This document defines and describes several types of adaptive cellular responses: atrophy, hypertrophy, hyperplasia, metaplasia, and dysplasia. It provides the definitions and examples of each type of response. Atrophy is a decrease in cell size, hypertrophy is an increase in cell size, hyperplasia is an increase in cell number, metaplasia is a change from one adult cell type to another, and dysplasia is disordered cellular development. The document also discusses the causes and mechanisms of these adaptive responses and includes images to illustrate examples.

1. DR PREETI AGRAWAL

2. DEFINITION
Adaptive disorders are the adjustments which the
cell make in response to stresses which may be for
physiologic need or response to pathologic injury.
There are following adaptive responses
Atrophy –decrease in size of cell
Hypertrophy – increase in size of cell
Hyperplasia – increase in number of cells
Metaplasia changing pathway of phenotypic
Dysplasia - diffrentiation of cell

3. Mechanisms which are involved in adaptive cellular
response
 Altered cell surface receptor
 Alterations in signal for protein synthesis
 Synthesis of new proteins by the target cell

4. ATROPHY
Definition – reduction of number and size of
parenchymal cells of an organ or its parts which
was once normal

5. Causes –
Physiologic atrophy- Atrophy is a normal
process of ageing
Atrophy of gonads after menopause
Atrophy of thymus in adult life
Pathologic atrophy-
 starvation atrophy
Disuse atrophy
Ischaemic atrophy

6. There are some muscle fibres here that show atrophy.
The number of cells is the same as before the atrophy occurred, but the size of
some fibres is reduced

7. HYPERTROPHY
Definition – It is an increase in size of
parenchymal cells which results in
enlargement of the organs.

8. Causes–
Physiological Hypertrophy –
Enlarged size of uterus during pregnancy is
an eg.of physiologic hypertrophy as well
hyperplasia
Pathological hypertrophy –
Hypertrophy of cardiac muscle (left
ventricle) occurs in systemic HT,
Hypertrophy of smooth muscle eg.pyloric
stenosis( in stomach)

9. This is cardiac hypertrophy involving the left ventricle.
The number of myocardial fibres does not increase, but their size can increase in response
to an increased workload, leading to the marked thickening of the left ventricle in this
patient with systemic hypertension.

10. HYPERPLASIA
Increased number of parenchymal cells resulting in an
enlargement of organ.
Hyperplasia may sometimes co-exist with hypertrophy.
Causes -
physiologic--hormonal (e.g., breast and uterus during
pregnancy)
compensatory--regeneration of liver following partial
hepatectomy.
pathologic--excessive hormonal stimulation eg.endometrial
hyperplasia following estrogen excess, viral infection (papilloma
viruses) eg skin wart

11. The prominent folds of endometrium in this uterus opened to reveal
the endometrial cavity are an example of hyperplasia.
Cells forming both the endometrial glands and the stroma have
increased in number.
As a result, the size of the endometrium has increased.
This increase is physiologic with a normal menstrual cycle.

12. METAPLASIA
Definition- It is reversible change of one
type of epithelial or mesenchymal adult
cells to another type of adult epithelial or
mesenchymal cells.
This adaptation is usually in response to
abnormal stimuli,and often revert back to
normal on removal of stimulus

13. Classification
Epithelial metaplasia-
more common type,Depending upon the
type of epithelium transformed two types of
epithelial metaplasia are seen
squamous
columnar
Mesenchymal metaplasia – eg osseous
metaplasia formation of bone in skeletal
muscle

14. Metaplasia of laryngeal respiratory epithelium has occurred
here in a smoker.
The chronic irritation has led to an exchanging of one type
of epithelium (the normal respiratory epithelium at the
right) for another (the more resilient squamous epithelium
at the left).

15. DYSPASIA
Definition –It is disordered cellular development
Dyslasia occurs most often in epithelial cells.

16. Epithelial dysplasia is characterised by cellular
proliferation and cytologic changes as under:
1. Incresed no.of layers of epithelial cells
2. Disorderly arrangment of cells
3. Loss of basal polarity
4. Cellular and nuclear pleomorphism
5. Incresed N:C ratio
6. Nuclear hyperchromatism
7. Increased mitotic activity

17. This is dysplasia. The normal cervical squamous epithelium has become
transformed to a more disorderly growth pattern, or dysplastic
epithelium.