The thyroid gland is located in the lower neck, extending from the C5 to T1 vertebrae. It has a H or U shape formed by two lateral lobes connected by an isthmus. Each lobe is 50-60mm long, 12-15mm wide, and weighs 25-30g in adults. The thyroid has an inner capsule and septae that divide it into lobes and lobules. The lobules contain follicles which are composed of epithelial cells that enclose a colloid-filled cavity containing thyroid hormones. The thyroid receives its blood supply from the superior and inferior thyroid arteries and drains into the internal jugular and innominate veins. Its lymphatic drainage is to the pretrache

1. ThyroidThyroid
AnatomyAnatomy
FahadFahad
zakwanzakwan
MD5MD5
20142014

2. Gross anatomyGross anatomy
• The thyroid is a highly vascularThe thyroid is a highly vascular brownish-red glandbrownish-red gland
located anteriorly in the lower neck, extending fromlocated anteriorly in the lower neck, extending from C5-T1C5-T1
• It varies from anIt varies from an HH to ato a U shapeU shape and it is formed byand it is formed by 22
elongated lateral lobeselongated lateral lobes with superior and inferior poleswith superior and inferior poles
connected by aconnected by a median isthmusmedian isthmus with an average heightwith an average height 1212
– 15 mm– 15 mm overlayingoverlaying 2nd – 4th tracheal rings2nd – 4th tracheal rings..
• Each lobe isEach lobe is
• 50 – 60 mm long.50 – 60 mm long.
• 12-15 mm wide12-15 mm wide
• It weighsIt weighs 25-3025-30 g in adultsg in adults
• slightly heavier in womenslightly heavier in women
• enlarges during menstruation and pregnancyenlarges during menstruation and pregnancy

5. histologyhistology
• Under the middle layer of deepUnder the middle layer of deep
cervical fascia, the thyroid hascervical 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 withinExtension of this capsule within
the substance of the gland formsthe substance of the gland forms
numerousnumerous septaeseptae, which divides it, which divides it
intointo lobeslobes andand lobuleslobules..
• The lobules are composed ofThe lobules are composed of
folliclesfollicles, the structural units of the, the structural units of the
gland, which consists of layer ofgland, which consists of layer of
simple epitheliumsimple epithelium enclosing aenclosing a
colloid filled cavitycolloid filled cavity

6. histologyhistology
• This colloid contains iodinatedThis colloid contains iodinated
glycoprotein calledglycoprotein called
iodothyroglobuliniodothyroglobulin, a precursor of, a precursor of
thyroid hormones.thyroid hormones.
• Epithelial cells are of 2 types:Epithelial cells are of 2 types:
• Principal (follicular) cellsPrincipal (follicular) cells
responsible for formation of colloidresponsible for formation of colloid
(iodothyroglobulin)(iodothyroglobulin)
• Parafollicular cellsParafollicular cells responsibleresponsible
for production of hormonefor production of hormone
calcitonin which is responsible forcalcitonin which is responsible for
calcium haemostasis.calcium haemostasis.

9. Relations:Relations:

11. Blood supplyBlood supply
Arterial supplyArterial supply
1.1.Superior thyroid arterySuperior thyroid artery, branch of, branch of
external carotid arteryexternal carotid artery
2.2.Inferior thyroid arteryInferior thyroid artery fromfrom
thyrocervical trunkthyrocervical trunk branch of thebranch of the
first part offirst part of subclavian arterysubclavian artery..
•SometimesSometimes thyroidea ima arterythyroidea ima artery aa
branch frombranch from arch of aortaarch of aorta oror
brachiocephalic trunk can bebrachiocephalic trunk can be
found.found.

14. VenousVenous
drainagedrainage
• 3 major veins drain the3 major veins drain the
thyroid gland.thyroid gland.
1.1.Superior thyroid veinSuperior thyroid vein
drains to thedrains to the internalinternal
jugular veinjugular vein..
2.2.Middle thyroid veinMiddle thyroid vein drain todrain to
thethe internal jugular veininternal jugular vein..
3.3.Inferior thyroid veinInferior thyroid vein draindrain
to innominate veinsto innominate veins

15. Lymphatic drainageLymphatic drainage
•the lymphaticthe lymphatic
drainage is todrainage is to
pretrachealpretracheal andand
prelaryngealprelaryngeal then tothen to
thethe Deep cervicalDeep cervical,,
supraclavicularsupraclavicular andand
mediastinalmediastinal lymphlymph
nodes.nodes.

16. LymphaticsLymphatics

17. Nerve supplyNerve supply
• ReceivesReceives SympatheticSympathetic innervationinnervation
from thefrom the cervical plexuscervical plexus, while, while
parasympatheticparasympathetic supply comes fromsupply comes from
thethe vagus nervevagus nerve..
• Although not supplying the thyroidAlthough not supplying the thyroid
gland, thegland, the recurrent laryngealrecurrent laryngeal
nervenerve course in the close proximitycourse in the close proximity
withwith inferior thyroid vesselsinferior thyroid vessels in thein the
tracheoesophageal groove and ittracheoesophageal groove and it
supplies all intrinsic muscles of thesupplies all intrinsic muscles of the
larynx exceptlarynx except cricopharyngiuscricopharyngius whichwhich
is supplied byis supplied by superior laryngealsuperior laryngeal
nervenerve related closely withrelated closely with superiorsuperior
thyroid arterythyroid artery..

20. Thank you!!Thank you!!