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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