Cellular and Tissue Adaptation

Dr. Raid Jastania

Stress

Injury

Cell Injury

Cell Death

Response

Adaptation

Cell Adaptation

• Cellular Adaptation in Growth and Differentiation

• Subcellular Responses to Injury

• Intracellular Accumulation

• Pathologic Calcification

Cellular Adaptation in Growth and Differentiation

• Atrophy:• Atrophy is shrinkage in the size of cells

(and the organ) due to loss of cell substance.

• apoptosis. • Causes: decrease in work load,

immobilization, loss of innervation, diminished blood supply, nutrients, or loss of endocrine stimulation and aging.

Atrophy

• Atrophy may occurs in any organ or tissue.

• Example: muscle atrophy due to paralysis or immobilization.

• Atrophy results when the production of cellular substance is less than the degradation. Degradation can occur in lysosomes or in ubiquitin-proteasome system.

• Hypertrophy:• Hypertrophy is the increase in the size of

cells (and organs) • caused by increased functional demand. • Example: Left ventricular hypertrophy due

to hypertension. Hypertrophy can result from mechanical stress or hormonal stimulation.

• Hyperplasia:• Hyperplasia is increase in the number of

cells in an organ.

• It can be physiological. Example: hormonal hyperplasia of breast during lactation.

• It can be pathological. Example: Hormone imbalance and endometrial hyperplasia.

Hypertrophy/Hyperplasia

• Metaplasia:• Metaplasia is a reversible change of one adult cell

type to another adult cell type.• Example: change of the respiratory mucosa in the

respiratory tract from the ciliated culomnar epithelium to squamous epithelium due to smoking.

• This change results from “genetic reprogramming”.

Subcellular Responses to Injury

1. Lysosomal catabolism: heterophagy, Autophagy

2. Hypertrophy of Smooth Endoplasmic Reticulum: increase in the ability of the cell to metabolize substance. This results in “drug tolerance”. Example: tolerance to Barbiturates, and Alcohol.

3. Mitochondrial Alteration: Example: increase or decrease in the number of mitochondria.

Subcellular Responses to Injury

4. Cytoskeletal Abnormalities: Occur in hypertrophy and atrophy of the cells.

5. Heat Shock Proteins: HSP are proteins involved in protein folding, disaggregation and transport. The production of HSP is increased in stress situations (injury).

Intracellular Accumulation:

1. Fatty Change: Defect in fat metabolism. This commonly occurs in alcoholics due to altered SER function and in toxicity with CCl4.

2. Cholesterol: is accumulated in histiocytes following ingestion of cellular parts in necrosis

3. Protein: Example: Mallory bodies in liver cells.

Intracellular Accumulation:

4. Glycogen: Example: diabetes mellitus in liver

5. Pigment: exogenous like carbon, and endogenous like: melanin, lipofuscin, and hemosiderin.

Pathologic Calcification:

1. Dystrophic calcification: occurs following tissue necrosis (and commonly inflammation). Example: calcification in atheroma.

2. Metastatic calcification: occurs in normal tissue as a result of high Ca++ level in the blood. Causes:

1. high PTH, 2. Renal failure3. Bone destruction4. Vit D intoxication.