Stages in the human life cycle
1) Embryo – conception to end of 8th week of prenatal development.
2) Fetus – beginning of 9th week of prenatal development to birth.
3) Neonate – birth to 4 week of age.
4) Infant – end of 4th week to 2 years of age (sometimes, ability to walk is considered end of infancy).
5) Child – two years to puberty.
6) Adolescent – Puberty (approximately ages – 11-14) to adult
7) Young adult – end of adolescent (approx. Age 20) to about age 40.
8) Middle – aged adult – age 40 about age 65.
9) Old adult age 65 to death.
Gerontology (Gr. Geron = old man; ligis = discourse). It is the branch of biology that deals with the study of the process of ageing, it is branch of madicine concerned with the medical problems and care of old people.
Geriatry is the branch of biology that study of details of development, treatment and prevention of diseases in old human.
Since development in its broadest sense includes any biological change with time, it also includes those changes that result in the decreased functional capacities of the mature organism, the changes commonly called ageing. Various changes that occur during to ageing are:
a) Decline in metabolic efficiency.
b) Decrease in the power of replacing the old worn out cells.
c) Decreased power of repairing the damaged tissues, argans and organ systems.
Death is a biological phenomenon which results in irreversible break down of body functions. Whatever the cause, death result from the failure of one of following: heart, blood or nervous system. It is terminal end of the degeneration changes of old age.