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Cellular adaptation

    Cellular adaptation refers to changes made by a cell in response to adverse environmental changesHuether S. E. & McCance K. L. (2008) ''Understanding Pathophysiology'' Ed 4, p. 62-65 The adaptation may be physiologic(al) or pathologic(al) which are changes that are normal and abnormal respectively Uterine/uterus enlargement is an example of a physiologic adaptation to pregnancy Cardiac muscle hypertrophy is an example of a pathologic adaptation to increased blood pressure
    Five major types of adaptation include atrophy hypertrophy hyperplasia dysplasia and metaplasia ref>Huether S. E. & McCance K. L. (2008) Understanding Pathophysiology Ed 4, p. 62-65
    Atrophy is a decrease in cell size and if enough cells in an organ atrophy the entire organ will decrease in sizeref>Huether S. E. & McCance K. L. (2008) Understanding Pathophysiology Ed 4, p. 62-65 Thymus atrophy during early human development is an example of physiologic atrophy Skeletal muscle atrophy is a common pathologic adaptation to skeletal muscle disuse (commonly called "disuse atrophy) Tissue and organs especially susceptible to atrophy include skeletal muscle cardiac muscle secondary sex organs and the brain
    Hypertrophy is an increase in cell size and if enough cells of an organ hypertrophy so will the whole organref>Huether S. E. & McCance K. L. (2008) Understanding Pathophysiology Ed 4, p. 62-65 The heart and kidneys have increased susceptibility to hypertrophy Hypertrophy involves in increase in intracellular protein rather than cytosol (intracellular fluid) Hypertrophy may be caused by mechanical signals (eg stretch) or trophic signals (eg growth factors) An example of physiologic hypertrophy is in skeletal muscle with sustained weight-bearing exercise An example of pathologic atrophy is in cardiac muscle as a result of hypertension
    Hyperplasia is an increase in the number of cellsref>Huether S. E. & McCance K. L. (2008) Understanding Pathophysiology Ed 4, p. 62-65 It is the result of increased cell mitosis or division The two types of physiologic hyperplasia are compensatory and hormonal Commpensatory hyperplasia permits tissue and organ regeneration It is common in epithelial cells of the epidermis and intestine liver hepatocytes bone marrow cells and fibroblasts It occurs to a lesser extent in bone cartilage and smooth muscle cells Hormonal hyperplasia occurs mainly in organs that depend on estrogen For example the estrogen-dependent uterine cells undergo hyperplasia and hypertrophy following pregnancy Pathologic hyperplasia is an abnormal increase in cell division A common pathologic hyperplasia in women occurs in the endometrium and is called "endometriosis"
    Dysplasia refers generally to abnormal changes in cellular shape size and/or organizationref>Huether S. E. & McCance K. L. (2008) Understanding Pathophysiology Ed 4, p. 62-65 Dysplasia is not considered a true adaptation; rather it is thought to be related to hyperplasia and is sometimes called "atypical hyperplasia" Tissues prone to dysplasia include cervical and respiratory epithelia Dysplasia often occurs in the vicinity of cancerous cells and it may be involved in the development of breast cancer
    Metaplasia occurs when a differentiated cell of a certain type is replaced by another cell type which may be less differentiated It is a reversible process thought to be caused by stem cell reprogramming Stem cells are found in epithelia and embryonic mesenchyme of connective tissue A prominent example of metaplasia involves the changes associated with the respiratory tract in response to inhalation of irritants such as smog or smoke The bronchial cells convert from mucus-secreting ciliated columnar epithelium to non-ciliated squamous epithelium incapable of secreting mucus These transformed cells may become dysplasic or cancerous if the stimulus (eg cigarette smoking) is not removed