Thyroid-Stimulating Hormone (TSH)

Thyroid-Stimulating Hormone (TSH)



Basic Information image



Definition




• Hyperthyrotropinemia: Increased circulating concentration of TSH


• Hypothyrotropinemia: Decreased circulating concentration of TSH



Synonym(s)




Thyrotropin



Typical Normal Range (US Units; SI Units)


There are no published reference intervals for equids. Inclusion of a blood sample from a clinically normal, nonaffected horse may be useful for comparison purposes.



Physiology


TSH is released from the pituitary gland upon stimulation by thyroid-releasing hormone (TRH) from the hypothalamus. Both hormones are part of the thyroid-pituitary-hypothalamic axis, which regulates systemic thyroid hormone levels. TSH then goes on to stimulate the release of triiodothyronine (T3) and thyroxine (T4) from the thyroid gland. Administration of exogenous TSH assesses the ability of the thyroid gland to secrete T3 and T4, which should increase in concentration upon stimulation. TSH level can also be assessed by administration of exogenous TRH which assesses the ability of the pituitary to secrete TSH.



Causes of Abnormally High Levels


Due to a defect in the thyroid gland leading to hypothyroidism, there is a lack of secretion of thyroid hormones and subsequently no negative feedback on the hypothalamus and pituitary, resulting in continued secretion of TRH and TSH in a homeostatic attempt to increase systemic concentrations of thyroid hormone.

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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Thyroid-Stimulating Hormone (TSH)

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