   Health is the level of functional or metabolic efficiency of a living organism. In humans it is the
    ability of individuals or communities to adapt and self-manage when facing physical, mental or
    social challenges.
   The World Health Organization (WHO) defined health in its broader sense in its 1948
    constitution as "a state of complete physical, mental, and social well-being and not merely the
    absence of disease or infirmity."
   A disease is a particular abnormal condition, a disorder of a structure or function that affects
    part or all of an organism.
   The causal study of disease is called pathology.
   Disease is often construed as a medical condition associated with specific symptoms and signs.
Types of Diseases                                       Noncommunicable (Noninfectious) Diseases
                                                        remain confined to the person who develops
The diseases may be broadly classified into             them and do not spread to others.
two types: Congenital and acquired.
                                                        The non-communicable diseases are of four
Congenital Diseases                                     kinds
These are anatomical or physiological                   1. Organic or Degenerative Diseases are
abnormalities present from birth. They may be               due to malfunctioning of some of the
caused by                                                   important organs, e.g, heart diseases,
                                                            epilepsy. Heart diseases result from the
   a single gene mutation (alkaptonuria,
                                                            abnormal working of some part of this
    phenylketonuria, albinism, sickle-cell
                                                            vital organ. Epilepsy may result from
    anaemia, haemophilia, colour blindness);
                                                            abnormal pressure on regions of the brain.
   chromosomal         aberrations     (Down’s
                                                        2. Deficiency Diseases are produced by
    syndrome,       Klinefelter’s     syndrome,
                                                            deficiency of nutrients, minerals, vitamins,
    Turner’s syndrome); or
                                                            and hormones, e.g., kwashiorkor, beriberi,
   environmental factors (cleft palate,
                                                            goitre, diabetes are just a few from a long
    harelip). Unlike the gene and chromosome
    induced           congenital         defects,
                                                        3. Allergies are caused when the body,
    environmentally caused abnormalities are
                                                            which has become hypersensitive to
    not transmitted to the children.
                                                            certain foreign substance, comes in contact
Acquired Diseases                                           with that substance. Hay fever is an
                                                            allergic disease.
These diseases develop after birth. They are            4. Cancer is caused by an uncontrolled
further of two types: communicable and non-                 growth of certain tissues in the body.
                                                        The Immune System
Communicable (Infectious) Diseases are
caused by viruses, rickettsias, bacteria, fungi,        1. Immunity – The ability of the body to
protozoans and worms.                                       protect against all types of foreign bodies
                                                            like bacteria, virus, toxic substances etc.
                                                            which enter the body.