Maharashtra Board Class 12 Biology Chapter 10 Human Health and Diseases PDF Download

10 Human Health and Diseases

Health does not simply mean absence of disease or physical fitness. In fact, it is difficult to aptly define health. According to the World Health Organization, health is defined as the state of complete physical, mental and social wellbeing and not merely the absence of disease or infirmity. In short, health is birth right of humans. Health also reflects the metabolic and functional efficiency of living organisms. Hygiene is a science of rules of health. To achieve good health, it is therefore, necessary that we have hygienic balanced diet, clean drinking water, personal and community hygiene, regular physical exercise, knowledge about diseases and their effect on body, proper disposal of waste and control of vectors.

Everyday we are exposed to various foreign bodies, including infectious agents like bacteria, viruses, etc. Despite constant exposure to variety of pathogens, most of us remain healthy. This is due to fact that the human body has ability to resist almost all type of these foreign bodies. The system which protects us from various infectious agents, is called immune system. Resistance is the ability to prevent the damage or disease, through our defense mechanism.

10.1 Immunity

The term immunity has traditionally referred to as the resistance exhibited by the host towards injury caused by pathogens and their products. However, protection against infectious diseases is only one of the many consequences of immune response, which is entirely concerned with the reaction of the body against any foreign antigen.

Immunity is in fact the freedom or exempt. The concept of immunity is believed to be started by Edward Jenner in England. He developed cowpox vaccine for the protection against the attack of small pox (virus). Immunology is a branch of science which deals with the study of immune system, immune responses to foreign substances and their role in resisting infection by pathogens.

The most important characteristic of immune system is that it distinguishes self (body's own cells) and non-self (foreign molecules or invading cells). So, the immune system differentiates between the body cells and the invaders. Any foreign substance invading body and capable of stimulating an immune response, is called an antigen. The protective chemicals produced by immune cells in response to antigens are called antibodies.

A. Types Of Immunity

There are two types of immunity as Innate or Inborn (inherited) immunity and Acquired or Adaptive immunity.

i. Innate Immunity Or Inborn Immunity

Innate immunity is the resistance to infections that an individual possesses by virtue of his or her genetic make-up. It is the natural (inborn) defense system of the body. It is not affected by prior contact with microorganisms or immunization. It is nonspecific, when it indicates a degree of resistance to infection in general, or specific where resistance to a particular pathogen is concerned. One form of innate immunity comprises the various types of barriers which prevent entry of foreign agents into the body.

Teacher's Note

Our body is like a fort that fights against germs. In India, we see many children get sick but some children do not get sick easily. This is because their body has a strong immune system, just like having strong walls in a fort.

Exam Trick

Remember: Innate = born with you. Like your mother tongue is innate (you get it from birth). Your immune system also has innate power from birth to fight germs.

Points To Remember

Innate immunity is present from birth.
It does not need any germs to activate it.
It is the first line of defense of our body.

a. Epithelial Surface

The intact skin and mucous covering the body, protect it considerably against invasion by microorganism(s).

The healthy skin possesses bactericidal activity due to the presence of high concentrations of salt in drying sweat. Sebaceous secretions and long chain of fatty acids have bactericidal and fungicidal properties. The mucosa of the respiratory tract has several innate mechanisms of defense. The nose prevents entry of microorganisms to a large extent, the inhaled particles being arrested through hair at or near the nasal orifices. Those that pass beyond are held by mucus lining the epithelium and are swept back to pharynx where they tend to swallowed or coughed out. The cough reflex is an important defence mechanism of respiratory tract. The mouth is constantly bathed in saliva which has inhibitory effect on microorganisms. The acidity of gastric secretions in the stomach destroys microorganisms. The flushing action of urine eliminates bacteria from the urethra. Spermine and zinc present in semen are antibacterial.

Teacher's Note

Our skin is like a protective wall around a city. Just like a wall stops enemies from entering a city, our skin stops germs from entering our body. In India, when children get small cuts, we tell them to wash with water to clean the wound.

Exam Trick

Remember: Skin = first protection. Saliva, sweat, tears = all are soap and water for germs. They kill germs naturally.

Points To Remember

Skin is the first barrier against germs.
Sweat has salt that kills germs.
Stomach acid kills germs we eat by mistake.
Cough and sneeze remove germs from our nose.

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