Adaptive disorder / changes are the changes which the cells make in response to stress. It may be for physiologic needs (like ageing) or a response to non-lethal pathologic injury. These changes are reversible on withdrawal of the stimulus.

Adaptive changes notes

Understand some terms:

"trophy" - nourishment ; "plasia" - growth of new cells.
"meta" - transformation ; "dys" - bad development.

Atrophy

        Reduction of the number and size of parenchymal cells of an organ or its parts.

Causes :

Physiologic atrophy - It is a normal process od ageing in some tissues.
    - Atrophy of lymphoid tissue with age.
    - Atrophy of thymus in adult life.
    - Atrophy of brain with age.

Pathologic atrophy -
    Starvation atrophy, there is first depletion of carbohydrate and fat stores.
    Disuse atrophy - Prolonged diminished functional activity is associated with disuse atrophy of the organ. E.g. Wasting of muscles of limb immobilized in cast.

cell adaptive changes

Hypertrophy

        It is an increase in the size of parenchymal cells resulting in enlargement of the organ or tissue, without any change in the number of cells.

Causes: Due to increased functional activity or hormonal stimulation.

Physiologic hypertrophy
   Increase in uterus size during pregnancy time is an example of hypertrophy.

Pathologic hypertrophy
    Hypertrophy of cardiac muscle - Systemic hypertension, Mitral insufficiency.
    Hypertrophy of smooth muscle - Pyloric stenosis, Intestinal strictures.

Hyperplasia

        Hyperplasia is an increase in the number of parenchymal cells resulting in enlargement of the organ or tissue. Hypertrophy and hyperplasia occurs together.

Causes:

Physiologic hyperplasia
    Hyperplasia of pregnant uterus and female breast at puberty
    Prostatic hyperplasia

Pathologic hyperplasia
    Endometrial hyperplasia following estrogen excess
    In wound healing, formation of granulation tissue

Metaplasia

        It is a reversible change of one type of epithelial or mesenchymal adult cells to another type of adult epithelial or mesenchymal cells, usually in response to abnormal stimuli. It often reverts back on removal of stimulus.

Two type of metaplasia: Epithelial and Mesenchymal

1.      Epithelial Metaplasia    

             It is a common one. It is further divided into squamous metaplasia and columnar metaplasia

2.      Mesenchymal Metaplasia

It occurs less often. Two types of mesenchymal metaplasia, they are

Osseous metaplasia is formation of bone in fibrous tissue, cartilage and myxoid tissue. E.g. In arterial wall in old age, In cartilage of larynx and bronchi in elderly people.

Cartilaginous metaplasia – In healing of fractures, cartilaginous metaplasis may occur where there is undue mobility.

Dysplasia

        It means ‘disordered cellular development’, often preceded or accompanied with metaplasia and hyperplasia. It occurs most often in epithelial cells. Epithelial dysplasia is due to,

    - Increased number of layers of epithelial cells

    - Cellular and nuclear pleomorphism

    - Disorderly arrangement of cells from basal layer to surface layer

    - Increased mitotic activity