Thymus gland
The thymus gland is a crucial organ located in front of the ascending aorta and beneath the sternum, characterized by its pinkish-gray hue. It consists of two lobes separated by a septum, with each lobe containing lobules composed of connective tissue. This organ is particularly prominent in infants, reaching its peak size by around age two, before gradually shrinking after puberty. The primary function of the thymus is to facilitate the maturation of T lymphocytes, a type of white blood cell essential for the immune response against infections. It also produces the hormone thymosin, which aids in the maturation of lymphocytes in other lymphatic organs.
Dysfunction of the thymus can severely impact a child's immune capability, leading to symptoms such as muscle weakness and visual disturbances. Conditions like myasthenia gravis have been linked to thymic issues, while thymic tumors, including thymomas and thymic carcinoma, can occur, primarily in middle-aged individuals. The understanding of the thymus has evolved significantly since the early sixteenth century, with its role in immunity being elucidated only in the 1960s. Ongoing research is exploring the potential of thymus-derived cells in treating various diseases, highlighting the gland's importance in both health and disease management.
Thymus gland
Anatomy
Anatomy or system affected: Blood, cells, endocrine system, glands, immune system, lymphatic system
Specialties and related fields: Biochemistry, endocrinology, immunology, oncology
Definition: A gland that produces types of white blood cells for maintaining the immune system.
Structure and Functions
The thymus gland is a pinkish-gray organ that lies in front of the ascending aorta, beneath the top of the sternum. It consists of two lobes that are divided into lobules by a septum, or wall. Each thymic lobule is made of connective tissue, which consists of a densely packed outer cortex and less-dense center (medulla). The thymus is relatively large in infants and typically grows to its maximum size around the age of two. After puberty, it gradually decreases in size until it blends in with surrounding tissue.
The major cells of the thymus are morphologically indistinguishable from small, circulating lymphocytes. Lymphocytes (white blood cells) divide, differentiate, and mature in the thymic cortex to become T cells, a heterogeneous group of cells that are essential in protecting the body against infections that can be produced by invading foreign organisms. Once T cells mature, they migrate into the thymic medulla and eventually enter the bloodstream and travel to other lymphatic organs, where they bolster the immune system against disease. The thymus also produces a hormone, thymosin, which stimulates the maturation of lymphocytes in other lymphatic organs.
Disorders and Diseases
The thymus is critical in developing the immune system in children. If it malfunctions or is surgically removed, then a child has little to no ability to fight off disease. Signs and symptoms of thymus dysfunction include shortness of breath, facial swelling, muscle weakness, blurred vision, double vision, flushing, diarrhea, and neck pain and swelling. Myasthenia gravis, a neuromuscular disease that causes fluctuating muscle weakness, has been linked to thymus dysfunction. Proper diagnosis is critical so that appropriate treatment can be administered.
Although uncommon, thymic cancer can occur. Thymomas are generally slow-growing tumors that are most often found in middle-aged people. A much rarer condition is thymic carcinoma, which develops more quickly than thymoma and is more likely to spread to other parts of the body. If a thymic tumor is found from images produced by chest X rays, computed tomography (CT) scanning, or magnetic resonance imaging (MRI), then the tumor may be surgically removed or treated with radiation.
Perspective and Prospects
The first description of the thymus gland was reported in the early sixteenth century by Italian anatomist Giacomo da Capri. The functions of the thymus were not well understood until the 1960s, when its role in the immune system was discovered. In 2007, it was reported that natural killer T (NKT) cells, a type of regulatory T cells that mature in the thymus, help regulate insulin-dependent diabetes mellitus. Research is focused on the development of NKT cell-based approaches for immunotherapeutic treatment of this disease.
Bibliography
Anastasiadis, Kyriakos, and Chandi Ratnatunga, editors. The Thymus Gland: Diagnosis and Surgical Management. Springer, 2007.
Dabrowski, Marek P., and Barbara Dabrowska-Bernstein. Immunoregulatory Role of Thymus. CRC Press, 1989.
Lavini, Corrado, et al., editors. Thymus Gland Pathology: Clinical, Diagnostic, and Therapeutic Features. Springer, 2008.
"Myasthenia Gravis." MedlinePlus, US National Library of Medicine, 15 Mar. 2016, medlineplus.gov/myastheniagravis.html. Accessed 17 Feb. 2017.
"What is Thymus Cancer?" American Cancer Society, 17 Mar. 2015, www.cancer.org/cancer/thymus-cancer/about/what-is-thymus-cancer.html. Accessed 17 Feb. 2017.