Chapter 13 Why Do We Fall Ill? Class 9 Science PDF

Chapter–13 Why do We Fall Ill? Class-9 Health The state of being well enough to function well physically, mentally and socially is defined as health. Disease The disturbance in the structure or function of any organ or part of body is called as disease. It may be caused due to th...

Chapter–13 Why do We Fall Ill? Class-9 Health The state of being well enough to function well physically, mentally and socially is defined as health. Disease The disturbance in the structure or function of any organ or part of body is called as disease. It may be caused due to the attack of pathogens (virus, bacteria), lack of nutrition and balanced diet. Difference between “Healthy” and “Disease-Free” Healthy Disease-Free It is the state of physical, mental It is the state of absence from and social well being. diseases. It refers to the individual, physical It refers only to the individual. and social environment. The individual has a good health The individual may or may not and is disease free. have good health. Types of Diseases- Acute Diseases  The diseases which last for only very short periods of time are called acute diseases. For example: Influenza (Flu), Common cold, etc. Chronic Diseases The diseases which last for a long period of time, even as much as a lifetime are called Chronic Disease. For example: Tuberculosis, Cancer, etc. Difference between Acute and Chronic Diseases Acute diseases Chronic Diseases These lasts for a small period of It lasts for a long period of time, time. even as much as lifetime. They do not have long term They have long term effects on effects. body. These diseases recover completely. These diseases do not recover completely. Example- Cold, cough, typhoid etc. Example- Diabetes, tuberculosis, elephantiasis etc. Causes of Diseases There are basically 2 causes of diseases - Immediate cause and contributory cause. Immediate cause- The organisms that enter our body and causes disease are called immediate cause. Example- virus, bacteria, protozoa etc. Contributory cause- The secondary factors which led these organisms enter our body are called as contributory cause. Example- dirty water, contaminated food etc. Diseases may be due to infectious and non-infectious causes. Infectious causes- Diseases where microbes are the immediate causes are called infectious diseases. The infection can spread from one person to other. Non-infectious causes- These are the diseases that are not caused by infectious agents and they remain internal. These diseases do not spread from one person to other. For ex- Cancer Types of Diseases Infectious diseases (Communicable diseases)- The diseases which can easily spread from one person to other are known as communicable diseases. The disease-causing organism enters the body, causes infection, multiplies and grows in the body of host. Antibiotics- They block biochemical pathways important for bacteria. These are effective only against bacterial diseases. Many bacteria, make a cell-wall to protect themselves. The antibiotic penicillin blocks the bacterial processes that build the cell wall. As a result, the growing bacteria becomes unable to make cell-walls and die easily. Human cells don’t make a cell-wall anyway, so penicillin cannot have such an effect on us. Penicillin will have this effect on any bacteria that use such processes for making cell-walls. Similarly, many antibiotics work against many species of bacteria rather than simply working against one. Viruses do not use these pathways and therefore antibiotics do not work against viral infections. Means of Spread of Infectious Diseases Air- common cold, pneumonia and tuberculosis. Food and water- cholera, typhoid and hepatitis Sexual Contact- AIDS and syphilis Animals and mosquitoes- The animals carry the infecting agents from a sick person to another potential host. These animals are thus the intermediaries and are called vectors. Mosquitoes feed on many warm- blooded animals and they can transfer diseases from person to person.  Inflammation- An active immune system recruits many cells to the affected tissue to kill off the disease-causing microbes. This recruitment process is called inflammation. There are effects such as swelling, pain and fever. PRINCIPLES OF TREATMENT There are two ways to treat an infectious disease- one is to reduce the effects of the disease (General method) and the other is to kill the cause of the disease (Specific method). Cause of the disease can be killed by properly cleaning the houses, drinking purified water, eating healthy food and maintaining a balanced diet. Effects of the disease can be reduced by using medicines, vaccination etc. IMMUNISATION If you had smallpox once, there was no chance of suffering from it again. So, having the disease once was a means of preventing subsequent attacks of the same disease. This happens because when the immune system first sees an infectious microbe, it responds against it and then remembers it specifically. So the next time that particular microbe, or its close relatives enter the body, the immune system responds with even greater vigour. This eliminates the infection even more quickly than the first time around. This is also known as immunisation.