0:00 Hello, in this video, we're going to talk about the anatomy of the thyroidic 0:08 gland. 0:09 The thyroid gland is a butterfly-shaped endocrine organ that sits and wraps 0:14 around the trachea. 0:16 It produces three main hormones, triderotherin and tharoxin, which are 0:22 important in metabolism 0:22 and calcitonin and calcium homeostasis. 0:26 The thyroid has two main lobes, the right and the left. 0:29 And, tearily, the thyroid glands are joined by the isthmus. 0:34 Posterially, the thyroid gland encircles the trachea but does not connect. 0:39 From this dorsal view, we can see that there are four parathyroid glands which 0:44 sit on 0:45 the thyroid gland, two on each side. 0:50 Developmentally, the thyroid isthmus can give rise to a structure called the py 0:54 ramidal lobe, 0:56 which extends upwards. 0:58 The pyramidal lobe is common in up to 55% of people and is a result of the 1:03 persistent 1:04 remnant of the thyroid-glossal duct. 1:08 The thyroid gland is one of the first endocrine organs to become active in 1:13 humans, becoming 1:14 active by the 24th week of gestation. 1:18 This early activity is important because much of fetal organ development 1:23 depends on thyroid 1:24 hormone. 1:25 So embryologically, the thyroid gland begins its development at the base of the 1:30 tongue, 1:30 a place called the frame and seek them. 1:35 From here, it will descend down to the trachea. 1:38 It goes down, forming the thyroid-glossal duct, which should atrophy with time. 1:46 The thyroid-glossal duct cyst is a common congenital midline mass caused by the 1:52 persisting thyroid-glossal 1:54 duct tract. 1:59 The thyroid-glossal duct tract does not atrophy, but forms a cyst instead. 2:05 The cysts are usually painless unless it becomes infected. 2:09 Clinically, because the thyroid-glossal duct arises from the base of the tongue 2:14 , the thyroid-glossal 2:15 duct cyst will move with tongue protrusion. 2:19 The parameter lobe is, again, a result of the thyroid-glossal duct, which may 2:25 have not 2:25 atrophied completely. 2:32 The thyroid gland is in the visceral compartment of the neck, along with the tr 2:37 achea, recurrent 2:38 laryngeal nerve, esophagus, and the pharynx. 2:43 The compartment is enclosed in the pre-tracheal fascia, which anchors the 2:48 thyroid gland to 2:49 the trachea, so that the thyroid moves up with swallowing. 2:55 The thyroid gland stands at the vertebral level C5 and T1. 3:01 Here is a cross-section of the C6 vertebral level. 3:06 While on this diagram, the crowded sheath is adjacent to the pre-tracheal fasc 3:12 ia, and 3:13 the crowded sheath is where the internal jugular vein and the common carotid ar 3:17 chery runs. 3:18 And these are two important structures in the venous drainage, as well as the 3:23 arterial 3:24 supply of the thyroid gland. 3:28 Some histology. 3:29 Now, the functional units of the thyroid gland are the follicles. 3:34 The follicles are made up of a central cavity filled with a sticky fluid called 3:40 colloid. 3:41 Surrounded by a wall of epithelial follicle cells, the colloid is the center of 3:47 thyroid 3:47 hormone production. 3:50 Surrounding the follicles are capillaries. 3:51 Now, these follicular cells produce the classical thyroid hormones, thyroxine 3:58 and triadothyranine. 4:00 The production of these hormones in the colloid rely on iodine. 4:06 Another cells called the paraffillicular cells, or the C cells, are located 4:10 between the follicles 4:11 and produce the polypeptide hormone calcitonin, which is important in calcium 4:22 homeostasis. 4:24 Focusing on the arterial supply of the thyroid gland, relative to its weight, 4:28 the thyroid 4:29 gland receives a greater flow of blood than most other tissues of the body. 4:33 This is probably because the thyroid hormones are extremely important and are 4:37 transported 4:37 via the blood. 4:39 The artery supplying the thyroid gland includes the branch of the external car 4:43 otid artery, 4:44 the superior thyroid artery, a branch of the subclavian artery, which is the 4:52 thyroid cervical 4:53 trunk, and another branch from the thyroid cervical trunk, the inferior thyroid 4:58 artery, 4:59 and then we have the ema artery, which is present in 3% of people, and it's a 5:04 branch of the 5:05 brachiocephalic artery. 5:09 Running along the arteries are nerves, which supply the laryngeal muscles, the 5:15 muscles 5:15 for speech and voice. 5:18 These nerves are important for the anatomy of the thyroid because of its close 5:24 proximity 5:25 to the thyroid gland. 5:27 Firstly, the thyroid gland is innervated by the sympathetic nerves from the 5:33 cervical ganglion, 5:35 but these nerves do not control secretion of the thyroid hormones. 5:40 The thyroid gland is also innervated by the parasympathetic nerve, which we 5:43 will talk 5:44 about now. 5:45 So the vagus nerve branches to form the superior laryngeal nerves, which partly 5:51 supply the thyroid 5:52 gland, but mainly the laryngeal muscles. 5:55 The right vagus nerve continues down and gives off another branch, the right 6:00 recurrent laryngeal 6:02 nerve, which may loop under the brachiocephalic artery and travel up, supplying 6:08 the thyroid 6:09 gland, but mainly supplying the laryngeal muscles. 6:13 After giving off the left superior laryngeal nerve, the left vagus nerve 6:18 continues down 6:20 and gives off another branch, the left recurrent laryngeal nerve, which loops 6:25 under the aortic 6:26 arch and travels back up, supplying the thyroid gland, but mainly supplying the 6:31 laryngeal muscles, 6:33 very important in speech. 6:36 And so, performing a thyroidectomy, removal of the thyroid can potentially 6:41 injure these 6:42 laryngeal nerves and so cause a change in voice. 6:51 The venous drainage of the thyroid is through the paired superior and middle 6:56 thyroid veins 6:57 into the internal jugular vein. 7:02 The internal jugular will drain into the brachiocephalic vein. 7:07 The inferior thyroid vein drains into the brachiocephalic vein, which will then 7:12 drain 7:13 into the superior vena cava. 7:16 The gland is also endowed with a rich lymphatic system that may play an 7:21 important role in 7:22 the delivery of hormones to the general circulation. 7:26 The lymphatic drainage of the thyroid gland is extensive and flows in multi- 7:31 directional 7:31 pattern. 7:33 The thyroid lymphatic drainage drains into the pre-trikyol lymph nodes, the 7:38 para-trikyol 7:38 lymph nodes, the inferior deep cervical lymph nodes, the superior deep cervical 7:44 lymph nodes, 7:44 the pre-laryngeal lymph nodes and even up to the submendibular and submental 7:49 lymph nodes. 7:50 The nodes are important as cancer from the thyroid gland can move to these 7:54 areas to these 7:55 lymph nodes. 7:59 Some clinical anatomy, let's talk about the tubercle of a zucco candle. 8:05 I don't know if I pronounced that right, I apologize. 8:07 Now the tubercle of zucco candle is a pyramidal extension of the thyroid glands 8:14 . 8:14 If present at the most posterior side of each lobe, now the recurrent laryngeal 8:21 nerves, 8:22 which we talked about on the right and the left, they actually transverse the 8:26 posterior 8:27 aspect of the tubercle. 8:31 And so this tubercle is a good area to help surgeons identify where the 8:36 recurrent laryngeal 8:38 nerve sits and to be careful. 8:42 Thank you for watching. 8:43 And I hope you enjoyed this video.
