The cells inside our body are in a continuous process of growing and dividing and differentiating during their life cycle. The extent of growing and maturating depend on the tissue that is involved.
Growth under normal conditions in addition to mitosis and differentiation are all controlled processes so that normal stucture of the tissue is maintained.
For example, the skin is characterized by proliferation of basal cells and their migration to the skin surface to become there squamous cells. Skin surface sheds continually so that a constant rate of basal cells formation and squamous cells shedding is maintained. Diseases of cellular growth can be caused by either high cell numbers in the tissue or by low cell count of that tissue.
The first disorder that I discuss in this article is atrophy of the tissue. Atrophy is defined as a decrease in the volume of a tissue which results from a decrease in the size of the tissue cells or due to a decrease in their number.
Atrophy occurs for example in muscle tissue after a prolonged period of inactivity. Skeletal muscles are prone to atrophy quickly if not in use for a period of time. Atrophy of skeletal muscles can also occur due to dysfunction of the nerves supplying the appropriate muscles. Physical therapy and electric stimulation of the muscles can prevent atrophy of that muscle.
Another cause of atrophy is seen in the endocrine glands of the body such as the adrenal gland and the thyroid gland. Atrophy of these glands occur due to the lack of hormones from the pituitary gland and which usually stimulate the growth of these glands.
For example, when estrogen is no longer secreted in women after menopause their endometrium atrophies in addition to atrophy of the vaginal epithelium and the breast tissue. A hypopituitarism that is associated with decreased secretion of its hormones can lead to atrophy of the thyroid and the adrenal gland and the gonads.
Treatment of patients with cortisol supplements can lead to atrophy of the adrenal gland due to the suppresion effect on the adrenocorticotropic hormone or ACTH by the cortisol excess. Under normal conditions ACTH stimulates the normal growth of the adrenal gland.
In cases of starvation that is called marasmus this leads to the use by the body of tissue proteins in muscles in order to generate energy. After this process muscles atrophy.
Aging is another cause of tissue atrophy. This is particularly prominent in tissues such as skeletal muscles and brain tissue.
Another type of atrophy can occur due to compression of the tissue by a neoplasm. For example a neoplasm in the spinal cord can lead to atrophy of the spinal cord and the vertebral column.
Hypertrophy of a tissue occurs as a result of increased amount of the cytoplasm and the organelles of the cells. This means that the size of the cell is increased. This process is in contrast to hyperplasia which is an increase in the number of cells in a given tissue.
As an example of hyperplasia I will take endometrial hyperplasia which occurs as a result of increased levels of estrogen in the blood as occurs during pregnancy.
Another example of hyperplasia occurs in the prostate gland. It is a common disorder in the old people. It is caused as a result of enlargement of the prostate gland. It is believed that the hyperplasia is caused due to the increased level of the male hormone testosterone.
Metaplasia is a change in the normal epithelium of a tissue to another normal epithelium without being malignant. Therefore this type of transformation is not considered malignant.
Metaplasia occurs in the esophagus due to acid reflux from the stomach to the esophagus. The typical stratified epithelium of the esophagus is changed to columnar epithelium.
The lung in smokers is liable to develop metaplasia from a columnar epithelium to stratified epithelium.
Dysplasia is defined as an abnormal differentiation and maturation of the tissue. The mucosa of the intestine can undergo dysplasia of its epithelium. Dysplasia can become malignant but by itself is not typical cancer.
