Lecture 01 The Thyroid & Parathyroid Glands By: Dr Farooq Khan PMC Date: 12 th March. 2018
INTRODUCTION LAYERS OF THE NECK The neck has four major compartments or layer which are enclosed by an outer musculofascial collar. 1. Vertebral compartment. Contains muscles of the neck. 2. Visceral compartment. Which contains important glands i.e.: thyroid,parathyroid and thymus.
LAYERS OF THE NECK.CON T And parts of the respiratory and digestive tracts that pass between head and thorax. 3. Vascular compartments. Two in numbers. It Contains major blood vessels and the vagus nerve.
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Embryology of the Thyroid Gland The thyroid gland arises as a midline evagination from the floor of the embryonic pharynx at the level of the second pharyngeal pouches (II). The thymus as bilateral buds off from the third pouches (III) The superior parathyroids as buds off from pouch (IV) on each side and The inferior parathyroids buds off from pouch (III) on each side.
EMbRYOLOGY OF THE THYROId GLANd..CON T The site where the embryonic thyroid diverticulum arose is marked in the adult by the foramen caecum of the tongue. It is endodermal derivative. The thyroglossal duct follows a path in the midline, through the tongue, to the hyoid bone. It then passes in front of it and in close relationship to the thyrohyoid membrane and thyroid cartilage. Finally it reaches the location normally occupied by the thyroid gland.
EMbRYOLOGY OF THE THYROId GLANd..CON T Its path may be indicated by a ligament or a muscle (levator glandulae thyroide) attaching the isthmus or a pyramidal lobe to the hyoid bone. The thyroglossal duct may persist as a cyst along this course. The thyroid tissue may also develop in great or small amount along the course of the thyroglossal duct to produce an ectopic I accessory thyroid, e.g., a lingual thyroid. The gland is functional during 3 rd month of development.
EMbRYOLOGY OF THE THYROId GLANd..CON T The pyramidal lobe based on the isthmus marks the inferior end of the embryonic thyroglossal duct. Either a ligament or an elevator muscle of the thyroid gland connects the tip of the pyramidal lobe to the body of the hyoid bone. The pyramidal lobe is the remnant of the thyroglossal duct.
Gross Anatomy of the Thyroid Gland The thyroid gland is composed of two lateral lobes connected by an isthmus which lies on tracheal rings 2, 3 and 4. It lies against vertebrae C5, C6, C7 and T1. The lateral lobes lie lateral to the trachea and the superior pole of each lateral lobe overlies the thyroid cartilage posterior to the oblique line. It usually weighs 25g but this varies, as the gland is slightly heavier in females, and enlarges during menstruation and pregnancy.
ANATOMY OF THE THYROId GLANd..CON T In the anterior view Identify: The hyoid bone (H) (body, greater and lesser horns The thyroid cartilage (TC) (superior and inferior horns); The thyrohyoid membrane (TM); The cricoid cartilage (CC); The cricothyroid membrane (CTM); and The tracheal rings (TR).
ANATOMY OF THE THYROId GLANd..CON T In the lateral view, identify: The oblique line of the thyroid cartilage (OBL) The cricothyroid joint (CTJ) between the inferior horn of the thyroid cartilage and, The lateral side of the lamina of the cricoid cartilage.
ANATOMY OF THE THYROId GLANd..CON T In the posterior view, identify: The lamina of the cricoid cartilage (LCC). Articulated with the lamina are the two arytenoid cartilages (AC). Note: The cricoid cartilage is the only complete hard tissue ring in the respiratory tree.
ANATOMY OF THE THYROId GLANd..CON T During swallowing the larynx, trachea, and thyroid gland (along with the pharynx and esophagus) undergo vigorous vertical movements. To know why the thyroid accompanies the larynx and trachea, one must have the knowledge of the attachments of the pretracheal fascia.
Capsule of thyroid Gland The thyroid gland is covered by a thin fibrous capsule, which has an inner and an outer layer. The outer layer (False capsule) is continuous with the pretracheal fascia, attaching the gland to the cricoid and thyroid cartilages, via a thickening of the fascia to form the posterior suspensory ligament of thyroid gland also known as Berry's ligament. This causes the thyroid to move up and down with swallowing. The inner layer (True Capsule) invaginates into the gland and forms the septae that divides the thyroid tissue into microscopic lobules.
Relation of The Thyroid Gland The thyroid gland lies in front of the neck, hidden by the anterior muscles of the neck, sternothyroid and sternohyoid muscles. Estimation of the size of the thyroid gland by diagnostic ultrasound is important clinically, so as to evaluate and manage thyroid disorders. The anterior border of the gland is thin, the posterior border is rounded and related inferiorly to the inferior thyroid artery.
RELATION OF THYROId GLANd.CON T Anterolaterally: Sternothyroid Superior belly of omohyoid Sternohyoid. Anterior border of sternocleidomastoid
RELATION OF THYROId GLANd CON T Posterolaterally: The carotid sheath with the common carotid artery, Internal jugular vein, and The vagus nerve.
RELATION OF THYROId GLANd CON T Medially: The larynx Trachea Pharynx and Oesophagus Associated with these structures are the cricothyroid muscle and its nerve supply, The external laryngeal nerve. In the groove between esophagus and the trachea is the recurrent laryngeal nerve.
Arterial Supply of the Thyroid Gland The thyroid gland is supplied by four (sometimes five) arteries: The two Superior Thyroids (ST), are branches of the external carotids (ECA); The two Inferior thyroids (IT) arise from the thyrocervical trunks (TCT), which are branches of the subclavian arteries (SA). Occasionally, there is an un paired 'thyroid ima' artery, usually a branch of the brachiocephalic artery (BCA) but sometimes arising directly from the arch of the aorta.
Arterial Supply of the Thyroid Gland The two superior thyroid arteries anastomose with each other after sending branches into the gland. The two inferior thyroids follows an S- shaped course posterior to the carotid sheath and its contents to reach the thyroid gland. To reach the gland they establish an important relationship with the recurrent laryngeal nerve
Inferior Thyroid Artery and Recurrent Laryngeal Nerve The relationship of the inferior thyroid artery (ITA) to the recurrent laryngeal nerve (RL) is important. This relationship is shown here. The diagram shows a posterior view of the esophagus (ESO), trachea (TR), lamina of cricoid cartilage (LCC); inferior horn of thyroid cartilage (IHTC); thyroid gland (TG); contents of carotid sheath; inferior thyroid artery (ITA) and recurrent laryngeal nerve (RL).
Inferior Thyroid Artery and Recurrent Laryngeal Nerve On the left side the Inferior thyroid artery (ITA) having passed posterior to the internal Jugular vein (IJ), vagus nerve (V), and common carotid artery (CC), passes anterior to the recurrent laryngeal nerve (RL). On the right side, the inferior thyroid artery passes posterior to the recurrent Laryngeal nerve (RL).
Inferior Thyroid Artery and Recurrent Laryngeal Nerve This diagram illustrates the danger in a situation in which the inferior thyroid artery courses posterior to the recurrent laryngeal nerve. In mobilizing the gland for removal. The lateral lobe when drawn anteriorly may pull the nerve with it. Hoarseness results if the recurrent laryngeal nerve is damaged.
Venous Drainage of the Thyroid Gland There is a venous plexus which occupies the area between the thyroid sheath and the capsule of the gland. Six veins emerge from this plexus and drain the thyroid gland. These are: Two Superior Thyroid veins, which are companions to the superior thyroid arteries. They are tributary to either the common facial vein, or to the internal jugular.
VENOUS drainage OF THE THYROId GLANd.CON T Two Middle Thyroid veins, which emerge from the lower part of each lateral lobe. They pass laterally anterior to the common carotid artery, and empty into the internal jugulars and, Two Inferior Thyroid veins, which may open separately into their respective innominate (left innominate and right innominate vein, or unite before opening as a single vein, usually into the left innominate.
Parathyroid Gland Development The parathyroid glands develop from the endoderm cells between the third and fourth pharyngeal pouch. The inferior parathyroid glands develop from the dorsal aspect of the third pharyngeal pouch. Because they travel far in foetal life, they may have a wide range of distribution in an adult.
PARATHYROId GLANd development.con T In contrast, the superior parathyroid glands develop from the dorsal recess of the fourth pharyngeal pouch. They remain superior to the thyroid lobes. The parathyroid glands have a different size and position in neonates than in adults, and the size is double between birth and puberty. The parathyroid hormone is produced from the 12th week of development onwards.
Gross AnatomyThe Parathyroid Glands The parathyroids are intimately related to the thyroid gland. The two Superior parathyroids are located in the posterior portion of the superior pole of each lateral lobe close to the vascular pedicle of the pole i.e near the point where the superior thyroid vessels reach (artery) or leave (vein) the gland. The position of the two superior parathyroids is quite constant. Each is about the size of a small pea, and has a distinct vascular pedicle. The superior parathyroids are commonly removed in a thyroidectomy.
The Parathyroid Glands The two inferior parathyroids are more variable in position. The arterial pedicle of each is derived from the inferior thyroid artery rather close to its entrance into the thyroid gland. One or both inferior parathyroids (parathyroid III) can occupy different positions, i.e., (1). between the prevertebral and pretracheal fasciae. (2) between the pretracheal fascia and the capsule of the thyroid gland (3) or embedded in the thyroid gland, its usual position.
Relations of the Thyroid Gland
Relations of the Thyroid Gland
Relations of the Thyroid Gland