Human Health and Diseases: Since time immemorial, human health has intrigued the intelligence of philosophers and thinkers. Earlier, health was the component of physical well-being only. The Greeks like Hippocrates as well as Indian Ayurveda system of medicine asserted health to be the balance of certain ‘humour’ in the body. However, with the advent of scientific discoveries, like the circulation of blood by William Harvey, that establish more than just ‘humour’ balance, these notions changed and health began to expand its horizon beyond physical well being.

Presently, the World Health Organization (WHO) defines health as "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity." As a consequence, the biological improvisations are made with this holistic view of health. Therefore, in order to achieve ‘healthy’ human populations across the globe, it is crucial to realise the threats to health and this is the essence of the chapter human health and diseases.

So, let us see the topics mentioned in this chapter of biology and human welfare:

Common diseases in humans: pathogens and parasites causing human diseases (Malaria, Filariasis, Ascariasis. Typhoid, Pneumonia, common cold, amoebiasis, ringworm)

Basic concepts of immunology: Innate immunity, Acquired immunity, Active and Passive Immunity, Vaccination and Immunisation, Allergies, Auto Immunity

Immune System in the Body

AIDS and HIV: Replication of retrovirus, enzyme-linked immunosorbent assay (ELISA), Prevention of AIDS,

Cancer: Causes of cancer, Cancer detection and diagnosis, treatment of cancer

Drugs and alcohol abuse: Opioids, Cannabinoids, Adolescence and Drug/Alcohol Abuse, Addiction and Dependence, Effects of Drug/Alcohol Abuse, Prevention and Control.

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Immunity – the ability of host cells to fight the disease causing microorganism due to immune system is called immunity. There are two types of immunity-

Innate immunity – non-specific types of defence presents at the time of birth and provide different kinds of barriers to the entry of foreign agents into the body. it consists of four types of barrier-

a. Physical barrier- skin, mucus coating of epithelium lining the respiratory, gastrointestinal and urogenital tract.

b. Physiological barrier- acid in stomach and saliva in mouth.

c. Cellular barrier- leucocytes, neutrophils, monocytes.

d. Cytokine barriers- virus infected cells secretes protein called interferon.

NoInnate ImmunityAcquired (Adaptive) Immunity

1Present from birth itselfDevelops during life time

2The immunity remains throughout life.Can be short lived or lifelong.

3Contact or exposure with pathogen or its antigen is not essential.Contact with pathogen or its antigen is essential.

4Innate immunity is inheritable.Acquired immunity cannot be passed to the next generation except for a brief period to neonates.

5It protects the individuals from contraction of diseases of other organisms.It protects the individuals from pathogens present on other members of the same species.

Acquired Immunity- pathogen specific defence characterised by memory. When our body encounters a pathogen first time produces a response called primary response of low intensity. Subsequent encounter by same pathogen produce highly intensified response called secondary response or anamnestic response due to memory of first encounter.

Primary and secondary responses are carried out with the help of B-lymphocytes and T-lymphocytes. B-lymphocytes produce army of protein called antibodies each having two light and two heavy chains.

It involves two types of lymphocytes –

B lymphocytes: Show humoral immune response (HI)

T lymphocytes: Show cell mediated immunity (CMI)

On the basis of production of antibodies, immunity can be further categorised as –

Active immunity: Body produces its own antibodies against antigens

Passive immunity: Readymade antibody is transferred from one individual to another

Colostrum (contains antibodies IgA) is an example of passive immunity provided by the mother to her child.

Different types of antibodies produce in blood include IgA, IgM, IgEete. They are called humoral immune response due to presence in blood.

Human immune system can distinguish between self and foreign molecules or foreign bodies. Sometimes, due to genetic or unknown reasons, the body attack self-cells. This results in damage to the body and called auto-immune disease. Rheumatoid arthritis is due to this effect

Allergies – the exaggerated response of immune system to certain antigens present in the environment is called allergy. The substance to which such immune response is produced is called allergens. The antibodies produced due to these are IgE types. Allergy is due to secretion of chemicals like histamine and serotonin from the mast cells.

Immune system in the body- the human immune system includes lymphoid organs, tissue, cells and soluble molecules like antibodies.

Lymphoid organs are the organs where origin and maturation and proliferation of lymphocytes occur. Primary lymphoid organs include bone marrow and thymus.

After maturation lymphocytes migrate to secondary lymphoid organ like spleen, lymph nodes, tonsils, peyer’s patches of small intestine and appendix. They provide the sites for interaction lymphocyte with antigens.

There is lymphoid tissue also located within the lining of respiratory, digestive and urogenital tract called mucosal associated lymphoid tissue ( MALT). It constitute 50% of lymphoid tissues in human body.

AIDS (Acquired Immuno Deficiency Syndrome) was first reported in 1981. It is caused by HIV (human Immuno deficiency virus), a retrovirus. Transmission of HIV virus occurs by-

b. Transfusion of contaminated blood and blood products

c. Sharing infected needles as in intravenous drug abusers

d. Infected mother to her child through placenta.