What Are the Subdivisions of the Thymic Lobe?

The thymic lobes are a vital part of the human body's immune system. The body's two thymic lobes make up the thymus, a small organ in between the thyroid and the lungs. A malfunctioning thymus can lead to fatigue, frequent illness, and muscle weakness. The thymus produces T lymphocytes, small cells that help the body produce an immunity to infectious diseases. The thymus is a unique organ because it is the only organ in the body that is temporary. It is biggest when the body completes puberty. After puberty, it begins to shrink.

Thymus Structure

• The thymus consists of two distinct lobes about the size of a pea. Each of these lobes can be divided into numerous smaller lobules. The thymus develops from pink-gray in children to yellow in adults. Each lobe has an outer part, called the cortex, and the inner part, called the medulla. The infection-fighting T-cells begin their earliest stages of development in the cortex. Later stages of lymphocyte development occur in the medulla.

Cortex: T-Cell Production

• The cortex is the breeding ground for T-cells. The cortex makes up the outer portions of each lobe of the thymus. It contains these lymphocytes and epithelial cells (skin cells). These skin cells create a structure that leads to the body's blood vessels. It also contains a type of ever-morphing bone marrow. Here, pre-T cells are introduced to antigens, molecules that trigger the production of the body's natural antibiotics. Through a sort of natural selection, the T-cells that are able to recognize and fend off the antigens develop into mature T-cells. The cells that do not serve this function die off.

Medulla: T-cell Maturity

• Cells in the medulla are put through further scrutiny before entering the blood stream.

  Past the cortex of the thymus lies the medulla. T-cells that have passed the strength test of the cortex region of the thymus enter the medulla. The medulla is coarser than the cortex and contains fewer lymphatic cells. The lymphatic cells it does contain can be found in pockets within the medulla that also contain other important cells. The main purpose of the medulla is to continue the natural selection process of the T-cells. In the medulla, more cells are eliminated due to being auto-reactive. These auto-reactive cells react against themselves and ultimately will not create an immunity to the antigens that enter the body. Such cells are eliminated.

Diseases of the Thymic Lobe

• Because the thymus is a critical part of the immune system, it must function properly for the body to be in good health. The first, and perhaps most common thymus disease is thymus cancer. Thymus cancer results when the epithelial cells in the thymus grow a tumor. Myasthenia gravis is another disease of the thymus. Myasthenia gravis results when the thymus' T-cells accidentally attack important receptors in the body called acetylcholine receptors. These receptors are located where nerves attach to muscles in the body. When the body's antibodies attack these proteins, muscle weakness results.