Adaptation
Adaptation is defined ad reaction to persistent stress or to changed environmental conditions.
Previously normal tissue changes. The adaptation can be physiological, where the cells or
tissue adapts to changing physiological demands, or pathological, where the tissue adapts
to some stress caused by change in the environment or by some disease of other organ or
organ systems. This system usually helps to survive various hostile conditions. Sometimes,
however, the adaptation itself causes another problems, which can be worse than the initiating
stimulus.
1 Atrophy
Defined as shrinkage1 in the size of the cell by loss of cell substance. Can occur at cellular
level or at the level of whole organs (when applied to whole organs, atrophy usually refers to
decreased number of cells).
Atrophy can be numeric, where the tissue (or organ) size is decreased due to decreases in the
number of cells. Typical example is the bone marrow. The space between the cells is filled
by some other tissue, like connective tissue or fat.
Another type of atrophy is simple atrophy, where decrease in tissue or organ size is caused by
decreased size of the cells. Typical example is the striated muscle after decreased workload
(e.g. after long lasting immobilization of an extremity). The number of the cells (muscle
fibres) remains the same, but the fibres are thinner.
1.1 Causes of atrophy
• decreased energy supply or nutrition
– dimished blood supply
– inadequate nutrition
• decreased workload or stimulation
– loss of neural stimulation
– loss of endocrine stimulation
• aging
2 Hypertrophy
Defined as increased size of cells. On organ level the increase in size is achieved by enlarging
the cells (but not by increased number of cells). Usually due to increased workload
(compensatory hypertrophy).
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The size of atrophic tissue is diminished, as opposed to hypoplasia, where the tissue never reached its
proper size and is small from the beginning
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4 DYSPLASIA
3 Hyperplasia
Defined as increased number of cells. Usually due to increased workload or hormonal stimulation.
It is a controlled process which stops when the stimulus ceases (in contrast to neoplasia
which is not controlled by normal physiologic stimuli).
4 Dysplasia
Cellular (especially nuclear) atypia. The cytoplasm of these cells is more basophilic, the
nuclei are larger, irregular, with more chromatin.
Dysplasia occurs in two settings:
Reactive dysplasia: changes are caused by some processes from outside of the cells (e.g.
inflammation). Such changes disappear if the irritation is removed (the cells return to
normal condition or die and are replaced by normal cells).
True (malignant) dysplasia: the change in the cell is irreversible; the changes are actually
malignant and without treatment progress into evident neoplastic process
Strictly speaking the term reactive dysplasia should not be used. Terms like cellular irritation
or irritative changes are better.
It may be very difficult to decide whether the cells (seen by the microscope, in a biopsy) show
reactive or neoplastic changes. The tissue specimens are often small (endoscopic biopsies).
Moreover it is known, that prolonged inflammation may lead to malignant transformation
(tissue near chronic ulcers, like in the skin or stomach). On the other hand many tumour are
surrounded by variable inflammation (sometimes caused by therapy).
Accumulation of cells with signs of dysplasia is usually called carcinoma in situ. Typical
example is the epithelium, where no other signs of malignancy (namely infiltrative growth)
are not found.
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