1. Cellular Adaptations of
Growth and Differentiation
By
Dr: Nassar Ayoub

2. Overview
• Adaptability of cells to an altered
environment
– Physiological and pathological stimuli
• Changes in growth pattern
– Hyperplasia, hypertrophy, atrophy,
involution, metaplasia
• Apoptosis
• Growth factors
– Role in altered environment

3. Why is this important?
• Extremely common responses in disease
• Certain adaptations in growth act as a fertile
ground for the later development of neoplasia
- cancer formation…
• Nomenclature is used in clinical work.

4. Adaptability of cells to an altered
environment
• Cells are constantly exposed to changes in
their environment
• Cells can adapt to acceptable changes in their
environment by modifying metabolism or
growth pattern
• Environmental changes can be physiological
or pathological

5. In respond to excessive physiologic stresses or
pathologic stimuli cell may adapt, where a new
altered steady state is achieved preserving cell
viability.
Adaptation

6. Examples of pathological stimuli
• Nutritional
• Immune
• Endocrine
• Physical agents
• Chemical agents
• Infections
• Anoxia
• Genetic

8. Metabolic regulation
• Cells may adapt by
metabolic regulation
– Induction of enzyme
– Downregulation of enzyme
– Increased synthesis of
product
– Reduced secretion of
product
• Metabolic adaptation is
usually not associated with
morphological changes

9. Increased functional demand
• Increased functional demand can be met by
two main responses
– Increase in cell size: hypertrophy
– Increase in cell number: hyperplasia
• These may occur independently or together.
• Reflected by an increase in size and weight of
an organ

10. • 1- Physiological adaptations
They represent response of cells to normal
stimulation by hormones or endogenous
chemical substances
e.g.
a. enlargement of the breast and induction of
lactation by pregnancy.
b. replacement of labile tissues, e.g. skin, bone
marrow
c. cyclic as endometrium.

11. • 2-Pathological adaptations
• adaptations occurring as a result of certain
stimuli which are not lethal,
• i.e. a state intermediate between normal
unstressed cells and injured overstressed ones.

12. Adaptive changes in cell growth
and differentiation include:
a- hyperplasia
b- hypertrophy
c- atrophy
d- metaplasia

13. Hyperplasia
• Definition:
It is an increase in the size of an organ or
tissue due to increase in the number of
constituent parenchymal cells. It may be
physiological or pathological.

14. • Physiological hyperplasia
• hormonal as in the female breast during
puberty and pregnancy
• compensatory as in hyperplasia of liver
hepatocytes after partial hepatectomy due
to increase in its functional demands.

15. Physiological hyperplasia
Normal uterus
Pregnant uterus

16. • Pathological hyperplasia
• Increased level of circulating hormones produce
hyperplasia in the target organs
e.g. a- hyperplasia of the endometrium
due to hyperestrinism
b-senile prostatic hyperplasia
due to increase in the level of
androgen and estrogen.

17. However,
hyperplasia
due to
certain
stimuli stops
with removal
of these
stimuli and
may serve a
useful
function.

18. Hypertrophy• Definition
• It is an increase in the size of an organ or tissue due to
enlargement of individual cells without increase in the number of
cells.
• It usually occurs in organs in which proliferation and mitosis are
restricted
e.g. skeletal muscle and heart muscles.
• It may be physiological or pathological.

19. • 1- Physiological
hypertrophy
e.g. pregnant uterus, and
muscles of athletes.
• 2- Pathological
hypertrophy
(adaptive hypertrophy)
e.g. a- hypertrophy of the
stomach in pyloric stenosis
b- cardiac muscle
hypertrophy in chronically
hypertensive patients.

21. Hypertrophy of the heart

22. Hypertrophy and hyperplasia
are closely related and both
may contribute to an overall
increase in the organ size.

23. Atrophy
Definition
• Reduction of the size of an organ
after reaching its normal adult size.
• As a result of decrease in both
the number and size of the cells.
• Often associated with fibrosis.
• May be physiological or pathological

24. • Physiological atrophy
• Involution:
• A form of physiologic atrophy.
• Return to normal size after hyperplasia and
hypertrophy, if the causative stimuli are removed and
equilibrium returns back..
Eg
• uterus after labour.
• atrophy of the ovary after menopause
• senile atrophy of geriatrics.

25. • Pathological atrophy
• It depends on the cause. It may be
localized or generalized
• Eg.
a- Ischemic atrophy: due to decrease of
blood supply e.g. atherosclerosis

26. Renal artery stenosis

27. • b- Pressure atrophy:
due to long continued
pressure on a tissue
leading to decrease in its
blood supply with
atrophy of its cells
• e.g. amyloidosis of the
liver in which the
extracellular deposition
of amyloid substance
leads to pressure
atrophy of hepatocytes. Amyloidosis of the liver

28. • c-Neuropathic atrophy:
• e.g. when a motor nerve
supplying a muscle is
affected as in
poliomyelitis
• d- Decreased work load:
• e.g. immobilized limb
• e- Starvation: leading to
generalized atrophy.
The atrophic cells in all
cases, are still surviving
cells, but with
diminished function.

29. Metaplasia
Definition
• It is a reversible change in which an adult cell
type (epithelial or mesenchymal) is replaced by
another adult cell type of the same tissue.

30. It may represent an adaptive
substitution of cells more sensitive to
stress by other cell types better able
to withstand the adverse
environment.
Metaplasia is thought to arise by
genetic 'deprogramming" of epithelial
stem cell or of undifferentiated
mesenchymal cells in connective
tissue.

31. • Epithelial squamous metaplasia
e.g. a- uterine endocervical glandular epithelium due to
chronic irritation
b-transitional epithelium of urinary bladder, ureter or
renal pelvis due to chronic irritation by bilharziasis or
stones
c-columnar epithelium of gall bladder due to chronic
irritation by stones or inflammation
d-pseudostratified ciliated columnar respiratory
epithelium due to chronic irritation by habitual cigarette
smoking or in vitamin A deficiency.

32. Squamous metaplasia Respiratory
epithelium

33. • The adaptive metaplastic epithelium is better able to
survive, but important protective mechanisms (such as
mucus secretion and ciliary clearance of particulate
matter in the respiratory epithelium) are lost.
• If the influences that induce metaplastic transformation
of the epithelium are persistent, they may lead to cancer
transformation in the metaplastic epithelium, e.g.
squamous metaplasia of transitional epithelium of the
urinary bladder by bilharziasis will lead to squamous cell
carcinoma.

34. • Mesenchymal cell metaplasia:
Myxomatous change of fibrous tissue.
Transformation of fibroblasts to osteoblasts
or chondroblasts to produce bone or cartilage
in soft tissues in foci of injury.

35. Examples of metaplasia
Bladder transitional epithelium (T) with metaplasia to squamous epithelium (S) in
response to a bladder stone…

36. • Hypoplasia
It is the decrease in size of an organ due to
incomplete development in embryonic or
fetal life e.g. kidney and uterus.

37. • Agenesis
• Complete
absence of an
organ or a part
of an organ e.g.
solitary kidney,
in such case the
other kidney is
absent.

38. • Dysplasia
• Dysplasia (dys-, "bad"
or "difficult" and plasis,
"formation") is an
ambiguous term used
in pathology to refer to
Abnormal development
or growth of tissues,
organs, or cells.