Cellular adaptations allow cells to change in response to environmental stresses or injuries. There are five main types of cellular adaptations: atrophy, hypertrophy, hyperplasia, metaplasia, and dysplasia. Atrophy involves cells decreasing in size in response to reduced demands. Hypertrophy is an increase in cell size to meet greater demands. Hyperplasia is an increase in cell number. Metaplasia is when cells change from one type to another. Dysplasia refers to abnormal cell development occurring with metaplasia or hyperplasia, typically in response to prolonged irritation.

1. http://xpharmedico.in/
BY
BHUKYA NOM KUMAR NAIK
#EDUCATIONALIST
Presentation on
Cellular
adaptations

2. Contents:
1. Introduction to cellular adaptations
2. Types of cellular adaptations
 Atrophy
 Hypertrophy
 Hyperplasia
 Metaplasia
 Dysplasia

3. Introduction:
 Body cells are able to adapt to new conditions by increasing or decreasing size, number or shape.
 The terms associated with these adaptations are atrophy, hypertrophy, hyperplasia, metaplasia and Dysplasia.
 Upon exposure to severe physiological stress or pathological injury, the affected cell undergoes a change in its state
which helps to preserve its viability and regulate its functioning according to the adverse environment. This is termed
as cellular adaptation.
 All these cellular adaptations are reversible i.e., the cells tend to revert back to their normal structure and functions
once the injurious stimuli are removed.
 However, when such stimuli persist for prolonged time period, there occurs progressive impairment of the cell
structure and function, thereby leading to irreversible cell injury and ultimately cell death.

4. There are mainly 5 types of cellular adaptations.
There are :
1. Atrophy
2. Hypertrophy
3. Hyperplasia
4. Metaplasia
5. Dysplasia
Types of cellular adaptations:

5. 1. Cell atrophy occurs when the demands on a population of cells decrease below normal or cannot be maintained at
normal levels.
2. The cells respond by decreasing in size
3. Both physiological and pathological conditions are capable of inducing atrophy.
(a) Physiologic Atrophy
1. It occurs either due to loss of endocrine stimulation or reduced blood supply.
2. Common with age.
Example
1. Atrophy of brain with age.
(b) Pathologic Atrophy
1. There are number of causes that causes pathologic atrophy
2. Occur either locally or in a generalized manner :
Atrophy:

6. (i) Disuse Atrophy
Reduced functional activity of an organ results in its atrophy.
It is reversible atrophy upon reverting to activity within shorter period.
Examples
1. Obstruction of the pancreatic duct results in atrophy of the pancreas.
(ii) Denervation Atrophy
Occurs due to blockade in the nerve supply to the muscles results in muscular wasting in motor neuron disease etc….
(iii) Ischemic Atrophy
Reduced blood supply to a tissue results in its atrophy, due to progressive loss of cells.
Examples
1. Atrophy of brain in old age due to atherosclerosis

7. (iv) Pressure Atrophy
Occurs due to compression of tissue due to pressure from the neighboring benign tumors, cysts or aneurysm results in
atrophy probably because of reduced blood supply.
(v) Starvation Atrophy;
Starvation leads to depletion of carbohydrate, fats and protein stores which ultimately results in cachexia as seen in
cancer.
(vi) Endocrine Atrophy;
Impairment in endocrinal activity leads to decreased metabolic activity of tissues followed by atrophy.
Example:
Atrophy of skin and its appendages observed in hypothyroidism.
(vii) Idiopathic Atrophy
Certain atrophies have no underlying cause for instance testicular atrophy.

8. 1. If the demands on cells are greater than normal, they may respond by increasing in size this is called Hypertrophy.
2. Hypertrophy is accompanied with hyperplasia (increased cell size).
3. It does not occur in non-proliferative cells such as myocardial fibers and muscles cells.
4. Induce Both hypertrophy physiological. and pathological conditions can.
(a) Physiologic Hypertrophy
It is induced by hormonal stimulation.
Examples
1. Hypertrophy of uterus during pregnancy
2. Hypertrophy of the mammary glands induced by estrogens and prolactin.
(b) Pathologic Hypertrophy
Certain diseased states which induce hypertrophy like Hypertension, mitral insufficiency, aortic valve stenosis etc., may
lead to left ventricular hypertrophy etc…..
Example
1. When one of the kidneys has been surgically removed (nephrectomy), then the nephrons of the other kidney undergo
hypertrophy and hyperplasia.
Hypertrophy:

9. 1. Hyperplasia is a condition characterized by an increase in the number of cells, which eventually add to the volume of
the associated organs or tissues. In many instances, hyperplasia and hypertrophy (which is an increase in the cell size)
occur simultaneously.
2. Hyperplasia might occur either due to physiological or pathological causes.
(a) Physiologic Hyperplasia
Physiologic hyperplasia is further divided into two types.
(I) Hormonal Hyperplasia
If the increase in number of cells occurs in response to hormones, then it is referred as hormonal hyperplasia.
Example:
Increase in the number of cells of female mammary glands under the influence of pituitary hormones during puberty,
pregnancy and lactation.
Hyperplasia:

10. (ii) Compensatory Hyperplasia
Increase in the number of cells either due to damage or removal of a tissue or organ oar paired organ is known as
compensatory hyperplasia.
Example:
Following skin abrasion, the epidermises restored by compensatory hyperplasia.
(b) Pathologic Hyperplasia
When hyperplasia occurs due to abnormal hormonal responses like excess hormonal stimulation or due to chronic
inflammatory response, then it is known as pathologic hyperplasia.
Example
1. Benign Prostatic Hyperplasia of prostate gland due to excessive release of androgens causes benign prostatic
hyperplasia especially in the elderly males.

11. 1. In metaplasia cells change from one cell type to another.
2. These cells are fully differentiated and, if the stimulus is removed, the cells can revert back to their original type.
3. Basically, metaplasia is of the following two types.
(a) Epithelial Metaplasia
In this type of metaplasia, which is most common, one type of epithelial cells is replaced by other type of epithelial cells
only.
(i) Squamous Metaplasia
Squamous metaplasia is a condition in which other types of epithelial tissues are replaced by squamous epithelium. Such
squamous metaplastic change is brought about due to exposure to infection or chronic irritation. Example: Bronchial tract
of chronic smokers undergo squamous metaplasia, while it is normally lined by pseudostratified ciliated columnar
epithelium.
(ii) Columnar Metaplasia
In this type of metaplasia, the other type of epithelial tissue gets transformed into columnar epithelium.
Example: Columnar metaplasia in case of healed chronic gastric ulcer.
Metaplasia:

12. (b) Mesenchymal Metaplasia
This type of metaplasia is relatively less common than epithelial metaplasia and involves the replacement of one type of
mesenchymal tissue with another.
(i) Osseous Metaplasia
Osseous metaplasia is a condition in which other types of mesenchymal tissues like fibrous tissue or cartilage, myxoid
tissue are replaced with bone tissue.
Example:
In elderly, the cartilage of larynx and bronchi is replaced with bone tissue.
(ii) Cartilaginous Metaplasia
This type of metaplasia is seen during healing of fractures

13. 1. Dysplasia refers to disorderly development of cells, occurring along with metaplasia and hyperplasia.
2. Dysplasia is restricted to epithelial cells and predominantly affects the uterine cervix and bronchial mucosa.
3. It occurs in response to prolonged inflammation or chronic irritation.
4. It reverses upon early removal of the noxious stimuli after which the chances of dysplasia progressing into malignant
conditions are high.
5. The cytological changes characteristic of dysplasia is outlined below.
 Increase in the layers of the epithelial cells.
 Haphazard arrangement of cells from the basement membrane to the surface.
 Loss of basal polarity of the cells i.e., arrangement of nuclei away from the basement membrane.
 Increase in the nucleo-cytoplasmic ratio.
 Increased rate of mitosis.
 Increased chromatin content in the nucleus.
Example: Epithelial dysplasia of the cervix.
Dysplasia:

14. References
1. ROBBINS & COTRAN pathologic basics of disease (Students
corner).
2. Principles of pathophysiology By shane bullock and
majella hales
3. Concise pathology for exam preparation by GEETIKA
KHANNA.
4. Text book of Pathology with pathology quick review and
MCQs by HARSH MOHAN.
5. A short text book of pathology by TAHMINUR RAHMAN.
6. BRS Pathology by M.D.SCHNEIDER, ARTHUR.
7. Exam preparatory manual for under graduates pathology by
RAMADAS NAYAK.

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