Changes experienced by cells in response to physiological or pathological stimuli. These changes usually make it easier for cells to tolerate adverse environments.

As cells encounter some stresses, they may make functional or structural adaptations to maintain viability or homeostasis. Cells may respond to these stimuli by either increasing or decreasing their content of specific organelles.

Cellular adaptation is the ability of cells to respond to various types of stimuli and adverse environmental changes. The adaptation may be physiologic (normal) or pathologic (abnormal). These adaptations include hypertrophy, hyperplasia, and atrophy, metaplasia, and dysplasia. Tissues adapt differently depending on the replicative characteristics of the cells that make up the tissue. If cells are not able to adapt to the adverse environmental changes then the cell death occurs physiologically in the form of apoptosis or pathologically in the form of necrosis. This provides an overview of the main cellular adaptive mechanisms and their different consequences in the human body.

FOUR TYPES OF MORPHOLOGICAL ADAPTATIONS:

ATROPHY:

Atrophy is a decrease in cell size. If enough cells in an organ undergo atrophy the entire organ will decrease in size. Skeletal muscle atrophy is a common pathologic adaptation to skeletal muscle disuse commonly called disuse atrophy. Tissue and organs especially susceptible to atrophy include skeletal muscle, cardiac muscle, secondary sex organs, and the brain. Decrease in the amount of a tissue or organ after normal growth has been attained. Adaptive response is caused by a tissue or organ which undergoes a reduction in mass (size), due to decrease in the size or number of cells.

HYPERTROPHY:

Hypertrophy is an increase in cell size and volume. Organs are increased in size due to an increase in cell size without cellular proliferation. Hypertrophy may involve an increase in intracellular protein as well as cytosol and other cytoplasmic components. Hypertrophy may be caused by mechanical signals or trophic signals.

HYPERPLASIA:

Hyperplasia is an increase in the number of cells. Increase in organ size or tissue mass caused by an increase in the number of constituent cells. It is the result of increased cell mitosis or division.

The two types of physiologic hyperplasia are compensatory and hormonal. Compensatory hyperplasia permits tissue and organ regeneration. It is common in epithelial cells of the epidermis, intestine, liver hepatocytes, bone marrow cells, and fibroblasts. It occurs to a lesser extent in bone, cartilage, and smooth muscle cells. Hormonal hyperplasia occurs mainly in organs that depend on oestrogens. Pathologic hyperplasia is an abnormal increase in cell division. A common pathologic hyperplasia in women occurs in the endometrium and is called endometriosis.

DYSPLASIA:

Dysplasia is a condition of abnormal cell changes in which the cells are structurally changed in size, shape, and appearance from the original cell type. Tissues prone to dysplasia include cervical and respiratory epithelium, where it is strongly associated with the development of cancer. It may also be involved in the development of breast cancer. Although dysplasia is reversible, if stress persists, then dysplasia progresses to irreversible carcinoma.

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Editorial office

Journal of Clinical and Experimental Pathology

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