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7. Where are the thyroid and parathyroid glands located? What are the functions of these glands? Vascular supply/drainage?
7. Where are the thyroid and parathyroid glands located? What are the functions of these glands? Vascular supply/drainage?
The thyroid gland has two lobes connected by a central isthmus, and sits between the C5-T1 vertebra. Nearly 50% of people have an accessory (pyramidal) lobe, which varies in size and typically connects the isthmus of the thyroid gland to the hyoid bone (Moore et al., 7th edition).
The thyroid gland is an endocrine gland --- meaning it secretes hormones and is ductless. The thyroid gland secretes thyroid hormones (controls rates of tissue metabolism) and calcitonin (important in calcium homeostasis).
The thyroid gland is typically supplied by two sets of arteries: superior & inferior thyroid aa.
The superior thyroid a. is the first branch of the external carotid a. It has several branches, one of which is the superior laryngeal a.
The inferior thyroid a. is a branch of the thyrocervical trunk (a branch of the first part of the subclavian a.). The inferior thyroid aa. typically cross the recurrent laryngeal nn. deep to the thyroid gland in the vicinity of the larynx.
The thyroid gland is typically drained via 3 sets of veins:
Superior thyroid vv., typically drain into the internal jugular vv.,
Middle thyroid vv., typically drain into the internal jugular vv.,
Inferior thyroid vv., typically drain into the L. brachiocephalic v.
Parathyroid glands may be found in a variety of locations, but are typically on the posterior aspect of the thyroid gland. There are typically four parathyroid glands (a superior pair and inferior pair), but there may be more or fewer. The superior parathyroids are the most constant in size and position. Parathyroid glands may be supplied by either set of thyroid arteries (as determined by location), but typically the inferior thyroid aa. supply the parathyroids. The parathyroid glands are also endocrine, and produce parathyroid hormone (PTH). The parathyroid glands are supplied by the inferior thyroid aa.
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