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Cellular Adaptation.pptx
- 1. Cellular Adaptation HNS 2201:HUMAN PATHOLOGY
- 2. Cellular Adaptations Adaptationsare reversible changes in the number, size, phenotype, metabolic activity, or functions of cells in response to changes in their environment. Physiologic adaptations usually represent responses of cells to normal stimulation by hormones or endogenous chemical mediators (e.g., the hormone-induced enlargement of the breast and uterus during pregnancy), or to the demands of mechanical stress (in the case of bones and muscles). Pathologic adaptations are responses to stress that allow cells to modulate their structure and function and thus escape injury, but at the expense of normal function, such as squamous metaplasia of bronchial epithelium in smokers.
- 3. Introduction Cells adaptto internal environment just as the total organism adapt to external environment Adaptation maybe by changes in>> Size Number Type Or Combination This leads to cellular Atrophy Hypertrophy Hyperplasia Metaplasia dysplasia
- 4. Atrophy Atrophy isshrinkage in the size of cells by the loss of cell substance. When a sufficient number of cells are involved, the entire tissue or organ is reduced in size, or atrophic . Although atrophic cells may have diminished function, they are not dead. Cellular atrophy results from a combination of decreased protein synthesis and increased protein degradation
- 7. Atrophy Atrophied cells… Reduce their oxygen consumption Other cellular functions By….decreasing the number and size of their organelles
- 8. Causes Of Atrophy A.Physiologic atrophy: a normal process of aging in some tissues, which could be due to loss of: Endocrine stimulation arteriosclerosis For example: Atrophy of lymphoid tissue in lymph nodes, appendix and thymus Atrophy of gonads after menopause Atrophy of brain with aging
- 9. Causes Of Atrophy B.Pathologic atrophy: the causes are as under: 1. Starvation atrophy: there is first depletion of carbohydrate and fat stores followed by protein catabolism. There is general weakness, emaciation and anemia referred to as cachexia seen in cancer and severely ill patients 2. Ischaemic atrophy: Gradual diminution of blood supply due to atherosclerosis may result in shrinkage of the affected organ e.g. i) Small atrophic kidney in atherosclerosis of renal artery ii) Atrophy of brain in cerebral atherosclerosis
- 10. Causes Of Atrophy B.Pathologic atrophy Cont.. 3.Disuse atrophy: Prolonged diminished functional activity is associated with disuse atrophy of the organ e.g. i) Wasting of muscles of limb immobilized in cast. ii) Atrophy of .the pancreas in obstruction of pancreatic duct. 4. Neuropathic atrophy: Interruption in nerve supply leads to wasting of muscles e.g. i) Poliomyelitis ii) Motor neuron disease iii) Nerve section
- 11. Causes Of Atrophy B.Pathologic atrophy Cont.. 5. Endocrine atrophy: Loss of endocrine regulatory mechanism results in reduced metabolic activity of tissues and hence atrophy e.g. i) Hypopituitarism may lead to atrophy of thyroid, adrenal and gonads ii) Hypothyroidism may cause atrophy of the skin and its adnexal structures.
- 12. Causes Of Atrophy B.Pathologic atrophy Cont.. 6. Pressure atrophy: Prolonged pressure from benign tumors or cyst or aneurysm may cause compression and atrophy of the tissues e.g. i) Erosion of spine by tumor in nerve root ii) Erosion of skull by meningioma arising from piaarachnoid iii) Erosion of sternum by aneurysm of arch of aorta 7. Idiopathic atrophy: There are some examples of atrophy where no obvious cause is present e.g. i) Myopathies ii) Testicular atrophy
- 13. Hypertrophy An increasein cell size and an increase in the functioning tissue mass Stated another way, in pure hypertrophy there are no new cells, just bigger cells containing increased amounts of structural proteins and organelles. Results in an increase in tissue mass Seen in cardiac, skeletal, and muscle tissue These cells are not capable of mitosis (so, no number or hyperplasia) May be a normal physiologic response as seen in an increase in muscle size with exercise
- 14. Hyperplasia isan adaptive response in cells capable of replication, whereas hypertrophy occurs when cells have a limited capacity to divide. Hypertrophy and hyperplasia also can occur together, and obviously both result in an enlarged organ
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- 17. • Hypertrophy canbe physiologic or pathologic and is caused either by increased functional demand or by growth factor or hormonal stimulation. PHYSIOLOGIC HYPERTROPHY 1.The massive physiologic enlargement of the uterus during pregnancy occurs as a consequence of estrogen stimulated smooth muscle hypertrophy and smooth muscle hyperplasia 2. In contrast, in response to increased workload the striated muscle cells in both the skeletal muscle and the heart undergo only hypertrophy because adult muscle cells have a limited capacity to divide.
- 18. Hypertrophy Pathologic hypertrophy Examples: 1. Hypertrophyof cardiac muscle: may occur in: Systemic hypertension Aortic valve disease (stenosis and insufficiency) Mitral insufficiency NB: There is an increase in size but function is compromised However, there is a LIMIT to the amount the tissue can enlarge
- 19. An adaptationto stress such as hypertrophy can progress to functionally significant cell injury if the stress is not relieved. Whatever the cause of hypertrophy, a limit is reached beyond which the enlargement of muscle mass can no longer compensate for the increased burden. When this happens in the heart, several degenerative changes occur in the myocardial fibers, of which the most important are fragmentation and loss of myofibrillar contractile elements. Why hypertrophy progresses to these regressive changes is incompletely understood. There may be finite limits on the abilities of the vasculature to adequately supply the enlarged fibers, the mitochondria to supply ATP, or the biosynthetic machinery to provide sufficient contractile proteins or other cytoskeletal elements. The net result of these degenerative changes is ventricular dilation and ultimately cardiac failure.
- 20. Hypertrophy 2. Compensatory hypertrophymay occur in an organ when the contralateral organ is removed e.g. Following nephrectomy on one side in a young patient, there is compensatory hypertrophy as well as hyperplasia of the nephrons of the other kidney Adrenal hyperplasia following removal of one adrenal gland
- 21. HYPERPLASIA Hyperplasia isan increase in the number of parenchymal cells resulting in enlargement of the organ or tissue Quite often, both hyperplasia and hypertrophy occur together Occurs due to a response from appropriate stimulus and ceases when stimulus is removed An increase in NUMBER of cells Restricted to cells capable of mitosis epidermis, intestinal epithelium, and glandular tissue Physiological hyperplasia uterus and breast enlarge in pregnancy
- 22. Causes Of Hyperplasia A. Physiologic hyperplasia. The two most common types are as follows: 1. Hormonal hyperplasia i.e. hyperplasia occurring under the influence of hormonal stimulation e.g. Hyperplasia of female breast at puberty, during pregnancy and lactation Hyperplasia of pregnant uterus Proliferative activity of normal endometrium after a normal menstrual cycle Prostatic hyperplasia in old age
- 23. Causes Of Hyperplasia 2.Compensatory hyperplasia i.e. hyperplasia occurring following removal of part of an organ or a contralateral organ in paired organ e.g. Regeneration of the liver following partial hepatectomy Regeneration of epidermis after skin abrasion Following nephrectomy on one side, there is hyperplasia of nephrons of the other kidney.
- 24. Causes Of Hyperplasia B.Pathologic hyperplasia: Most examples of pathologic hyperplasia are due to excessive stimulation of hormones or growth factors e.g. Endometrial hyperplasia following estrogen excess In wound healing, there is formation of granulation tissue due to proliferation of fibroblasts and endothelial cells Formation of skin warts from hyperplasia of epidermis due to human papilloma virus Pseudocarcinomatous hyperplasia of the skin Intraductal epithelial hyperplasia in the breast in fibrocystic breast disease. prostatic hypertrophy (BPH or thyroid enlargement
- 25. Nevertheless,in manycases, pathologic hyperplasia constitutes a fertile soil in which cancers may eventually arise. For example, patients with hyperplasia of the endometrium are at increased risk of developing endometrial cancer
- 26. METAPLASIA Metaplasia isa change in which one adult cell type (epithelial or mesenchymal) is replaced by another adult cell type. In this type of cellular adaptation, a cell type sensitive to a particular stress is replaced by another cell type better able to withstand the adverse environment. Metaplasia is thought to arise by the reprogramming of stem cells to differentiate along a new pathway rather than a phenotypic change (transdifferentiation) of already differentiated cells Epithelial metaplasia is exemplified by the change that occurs in the respiratory epithelium of habitual cigarette smokers, in whom the normal ciliated columnar epithelial cells of the trachea and bronchi often are replaced by stratified squamous epithelial cells The rugged stratified squamous epithelium may be able to survive the noxious chemicals in cigarette smoke that the more fragile specialized epithelium would not tolerate. Metaplasia: change in phenotype of differentiated cells, often in response to chronic irritation, that makes cells better able to withstand the stress; usually induced by altered differentiation pathway of tissue stem cells; may result in reduced functions or increased propensity/tendancy for malignant transformation
- 27. Although themetaplastic squamous epithelium has survival advantages, important protective mechanisms are lost, such as mucus secretion and ciliary clearance of particulate matter. Because vitamin A is essential for normal epithelial differentiation, its deficiency also may induce squamous metaplasia in the respiratory epithelium. Metaplasia need not always occur in the direction of columnar to squamous epithelium; in chronic gastric reflux, the normal stratified squamous epithelium of the lower esophagus may undergo metaplastic transformation to gastric or intestinal-type columnar epithelium. Metaplasia also may occur in mesenchymal cells, but in these situations it is generally a reaction to some pathologic alteration and not an adaptive response to stress. For example, bone is occasionally formed in soft tissues, particularly in foci of injury. The influences that induce metaplastic change in an epithelium, if persistent, may predispose to malignant transformation.
- 28. In fact,squamous metaplasia of the respiratory epithelium often coexists with lung cancers composed of malignant squamous cells. It is thought that cigarette smoking initially causes squamous metaplasia, and cancers arise later in some of these altered foci
- 29. DYSPLASIA Dysplasia means‘disordered cellular development’, often accompanied with metaplasia and hyperplasia; it is therefore also referred to as atypical hyperplasia Dysplasia occurs most often in epithelial cells Epithelial dysplasia is characterized by: cellular proliferation cytologic changes. Dysplastic changes often occur due to: chronic irritation prolonged inflammation
- 30. DYSPLASIA On removalof the inciting stimulus, the changes may disappear In a proportion of cases, however, dysplasia progresses into: carcinoma in situ (cancer confined to layers superficial to basement membrane) or invasive cancer The Dysplasia Changes include: Increased number of layers of epithelial cells Disorderly arrangement of cells from basal layer to the surface layer
- 31. DYSPLASIA Loss of basalpolarity i.e. nuclei lying away from basement membrane Cellular and nuclear pleomorphism Increased nucleocytoplasmic ratio Nuclear hyperchromatism Increased mitotic activity
- 33. Differences between Metaplasiaand Dysplasia Metaplasia Change of one type of epithelial or mesenchymalcell to another type of adult epithelial or mesenchymal cell Epithelial (squamous, columnar) and mesenchymal (osseous, cartilaginous) Most commonly affects bronchial mucosa, uterine endocervix; others mesenchymal tissues (cartilage, arteries) Dysplasia Disordered cellular development, may beaccompanied with hyperplasia or metaplasia Epithelial only Uterine cervix, bronchial mucosa
- 34. Differences between Metaplasiaand Dysplasia Metaplasia Mature cellular development Reversible on withdrawal of stimulus Dysplasia Disordered cellular development (pleomorphism,nuclear hyperchromasia, mitosis, loss of polarity) May regress on removal of inciting stimulus, or may progress to higher grades of dysplasia or carcinoma in situ
- 35. Anaplasia Cells differentiateto a more IMMATURE or embryonic form. Malignant tumors are characterized by anaplastic cell growth.
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