Function

Update November 20, 2020

The thymus is active in children, but at the start of puberty, until old age, it starts to atrophy, producing fewer T-cells. The thymus also produces thymic hormones that support the growth and differentiation of T-cell progenitors.

 

This organ is important for development of immunocompetent T-cells, proliferation of clones of of mature T-cells, developing immunological self-tolerance, and secretion of hormones for T-cell development. At least three hormones are made: thymosin, thymulin and thymopoietin. These hormones are produced by reticular epithelial cells in the cortex.

The thymus is the primary organ of T-cell Development

The thymus has a key role in the development of an effective immune system as well as an endocrine function.

In the adult thymus, specialised microenvironments allow the production of self-tolerant T cells from immature precursors.

• The thymus is the primary organ of T-cell Development and is divided into an outer cortex and inner medulla. The entire organ is surrounded by a collagenous capsule which lobulates the organ's mass with occasional septae. As T-cells progress through their developmental stages, they migrate from the cortex to the medulla.

Basic Components

• Overview
• The thymus is composed of a mixture of developing T-cells enmeshed in a network of Thymic Epithelial Cells. Thymic epithelial cells are thought to present self-peptides in complex with MHC on their surface which is used for both positive and negative selection during T-cell Development.
• Thymic Cortex
• The Thymic Cortex is highly cellular, consistent with the large numbers of T-cells which exist prior to the stringent selection that occurs during T-cell development.
• Thymic Medulla
• The Thymic Medulla is significantly less cellular and represents the exit point of mature T-cells into the peripheral circulation.

Age-related Changes

• The human thymus is most cellular and active during childhood and begins a long, slow process of involution following pubescence. By the time of the later decades the majority of the thymus has been replaced with adipose tissue.

 

Thymus

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