The British Medical dictionary (1961) defines growth as ‘the progressive developments of a living organisms or part of an organism from its earliest stage to maturity including the attendant increase in size.”
| Growth may be defined as quantitative increase in size of the body as a whole or size attained by pecific part of the body. The increase in size is a result of assimilation of nutrients into the protoplasm and includes both cell multiplication and expansion of cell cytoplasm. |
Thus, according to Malina et al. (2004), the cellular process responsible for growth can be summarized as:
Hyperplasia: an increase in cell number
It is a function of cell division which involves the replication of DNA and subsequent migration of the replicated chromosomes into functional and identical cells.
Hypertrophy: an increase in cell size
The increase in cell size involves an increase in functional units within the cell, particularly protein and substrates, as is especially evident in the muscular hypertrophy that occurs during growth.
Accretion: an increase in intercellular substances
The intercellular substances are both organic and inorganic, and the) often function to bind the cells in complex networks, as collagen fibers provide matrix for the adipocytes of adipose tissue.
These processes occur during growth, but predominance of one or another process varies with age and all the tissue involved.