Atrophy and Early Metaplasia Concepts

Notes

Hyperplasia, being an increase in cell number, involves the production of new cells from stem cells. This process is generally straightforward to understand. Hyperplasia and hypertrophy often occur together; for example, during pregnancy, the uterus increases in size to accommodate the developing fetus. The uterus enlarges through both hyperplasia (increased cell number) and hypertrophy (cell size increase). The smooth muscle cells of the uterus undergo hyperplasia, producing more cells, and hypertrophy, with cells becoming larger. Usually, these two processes happen simultaneously. An important exception to this rule is permanent tissues, which do not have stem cells and cannot produce new cells. Therefore, they only undergo hypertrophy, not hyperplasia. The three permanent tissues in the human body are: These tissues cannot make new cells and will only undergo hypertrophy. For example, the thickening of the left ventricle of the heart occurs via hypertrophy because cardiac myocytes cannot proliferate. Another key point is that pathologic hyperplasia can progress to dysplasia and cancer. Pathologic hyperplasia occurs due to underlying disease processes, unlike physiologic hyperpla...