Lecture 8.2 - Thyroid Dysfunction.pdf

Thyroid gland - anatomy: ◦Location - anterior to the trachea and inferior to the larynx ◦Shape - a butterfly (bow-tie) shape with two lateral lobes joined by a central isthmus ◦Size - (varies) usually 2-3cm across (~15-20g) ◦Vasculature - thyroid gland is highly vascularised...

Thyroid gland - anatomy: ◦Location - anterior to the trachea and inferior to the larynx ◦Shape - a butterfly (bow-tie) shape with two lateral lobes joined by a central isthmus ◦Size - (varies) usually 2-3cm across (~15-20g) ◦Vasculature - thyroid gland is highly vascularised ‣ It receives blood from the superior (branch of the external carotid artery) and inferior thyroid arteries (branch of of the thyrocervical trunk) ‣ It is drained via the superior, middle and inferior thyroid veins Thyroid hormone regulation: ◦Thyroid function is regulated between the hypothalamic-pituitary-thyroid (HPT) axis ◦When stimulated by decreased peripheral thyroid hormone levels, the hypothalamus produces thyroid-releasing hormone (TRH), which stimulated the anterior pituitary to produce thyroid- stimulating hormone (TSH) ◦TSH acts upon the thyroid gland to increase iodine uptake and subsequent release of triiodothyronine (T3) and thyroxine (T4) ◦Circulating thyroid hormone levels are controlled through the process of negative feedback on the hypothalamus and pituitary ◦T3 and T4 are hydrophobic molecules and are transported in the blood reversibly bound to carrier proteins (thyroxine-binding globulin (TBG), transthyretin (TTR, or prealbumin) and albumin) ◦Only a small amount (