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- 

Physiologic 

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

Pathological

• Tissues showing hypertrophy in cardiac muscles (left ventricular hypertrophy) , 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 takes place in cells, which are capable of synthesizing DNA.
• 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, BPH.

 

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, salivary gland, pancreas in chronic cholecystitis with cholelithiasis.
3. Bronchus in chronic smoker.
4. Connective tissue metaplasia
5. bone formation in muscle (myositis ossificans)

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

b) Mesenchymal-

• 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.
• Lysosomal acid hydrolases 

Types- 

a)  Physiological atrophy- eg. atrophy of notochord or thyroglossal duct during fetal development and uterus after parturition.

b) Pathologial atrophy-
Eg. In denervation atrophy
Atherosclerosis can cause ischaemic atrophy
Nutritional deficiency, eg, marasmus and cancer cachexia (nutritional atrophy)
Senile atrophy is an ageing-associated eg. brain and heart or testes

5. Dysplasia-

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