Hypertrophy is an increase in cell size. Cell size increases when there is an increase in structural protein (intracellular protein) and organelles, rather than intracellular fluid (cytosol).
Hypertrophy may be caused by mechanical signals like stretch, or trophic signals like growth factors.
Physiologic hypertrophy is a temporary increase in size of an organ to provide for a natural increase of function, an example is increase in the walls of the uterus and the breast during pregnancy.
While pathologic hypertrophy occurs due to an abnormal stressor. Example is increase in cardiac muscle due to hypertension.
Hyperplasia is an increase in the number of cells. It occurs as a result of increase in cell division (Mitosis). It’s a controlled proliferation, but excessive stimulation leads to pathologic hyperplasia – example is endometrial hyperplasia and this may progress to dysplasia and cancer.
There are two types of physiologic hyperplasia- compensatory and hormonal hyperplasia.
Compensatory hyperplasia allows tissue and organ regeneration and it is common in epithelial cells of liver hepatocytes, epidermis and intestines, bone marrow cells, and fibroblasts. It occurs less in bone, cartilage, and smooth muscle cells.
Hormonal hyperplasia occurs mainly in organs that depend on estrogen. For example, the uterine cells is estrogen-dependent, and it undergoes hyperplasia and hypertrophy following pregnancy.