HUMAN HEALTH AND DISEASE
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INTRODUCTION
Health, for a long time, was considered as a state of body and mind where there was a balance of certain
‘humors’.
This is what early Greeks like Hippocrates as well as Indian Ayurveda system of medicine asserted. It
was thought that persons with ‘blackbile’ belonged to hot personality and would have fevers. This idea was
arrived at by pure reflective thought.
The discovery of blood circulation by William Harvey using experimental method and the demonstration of
normal body temperature in persons with blackbile using thermometer disproved the ‘good humor hypoth-
esis’ of health.
In later years, biology stated that mind influences, through neural system and endocrine system, our immune
system and that our immune system maintains our health. Hence, mind and mental state can affect our health.
Of course, health is affected by –
(i) genetic disorders – deficiencies with which a child is born and deficiencies/defects which the child
inherits from parents from birth;
(ii) infections
(iii) life style including food and water we take, rest and exercise we give to our bodies, habits that we have
or lack etc.
Some terms related to immunity :
(1) Immunity : Resistance of the body against a pathogen or disease.
(2) Antigen or Agglutinogen : Substance which stimulates the production of antibodies.
(3) Antibody or Agglutinin : It is a complex glycoprotein secreted by B-lymphocytes in response to an antigen.
(4) Antiserum : Serum of any animal which contains the antibody for a specific antigen is called antiserum.
(5) Venom (poison) : Toxic substances secreted by snake and some insect.
(6) Agglutination : Antigen antibody reaction is called agglutination and study of antigen-antibody reaction is
called serology.
IMMUNITY
Everyday we are exposed to large number of infectious agents. However, only a few of these exposures result
in disease. Why? This is due to the fact that the body is able to defend itself from most of these foreign agents.
This overall ability of the host to fight the disease-causing organisms, conferred by the immune system is called
immunity.
Immunity is of two types:
(i) Innate immunity
(ii) Acquired immunity.
INNATE IMMUNITY
Innate immunity is non-specific type of defence, that is present at the time of birth. This is accomplished by providing
different types of barriers to the entry of the foreign agents into our body. Innate immunity consist of four types of
barriers. These are :-
(1) Physical / Anatomical Barrier : It is made up of two parts :-
(i) Skin : Skin on our body is the main barrier which prevents entry of the micro-organisms. Outermost
layer of skin is dead (str. corneum), so the bacteria do not grow or enter into it. pH of skin (3 to 5) destroy
the bacteria.
(ii) Mucosa : Mucus coating of epithelium lining of the respiratory, gastrointestinal and urogenital tracts
also help in trapping microbes entering our body. Mucosa contain mucosal cells and cilia. Mucosa
entraps the micro-organism and cilia propel the microbes.
(2) Physiological Barriers : Some physiological processes of body create adverse environment for growth of
bacteria. Acid in the stomach, saliva in the mouth, tears from eyes–all prevent microbial growth
(i) Fever : High temperature of body, inhibit the growth of microbes.
(ii) pH of body : Acidic pH of various part of body like oral cavity, stomach and vagina inhibit the growth
of microbes.
(iii) Secretions : Secretions of body like eyes, sebum contain lysozyme, this enzyme destroys the mi-
crobes.
(3) Cellular Barrier :-
Polymorpho-nuclear leukocytes (PMNL-neutrophils), monocytes and natural killer cells (type of lymphocytes) in
the blood as well as macrophages in tissues can phagocytose and destroy microbes.
(A) Phagocytic Cells - (e.g. Monocytes, PMNL - neutrophil, Macrophage). In response to pathogenic
infection, the total count of WBC in body increases. Phagocytosis is exhibited by some types of WBC's
such WBC's are called phagocytes.
Most important phagocytes are macrophages and neutrophils. Monocytes are liberated at the site of
infection these later converted into macrophages.
Macrophages are large irregular shaped cells that engulf microbes, virus, cellular debris etc. in
response to an infection.
(B) Non-Phagocytic cells : (Eg : Natural Killer Cell)
It is a large granular lymphocyte cell. During this process apart from the phagocytes, another type of cells
called Natural killer cells kill virus infected cells and tumour cells of body by creating perforin lined pores in
the plasma membrane of target cells (i.e. infected cells). Water enters through these pores causing swelling and
bursting of the diseased cells
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