This document discusses various types of cellular adaptations including atrophy, hypertrophy, hyperplasia, metaplasia, and dysplasia. It provides examples of physiological and pathological adaptations and their clinical relevance. Physiological adaptations are reversible responses to normal stimulation, while pathological adaptations can be irreversible. The summary highlights examples of the clinical significance of hypertrophy in pregnancy, weightlifting, and heart disease. It also discusses the significance of hyperplasia in the breast, liver, and endometrium. Finally, it provides examples of the clinical relevance of metaplasia in smokers and vitamin A deficiency.

1. DEPARTMENT OF PHARMACY
LARAIB TARIQ
PATHOLOGY
CELLULAR ADAPTATIONS & THEIR CLINICAL RELEVANCE
DATE: 26 October
2021

2. Cellular Adaptation
Introduction:
Cellular adaptation is the ability of cells to respond to various types of stimuli and adverse
environmental changes. The adaptation may be
 PATHOLOGICAL
 PHYSIOLOGICAL
Adaptations are reversible changes in the size, number, phenotype, metabolic activity or functions of
cells in response to changes in their environment.
These physiological adaptations usually represent responses of cells to normal stimulation by hormones
or endogenous chemical substances.
FOR EXAMPLE
The enlargement of the breast and induction of lactation by pregnancy.

3. The cell proliferation in hyperplasia remains under physiological control and is reversible, unlike in
neoplasia (cancer) which is irreversible.
Types of Cellular Adaptation:
Five major types of adaptations include:
Atrophy: is the shrinkage in cell size by loss of cellular
substance.
 Causes of atrophy include decreased work load, pressure,
diminished blood supply or nutrition, loss of endocrine
stimulation and aging.
 Physiological: aging in some tissues; atrophy of gonads
after menopause.
 Pathological: Neuropathic atrophy, endocrine atrophy
Hypertrophy: is an increase in cell size by gain of cellular
substance.
 It is caused either by increased functional demand or by
specific endocrine stimulations.
 Physiological: physiologic growth of uterus during
pregnancy.
 Pathological: hypertrophy of heart

4. Hyperplasia: it constitutes an increase in the number of
indigenous cells in an organ or tissue.
 Pathological hyperplasia is typically the result excessive
endocrine stimulation.
 Physiological hyperplasia: female breast epithelium at
puberty or in pregnancy.
 Pathological: Endometrial hyperplasia
Metaplasia: is a reversible change in which one adult cell type is replaced by another adult cell
type.
 Metaplasia is triggered by environmental stimuli, which may act with the deleterious effects if
microorganisms and inflammation.
Dysplasia: the presence of abnormal cells within a tissue or organ. Dysplasia is not cancer, but it
may sometimes become cancer. Dysplasia can be mild, moderate, or severe.
 Dysplastic changes often occur due to chronic
irritation or prolonged inflammation.

5. Laraib Tariq
3199
Clinical relevance of cellular adaptations
 In medical terms, clinical significance (also known as practical significance) is assigned to
a result where a course of treatment has had genuine and quantifiable effects. Broadly
speaking, statistical significance is assigned to a result when an event is found to be
unlikely to have occurred by chance.
 Adaptation is very necessary for our body to adjust in a new environment and also to preserve
function and viability of cells.
Example of clinical significance of hypertrophy:
 Uterine hypertrophy during pregnancy:
As the pregnancy progresses, the growing fetus requires more space for his development.
Uterine smooth muscle cannot replicate (cannot divide and increase in number). So
that’s why under the stimulation of pregnancy hormone (estrogen) they only increase in
size (hypertrophy).
 Skeletal muscle hypertrophy in weightlifter:
In response to increase work load during weightlifting and exercise, the individual
skeletal muscle cell will undergo hypertrophy and shows a strong physique.

6.  Heart enlargement in hypertrophic and aortic valve disease:
In hypertension and aortic valve disease, heart has to contract forcefully to fulfill the
requirement of body. For this forceful contractility the cardiac muscle cells goes into
hypertrophy (because they cannot divide and they cannot go into hyperplasia).
Example of clinical significance of hyperplasia:
 Hyperplasia of female breast at puberty and pregnancy:
Under the influence of female hormones, the glandular epithelium of female breast
proliferates at puberty and during pregnancy.

7.  Compensatory hyperplasia in liver:
This type of hyperplasia occur when a part of organ is removed or diseased e.g when
some portion of liver is removed in the transplantation, the remaining portion of liver
starts replication and eventually the normal weight of liver restored. The stimulus for
this restoration is growth factors, produced by remaining liver cells. After restoring the
normal weight, the growth is turned off by growth inhibitors.
 Endometrial hyperplasia:
The endometrial lining of uterus is maintained at a normal thickness by growth
stimulatory and growth inhibitory pituitary and ovarian hormones. When this hormonal
balance is disturbed by any disease, the thickness of endometrium is increased and
eventually results in endometrial hyperplasia. This endometrial hyperplasia can lead to
cancer.
Examples of clinical significance of hypertrophy:
 Loss of innervations:
In polio virus, loss of innervations, atrophy of limb.
 Loss of blood supply:
In atherosclerosis……..atrophy of brain.
 Decreased work load:
In fracture, because of immobilization, of brain occurs.

8. Ageing:
Brain and other body parts atrophy.
 Loss of endocrine hormonal stimulation:
Post menuposal atrophy of female genital organs.
Examples of clinical significance of metaplasia:
 Metaplasia in smokers:
In smokesrs, the normal columnar ciliated epithelium of respiratory rack is replaced by
stratified squamous epithelium. This metaplasia will enable respiratory track to surviv
under tough circumstances that has created by cigratte smoke. It may lead to lung
cancer in future.
 Vitamin A deficiency:
Causes metaplasia in respiratory track and eye.
 Esophagal metaplasia:

9. In gastric esophageal reflux disease, the normal squamous epithelium of lower esophagus
is replaced by columnar epithelium.
 Bone metaplasia:
Sometimes bone is formed in soft tissues especially after injury.
 Reference:
https://slideplayer.com/slide/10974399/.