thymus

Examples of thymus in the following topics:

• Thymus

  • Surprisingly, removal of the thymus does not result in a T cell immunodeficiency.
  • The thymus is a specialized organ of the immune system.
  • The thymus is of a pinkish-gray color, soft, and lobulated on its surfaces.
  • Though removal of the thymus in childhood causes severe immunodeficiency, later in life this is not an issue because of the proliferation of thymus activity early in life.
  • Central tolerance is another function of the thymus.

• Maturation of T Cells

  • T cells are produced in the bone marrow but travel to the thymus to mature.
  • Immature T cells that migrate to the thymus are called thymocytes.
  • The thymus contributes fewer cells as a person ages.
  • The thymus is thus thought to be important in building a large stock of naive T cells soon after birth that can later function without thymus support.
  • The remaining cells exit the thymus as mature naive T cells.

• Lymphoid Tissue

  • The thymus gland and bone marrow contain primary lymphoid tissue where B and T cells are generated.
  • T cells mature in the thymus, while B cells mature in the bone marrow.
  • T cells born in bone marrow travel to the thymus gland to mature.
  • More specialized primary lymph tissue, such as the thymus, develops from pharyngeal pouches (embryonic structures that differentiate into organs near the pharynx and throat) by the eighth week of gestation.
  • The thymus and bone marrow are primary lymphoid tissue, while the lymph nodes, tonsils, and spleen are secondary lymphoid tissue.

• Lymphocytes

  • T cells mature in the thymus and contain T cell receptors (TCRs) that allow them to bind to antigens on MHC complexes.
  • They have an immunosuppressive effect that inhibits cell-mediated immunity at the end of a response and destroys autoimmune T cells that aren't filtered out by negative selection in the thymus.
  • While in the bone marrow, B cells are sorted through positive and negative selection in a manner somewhat similiar to T cell maturation in the thymus, with the same process of killing B cells that are nonreactive to antigens or reactive to self-antigens.
  • Mature B cells leave the thymus and travel to secondary lymphoid tissue such as the lymph nodes.

• WBC Formation

  • However, maturation, activation, and some proliferation of lymphoid cells occurs in lymphoid organs (spleen, thymus, and lymph nodes).
  • In some cases, the liver, thymus, and spleen may resume their haematopoietic function if necessary.

• Tonsils

  • Like the thymus, the tonsils reach their largest size near puberty and gradually atrophy thereafter.
  • Additionally, evidence exists that suggests that tonsils may play a role in  T cell maturation and development like the thymus does, but more research is needed.

• Transport of Hormones

  • Thymus 5.

• Organ Transplants

  • Organs capable of transplantation include hearts, kidneys, livers, lungs, pancreases, intestines, and thymus glands.

• Lymphatic Tissue Development

  • The thymus arises as an outgrowth of the third pharyngeal pouch.

• Ascending Aorta

  • The ascending aorta is covered at its beginning by the trunk of the pulmonary artery and, higher up, is separated from the sternum by the pericardium, the right pleura, the anterior margin of the right lung, some loose areolar tissue, and the remains of the thymus.