adaptations in human cellular growth

1. Adaptations of Cellular Growth
Dr Debasis Mukhopadhyay
Associate Professor
Dept. of Pathology

2. What is cellular adaptation?
• Adaptations are reversible changes in the size,
number,phenotype, metabolic activity, or
functions of cells in response to changes in
their environment.

3. What are the different forms of
cellular adaptations?
• Hypertrophy
• Hyperplasia
• Atrophy/hypoplasia
• Metaplasia

4. Definition of hypertrophy
• Hypertrophy refers to an increase in the size of
cells, that results in an increase in the size of
the affected organ.

5. Mechanism of hypertrophy
• Key fact :
Hypertrophy is the result of increased production of
cellular proteins.

7. Few examples
• Bulging muscles of bodybuilders engaged in “pumping iron” result from
enlargement of individual muscle fibers in response to increased demand.
• In the heart, the stimulus for hypertrophy is usually chronic hemodynamic
overload, resulting from either hypertension or faulty valves.
In both tissue types the muscle cells synthesize more proteins and the number of
myofilaments increases. This increases the amount of force each myocyte can
generate, and thus increases the strength and work capacity of the muscle as a
whole.
• The massive physiologic growth of the uterus during
pregnancy is a good example of hormone-induced enlargement an organ that
results mainly from hypertrophy of muscle fibers . Uterine hypertrophy is
stimulated by estrogenic hormones acting on smooth muscle through estrogen
receptors.

8. Definition of Hyperplasia
• Hyperplasia is defined as an increase in the
number of cells in an organ or tissue in
response to a stimulus.

9. Mechanism of hyperplasia
• Key fact:
• Hyperplasia is the result of growth factor-driven
proliferation of mature cells and, in some cases, by
increased output of new cells from tissue stem cells

10. Different types
• Physiologic Hyperplasia
Physiologic hyperplasia due to the action of hormones or
growth factors occurs in several circumstances: when there
is a need to increase functional capacity of hormone
sensitive organs; when there is need for compensatory
increase after damage or resection.
• Pathologic Hyperplasia
Most forms of pathologic hyperplasia are caused by
excessive or inappropriate actions of hormones or growth
factors acting on target cells.

11. Few examples
• Physiologic hyperplasia
 Hormonal hyperplasia is well illustrated by the
proliferation of the glandular epithelium of the
female breast at puberty and during pregnancy,
usually accompanied by enlargement (hypertrophy)
of the glandular epithelial cells.
 liver regeneration after trasnplantation.

12. Few examples
• Pathologic hyperplasia
• Endometrial hyperplasia is an example of abnormal hormone-
induced hyperplasia.
• Benign prostatic hyperplasia is another common example of
pathologic hyperplasia induced in responses to hormonal
stimulation by androgens.
• Hyperplasia is a characteristic response to certain viral
infections, such as papillomaviruses, which cause skin
warts and several mucosal lesions composed of masses of
hyperplastic epithelium.

13. Definition of atrophy
• Atrophy is defined as a reduction in the size
of an organ or tissue due to a decrease in cell
size and number.

14. Types of atrophy
• Physiologic atrophy
• Pathologic atrophy

15. Mechanism of atrophy
• Key facts:
• The initial response is a decrease in cell size and organelles, which may
reduce the metabolic needs of the cell sufficiently to permit its survival.
• Atrophy results from decreased protein synthesis and increased
protein degradation in cells.
• Protein synthesis decreases because of reduced metabolic activity.
• The degradation of cellular proteins occurs mainly by the ubiquitin-
proteasome pathway.
• Nutrient deficiency and disuse may activate ubiquitin ligases, which attach
the small peptide ubiquitin to cellular proteins and target these proteins
for degradation in proteasomes.

16. Mechanism (causes) of atrophy
(pathologic)
• Decreased workload (atrophy of disuse).
• Decreased workload (atrophy of disuse).
• Diminished blood supply.
• Inadequate nutrition.
• Loss of endocrine stimulation.
• Pressure.

17. Few examples
• Physiologic atrophy
 Some embryonic structures, such as the notochord and thyroglossal duct,
undergo atrophy during fetal development.
 The decrease in the size of the uterus that occurs shortly after parturition
is another form of physiologic atrophy.
• Pathologic atrophy
 prolonged immobilization- disuse atrophy of muscles of lower limb
 senile atrophy of brain and heart in old age due to diminished blood
supply due to atherosclerosis
 The loss of estrogen stimulation after menopause results in physiologic
atrophy of the endometrium, vaginal epithelium, and breast.

18. Definition of metaplasia
• Metaplasia is a reversible change in which
one differentiated cell type (epithelial or
mesenchymal) is replaced by another cell
type.

19. Mechanism of metaplasia
• Key facts:
• Metaplasia does not result from a change in the
phenotype of an already differentiated cell type;
instead it is the result of a reprogramming of stem
cells that are known to exist in normal tissues, or of
undifferentiated mesenchymal cells present in
connective tissue.

20. Few examples
• The most common epithelial metaplasia is columnar to squamous, as occurs in the
respiratory tract in response to chronic irritation. In the habitual cigarette
smoker, the normal ciliated columnar epithelial cells of the trachea and bronchi are
often replaced by stratified squamous epithelial cells.
• A deficiency of vitamin A (retinoic acid) induces squamous metaplasia in the
respiratory epithelium.
• Metaplasia from squamous to columnar type may also occur, as in Barrett esophagus,
in which the esophageal squamous epithelium is replaced by intestinal-like columnar
cells under the influence of refluxed gastric acid.
• Connective tissue metaplasia is the formation of cartilage, bone, or adipose tissue
(mesenchymal tissues) in tissues that normally do not contain these elements. For
example, bone formation in muscle, designated myositis ossificans, occasionally occurs
after intramuscular hemorrhage.

21. QUIZ TIME
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22. Dx??

23. Answer is
• Physiological hypertrophy of uterus during
pregnancy

24. Dx??

25. Answer is
• Picture A- Normal brain
• Picture B- Senile atophy of the brain in old age

26. Dx??

27. Answer is
• Squamous metaplasia of respiratory ciliated
columnar epithelium in a habitual smoker

28. Thank you………..