do The Signs And Symptoms Of The Disease Depend?

The signs and symptoms of the disease depend upon the tissue or the organ which the microbe targets. If the lungs are the target then the symptoms will be cough and breathlessness. If the liver is the target the person will have jaundice. If the brain is the target the person will have headaches, vomiting, fits etc.

Acute And Chronic Diseases

Acute Diseases

The diseases which last for a short duration of time are called 

acute diseases. Being of short duration the acute diseases are unable to cause major ill effects on health. For example: - common cold, malaria, typhoid etc.

Chronic Diseases

The diseases which last for a long duration of time or even for life time are called chronic diseases. As the disease remains in the body for a long time, it affects the body also e.g., diabetes, tuberculosis etc.

Chronic Diseases And Poor Health

If a person is suffering from a chronic disease, he or she may have prolonged general poor health. Therefore it leads to drastic long term bad effects on the body. For example, loss of weight and fatigue in the body start appearing. There may be a shortness of breath, poor appetite, weakness etc..

Causes Of Diseases

Infectious Agents

The infectious agents are the organisms that cause the disease. They are categorized as follows: -

Viruses, Bacteria, Fungi, Protozoa, Worms 

Diseases Caused By These Infectious Agents Are As Follows: -

(i)    Viral Diseases Common cold, rabies, influenza, dengue fever and AIDS

(ii)   Bacterial Diseases Typhoid fever, tuberculosis, cholera and anthrax

(iii)  Fungal Diseases Many common skin infections

(iv)  Protozoan Diseases  Malaria and Kala azar

(v)   Diseases caused by worms  Intestinal worm infections and elephantiasis

Why Do We Need To Study Various Categories Of Infectious Agents?

By studying the categories of infectious agents we will be able to know their life processes and it will be easier to us to find ways to kill them when they attack the body.

What Are Antibiotics? How Do They Work?

Antibiotics are the drugs that kill bacteria. They commonly block biochemical pathways important for bacteria. Many bacteria make a cell wall to protect them. The antibiotic penicillin blocks the bacterial processes that build the cell wall. As a result the growing bacteria become unable to make cell walls and die easily. 

Why Antibiotics Do Not Kill Viruses?

It is because the viruses do not use the pathways such as bacteria use. They do not make cell walls. Viruses have few biochemical mechanisms of their own. They enter our cells and use our machinery for their life processes. This means that there are very few virus specific targets to aim at.

Means Of Spread

The diseases may spread from one person to another by the following ways: -

By Air 

This occurs through the little droplets thrown out by the infected person who sneezes or coughs. Someone standing close by can breathe in these droplets, and the microbes get a chance to start the new infection. 

Example  Common cold, pneumonia, tuberculosis.

By Water

This occurs if excreta of someone suffering from an infectious gut disease such as cholera, get mixed with the drinking water used by people nearby. The cholera causing microbes will enter new hosts through the water they drink and cause disease in them.

Example  Cholera, Diarrhoea

By Sexual Contact

There are certain diseases that are transmitted by the sexual 

contact from one partner to the other. However such diseases are not transmitted by casual physical contact such as handshakes, hugs or other ways by which we touch each other socially.

Example  AIDS, Syphilis, Gonorrhea, Warts

By Vectors

The animals that carry the infectious agents from one person to other are called vectors. The commonest vectors we know are mosquitoes and houseflies. 

Example  Malaria, dengue, Plague, Rabies

Organ Specific And Tissue Specific Manifestations

The disease causing microbes enter the body through different means. The body is very large as compared to the microbes so there are many possible places, tissues where they can go.

Do All Microbes Go To The Same Tissues Or Organ Or Do They Go To Different Ones?

If they enter from the air through the nose, they are likely to go to the lungs. If they enter through the mouth they can stay in the gut lining or they can go to the liver.

But this needn’t always be the case. An infection like HIV that comes into the body by the sexual organs will spread to lymph nodes all over the body and so on.

On What Factors Does The Severity Of The Disease Depend?

The severity of the disease depends upon the number of microbes in the body. If the number of microbes is very small, the disease may be minor or unnoticed. But if the number of the same microbe is large, the disease can be severe enough to be life threatening. 

Principles Of Treatment

There are two methods for the treatment of the disease: -

(i)    By reducing the symptoms of the disease

(ii)   By killing the microbes 

By Reducing The Symptoms Of Disease

We can provide treatment that will reduce the symptoms. The symptoms are usually because of inflammation. For example we can take medicines to bring down fever, reduce pain or loose motions. We can take bed rest so that we can conserve our energy. But even by reducing the symptoms of the disease the infectious microbes still keep on existing in the body which may even increase the symptoms again.

By Killing The Microbes

We can kill the microbes by using medicines. All the microbes have different biochemical life processes, therefore each of them needs a separate drug for killing.  We cannot use anti bacterial drugs to kill viruses. When the microbes of the disease get killed the body becomes disease free.

Principles Of Prevention

There are two ways to prevent the diseases:-

(i)    General ways

(ii)   Specific ways

General Ways

The general ways of preventing infections mostly relate to preventing exposure to the diseases.

How Can We Prevent Exposure To The Infectious Microbes?

It depends upon means of their spreading. For example: -

(i)   For Airborne Microbes

We can prevent exposure by providing living conditions that are not over crowded.

(ii)  For Waterborne Microbes

We can prevent exposure by providing safe drinking water. 

This can be done by treating the water for any microbial contamination.

(iii) For Vector borne Infections

We can prevent exposure by providing clean environments which are free from mosquitoes, flies, rats etc.

Another general way of preventing the disease is the availability of proper and sufficient food for everyone with the help of which the immune system will become healthy and work properly for fighting off the microbes causing the disease.

Specific Ways

The specific ways relate to a peculiar property of the immune system that usually fights off microbial infections because when the immune system first sees an infectious microbe it responds against it and then remembers it specifically. So the next time the particular microbe or its close relatives enter the body, the immune system responds with more vigour. This removes the infection even more quickly than the first time.

Vaccination (Immunization)

During vaccination we put something in the body that mimics the microbe we want to vaccinate against. This does not actually cause the disease but this would prevent any further exposure to the infecting microbe from turning into actual disease. Vaccinations are available for the following diseases: -

tetanus, diphtheria, whooping cough, measles, polio, rabies.

Why Prevention Of Disease Is Said To Be Better Than Its Treatment

It can be explained by giving the following three reasons: -

(i)    One someone had a disease, their body functions get damaged and may never recover completely. 

(ii)   The treatment will take time which means that someone suffering from a disease is likely to be bedridden for some time even if we can give proper treatment.

(iii)  The person suffering from an infectious disease can also cause diseases to the other persons.