The primary, or central, lymphoid organs are the thymus and bone marrow, according to microbiologybytes.com. They are part of a broader lymphatic system made up of lymph nodes, tonsils, the spleen, and Peyer's patches in the intestinal wall. The function of the primary lymphoid organs is for production and maturation of the white blood cells in order to defend the body from disease.
Primary Lymphoid Organ
Although the ancient Greeks were aware of the existence of a white fluid in the body, it wasn't until 1622 when the Italian anatomist Gasparo Aselli witnessed a milky substance in the vessels of a dog, that the lymphatic system was truly discovered, according to nature.com. The thymus gland as a lymphoid organ was discovered in 1961 by Jacques Miller during his work using mice. Later, Miller and Graham Mitchell discovered the interaction between the thymus and bone marrow with regard to antibody production, reports nature.com.
Thymus
The thymus gland is a two lobed, glandular organ that lies in the chest under the breast bone. It is largest after birth and during childhood. The thymus begins to decrease in size after puberty, although it remains a functioning organ throughout life. The cells housed within the thymus are primarily white cells called T lymphocytes, along with smaller amounts of other lymphoid cells, according to Sage Online Journal. The main function of the thymus gland is to mature, or "educate" antibody producing white cells called T lymphocytes after they travel to the thymus from the bone marrow, says The Microbial World. This maturation process allows the T cells to tell the difference between self and a foreign invader. The different types of T cells function within the immune system by either directly attacking pathogens, or by communicating with and stimulating other types of immune cells, says the National Institute of Allergy and Infectious Disease.
Bone Marrow
All blood cells come from what are called stem cells within the bone marrow. It is in the marrow that the various white blood cells of the immune system form and migrate out into the circulation. The bone marrow is found primarily in the inner, hollow spaces of the flat bones and long bones of the skeleton, and comprises about 5 percent of human body weight, according to Sage Online Journal. The immune cells arising from the bone marrow are natural killer cells, B-cells, immature T cells called thymocytes, granulocytes, macrophages, and mast cells, reports The Microbial World.
