Thymus

related topics
{disease, patient, cell}
{specie, animal, plant}
{acid, form, water}
{area, part, region}
{build, building, house}
{country, population, people}

The thymus is a specialized organ in the immune system. The functions of the thymus are the "schooling" of T-lymphocytes (T cells), which are critical cells of the adaptive immune system, and the production and secretion of thymosins, hormones which control T-lymphocyte activities and various other aspects of the immune system. The thymus is composed of two identical lobes and is located anatomically in the anterior superior mediastinum, in front of the heart and behind the sternum.

Histologically, the thymus can be divided into a central medulla and a peripheral cortex which is surrounded by an outer capsule. The cortex and medulla play different roles in the development of T-cells. Cells in the thymus can be divided into thymic stromal cells and cells of hematopoietic origin (derived from bone marrow resident hematopoietic stem cells). Developing T-cells are referred to as thymocytes and are of hematopoietic origin. Stromal cells include thymic cortical epithelial cells, thymic medullary epithelial cells, and dendritic cells.

The thymus provides an inductive environment for development of T-lymphocytes from hematopoietic progenitor cells. In addition, thymic stromal cells allow for the selection of a functional and self-tolerant T-cell repertoire. Therefore, one of the most important roles of the thymus is the induction of central tolerance.

The thymus is largest and most active during the neonatal and pre-adolescent periods. By the early teens, the thymus begins to atrophy and thymic stroma is replaced by adipose (fat) tissue. Nevertheless, residual T lymphopoiesis continues throughout adult life.

Contents

Full article ▸

related documents
Chagas disease
Prader-Willi syndrome
Group A streptococcal infection
Encephalitis
Surgery
Psychosurgery
Abscess
Cataract
Sleep disorder
Phenytoin
Systemic lupus erythematosus
Niacin
Pancreas
Tinnitus
Sodium thiopental
Theophylline
Insulin-like growth factor
Scleroderma
Jaundice
Repetitive strain injury
Skin cancer
Stomach
Immunology
Coronary circulation
Cardiology diagnostic tests and procedures
Riboflavin
Chlamydia infection
Orthostatic hypotension
Albinism
Homocysteine