Growth Adaptations - Pathoma PDF

## Adaptations ### II. Hyperplasia and Hypertrophy - An increase in stress leads to an increase in organ size. - This occurs via an increase in the size (hypertrophy) and/or the number (hyperplasia) of cells. - Hypertrophy involves gene activation, protein synthesis, and production of organell...

## Adaptations ### II. Hyperplasia and Hypertrophy - An increase in stress leads to an increase in organ size. - This occurs via an increase in the size (hypertrophy) and/or the number (hyperplasia) of cells. - Hypertrophy involves gene activation, protein synthesis, and production of organelles. - Hyperplasia involves the production of new cells from stem cells. - Hyperplasia and hypertrophy generally occur together (e.g., uterus during pregnancy). - Permanent tissues (e.g., cardiac muscle, skeletal muscle, and nerve), however, cannot make new cells and undergo hypertrophy only. - For example, cardiac myocytes undergo hypertrophy, not hyperplasia, in response to systemic hypertension. - Pathologic hyperplasia (e.g., endometrial hyperplasia) can progress to dysplasia and, eventually, cancer. - A notable exception is benign prostatic hyperplasia (BPH), which does not increase the risk for prostate cancer. ### III. Atrophy - A decrease in stress (e.g., decreased hormonal stimulation, disuse, or decreased nutrients/blood supply) leads to a decrease in organ size (atrophy). - This occurs via a decrease in the size and number of cells. - Decrease in cell number occurs via apoptosis. - Decrease in cell size occurs via ubiquitin-proteosome degradation of the cytoskeleton and autophagy of cellular components. - In ubiquitin-proteosome degradation, intermediate filaments of the cytoskeleton are "tagged" with ubiquitin and destroyed by proteosomes. - Autophagy of cellular components involves generation of autophagic vacuoles. These vacuoles fuse with lysosomes whose hydrolytic enzymes breakdown cellular components. ### IV. Metaplasia - A change in stress on an organ leads to a change in cell type (metaplasia). - Most commonly involves change of one type of surface epithelium (squamous, columnar, or urothelial) to another. - Metaplastic cells are better able to handle the new stress. - Barrett esophagus is a classic example. - For example, Barrett esophagus may progress to adenocarcinoma of the esophagus. - A notable exception is apocrine metaplasia of breast, which carries no increased risk for cancer. - Vitamin A deficiency can also result in metaplasia. - Vitamin A is necessary for differentiation of specialized epithelial surfaces such as the conjunctiva covering the eye. - In vitamin A deficiency, the thin squamous lining of the conjunctiva undergoes metaplasia into stratified keratinizing squamous epithelium. This change is called keratomalacia. - Mesenchymal (connective) tissues can also undergo metaplasia. - A classic example is myositis ossificans in which connective tissue within muscle changes to bone during healing after trauma. ### V. Dysplasia - Disordered cellular growth - Most often refers to proliferation of precancerous cells - For example, cervical intraepithelial neoplasia (CIN) represents dysplasia and is a precursor to cervical cancer. - Often arises from longstanding pathologic hyperplasia (e.g., endometrial hyperplasia) or metaplasia (e.g., Barrett esophagus) - Dysplasia is reversible, in theory, with alleviation of inciting stress. - If stress persists, dysplasia progresses to carcinoma (irreversible). ### VI. Aplasia and Hypoplasia - Aplasia is failure of cell production during embryogenesis (e.g., unilateral renal agenesis). - Hypoplasia is a decrease in cell production during embryogenesis, resulting in a relatively small organ (e.g., streak ovary in Turner syndrome). The document describes different types of cellular adaptations that occur in response to various stresses. These are: - **Hyperplasia**: An increase in the number of cells - **Hypertrophy**: An increase in the size of cells - **Atrophy**: A decrease in the size of cells - **Metaplasia**: A change in cell type - **Dysplasia**: Disordered cellular growth - **Aplasia**: Failure of cell production - **Hypoplasia**: Decrease in cell production The text gives examples and different scenarios for each adaptation type.