Class 9 th Why do we fall ill?

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1 Class 9 th Why do we fall ill? Health: health is a state of physical, mental and social well being. The health of all individuals is dependent on their physical environment, social environment, and their economic status. Disease: It is any disturbance in the normal functioning of the body that probably has a specific cause and identifiable symptoms. In other words disease means being uncomfortable. Disease may be due to various external or internal factors, such as disease causing microbes, psychological or physiological problems. Distinction between being Healthy and Disease-free : Being healthy is more than being physically fit and disease free It is possible to be in poor health without actually suffering from a particular disease. Being healthy entails both physical and mental health to develop a happy and productive life. How can we detect a disease When there is a disease, either the functioning or the appearance of ne or more systems of the body will change for the worse, thus the disease can be detected by its signs and symptoms. Sign: it is the physical manifestation of an illness, injury or other bodily disorders. It is objective and can be observed by others. Signs can be felt, heard, seen or measured by a doctor. These include pilse, body temperature, respiration, blood pressure and physical signs such as loose motions, cough, bruising, bleeding, a wound with pus etc. Symptoms: symptoms are what the patient experiences about an illness, disease or an injury. It is subjective and may be only known to the patient experiencing it. It is not visible to others including doctors. Symptoms include pain, discomfort, headache, fever, chills, cold, nausea etc. Acute and chronic diseases: diseases are classified as acute and chronic depending on their duration. Acute disease 1. They last for only very short periods of time. 2. They do not have time to cause major effect on general health. 3. Eg. Common cold, pneumonia, influenza Chronic diseases 1. These are long lasting or recurrent and may even last a lifetime. 2. These are likely to have drastic long-term effects on a person s health and may cause prolonged poor health. 3. Eg. Elephantiasis, heart disease, cancer, diabetes etc. Causes of diseases: Causative organism: infectious agents like the microbes are generally the immediate cause of a disease. 1

2 Lack of good nourishment: poverty and lack of awareness cause lack of good nourishment. This may be contributory cause of a disease because it lead to low immunity against diseases. Lack of public services: absence of community health services and hygiene are also immediate or contributory causes of diseases. Diseases may be due to infectious or non-infectious causes: Infectious Diseases 1. Are caused by microbes like bacteria, fungi, virus 2. These Diseases can spread in the community through the microbes, directly or indirectly, from one person to other. Thus microbes are the external causes of these Diseases 3. Eg. Influenza, cold, tuberculosis etc. Non-infectious Diseases 1. Are not caused due to microbes, but caused due to internal body problems. 2. These Diseases do not spread in the community, their causes are internal. 3. Eg. Heart diseases, diabetes Peptic ulcers This disease cause acidity related pain and bleeding in the stomach and intestine. Two Australian Barry J. Marshell and Robin Warren discovered that bacterium Helicobactor pylori, was responsible for peptic ulcer. For a long time it was thought to be a chronic lifestyle Disease, but now it can be cured with antibiotics. Agents of infectious Diseases: Disease causing microbes are called pathogens. Categories of infectious agents are viruses, bacteria, fungi, protozoa, worms etc. Infectious agents common diseases 1. Viruses common cold, influenza, dengue, fever and AIDS etc. 2. Bacteria: typhoid, cholera, tuberculosis, anthrax etc. 3. Fungi fungal infections of hair, nail, skin 4. Protozoan: malaria, kala-azar 5. Worms elephantiasis, intestinal worm infections Antibiotics: Antibiotics are compounds used to treat infections caused by bacteria. They commonly block biochemical pathways important for bacteria. Many bacteria make a cell wall to protect themselves. Penicillin, an antibiotic, block the bacterial processes that build the cell wall. As a result, the growing bacteria become unable to build a cell wall and die rapidly. Antibiotic are not effective against viral infections because viruses do not use the biochemical pathways that build the cell wall. Why it is harder to make antiviral medicines than antibacterial? Viruses do not have cellular organization. They enter our cells and use our cellular machinery for their life processes, as they have very few biochemical mechanism of their own, due to this antiviral medicines are difficult to make. 2

3 Communicable diseases: Infectious diseases that can be spread by microbial agents that move from an infected person to someone else in a variety of ways are called communicable diseases. Mode of spread of communicable diseases: Infectious agents are spread through air, water, food, physical contact or vectors. Mode of spread and diseases Mode of transmission Point of entry and targeted organs/ tissues Spread through air (common cold, pneumonia, tuberculosis) They are transmitted when an infected person sneezes or coughs. The little droplets containing microbes thrown out in the air may be inhaled by a person They enter the nose along with the air that we inhale to reach the lungs and are likely to infect them. Spread through water and food (cholera, typhoid) Spread through sexual contact (AIDS, Syphilis) Spread through casual / close physical contact (tuberculosis, leprosy, scabies, eye and skin infections) Spread through blood to blood contact (AIDS, hepatitis B, hepatitis C) Transmitted by vectors (malaria, filarial, dengue, Japanese encephalitis) standing close by. They are transmitted when the source of drinking water is contaminated by the excreta of a person containing the microbes of an infectious intestinal disease, such as cholera These are spread through sexual contact from an infected person to the other. These are called sexually transmitted disease (STD) are not spread by casual physical contact These are spread through handshakes or hugs or through contact sport such as wrestling, boxing and judo. Also close physical contact like sharing clothes, beds and furniture. These are transmitted by blood of an infected person during blood transfusion or by infected injection needle or syringe. Also from an infected mother to her baby during pregnancy or through breast feeding They are transmitted by animals that carry the infectious agents from a sick person to another potential host. These animals are thus the intermediaries and are called vectors. food or water contaminated by bacteria that cause cholera or typhoid, enters through the mouth and reaches the intestinal lining or the viruses that cause jaundice, present in contaminated food or water, go to the liver. Entry point is sexual organs but syphilis bacteria cause sores on the skin and AIDs virus reduce the effectiveness of the immune system. Eye & skin infections can spread though physical contact. Mites of scabies cause an itchy skin HIV that causes AIDS comes into the body via the infected blood and spread to lymph nodes all over the body. Malaria causing microbes enter though mosquito bite. It then infects the liver and the red blood cells. The virus causing Japanese encephalitis enters through mosquito bite and infects the brain. Immune system of the body: 3

4 An active immune system recruits many cells to the affected tissue to kill off the disease- causing microbes. The recruitment process is called inflammation. Not all persons exposed to or infected with a particular infectious microbe develop a noticeable disease. This happens because the immune system of our body is normally fighting off microbes. The severity of disease manifestation depend on the no. of microbes in the body. The manifestation of disease will be minor if no. of infecting microbes is controlled. Severe infectious disease represents lack of active immune system. What is HIV- AIDS HIV stands for Human Immunodeficiency Virus. Virus that causes AIDS. This virus goes to the immune system and damage its function. AIDS stands for Acquired Immune Deficiency Syndrom. Syndrome means a set of signs and symptoms which together indicate a particular disease. Thus many of the signs and symptoms of HIV-AIDS are due to the infectious diseases caused by bacteria, viruses, fungi and other parasites that we face every day. These parasites are normally controlled by the immune system. But when the immune system get damaged by the HIV, it may result in death if not treated. Mode of spread of HIV: i) blood transfusion by infected person to healthy person ii) infected mother to her baby during pregnancy or by breastfeeding iii)by using infected syringes or injection needles. iv) through sexual contact with infected person, but not by casual physical contact. Principle of treatment: The category to which a disease causing organisms belongs decide There are two ways to treat an infectious disease: i) Symptoms directed treatment: this treatment is provided to reduce the severity of the symptoms that are usually because of inflammation. For ex. We can take medicine to bring down fever, reduce pain or loose motions. ii) To use medicines that kill microbes: antibiotics and other drugs are used to kill the microbes that block the biochemical pathways without affecting our own. iii) Take rest: on taking rest, most of the energy in the body is used in healing Principles of prevention of diseases.: After the spread of diseases, its control faces problems like : The body functions are damaged and the person may not recovered completely. The treatment or medication takes long time. The patient can serve as the source of infection to other people. It is because of such limitations of treatment that Prevention of diseases is much better than their cure. There are two ways of prevention of diseases.- general and specific General ways of prevention of diseases: The general ways of preventing an infections mostly related to adopting public health hygiene measures that reduce exposure to infectious agents. Some of them are: Preventing exposure to microbes: 4

5 i) Avoiding crowded places ii) Cover nose and mouth during coughing and sneezing iii) Drink purified or boiled water iv) Avoid stagnated water v) Avoid sex with infected/ unknown person Building an active immune system Availability of food and nourishment: make immune system stronger by taking well balanced,nourished food Specific ways of prevention of diseases- immunization Principle of immunization: suffering from a disease once is a means of preventing subsequent attacks by the same pathogen. In case of any infection for the first time our immune system responds against it specifically. Next time when the same microbes enter our body the immune system respond with greater vigour which eliminates the infection more quickly than the first time. The process of immune system becoming stronger towards the agent is called immunization Thus immunization is a process by which a person is made immune or resistant to an infectious disease. Immunization is done through artificially by vaccination. Vaccination: by providing vaccination,we can fool the immune system into developing a memory for a particular infection by putting something that mimics the microbe we want to vaccinate against, into the body. This does not actually cause the disease but this would prevent any subsequent exposure to the infecting microbes from turning into actual disease. What is vaccine: vaccines are suspensions of disease producing microbes which is modified by killing or weakening so that the suspension will not cause disease. When given to a healthy person, the vaccine triggers the immune system to respond and thus build immunity. Under the public health programme of immunization of children for prevention of infectious diseases, there are vaccines against tetanus, diphtheria, whooping cough, measles, polio, hepatitis A,/B.etc. What is immunity? Natural and acquired immunity: Immunity means resistance of a body to a disease.it is due to the presence of antibodies in our body against disease causing microbes known as antigens. When these antigens enter our body, antibodies are formed which kills the antigens. Natural immunity means that a person has these antibodies since birth. Eg whenever antigens, say of cholera enter the body, the person will not suffer from the disease. Acquired immunity means that when a person suffers from a disease once, antibodies for these particular disease-causing antigens will be formed in the body and he will not get the same disease again. Mother s milk is best for babies: Mother s milk is rich in proteins and other nutrients. It provides the complete diet for babies. It also provides antibodies for a disease due to which baby gets immunity. 5

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Downloaded from Class IX: Biology Chapter: Why do we fall ill Chapter Notes Key learnings: 1) Our body s well-being is dependent on the proper functioning of its cells and tissues. 2) All our body parts and activities