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14.12: Thymosin

Last updated

Oct 22, 2023
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- 14.11: Parathormone
- 14.13: Cholecystokinin (CCK)

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Source and Control of Secretion

Thymosin is a group of several related hormones produced by the thymus gland (Figure 14.1). The mechanisms controlling thymosin secretion and blood levels are not understood, though secretion and blood levels of thymosin seem to be positively correlated with the size of the thymus. As the thymus increases in size during childhood, thymosin secretion and blood levels rise. Later, the increase in sex steroid hormones that accompanies puberty causes the thymus to stop growing. At about age 20 the thymus begins to shrink, and thymosin production and blood levels begin to decline slowly. After age 30, thymosin secretion and blood levels decrease more quickly as shrinkage of the thymus continues. By age 60, secretion stops and thymosin levels reach zero.

Effects

Thymosin is necessary for the maturation of lymphocytes, which are specialized white blood cells. Lymphocytes constitute a major part of the immune system, whose overall function is defense. This system identifies, destroys, and eliminates many types of undesirable materials, microbes, and viruses that may either enter the body or be produced within it.

Age Changes

As thymosin decreases with age, fewer immature lymphocytes are able to mature and become functional defense cells. Therefore, the ability of the immune system to protect the body declines. The consequences include an increased susceptibility to infection and an increased risk of cancer.

Source and Control of Secretion

Effects

Age Changes

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