Cellular Adaptation

Dr. Adeboye OO (MBBS, Cert. LMIH, FMCPath)

Dept of Anatomic PathologyBowen University

Cellular adaptation

• Cell death is not the only consequence of cellular injury or stress

• Cells can respond to excessive physiologic or pathologic stimuli by undergoing both functional and morphologic change in which a new steady state is achieved that preserves the viability of the cell(Adaptation) .

• The adaptive response include-

• Adaptation of growth and differentiation

• Intracellular accumulation

• Pathologic calcification

• Hyaline change

• Cellular aging

Adaptation of growth and differentiation

• Adaptations are reversible changes in the size, number,phenotype, metabolic activity, or functions of cells in response to changes in their environment. Such adaptations may take several distinct forms :

• 1. hyperplasia

• 2. hypertrophy

• 3. atrophy

• 4. metaplasia

hypertrophy

• Increase in the size of cells that result in the increase in size of the affected organ.

• No new cells just larger cells

• May coexist with hyperplasia in cells capable of division( eg epithelial, hematopoesis etc), in non dividing cells (eg the nerve ,cardiac and skeletal muscle) increase tissue mass is due to hypertrophy

• Can be physiologic or pathologic

Physiologic hypertrophy

• Caused by- (a) increased functional demand eg hypertrophy of striated muscle in muscle builder.(b) stimulation by hormones or growth factors eg physiologic hypertrophy of the uterus during pregnancy

Hypertrophy of uterus during pregnancy

Micrograph showing smooth muscle hypertrophy

Pathologic hypertrophy

• Chronic hemodynamic overload due to hypertension or faulty valves causes cardiac hypertrophy

Cardiac hypertrophy

hyperplasia

• Increase in the number of cells in a tissue or an organ in response to a stimulus

• Frequently occur with hypertrophy and may be triggered by same external stimulus

• Can only occur in tissue containing cells capable of dividing

• Can be physiologic or pathologic

Physiologic hyperplasia

• Causes – (a) hormone or growth factor stimulation eg proliferation of glandular epithelium of the female breast at puberty and during pregnancy(usually accompanied by hypertrophy) (b). Compensatory increase after damage or resection eg liver regeneration after partial hepatectomy

Pathologic hyperplasia

• Causes- inappropriate or excessive action of hormone or growth factors on target cells egendometrial hyperplasia due to unopposed oestrogen level, benign prostatic hyperplasia(BPH) due to excessive androgen stimulation.

Atrophy

• Reduction in the size of an organ or tissue due to decrease in cell size and number.

• Can be physiologic or pathologic

• Physiologic atrophy- decrease in the size of uterus after parturition, atrophy of some embryonic structure during normal development eg notochord and thyroglossalduct

• Pathologic atrophy- causes :

a) Disuse or decrease workload-Disuse atrophy

b) Denervation atrophy

c) Diminished blood supply

d) Inadequate nutrition

e) Loss of endocrine stimulation

f) Pressure

g) Aging/senility- senile atrophy

Metaplasia

• Reversible change in which one differentiated (adult) cell type(epithelial/mesenchymal) is replaced by another cell type

• Adaptive response in which one cell that is sensitive to a particular stress is replaced by another cell type that is better able to withstand the adverse environment.

• 1) Epithelial metaplasia- (a)meteplasia from columnar to squamous eg squamous metaplasia

• of the respiratory epithelium in response to chronic irritation as occur in protracted cigarette smoking, squamous metaplasia of the bladder due to schistosomiasis, Vitamin A deficiency causes squamous metaplasia in the respiratory epithelium.

Fig: squamous metaplasia of the bronchus

• The influence that predispose to metaplasia if persistent, can initiate malignant transformation eg squamous cell carcinoma in the metaplasticepithelium of the resp. tract.

• 2. metaplasia from squamous to columnar eg in barett oesophagus in which the oesophagealsquamous epithelium is replaced by intestinal-like columnar epithelium under the influence of reflux of gastric acid.

• Cancers may arise in this site (Adenocarcinoma).

Metaplasia

• Connective tissue metaplasia- formation of mesenchymal tissue (cartilage,bone ,adipose tissue) in tissues that normally do not contain these elements eg myositis osificansoccasionally occurs after intramuscular hemorrhage. This type of metaplasia is less clearly seen as an adaptive response, and may be a result of cell or tissue injury.