hypertrophy

hypertrophy, enlargement of a tissue or organ of the body resulting from an increase in the size of its cells. Such growth accompanies an increase in the functioning of the tissue. In normal physiology the growth in size of muscles (e.g., in an athlete as a result of increased exercise) and also the enlargement of a uterus in pregnancy are caused by hypertrophy of muscle cells. In pathology the thickening of the heart muscle from overstrain, as in hypertension (high blood pressure), is the result of hypertrophy. An organ subjected to extra work (e.g., the one kidney left to function after surgical removal of the other) usually compensates by enlarging; in such cases hyperplasia, an increase in the number of cells, generally accompanies hypertrophy.

Hypertrophy is the increase of the size of an organ or in a select area of the tissue. It should be distinguished from hyperplasia which occurs due to cell division increasing the number of cells while their size stays the same; hypertrophy occurs due to an increase in the size of cells, while the number stays the same.

Examples of hypertrophy

Muscular hypertrophy

One of the most common and visible forms of organ hypertrophy occurs in skeletal muscles in response to strength training (known as muscle hypertrophy). Depending on the type of training, the hypertrophy can occur through increased sarcoplasmic volume or increased contractile proteins.

Ventricular hypertrophy

Ventricular hypertrophy is the increase in size of the ventricles of the heart. Changes can be beneficial or healthy if they occur in response to aerobic or anaerobic exercise, but ventricular hypertrophy is generally associated with pathological changes due to high blood pressure or other disease states.

Hypertrophy of the breasts

Gigantomastia is the extreme growth of the breasts, i.e. 10 pounds (5 kg) per breast and more. In severe cases it is possible for women to have breasts that weigh well in excess of 20 lb (9 kg) each. Gigantomastia can occur as a rare complication of pregnancy, but also with the more frequently juvenile gigantomastia during puberty (virginal breast hypertrophy).

Hypertrophy of the clitoris

In the most pronounced cases, clitoromegaly is a symptom of intersexuality since the large clitoris resembles a penis (the different grade of genital ambiguity is commonly measured by the Prader classification ranging, in ascending order of masculinisation, from 1: Female external genitalia with clitoromegaly through 5: Pseudo-phallus looking like normal male external genitalia).

See also

• Atrophy

External links

• University of California Muscle Physiology Home Page: Hypertrophy