Cellular adaptationcellular adaptation, cellular adaptation pathophysiology
In cell biology and pathophysiology, cellular adaptation refers to changes made by a cell in response to adverse environmental changes The adaptation may be physiological normal or pathological abnormal Five minor types of adaptation include atrophy, hypertrophy, hyperplasia, dysplasia, and metaplasia
- 1 Atrophy
- 2 Hypertrophy
- 3 Hyperplasia
- 4 Metaplasia
- 5 Dysplasia
- 6 See also
- 7 Notes and references
Atrophy is a decrease in cell size If enough cells in an organ atrophy the entire organ will decrease in size Thymus atrophy during early human development childhood 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 If enough cells of an organ hypertrophy so will the whole organ The heart and kidneys have increased susceptibility to hypertrophy Hypertrophy involves an 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 hypertrophy is in cardiac muscle as a result of hypertension
Hyperplasia is an increase in the number of cells It is the result of increased cell mitosis, or division The two types of physiologic hyperplasia are compensatory and hormonal Compensatory 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
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 The most common example of metaplasia is Barrett's esophagus, when the non-keratinizing squamous epithelium of the esophagus undergoes metaplasia to become mucinous columnar cells, ultimately protecting the esophagus from acid reflux originating in the stomach If stress persists, metaplasia can progress to dysplasia and eventually carcinoma; Barrett's esophagus, for example, can eventually progress to adenocarcinoma of the esophagus if not treated
Dysplasia refers to abnormal changes in cellular shape, size, and/or organization 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 epithelium, where it is strongly associated with the development of cancer; it may also be involved in the development of breast cancer Although dysplasia is reversible, if stress persists, then dysplasia progresses to irreversible carcinoma
- Cell damage
Notes and references
- ^ Huether, S E & McCance, K L 2008 Understanding Pathophysiology, Ed 4, p 62-65
- ^ Porth, Carol Mattson 2005 Pathophysiology : Concepts of Altered Health States PDF 7th ed Philadelphia, Pa: Lippencott, Williams & Wilkins p 105 ISBN 0-7817-4988-3 Retrieved 28 December 2016
|Principles of pathology||
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