Thymus Gland

The thymus gland is located in the upper thorax behind the sternum,

but below the thyroid gland. It has two lobes, each divided into lobules

by a partitian called a septum or wall. Each lobule consists of a densel

packed outer cortex and a paler center, called the medulla.

Lymphocytes divide in the cortex, and, as the T-cells mature, they

migrate into the medula and eventually enter one of the blood vessels in

that region. Other cells within the lobules produce hormones,collectively

known as thymosins. Thymosins promote the maturation of lymphocytes

within the gland, as well as the growth and activity of lymphocytes

throughout the body. When the gland begins to shrink, the amount of

thymosins and T-cells that are produced also is reduced. Because of

these changes, the defensive mechanisms of the body diminish with age.

The thymus gland is most active during early life, playing a critical

role in the development of a child's immune system before birth and

for a time thereafter. Usually by the age of two, the thymus gland has

reached its maximum size (weighing about 30 to 40 grams or 1.06 to

1.41 ounces) with the immune system becoming fully functional.

Because of this, vaccinations before the age of two are not really

necessary since these young immune systems are not mature enough

to handle the strength of a vaccine. After puberty, the gland begins to

shrink and is replaced by connective tissue and fat. The main function

of the thymus gland is in the processing and maturation of special

lymphocytes called T-cells.

DiGeorge Syndrome is associated with the thymus gland. DiGeorge

Syndrome, a complex congenital disorder, affects the growth and

development of the thymus gland. Abnormalities in fetal development

may result in an underdeveloped thymus. Repeated infections result

from a diminished immune system. There is no cure for...