adaptation of cellular growth & differentiation

ADAPTATION OF CELLULAR GROWTH &

DIFFERENTIATION

PRESENTED BY:Dr. Hrudi Sundar Sahoo

CONTENTS:IntroductionAdaptation of cellsMechanismsAdaptive disorders Atrophy Hypertrophy Hyperplasia Metaplasia Dysplasia

INTRODUCTION:On exposure to stress, the cells make

adjustments with the changes in their environment to:

* Physiologic needs

*Pathologic injury

ADAPTATION:PHYSIOLOGIC: Represents cells to

normal stimulation by hormones/ endogenous chemical substances.

PATHOLOGIC: The cells have the ability to modulate their environment.

SURVIVAL OF THE FITTEST:

Adaptive responses are reversible on withdrawal of stimulus.

If the irritant / stimulus persists for a longer time cell may not be able to survive.

Thus, the concept of evolution “ survival of fittest” holds true for adaptation as “survival of adaptable”.

MECHANISM:Altered cell surface receptor binding.

Alterations in signal for protein synthesis.

Synthesis of new proteins by the target cell such as heat-shock proteins.

ADAPTIVE DISORDERS OF GROWTH:

SIZE & NUMBER:Atrophy HypertrophyHyperplasia

DIFFERENTIATION OF CELLS: MetaplasiaDysplasia

ATROPHY:Shrinkage in the size of the cell by loss of

cell substance.It represents a form of adaptive response.

CAUSES:PHYSIOLOGIC: Normal process of aging in some tissues,

which could be due to endocrine stimulation & arteriosclerosis.

Eg: Atrophy of lymphoid tissue.

CAUSES:PATHOLOGIC:Starvation atrophy- carbohydrate/fatIschemic atrophy- atrophic kidneyDisuse atrophy- atrophy of pancreaseNeuropathic atrophy- poliomyelitisEndocrine atrophy- hypopituitarismPressure atrophy- erosion of spineIdiopathic atrophy- testicular atrophy

HYPERTROPHY:An increase in the size of the cells, which

results in enlargement of organ without any changes in the number of cells.

Occurs due to incresed functional demand & hormonal stimulation.

CAUSES:PHYSIOLOGIC: Enlargement of uterus

in pregnancy.

PATHOLOGIC: Hypertrophy of:

* cardiac muscle

*smooth muscle

* skeletal muscle

*compensatory hypertrophy

HYPERPLASIA:An increase in number of parenchymal

cells, which results in enlargement of organ/tissue.

CAUSES:PHYSIOLOGIC: HORMONAL:

Eg: Hyperplasia of pregnant uterus

COMPENSATORY:

Eg: Regeneratio of liver.

CAUSES:PATHOLOGIC: Occurs due to excessive stimulation of

hormones & growth factors.

Eg: Endometrial hyperplasia-following oestrogen excess.

METAPLASIA:META-TransformationPLASIA-GrowthIt is a reversible change of one type of

epithelial or mesenchymal cells, usually in response to persistant abnormal stimulus which in turn may change into a malignant cell.

CLASSIFICATION:EPITHELIAL METAPLASIA:

*Sqamous metaplasia

*Columnar metaplasia

MESENCHYMAL METAPLASIA:

*Osseous metaplasia

*Cartilaginous metaplasia

EPITHELIAL METAPLASIA:The most common type.Metaplastic change cane either patchy or

diffuse. Leads to alterations in the epithelium.

Deprivation of protective mucous secretion.

More prone to infection.

TYPES:SQAMOUS METAPLASIA:Occurs due to chronic irritation

(chemical/mechanical/infective)

Eg: Bronchus in chronic smokers.

COLUMNAR METAPLASIA:

Eg: Intestinal metaplasia in healed chronic gastric ulcer.

MESENCHYMAL METAPLASIA:

Less often there is transformation of one type of mesenchymal tissue to another.

OSSEOUS: Formation of bone in fibrous tissue, cartilage & myxoid tissue.

Eg: In arterial wall in old people.

CARTILAGENOUS: In healing of fractures, where there is undue mobility.

DYSPLASIA:Disordered cellular development often

accompanied with metaplasia & hyperplasia (ATYPICAL HYPERPLASIA).

Occurs most often in epithelial cells, which is characterised by cellular proliferation & cytologic changes.

CAUSES:Occurs due to chronic irritation or

prolonged inflammation.On removal of simulus, the changes may

disappear.In majority of cases dysplasia progresses

into carcinoma insitu or invasive cancer.

CHANGES:Increased number of layers of epithelial

cells.Disorderly arranged cells.Loss of basal polarity.Cellular & nuclear pleomorphism.Increased nucleocytoplasmic ratio.Nuclear hyperchromatism.Increased mitotic activity.

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