Cellular adaptation-1.doc

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Cellular adaptation

Physiological response of cells to normal stimulation.

Hypertrophy

Def.:A reversible increase in the size of an organ or tissue due to increase in size of it's specialized cells through an accumulation of more structural components. So the purely hypertrophied organ has no new cells just bigger ones. The increase size of cells is due to the synthesis of more structural components. The concentration of DNA per unit of tissue weight is less in hypertrophic tissue, and

there is sharp rise in the RNA\DNA ratio during the enlargement phase. Hypertrophy is usually a response of an individual cell to an increased functional demand

or by specific hormonal stimulation.Hypertrophy is mediated by i. Growth factors, cytokines, and other trophic stimuli

ii. Increased expression of genes and increased protein synthesisHypertrophy and hyperplasia often occur together

Pure hypertrophy without accompanying hyperplasia occurs only in striated muscle cells.

Prof. Salha A. Sallam, Pathology Department , Tripoli Univ. 2012-2013

21. Skeletal muscles: As a response to increase muscle activity ,during exercise.

2. Cardiac muscle: Any demand for increased work leads to hypertrophy of the fibers of the chambers affected.

3.Smooth muscles: i. Uterus. ii. Arteries. iii. Alimentary tract. iv. Urinary bladder.

The muscle fibers return to a normal size when the increased work stimulus is removed.

Compensatory hypertrophy: May occur in the survivor of a pair of organs when one is removed. E.g: Following nephrectomy.

Hypertrophy due to hormonal changes : E.g: Excessive secretion of growth hormone (usually due to a tumour of the anterior pituitary) results in acromegally .


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HYPERPLASIADef.: Hyperplasia is the increase in size of an organ or tissue due to an increase in THE NUMBER of it's specialized cells, due to specific stimulus.HORMONAL INFLUENCES ARE IMPORTANT IN THIS GROWTH RESPONSE .1. Hyperplasia in the endocrine glands: e.g. Parathyroid hyperplasia occurring in chronic renal failure.Hyperplasia of the thyroid gland in pregnancy.

2. Hyperplasia in the target organs of the endocrine glands: e.g. i- Breasts: (physiological):Hyperplasia of the epithelial tissue and surrounding specialized connective tissue is a normal feature of the female breast at puberty, during pregnancy and lactation.Pathological hyperplasia in cystic hyperplasia (cystic disease of the breast ).ii- Endometrial hyperplasia.

iii- Prostate (benign nodular hyperplasia).

vi- Bone marrow: Hyperplasia is most commonly seen where demand for red blood cells is increased.Compensatory hyperplasia:

It occurs when a portion of the tissue is removed or diseased . Irritative: surface epith., lymph node.

Clinical effects:1- mass (breast, prostate, thyroid).2- uterine bleeding 3- Mechanical obstructionPrognostic significance:- usually reversible,- May progress to malignancy, as in surface epithelium.


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Adaptive responses resulting in reduced tissue massi. Developmentalii. Acquired

Developmental: * Agenesis: is a complete failure of development. *Hypoplasia: is a partial failure of the tissue to reach normal size.

Acquired:*Aplasia : It used in medicin as for example in aplastic anaemia .

ATROPHYAtrophy is a reversible decrease in the mass of functioning cells in a tissue by decrease in size and / or number of its cells .There are two mechanisms of reduction :-

1) decrease in the size and volume of individual cells:a) reduction in cellular metabolism .b) Reduction in synthesis of structural proteins.c) Increase in the catabolism.2)Death of established cells:Loss of cells by single cell necrosis (apoptosis) causing a reduction in the number of functioning cells.

Involution : is a form of physiological organ atrophy involving apoptosis of cells.

In Atrophy there is an increase in the concentration of DNA per unit tissue weight .Atrophy can occur under physiological or pathological conditions .

1) Physiological atrophy: Examples: a) Atrophy of ductus arteriosus in infants b) Atrophy of thymus in adults .

c) Atrophy of gonads and other reproductive organ in old age. 2) Pathological atrophy : May be either general or local.1) Generalized atrophy results from :

i) Simple starvation severe malnutrition ,mal absorption and malignant cachexia .


5 ii)Osteoporosis : iii)Atrophy due to increased catabolism .

2)Localized Atrophy :-i)Disuse atrophy .

ii)Pressure Atrophy . iii)Neuropathic Atrophy.iv)Endocrine Atrophy . v)Post –irradiation atrophy .vi)Reduced blood supply (when the reduction is not sufficiently severe to cause necrosis).

ABNORMALITIES OF CELLULAR DIFFERENTIATION : METAPLASIA

Metaplasia is a reversible transformation of one type of differentiated tissue in to another type of similar differentiation .

It' usually appears to be the result persistent trauma (chronic irritation ) .It is thought to arise by genetic reprogramming of epithelial stem cells or of un differentiated mesenchymal cells in C.T.The cells sensitive to stress are replaced by other cell type better capable to stand adverse environment .

FORMS OF METAPLASIA : Epithelial

Connective tissue Mesothelial

A)Epithelial :

Causes: Chronic irritation Avitaminosis A Gene activation Unknown causes.


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1) Squamous metaplasia :

i) From pseudostartified columnar epithelium :a)In bronchi in chronic bronchitis or due to cigarette smoking .

b)In nasal sinuses ,in chronic sinusitis .

ii)From simple columnar epithelium :a) endometrium in senility .b)Gall bladder in chronic cholecystitis .c)Prostatic ducts in ageing and oestrogen therapy .d)Endocervical mucosa and glands associated with cervical erosion .

iii)From transitional cell epithelium:

a)Renal pelvis with calculi .b)Urinary bladder with chronic cystitis or schistosomiasis .iv)From mesothelium of the pleura (Asbestosis) .2)Columnar metaplasia:i)Pink cell or apocrine metaplasia seen in cystic disease of the breast.ii)Intestinal metaplasia of the gastric mucosa in chronic atrophic gastritis .


7iii)The oesophageal squamous epithelium is replaced by gastric epithelium in response to exposure to gastric acid in cases of gastric reflux (glandular or gastric metaplasia Barrett's aesophagus).

B)Connective tissue:

1)osseous metaplasia: i)In sites of dystrophic calcification:a)Scarsb)Old tuberculous lesions.c)Medial calcification of arteries .

ii)In muscle. E.g: myositis ossificans trauma to a muscle may lead to a haematoma ,the haematoma undergoes organization.The fibroblasts invading the haematoma may change to osteoblasts which lay down osteoid tissue.

C)Serosal(Mesothelial):Irritation of serosal cells lining the serous sacs my change them to cubical, columnar , glandular or stratified squamous .E.g :Asbestosis.


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DYSPLASIADef.A disturbance of cell proliferation and maturation with in an epithelium.The changes consist of increased mitosis .the production of abnormal cell in varying numbers and a tendency to disorder in their arrangement.*It is usually accompanied by chronic inflammatory change or on exposure to carcinogenic substance.

• Dysplasia is a non-neoplastic proliferation.• Dysplasia may or may not progress to cancer.


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