Overview of Human Health and Diseases

A state of complete physical, mental and social well-being and not merely the absence of disease or infirmity is called health.

Adverse functioning of one or more organs or systems of the body, characterised by specific signs and symptoms, is called disease.

Diseases that are easily transmitted from one person to another are called infectious diseases.

Diseases that do not spread from one person to another and arise due to genetic factors, lifestyle or physiological disorders are called non-infectious diseases.

Organisms such as bacteria, viruses, fungi, protozoans and helminths that cause diseases in humans are called pathogens.

Innate immunity is the inborn, non-specific defence that protects the body from pathogens from birth.

The immunity developed when the body produces its own antibodies in response to exposure to antigens through infection or vaccination is called as active immunity.

The immunity obtained by the direct transfer of ready-made antibodies from another individual is called as passive immunity.

The process of introducing weakened or inactivated pathogens or their antigenic components into the body to induce immunity is called as vaccination.

The process by which an individual acquires protection against a specific disease through vaccination or antibody administration is called as immunisation.

The process of providing immediate protection by injecting preformed antibodies into the body is called as passive immunisation.

The exaggerated or hypersensitive immune response of the body to certain harmless environmental substances is called as allergy.

The substance that triggers an allergic immune response in a sensitive individual is called as allergen.

The condition in which the immune system fails to distinguish self from non-self and attacks the body’s own cells is called as autoimmunity.

• The immune system consists of lymphoid organs, tissues, cells and soluble molecules like antibodies that protect the body against foreign antigens.
• It has the unique ability to recognise antigens, respond to them and retain memory for faster and stronger responses on repeated exposure.
• Primary lymphoid organs (bone marrow and thymus) are responsible for the origin, development and maturation of lymphocytes.
• Secondary lymphoid organs such as spleen, lymph nodes, tonsils, Peyer’s patches and appendix are sites where lymphocytes interact with antigens and initiate immune responses.
• Mucosa-associated lymphoid tissue (MALT), present in respiratory, digestive and urogenital tracts, forms nearly 50% of the body’s lymphoid tissue and provides defence at body surfaces.