Lecture # 16
CELL ADAPTATION - I
Dr. Iram Sohail
Assistant Professor
Pathology
College of Medicine
Majmaah University
OBJECTIVES
• Definition of adaptation
• Classification of adaptation
• Mechanism of adaptation
ADAPTATION
• Adaptation is a reversible change in
– Size
– number
– morphology
– or function
of cell in response to change in environment.
Adaptation can be
• Physiological
• Pathological
CLASSIFICATION OF ADAPTATION
There are four types of adaptations
1. Hypertrophy
2. Hyperplasia
3. Atrophy
4. Metaplasia
1. HYPERTROPHY
• Hypertrophy is an increase in the size of cell
that results in increase in the size of organ.
• Hypertrophy occurs in non-dividing cells.
Mechanism
Hypertrophy can be
i. Physiological
– Increased levels of estrogen during pregnancy
causes enlargement of smooth muscles of uterus
and eventually the whole uterus will enlarge.
ii. Pathological
• Heart enlargement in hypertension
– Cardiac cell enlargement is caused by 2 types of
signals
a. Mechanical triggers
– Such as stretch
b. Trophic triggers
• Increased production of growth factors,
structural proteins, myofilaments ---- size &
functional capacity of cell will increased.
2. HYPERPLASIA
• Hyperplasia is the increased in the numbers of
cells.
• Occurs in dividing cells only.
Hyperplasia can be physiologic or pathologic
1) physiologic:
1- hormonal (breast in pregnancy,
endometrium: pregnancy)
2- compensatory :
Hyperplasia that occurs when a portion of
tissue is removed (resected liver can be
restored after time by growth factors
produced by remaining hepatocytes)
2) Pathologic:
1- Endometrial hyperplasia if balance
between estrogen and
progesterone is disturbed
2- Prostatic hyperplasia
(dihydrotestosterone + estrogen)
3- Gyenecomastia
(Estrogen)
Mechanism
Hyperplasia can be
i. Physiological
– Breast enlargement at puberty & during
pregnancy.
• The mechanism behind this type of
hyperplasia is increased hormonal stimulation
at puberty and during pregnancy causes
increased in the number of breast cells.
ii. Pathological
• Endometrial hyperplasia in response to
hormonal imbalance between estrogen and
progesterone.
3. ATROPHY
• Decrease in the size of cell (by the loss of cell
substances)
• Atrophy results in shrinkage of organ and also
the function of organ will decrease.
Causes
• Decreased workload
• Loss of nerve supply
• Loss of blood supply
• Inadequate nutrition
• Loss of hormonal stimulation
• Aging
Mechanism
• Decrease protein synthesis
• Increase protein degradation
• Autophagy (self-eating)
– Starved cell eats its own components
Renal atrophy
Testicular atrophy
Brain atrophy
4. METAPLASIA
• One adult cell type is replaced by another cell
type.
• In metaplasia the metaplastic cell will be able
to withstand the adverse environment.
Mechanism
• Genetic re-programming of stem cells
• Example
– In smokers, the normal ciliated columnar
epithelial cells of respiratory tract are replaced by
stratified squamous epithelium.
Dysplasia:
• Not truly adaptation
• It is a pre-malignant disturbance of the cell proliferation,
maturation and growth
• The cells show:
– Change in size, shape
– Change in nuclei
– Loss of organization
– Increased mitotic activity
• Seen in hyperplastic and metaplastic
epithelium
• May progress to cancer if stimulus not
removed but it is a reversible change
Cervical dysplasia
Agenesis :
•
Is complete failure of development of an organ ( absent)
–
Kidney , Testis
Hypoplasia :
•
Is the failure of development to reach normal mature size of organ
Uterus, kidney, testes
Aplasia :
•
Is complete cessation of multiplication of cells, which are in state of
continuous multiplication to do their normal function
–
Bone Marrow cells ( radiation , drugs )