Cellular Adaptations of Growth and Differentiation

1. Cellular Adaptations of Growth and Differentiation

2. Adaptation In respond to excessive physiologic stresses or pathologic stimuli cell may adapt, where a new altered steady state is achieved preserving cell viability.

3. 1-Physiological adaptations They represent response of cells to normal stimulation by hormones or endogenous chemical substances e.g. a. enlargement of the breast and induction of lactation by pregnancy. b. replacement of labile tissues, e.g. skin, bone marrow c. cyclic as endometrium.

4. 2-Pathological adaptations adaptations occuring as a result of certain stimuli which are not lethal, i.e. a state intermediate between normal unstressed cells and injured overstressed ones.

5. Adaptive changes in cell growth and differentiation include: a- hyperplasia b- hypertrophy c- atrophy d- metaplasia

6. Hyperplasia • Definition: It is an increase in the size of an organ or tissue due to increase in the number of constituent parenchymal cells. It may be physiological or pathological.

7. Physiological hyperplasia hormonal as in the female breast during puberty and pregnancy compensatory as in hyperplasia of liver hepatocytes after partial hepatectomy due to increase in its functional demands.

8. Hyperplasia of the breast

9. Pathological hyperplasia Increased level of circulating hormones produce hyperplasia in the target organs e.g. a- hyperplasia of the endometrium due to hyperestrinism b-senile prostatic hyperplasia due to increase in the level of androgen and estrogen.

10. However, hyperplasia due to certain stimuli stops with removal of these stimuli and may serve a useful function.

12. Hypertrophy • Definition • It is an increase in the size of an organ or tissue due to enlargement of individual cells without increase in the number of cells. • It usually occurs in organs in which proliferation and mitosis are restricted e.g. skeletal muscle and heart muscles. • It may be physiological or pathological.

13. 1-Physiological hypertrophy e.g. pregnant uterus, and muscles of athletes. 2-Pathological hypertrophy (adaptive hypertrophy) e.g. a- hypertrophy of the stomach in pyloric stenosis b- cardiac muscle hypertrophy in chronically hypertensive patients.

16. Hypertrophy and hyperplasia are closely related and both may contribute to an overall increase in the organ size.

17. Atrophy Definition • Reduction of the size of an organ after reaching its normal adult size. • As a result of decrease in both the number and size of the cells. • Often associated with fibrosis. • May be physiological or pathological

18. Physiological atrophy Involution: A form of physiologic atrophy. Return to normal size after hyperplasia and hypertrophy, if the causative stimuli are removed and equilibrium returns back.. Eg uterus after labour. atrophy of the ovary after menopause senile atrophy of geriatrics.

19. Pathological atrophy It depends on the cause. It may be localized or generalized Eg. a- Ischemic atrophy: due to decrease of blood supply e.g. atherosclerosis

20. Renal artery stenosis

21. b-Pressure atrophy: due to long continued pressure on a tissue leading to decrease in its blood supply with atrophy of its cells e.g. amyloidosis of the liver in which the extracellular deposition of amyloid substance leads to pressure atrophy of hepatocytes.

22. Amyloidosis liver

23. c-Neuropathic atrophy: e.g. when a motor nerve supplying a muscle is affected as in poliomyelitis d-Decreased work load: e.g. immobilized limb e- Starvation:leading to generalized atrophy. The atrophic cells in all cases, are still surviving cells, but with diminished function.

24. Metaplasia Definition • It is a reversible change in which an adult cell type (epithelial or mesenchymal) is replaced by another adult cell type of the same tissue.

25. It may represent an adaptive substitution of cells more sensitive to stress by other cell types better able to withstand the adverse environment. Metaplasia is thought to arise by genetic 'deprogramming" of epithelial stem cell or of undifferentiated mesenchymal cells in connective tissue.

26. Epithelial squamousmetaplasia e.g. a- uterine endocervical glandular epithelium due to chronic irritation b-transitional epithelium of urinary bladder, ureter or renal pelvisdue to chronic irritation by bilharziasis or stones c-columnar epithelium of gall bladder due to chronic irritation by stones or inflammation d-pseudostratified ciliated columnar respiratory epithelium due to chronic irritation by habitual cigarette smoking or in vitamin A deficiency.

27. Squamousmetaplasia Respiratory epithelium

28. The adaptive metaplastic epithelium is better able to survive, but important protective mechanisms (such as mucus secretion and ciliary clearance of particulate matter in the respiratory epithelium) are lost. If the influences that induce metaplastic transformation of the epithelium are persistent, they may lead to cancer transformation in the metaplastic epithelium, e.g. squamousmetaplasia of transitional epithelium of the urinary bladder by bilharziasis will lead to squamous cell carcinoma.

29. Mesenchymal cell metaplasia: Myxomatous change of fibrous tissue. Transformation of fibroblasts to osteoblasts or chondroblasts to produce bone or cartilage in soft tissues in foci of injury.

30. Hypoplasia It is the decrease in size of an organ due to incomplete development in embryonic or fetal life e.g. kidney and uterus.

32. Agenesis Complete absence of an organ or a part of an organ e.g. solitary kidney, in such case the other kidney is absent.

33. Dysplasia A term used to describe disorderly but non-neoplastic proliferation. It is a loss in the uniformity of individual cells as well as in their architectural orientation

34. Dysplastic changes reveal pleomorphism, hyperchromatism, abundant mitoses, and loss of normal orientation. Dysplastic changes are mostly seen in epithelial cells especially in the cervix uteri.

35. When dysplastic changes are mild they are often reversible by removal of the inciting cause (e.g. chronic irritation). On the other hand, when dysplastic changes are marked and involve the entire thickness of the epithelium, the lesion in this case is considered as pre-invasive neoplasm and is referred to as "carcinoma in situ".