Thyroid Thyroid AnatomyAnatomy

Fahad Fahad zakwanzakwan

MD5MD520142014

Gross anatomyGross anatomy• The thyroid is a highly vascular The thyroid is a highly vascular brownish-red gland brownish-red gland

located anteriorly in the lower neck, extending from located anteriorly in the lower neck, extending from C5-C5-T1T1• It varies from an It varies from an HH to a to a U shape U shape and it is formed by and it is formed by 2 2

elongated lateral lobes elongated lateral lobes with superior and inferior poles with superior and inferior poles connected by a connected by a median isthmus median isthmus with an average height with an average height 12 – 15 mm 12 – 15 mm overlaying overlaying 2nd – 4th tracheal rings2nd – 4th tracheal rings..• Each lobe is Each lobe is • 50 – 60 mm long.50 – 60 mm long.• 12-15 mm wide12-15 mm wide

• It weighs It weighs 25-3025-30 g in adults g in adults • slightly heavier in womenslightly heavier in women• enlarges during menstruation and pregnancyenlarges during menstruation and pregnancy

histologyhistology• Under the middle layer of deep Under the middle layer of deep

cervical fascia, the thyroid has cervical fascia, the thyroid has inner true capsuleinner true capsule, which is thin , which is thin and adheres closely to the gland.and adheres closely to the gland.• Extension of this capsule within Extension of this capsule within

the substance of the gland forms the substance of the gland forms numerous numerous septaeseptae, which divides , which divides it into it into lobeslobes and and lobuleslobules..• The lobules are composed of The lobules are composed of

folliclesfollicles, the structural units of , the structural units of the gland, which consists of the gland, which consists of layer of layer of simple epithelium simple epithelium enclosing a enclosing a colloid filled cavitycolloid filled cavity

histologyhistology• This colloid contains iodinated This colloid contains iodinated

glycoprotein called glycoprotein called iodothyroglobuliniodothyroglobulin, a precursor , a precursor of thyroid hormones.of thyroid hormones.• Epithelial cells are of 2 types:Epithelial cells are of 2 types:• Principal (follicular) cells Principal (follicular) cells

responsible for formation of responsible for formation of colloid (iodothyroglobulin)colloid (iodothyroglobulin)

• Parafollicular cells Parafollicular cells responsible responsible for production of hormone for production of hormone calcitonin which is responsible for calcitonin which is responsible for calcium haemostasis.calcium haemostasis.

Relations:Relations:

Blood supplyBlood supply

Arterial supplyArterial supply1.1.Superior thyroid arterySuperior thyroid artery, branch of , branch of external carotid arteryexternal carotid artery2.2.Inferior thyroid artery Inferior thyroid artery from from thyrocervical trunk thyrocervical trunk branch of the branch of the first part of first part of subclavian arterysubclavian artery..•Sometimes Sometimes thyroidea ima arterythyroidea ima artery a a branch from branch from arch of aorta arch of aorta or or brachiocephalic trunk can be brachiocephalic trunk can be found.found.

Venous Venous drainagedrainage• 3 major veins drain the 3 major veins drain the thyroid gland.thyroid gland.

1.1.Superior thyroid vein Superior thyroid vein drains to the drains to the internal internal jugular veinjugular vein..

2.2.Middle thyroid vein Middle thyroid vein drain drain to the to the internal jugular veininternal jugular vein..

3.3.Inferior thyroid vein Inferior thyroid vein drain drain to innominate veinsto innominate veins

Lymphatic drainageLymphatic drainage

•the lymphatic the lymphatic drainage is to drainage is to pretrachealpretracheal and and prelaryngealprelaryngeal then to then to the the Deep cervicalDeep cervical, , supraclavicularsupraclavicular and and mediastinalmediastinal lymph lymph nodes.nodes.

LymphaticsLymphatics

Nerve supplyNerve supply• Receives Receives SympatheticSympathetic innervation innervation

from the from the cervical plexuscervical plexus, while , while parasympatheticparasympathetic supply comes supply comes from the from the vagus nervevagus nerve..• Although not supplying the thyroid Although not supplying the thyroid

gland, the gland, the recurrent laryngeal recurrent laryngeal nerve nerve course in the close course in the close proximity with proximity with inferior thyroid inferior thyroid vessels vessels in the tracheoesophageal in the tracheoesophageal groove and it supplies all intrinsic groove and it supplies all intrinsic muscles of the larynx except muscles of the larynx except cricopharyngiuscricopharyngius which is supplied which is supplied by by superior laryngeal nervesuperior laryngeal nerve related related closely with closely with superior thyroid arterysuperior thyroid artery..

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