cell adaptation

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By:Suraj Choudhary

IInd B.pharm2009-10

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Homeostasis : The “steady state” that cell exists in normally.

An equilibrium of the cells with their environment

for adequate function.

When disturbed there is a predisposal for the onset of pathology.

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1. Cells adapt to changes (stimuli, stressors). Adaptations occur on a spectrum. Some are:

helpful: hypertrophy or hyperplasia increase organ size so it can function better

more harm than good. Example: increased organ size requires more blood supply. If that is not available, organ becomes ischemic

2. Adaptation can involve: change in cell size or number change to different type of cell

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On application of Stress

NORMALCELL

ADAPTATION

CELL INJURYCELL DEATH

Stress,demand

Fails toadapt

Injuriousstress

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Atrophybrown atrophy

Hypertrophy

Hyperplasia

Metaplasia: simple columnar to stratified squamous (lungs)

Dysplasia: some loss of control as in cervix

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DEFINITION: SHRINKAGE OF CELLS

CAUSES:

Physiologic

due to decreased work load (e.g., decreased size of uterus following child birth, or disease)

Pathologic

Starvation Endocrine

Ischaemic Pressure

Disuse Idiopathic

Neuropathic

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Example of Atrophy

I’m Normal !

Atrophy Attack!:????

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DEFINITION: In the size of cells which results in enlargement of the organs , without any change in the no. of cells

It is mostly seen in cells that cannot divide, such as skeletal muscle (pumping iron), and cardiac muscle (hypertension).

These changes usually revert to normal if the cause is removed.

Hypertrophy is mediated by different mechanisms.

Dividing cell Hypertrophy + Hyperplasia

Non-dividing cell Hypertrophy

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Causes of Hypertrophy

Physiologic Enlarged size of uterus in pregnancy Action of estrogenic hormones

Pathologic Hypertrophy of cardiac muscle Hypertrophy of Smooth muscle Hypertrophy of skeletal muscle Compensatory Hypertrophy

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DEFINITION: Increased number of cells in an organ or tissue.

Hyperplasia may sometimes co-exist with hypertrophy.

Hyperplasia can be classified as: Physiologic--hormonal (e.g., breast and uterus during

pregnancy)

Compensatory--regeneration of liver following partial hepatectomy. Various growth factors and interluekins are important in such hyperplasia.

Pathologic--excessive hormonal stimulation viral infection (papilloma viruses); neoplasms

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Example of Hyperplasia

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DEFINITION: Transformation or replacement of one adult cell type to another adult cell type

(e.g., the change from columnar to squamous cells in respiratory tract, from squamous to columnar in Barrett esophagitis).

Metaplasia also occurs in mesenchymal tissue (e.g., formation of bone in skeletal muscle).

Metaplastic changes usually result from chronic irritation.

Metaplastic changes seem to precede the development of cancer, in some instances.

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Types of Metaplasia

Epithelial Metaplasia

Squamous metaplasia

Columnar metaplasia

Mesenchymal Metaplasia

Osseous metaplasia

Cartilagenous metaplasia

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DYSPLASIA

The term “dysplasia” means “disordered cellular development”

It often accompanied by metaplasia & hyperplasia,thereby also referred as Atypical Hyperplaisa

Short Duration Reversible

Long Duration CarcinomaCancer

It may occurs due to Chronic Irritation or Prolonged inflammation.

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Example of Dysplasia

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Key Facts

Adaptable within physiological limits.

Heat Shock Proteins (HSPs): Can respond to injury by producing cell stree proteins.

Demand met by Hypertrophy & Hyperplasia.

Demand met by Atrophy.

Apoptosis : Cell loss can be achieved from Programmed cell death

Tissue can adapt to demand by a change in differentiation known as Metaplasia.

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