Thyroid Gland PDF - BDS-202

THYROID GLAND Head and Neck Anatomy II BDS-202 Dr. Jayaraj Ajman University 1-Oct-24 1  LEARNING OUTCOMES ▪ Describe structure and relations of the thyro...

THYROID GLAND Head and Neck Anatomy II BDS-202 Dr. Jayaraj Ajman University 1-Oct-24 1  LEARNING OUTCOMES ▪ Describe structure and relations of the thyroid gland ▪ Describe arterial supply and venous drainage of the thyroid gland ▪ List Lymphatic and nerve supply of the thyroid gland ▪ Discuss the clinical anatomy related to the relation and function of the thyroid gland Ajman University 1-Oct-24 2  Thyroid Gland ❑ Thyroid gland Butterfly-shaped or H-shaped Largest endocrine gland of the body ▪ Location Lower part of the front of the neck Located just inferior to the larynx Opposite to the C5, C6, C7, and T1 vertebrae ▪ Mass of the thyroid is about 30 g Ajman University 1-Oct-24 3  Parts and Features of Thyroid Gland Composed of right and left lateral lobes One on either side of the trachea Connected by an isthmus across the midline About 50% of thyroid glands Have a small third pyramidal lobe Extends superiorly from the isthmus Connected to the body of the hyoid bone By a fibromuscular band called levator glandulae thyroideae Ajman University 1-Oct-24 4  Capsule of the Thyroid Gland ❑ Thyroid gland is invested by two capsules True capsule Formed by the fibrous stroma of the gland Encloses venous plexus False capsule Derived from the pretracheal fascia o Pretracheal fascia Encloses the thyroid gland And attached to the thyroid cartilage and body of the hyoid bone o Suspensory ligament of Berry Medial surface of thyroid lobe connects to the cricoid cartilage Ajman University 1-Oct-24 5  Relations of the Thyroid Lobe Apex Extends up to the oblique line of thyroid cartilage Between the inferior constrictor medially and sternothyroid laterally Base Extends up to the 5th or 6th tracheal ring Inferior thyroid artery and recurrent laryngeal nerve Lateral surfaces Sternothyroid, sternohyoid and superior belly of omohyoid Anterior border of sternocleidomastoid Ajman University 1-Oct-24 6  Relations of the Thyroid Lobe Medial surface Trachea and esophagus Inferior constrictor and cricothyroid muscle Cricoid and thyroid cartilage Posterolateral surface Carotid sheath and its contents Ansa-cervicalis, cervical sympathetic chain Anterior border Anterior branch of superior thyroid artery Posterior border Anastomosis between superior and inferior thyroid arteries Parathyroid glands Ajman University 1-Oct-24 7  Relations of Isthmus ❑ Relations of Isthmus Anterior surface Sternohyoid and sternothyroid Anterior jugular veins Posterior surface 2nd, 3rd, and 4th tracheal rings Superior border Anastomosis between superior thyroid arteries Inferior border Inferior thyroid vein Ajman University 1-Oct-24 8  Arterial Supply ❑ Thyroid gland, is highly vascular Superior thyroid artery Branch of the external carotid artery Runs downwards with the external laryngeal nerve ▪ Supplies Upper 1/3rd of the lobe and upper 1/2 of the isthmus ▪ At the apex of the lobe divides into o Anterior branch (Anastomose with its opposite side branch) Descends along the anterior border of the lobe o Posterior branch (Anastomose with inferior thyroid artery) Descends along the posterior border of the lobe Ajman University 1-Oct-24 9  Arterial Supply Inferior thyroid artery Branch of thyrocervical trunk Runs upwards along the medial border of scalenus anterior Then passes behind the carotid sheath Intimately related to the recurrent laryngeal nerve ▪ Gives 4 or 5 branches ▪ Supplies Lower 2/3rd of the lobe and lower ½ of the isthmus Ajman University 1-Oct-24 10  Arterial Supply Thyroidea ima artery (in 30% cases) Branch of the brachiocephalic trunk Or may arise directly from the arch of aorta Enters the isthmus from below Accessory thyroid arteries Arise from tracheal and esophageal arteries Ajman University 1-Oct-24 11  Venous Drainage Superior thyroid vein Emerges at the upper part of the thyroid lobe Drains into the internal jugular vein Middle thyroid vein Emerge at the middle of the lobe Enter into the internal jugular vein Inferior thyroid vein Thyroid vein (of Kocher) Emerge at the lower border of the isthmus Emerges (sometimes) between the middle and inferior thyroid veins Form plexus in front of the trachea Drain into the internal jugular vein Drain into the left brachiocephalic vein Ajman University 1-Oct-24 12  Lymphatic Drainage Upper group of lymph vessels Follow superior thyroid artery Drains into the prelaryngeal lymph nodes And Jugulodigastric lymph nodes Lower group of lymph vessels Follow inferior thyroid arteries Drains into pretracheal lymph nodes And lower deep cervical lymph nodes ▪ Lower part of isthmus Drain into brachiocephalic nodes Ajman University 1-Oct-24 13  Nerve Supply Parasympathetic Supply is derived from Vagus and recurrent laryngeal nerves Sympathetic ▪ Supply is derived from Superior cervical sympathetic ganglia Middle cervical sympathetic ganglia (mainly) Inferior cervical sympathetic ganglia Ajman University 1-Oct-24 14  Microscopic Structure ❑ Thyroid gland consists of two types of secretory cells Follicular cells Cuboidal epithelial cells Forms the wall of thyroid follicles Secrete thyroxine (T3) and triiodothyronine (T4) ✓ Essential for normal growth and development Parafollicular cells (C – Cells) Lie between the basement membrane and the follicular cells Some lie in the spaces between the follicles Secrete thyrocalcitonin (calcitonin) ✓ Lower the blood level of calcium ions and promote deposition of Ca2+ into bone matrix Ajman University 1-Oct-24 15  Clinical Correlation Goitre Enlargement of the thyroid gland Associated with hypofunction or hyperfunction of the gland o Hypothyroidism Insufficient secretion of the T3 and T4 Causes cretinism in children and myxedema in adults o Hyperthyroidism (or thyrotoxicosis) Due to excess secretion of T3 and T4 Cause increased Basal Metabolic Rate (BMR) Clinically presents as: tachycardia, tremors, and systolic bruit Ajman University 1-Oct-24 16  Clinical Correlation Simple goiter/puberty goiter Enlargement of the thyroid gland without signs of hyperthyroidism Occurs due to deficiency of iodine in diet (iodine is essential for synthesis of thyroid hormone) The decreased levels of T3 and T4 lead to increased secretion of thyroid stimulating hormone (TSH) from the pituitary gland TSH causes hyperplasia of the thyroid gland. Simple goiter commonly occurs in females at the age of puberty, hence it is also called puberty goiter. ▪ Thyroid gland Capsule is attached to laryngeal cartilages and hyoid bone So moves up and down during swallowing Ajman University 1-Oct-24 17  Clinical Correlation Effects of massive enlargement of thyroid gland Thyroid gland can enlarge backwards or downwards Cannot enlarge upwards -Due to attachment of fascial sheath and sternothyroid muscle to the thyroid cartilage ▪ Backward enlargement is common (Posterior thyroid capsule is relatively thin) Compresses trachea and oesophagus leading to: o Dyspnea - Due to pressure on trachea o Dysphagia - Due to pressure on esophagus o Dysphonia (hoarseness of voice) - Due to pressure on the recurrent laryngeal nerve o It can also causes severe venous compression Ajman University 1-Oct-24 18  Clinical Correlation Ligation of superior thyroid arteries during thyroidectomy Superior thyroid artery lies superficial to the apex External laryngeal nerve lies deep to the apex ▪ During thyroidectomy Superior thyroid artery ligated as close to the apex To avoid injury to the external laryngeal nerve Ligation of thyroid arteries during thyroidectomy Recurrent laryngeal nerve lies very close to the inferior thyroid artery near the base the thyroid lobe ▪ During thyroidectomy Inferior thyroid artery ligated as away from the base To avoid injury to the recurrent laryngeal nerve Ajman University 1-Oct-24 19  Clinical Correlation Ectopic thyroid Thyroid gland (thyroid tissue) may be found at an abnormal position anywhere along the course of thyroglossal duct 1. At the base of the tongue (lingual thyroid) The mass of thyroid tissue is located within the tongue just beneath the foramen caecum Large lingual thyroid may cause difficulty in swallowing by the infant 2. Above, behind or below the hyoid bone (suprahyoid, retrohyoid, or infrahyoid thyroid). Ajman University 1-Oct-24 20  Parathyroid Glands ❑ Parathyroid glands Two pairs (superior and inferior) of small endocrine glands Located along the posterior borders of the thyroid lobes within the thyroid capsule They appear as small yellowish-brown bodies ▪ The parenchymal cells are of two types: Principal or chief cells Secrete parathyroid hormone parathormone ✓ Which maintains blood calcium level by releasing the calcium from the bones. Oxyphil cells Ajman University 1-Oct-24 21  Parathyroid Glands ❑ Blood supply Superior parathyroid: Supplied by the superior parathyroid artery, from inferior thyroid artery (or a branch from anastomotic artery joining the superior and the inferior thyroid arteries) Inferior parathyroid: Supplied by the inferior parathyroid artery, a branch of inferior thyroid artery ❑ Nerve supply Supplied by the sympathetic fibres, derived from the superior and middle cervical sympathetic ganglia or sympathetic plexus around the inferior thyroid artery. Ajman University 1-Oct-24 22  Clinical Correlation Hypoparathyroidism May occur spontaneously or due to inadvertent removal of parathyroid glands during thyroidectomy It results in tetany due to low blood calcium level (decreased parathormone) Clinically the tetany presents as increased neuromuscular excitability, causing convulsions and carpopedal spasms Hyperparathyroidism Seen in the tumors of the parathyroid glands Removes excessive calcium from bones (Increased parathormone) Which makes the bones soft due to decalcification leading osteitis fibrosa May cause formation of stones in the kidney Ajman University 1-Oct-24 23  Ajman University 1-Oct-24 24