Endocrine Functions of the Thymus
The thymus is a primary lymphoid organ bestowed with the site of development, maturation, and differentiation of T-lymphocytes to direct adaptive immune responses. In addition, it produces hormones that modulate the function of T-lymphocytes present in the thymus and peripheral circulation.
Thymulin, thymopoietin, and thymosin-α1 β4 are some of the important thymic hormones produced by thymicFig. 17.2 Regulation of erythropoietin secretion and its effect on erythrocytes. [The peritubular cells in the kidney secrete erythropoietin in response to tissue hypoxia. It increases the rate of erythropoiesis and subsequently establishes normal oxygen levels in the tissue.
" = Increase, (-) = Feedback inhibition]
Table 17.1 List of thymic hormones and their function concerning the immune system
| S. No | Hormone | Chemical nature | Function |
| 1. | Thymulin (Facteur thymique serique) | Nonapeptide containing zinc | 1. Increased generation of cytotoxic T-cells. 2. Intrathymic and extrathymic T-cell differentiation |
| 2. | Thymopoietin | Polypeptide 49 amino acids | Induces the differentiation of T-lymphocytes |
| 3. | Thymosin α1, Thymosinβ4 | 28 amino acids 43 amino acids | Stimulates lymphopoiesis and T-cell proliferation |
epithelial cells (TECs), which have well-documented effects on the immune system (Table 17.1). Hormones such as GH, PRL, THs, and sex steroids influence the endocrine function of the thymus by acting on TECs. Nonetheless, the thymic hormones can also affect the production of hormones from the hypothalamic-pituitary axis and their target endocrine glands including the gonads.
17.4