Name three different types of cellular adaptations Discuss t

Solution

Cellular adaptations are the modifications undergone by the cell to overcome the environmental effects. Adaptations are of 5 types, atrophy, hypertrophy, hyperplasia, dysplasia and metaplasia.

Atrophy

Shrinkage in the size of the cell by loss of cell substance is known as atrophy.

Causes : Decreased workload, loss of innervation, diminished blood supply, inadequate nutrition, loss of endocrine stimulation and aging.

The regularity with which a muscle is used, as well as the duration and intensity of its activity, affects the properties of the muscle. If the neurons to a skeletal muscle are severed and otherwised destroyed, the denervated muscle fibres will progressively become smaller in diameter, and the amount of contractile proteins they contain will decrease. This condition is known as denervation atrophy. A muscle can also atrophy with its nerve supply intact if teh muscle is not used for a long period of time, as when a broken arm or leg is immobilised in a cast. Ths condition is called disuse atrophy. Obviously, atrophy may progress to the point at which cells are injured and die. If the blood supply is inadequate even to maintain the life of shrunken cells, injury and cell death may supervene. The atrophy tissue may then be replaced by fatty ingrowth.

Hypertrophy

Increase in the size of a cell, and with such change, increase in size of organ.

In contrast to the decrease in muscle mass that results from a lack of neural stimulation, increased amounts of contractile activity - in other words, exercise - can produce an increase in the size of muscle fibres as well as changes in their chemical composition

Hyperplasia

Hyperplasia constitutes an increase in the number of cells in a organ or tissue, which may then have increased volume. Hyperplasia can be physiologic or pathologic.

Physiologic hyperplasia

a. Hormonal hyperplasia : the proliferation of the glandular epithelium of female breast at puberty and during pregnancy

b. Compensatory hyperplasia: The best exemplified is the removal of a portion of liver.

Cell proliferation is dependent on the action of polypeptide growth factors - TGF and hepatocyte growth factor.

Pathologic hyperplasia

These are due to excessive hormonal stimulation or are the effects of growth factors on target cells, an example is hyperplasia of the endometrium.

Metaplasia

It is reversible change in which one adult cell type (epithelial or mesenchymal) is replaced by another adult cell type. The most common adaptive metaplasia is columnar to squamous, as occurs in the respiratory tract in response to chronic irritation. The stratified squamous epithelium is able to survive under adverse circumstances. The influences that predispose to such metaplasia, if persistent, may induce cancer transformation in metaplasic epithelium. Metaplasia is thought to arise from genetic reprogramming of stem cells that are known to exist in most epithelia, or or undifferentiated mesenchymal cells present in connective tissue.

Dysplasia

Some of the early stages of transformation result in changes in the cell\'s morphology, known as dysplasia, a precancerous state that can be detected by microscopic examination. At this stage the cell has not yet acquired a capacity for unlimited growth or an ability to invade surrounding tissues.