Veterinary Physiology-III

REGULATION OF THYROID SECRETION

• TSH from anterior pituitary stimulates the secretion of T₄ and T₃ by the thyroid gland.
• The TSH promotes iodide trapping, increases iodination of tyrosine and coupling of iodotyrosines to form thyroid hormones.
• TSH increases follicular cell size and number thereby thyroid hormones synthesis.
• TSH and T₄ secretions are controlled by the level of hormones in blood by long ‑ loop negative feedback or servomecha­nism.
• TRH from hypothalamus regulates thyroxine release through TSH release.
• Exposure to cold increases TRH secretion from hypotha­lamus causes increased secretions of TSH and thyroid hormones and increased meta­bolic rate.