Cellular adaptation

Cellular adaptation


       CELLULAR ADAPTATIONS

  • Adaptations are reversible changes in the cell which can be physiologic (normal stimulation by hormones or mediators) or pathological (stress changes structure & function). It includes-    
  1. Hypertrophy-
  • Hypertrophy is an increase in the size of cells resulting in increase in the size of the organ.
  • There is no change in the number of cells.

Hypertrophy can be of two types- 

  1. Physiologic 
  • Enlarged size of uterus in pregnancy, breast tissue in puberty & pregnancy is an example of hypertrophy as well as hyperplasia.

b. Pathological

  • Tissues showing hypertrophy in cardiac muscles, smooth muscle, skeletal muscle.

2. Hyperplasia-

  • Hyperplasia is an increase in the number of cells but there is no change in the size of tissue.

Hyperplasia can be-

a) Physiologic- 2 types

  1. Hormonal- Examples are- female breast at puberty, pregnancy and pregnant uterus.
  2. Compensatory- E. g.- regeneration of liver, epidermis.

b) Pathological– Endometrial hyperplasia, wound healing.

3. Metaplasia-

  • Metaplasia is a reversible change in which one adult cell type (epithelial or mesenchymal) is replaced by another adult cell type.
  • It is due to re- programming of stem cells.
  • Vitamin A deficiency (in respiratory epithelium) or excess leads to metaplasia.

Metaplasia is of 2 types-

a) Epithelial- It is of two types

i) Squamous- examples are

  1. Uterine endocervix in prolapsed uterus & old age.
  2. Gallbladder in chronic cholecystitis with cholelithiasis.
  3. Bronchus in chronic smoker.

ii) Columnar – Columnar metaplasia in Barrett’s oesophagus (intestinal metaplasia).

b) Mesenchymal-

i) Osseous-

  1. In soft tissues in myositis ossificans.

2. In arterial wall in old age.

ii) Cartilaginous- Healing of fractures.

4. Atrophy-

  • Both number and size of cells are decreased.
  • Mechanism of atrophy consists of combination of decreased protein synthesis & increased protein degradation by Ubiquitin proteasome pathway.

It is of 2 types-

  1. Physiologic
  2. Pathological

5. Dysplasia-

  • Dysplasia is disordered cellular development.
  • It affects only epithelial cells.
  • Most common examples are uterine cervix and respiratory tract.

Exam Important

  • Hypertrophy is an increase in the size of cells resulting in increase in the size of the organ and there is no change in the number of cells.

Hypertrophy examples- Physiologic –

  • Enlarged size of uterus in pregnancy, breast tissue in puberty & pregnancy is an example of hypertrophy as well as hyperplasia.
  • Hyperplasia– Hyperplasia is an increase in the number of cells but there is no change in the size of tissue.
  • Hyperplasia examples- Physiologic (Hormonal)-  female breast at puberty, pregnancy and pregnant uterus.
  • Metaplasia– Vitamin A deficiency (in respiratory epithelium) or excess leads to metaplasia.

Metaplasia can be two types-

  1. Epithelial-
  • Squamous- Uterine endocervix in prolapsed uterus & old age, Bronchus in chronic smoker.
  • Columnar- Columnar metaplasia in Barrett’s oesophagus (intestinal metaplasia).

2. Mesenchymal example is myositis ossificans

  • Mechanism of atrophy is by Ubiquitin proteasome pathway.
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