cellular adaptations
Cells respond to increased demand and external stimulation by Hyperplasia or Hypertrophy.
Cells respond to reduced supply of nutrients and growth factors by atrophy.
In some situations, cells change from one type to another, a process called Metaplasia.
There are numerous molecular mechanisms for cellular adaptations. Some adaptations are induced by direct stimulation of cells by factors produced by the responding cells themselves or by other cells in the environment.
Others are due to activation of various cell surface receptors and downstream signaling pathways. Adaptations may be associated with the induction of new protein synthesis by the target cells, as in the response of muscle cells to increased physical demand, and the induction of cellular proliferation, as in responses of the endometrium to estrogens.
Adaptations can also involve a switch by cells from producing one type of proteins to another or markedly overproducing one protein; such is the case in cells producing various types of collagens and extracellular matrix proteins in chronic inflammation and Fibrosis.
See also
growth
differentiation