the butter-fly shaped thyroid gland is located in the anterior neck, on the trachea just inferior to the larynx
a median tissue mass - isthmus - connects its 2 lateral lones
has a prodigious blood supply - superior + inferior thyroid arteries
Internal Strucuture - Follicles
internally, the gland is composed of hollow, spherical follicles
the walls of each follicle r formed largely by squamous epithlial cells - follicular cells - which produce the glycoprotein thyroglobulin
Internal Structure - Central Cavity
the central cavity of the follicle stores colloid, a sticky material consisting of thyroglobulin mols w attached iodine atoms
thyroid hormone is derived from this iodinated thyroglobulin
Process of Hormone Synthesis
follicular cells take up iodide from the blood, covert it intoiodine + attach it to tyrosine residues on thyroglobulin w in the colloid
this process produces T3 +T4, which r stored in the colloid until needed
Parafollicular Cells - Location & Function
parafollicular cells r located in the spaces between the thyroid follicles
secrete calcitonin a hormone involved in calcium homeostasis
Calcitonin
unlike T3 + T4, calcitonin is not a major metabolic regulator
it helps reduce blood calcium levels by inhibiting osteoclast activity in bones + promotion calcium excretion by the kidneys
its secretion is primarily stimulated by high blood calcium levels
Thyroxine & Triiodothyronine
thyroxine (T4) + trioodothyronine (T3) r essential thyroid hormones that play a critical role in regulating metabolism, growth + development in the human body
T4 = the primary hormone produced by the thyroid gland + is later converted into the more active T3 in target tissues
