The thyroid gland is located in the neck and produces thyroid hormones that regulate metabolism. It consists of two lobes connected by an isthmus. During development it arises from an endodermal diverticulum. The thyroid traps iodine from the blood and uses it along with the amino acid tyrosine to produce the hormones thyroxine (T4) and triiodothyronine (T3) via a series of coupling reactions within the thyroid follicles. T4 makes up 90% of secretion but T3 is the active hormone. Thyroid hormone production is regulated by TSH from the pituitary gland.

1. ANATOMY AND PHYSIOLOGY OF
THYROID GLAND
BY:- Dr. JINU IYPE
2nd YEAR POSTGRADUATE
DEPARTMENT OF ENT

2. • Scott Brown 7th edition vol 1
• Textbook otorhinolaryngology-Zakir Hussain
• Textbook of Sabiston 19 edition
• Guyton textbook of physiology 12th edition

3. FROM GREEK thyreoeides = SHIELDSHAPE

4. • Butterfly/H shaped
• Brownish-Red
• Highly vascular
• Ductless gland
• Adult gland weighing 20 to 25gm.
• Larger in female
• Enlarges further during puberty, menstruation
& pregnancy

5. • Consist of right and left cone shaped lobes
5*3*2cm
• Connected by a narrow region of gland - Isthmus
1.2*1.2cm
• Situated anteriorly in the visceral
compartment of the neck at the level of C5-T1
vertebrae

6. Location:
C5
T1 / 4th or
5th tracheal
ring
2nd
Trachealrings
4th

7. DEVELOPMENT OF THYROID GLAND
•Median endodermal thyroid diverticulum(median
anlage)
Foramen caecum
Thyroglossal duct(usually reabsorbed after
6 weeks of age)
The very distal end of this remnant may be
retained and mature as a pyramidal lobe in the
adult thyroid

8. THE THYROID begins to function- end of 3month,
at which time, the first follicles containing colloid
can be seen
• Ultimobranchial body gives parafollicular C cells
to thyroid gland - Parafollicular cells(Ccells)from
the neuralcrest reachthethyroidviatheultimobranchial
body-arises from 4th & 5th Brachial pouch.
• Superior parathyroid gland- arises from 4th
Brachial pouch.

9. • Inferior
parathyroid gland
– arises from 3rd
brachial pouch

11. • A lateral or posterior projection of the thyroid
lobe,
known as the tubercle of Zuckerkandl, identified
in
up to 60 % of surgical dissections
• It is represent the point of embryological fusion
of the ultimobranchial body and median
anlage.
Its surgical importance is :
(a) RLN runs medial to it;
(b) the superior parathyroid gland attached to its
cranial aspect;

12. CAPSULES
• Truecapsule (fibrous) –contains
the parenchyma & sends fine
septaebetween lobules of the
thyroid gland.
• Arteries and plexus of veins deep
toit
• Falsecapsule–pretracheal fascia

13. Deep cervicalfascia

14. Suspensory ligament of berry
The pretracheal layeris
thin alongthe posterior
border of the lobes, but
thick on theinner surface
of thegland where it
forms a suspensory
ligament of berry which
connects the gland to the
cricoidcartilage

15. Why thyroid moves withdeglutition?
• During 1st stage ofdeglutition
• Hyoid bone movesup
• Pulls pre-tracheal fasciaup
• This pulls ligament of berryupward
• This pulls thyroidupward

16. • A fibromuscular band levatorglandulae thyroideae
descendfrom thebodyofthe hyoid bone to
isthmus or topyramidal lobe

17. RELATIONS
• The lobes are conical in shape having
– Apex
– Base
– Three surfaces : Lateral, Medial, Posterolateral
– Two borders : Anterior & posterior

18. • APEX: Directed upward & slightly laterally.
limited superiorly – sternothyroid on the
oblique line of thyroid cartilage
• BASE: At the level of 4th or 5th tracheal length

19. • Lateral surface –convex,
• Coveredwith sternohyoid, SCM, superior belly of
omohyoid, sternothyroid

20. • Medial surface- Trachea & Oesophagus
2muscles-cricothyroid, inferior constrictor
2 nerves-external laryngeal &recurrent laryngeal N
• Posterolateral surface –carotidsheath

21. • Ant border – anterior branch of Superior thyroid artery

22. • Posteriorborder -
• Thick and round
1. InferiorThyroidArtery
2. Anastomosisb/w STA
&ITA
3. Parathyroid glands
4. Thoracic duct onleft

23. ISTHMUS
• 2 surfacesAnt& Post
• 2 borders Sup& Inf
• Anteriorsurface –skin &
fascia
- anterior jugularveins
- R& L sternohyoid &
sternothyroid
• Posteriorsurface- 2nd –3rd
trachealrings
• Supborder –anastomosis b/w
R&L SupThyroidArtery
• Inf border -ITVleave

24. Blood supply
Superior thyroid artery:
• 1st anterior branch of external
carotid artery
• Runs downwards & forward
with close relation with
external laryngeal nerve
• Pierces pretracheal fascia-
upper pole of lobe
anterior Posterior branch

25. • Anterior branch descends on the anterior border of
the lobe
anastomosing branch which runs along the upper
border of the isthmus to anastomosis with opp. side

26. • Posterior branch – Posterior border of the lobe
Anastomosis with ascending
branch of inferior thyroid
artery
Superior thyroid artery
Supplies Upper 1/3rd of the lobe
Upper ½ of the isthmus

27. Inferior thyroid artery:
• Branch of thyrocervival trunk
Subclavian artery
• Runs forward then medially
& finally downward to reach
lower pole of the gland.
• Pass behind carotid sheath,
Middle CervicalGanglion and in
front of vertebral vessels
• Close related Recurrent laryngeal
Nerve

28. • Artery divides into 4 or 5 Glandular branch
pierces the fascia separately to reach the lower
part of the gland
• Ascending branch anastomoses with posterior branch
of superior thyroid artery
Supply Parathyroid gland
Inferior thyroid artery
Supplies Lower 2/3rd of the lobe
Lower ½ of the isthmus & Parathyroid gland

29. THYROIDEA IMA ARTERY
( lowest thyroid artery)
• 12 % present ascending in front
of the trachea to end at the
isthmus.
• most commonly arises from the
brachiocephalic artery
• it can also originate from the
aorta, the right common carotid,
subclavian or internal thoracic
arteries.

30. VENOUS DRAINAGE :
The superior, middle and inferior thyroid vein
Superior thyroid vein (STV)
•Accompany SupThyroid Artery
•Drain to IJV/ facial vein

31. Middle thyroid vein
• Very short, may be
double or absent.
• They receive blood
from the inferior
and antero-lateral
part of the gland as
well as the larynx
and trachea.
• most commonly
cross the common
carotid artery
• Drain to IJV

32. Inferior thyroid vein
•Plexus anterior
surface of the
trachea on leaving
the gland.
• usually drain into
right and left
inferior veins,
superior vena cava or
left brachiocephalic

33. 4THVEINOFKOCHER’S
• Seen b/w middle and inferior thyroidvein
• drain intoIJV

34. LYMPHATIC DRAINAGE
The thyroid gland contains a rich network of lymphatics
The lateral aspects of the gland drain into levels III and IV and
those of the posterior triangle (level V).
The more medial aspects of the
gland also drain into the nodes
of the anterior compartment
of the
neck (level VI),
drain into those of the superior
mediastinum (level VII).

36. Nerve supply:
• Parasympathetic fibers –fromVagus
• Sympatheticfibers–from
superior,middle,and
inferiorganglia ofthe
sympathetictrunk
• Entertheglandalong
withthebloodvessels.

37. Recurrent laryngeal nerves
• The recurrent laryngeal nerve is variable in
size 1.5-4 mm in diameter.
• Identified by its
whitish appearance,
characteristic longitudinal vessel
flattened,
rounded surface.
In up to 39 % of cases the nerve divides into 2
(and occasionally up to 6) terminal branches
between 6 and 35 mm from the cricoid cartilage.

38. A non recurrent laryngeal nerve is found in 0.2-
0.4% of patients
 It tends to be thicker than a normally sited
nerve
Usually associated with a vascular anomaly of
the subclavian artery on the right side
 Transposition of the great vessels on the left
side.

39. Recurrent laryngeal nerves
• Branches of the vagus nerve, which
supply all the intrinsic muscles of the larynx
except the cricothyroid muscle.(External laryngeal
N – Superior Laryngeal N)
• They also supply sensory fibres to the mucous
membrane below the level of the vocal folds
• Accidentaldamage tothis nerveduring surgery
causes ipsilateralvocal cord paralysis& difficultyin
phonation

40. Left Recurrent laryngeal nerves
• The approximate length of the left RLN is 12 cms
• The nerve leaves the
vagus in the mediastinum
anterior to the arch of the
aorta passing behind the
ligamentum arteriosum &
then posteriorly under the
concavity of the arch before
passing superiorly to lie in
the tracheo-oesophageal
groove.

41. • It most usually passes
behind the inferior
thyroid artery
• Then posterior to the
ligament of Berry
before passing under or
between the fibres of
the cricopharyngeal part
of the inferior
constrictor

42. Right Recurrent laryngeal nerves
• The approximate length of right RLN 6 cms
• Rtside itoriginates
from vagus crosses
firstpartof subclavian
artery .
• More oblique course
to the tracheo-
oesophageal groove.

43. SUPERIORLARYNGEALNERVE
• Arises from inferior ganglion of vagus
• Descends behind internal carotid artery
• At the level of greater cornua of hyoid it divides:-
Internal branch(sensory) Externalbranch(motor)

45. • The external branch of the superior laryngeal
nerve, which supplies the cricothyroid muscle,
runs parallel to the superior thyroid vessels
• The Internal branch of the superior laryngeal
nerve supply sensory fibres to the mucous
membrane above the level of the vocal folds

47. External branch of superior laryngeal nerve
and joll’s triangle
• Joll's triangle is used to identify the location
of external branch of superior laryngeal nerve
during thyroid surgeries.
• Damage to this nerve during the surgical
procedure may reduce the voice range in those
patients.
• This triangle is also known as
sternothyrolaryngeal triangle.

48. Boundaries of Joll's triangle :
Lateral - Upper pole of
thyroid gland and superior
thyroid vessels
Superior - Attachment of
the strap muscles and deep
investing layer of fascia to
the hyoid
 Medial - Midline
Floor - Cricothyroid
muscle
External branch of superior laryngeal
nerve lies within this triangle.

49. Beahrs Triangle or Riddle’s triangle
Boundaries
Medial :The RL nerve in the
lower part of tracheo -
oesophageal groove
Lateral :Common carotid
Superior: Inferior thyroid
artery

50. Microscopic anatomy
• The thyroid gland consists mainly of follicular cells,
one cell thick around a central pool of colloid to form
follicles.
• The follicles spherical in shape & 0.02- 0.9 mm in
diameter
• A thyroid lobule
consists of 20 to 40
follicles and is supplied
by a lobular artery.

51. When the gland is relatively inactive, the cells
are flattened and the colloid is abundant, dense.
On prolonged and excessive TSH stimulation,
the follicular cells become hypertrophied and
hyperplastic and they adopt a more columnar
shape.
This cellular enlargement is associated with
development of microvilli which helps in reduction
in the size of the follicular lumen.

53. PHYSIOLOGY OF THE THYROID
The thyroid follicles secretestri-iodothyronine
(T3) and thyroxin(T4)
Synthesis involves combination of iodine with
tyrosine group toform mono and di-iodotyrosine
which are coupled to form T3 andT4.
 The hormones are stored in follicles bound to
thyrogobulin

54. When hormones released in the blood they
are bound to plasma proteins and small
amount remain free in the plasma
The metabolic effect of thyroid hormones
are due to free (unbound)T3 andT4.
90%of secreted hormones is T4 butT3is
the active hormone so,
T4is converted to T3peripherally.

55. Regulation of thyroid gland metabolism
CirculatingT3
andT4exert -
- ve feedback
mechanism
on
hypothalamus
and anterior
pituitary gland
So, in hyperthyroidism
where hormone level
in blood is high ,TSH
production is
suppressed and
vice versa.

56. STEPS OF THYROID HORMONE
SYNTHESIS
1.Thyroglobulin Synthesis
2.Iodine trapping
3.Oxidation
4.Iodination
5.Coupling
6.Storage & Release

57. 1. Thyroglobulin Synthesis
• Endoplasmic reticulum and Golgi apparatus in
the
follicular cells of thyroid gland synthesize and
secrete thyroglobulin continuously.
• Thyroglobulin molecule is a large glycoprotein
containing 140 molecules of amino acid
tyrosine.
• After synthesis, thyroglobulin is stored in the
follicle.

58. 2. Iodine trapping
 Iodide is actively transported from blood
into follicular cell, against electrochemical
gradient. This process is called iodide
trapping.
 Iodide is transported into the follicular cell
along with sodium by Sodium iodide (Na +
/ I-) symporter , which is also called iodide
pump. Whereby two sodium ions are
transported for each iodide ion.

59. The accumulated iodide in the follicular cells
is then transferred to the apical plasma
membrane down an electrochemical gradient.
TSH stimulation increases adenosine
triphosphate (ATP) and ATPase activity at
the apex of the cell increasing the efflux of
iodide into the colloid down a further electrical
gradient.
 Iodine available through certain foods (eg,
seafood, bread, dairy products), iodizedsalt, or
dietarysupplementsetc

60. 3. Oxidation of Iodide
• Iodide must be oxidized to elementary
iodine, because only iodine is capable of
combining with tyrosine to form thyroid
hormones.
• The oxidation of iodide into iodine occurs
inside the follicular cells in the presence
of thyroid peroxidase.

61. 4. Iodination of Tyrosine
• Iodine is transported from follicular cells into
the follicular cavity, where it binds with
thyroglobulin.
• Then, iodine (I) combines with tyrosine, which
is already present in thyroglobulin
• Tyrosine is iodized first into monoiodotyrosine
(MIT) and later into di-iodotyrosine (DIT)-
thyroglobulin(Tg) tyrosine residues

62. 5. Coupling Reactions
i. One molecule of DIT and one molecule of MIT combine to
form tri-iodothyronine (T3)
DIT + MIT = Tri-iodothyronine (T3)
ii. One molecule of MIT and one molecule of DIT combine
to produce another form of T3 called reverse T3 or rT3.
Reverse T3 is only 1% of thyroid output
MIT + DIT = Reverse T3
iii. Two molecules of DIT combine to form
tetraiodothyronine (T4) thyroxine.
DIT + DIT = Tetraiodothyronine or Thyroxine (T4)

65. FUNCTIONS OF THYROID HORMONES
1. Action on basal metabolic rate (BMR)
 Thyroid hormones (specificallyT3)regulate rate
of overall bodymetabolism
–T3increases basal metabolicrate
 Calorigeniceffects
–T3increases oxygen consumption bymost
peripheraltissues
–Increases body heatproduction

66. 2. Action on carbohydrate metabolism
• Thyroxine stimulates almost all processes involved
in
the metabolism of carbohydrate.
Thyroxine:
i. Increases the absorption of glucose from GI tract
ii. Enhances the glucose uptake by the cells, by
accelerating the transport of glucose through
the cell membrane
iii. Increases the breakdown of glycogen into
glucose
iv. Accelerates gluconeogenesis.

67. 3. Action on fat metabolism
Thyroxine decreases the fat storage by
mobilizing it from adipose tissues and fat
depots.
Thus, thyroxine increases the free fatty acid
level in blood.

68. 4.Action on Growth andDevelopment
• Thyroid hormone is essential for normal
braindevelopment
• Essential for childhoodgrowth
–Untreated congenital hypothyroidism or
chronic hypothyroidism during
childhood can result in incomplete
development and mentalretardation

69. 5.Action on CNS
• Thyroid hormones are essential for neural
development and maturation and function ofthe
CNS
• Decreased thyroid hormone concentrations maylead
to alterations in cognitivefunction
–Patients with hypothyroidism may develop
impairment of attention,slowed motorfunction,
and poormemory
–Thyroid-replacementtherapy may improve
cognitive function when hypothyroidism is
present

70. 6.Action on BoneGrowth
– T3also may participate in osteoblast
differentiation and proliferation, and
chondrocyte maturation leading to
boneossification

71. 7.Action on femaleReproductiveSystem
• Normal thyroid hormone function is
important for reproductivefunction
– Hypothyroidism may be associated with
menstrual disorders, infertility, risk of
miscarriage, and other complications of
pregnancy

72. 8.ACTION ON GASTROINTESTINAL TRACT
• Generally, thyroxine increases the appetite and
food intake.
• It also increases the secretions and movements
of GI tract.
• So, hypersecretion of thyroxine causes
diarrhoea and the lack of thyroxine causes
constipation.

73. 9. Actions on:-
• Heart
In Increase cardiac output, heart rate
• Adipose tissue
Stimulate lipolysis
• Muscle
Increase protein breakdown

74. APPLIEDANATOMY
• Presenceof thyroidae imaA-chanceof profusebleeding
procedures in neckbelow
isthmus
• Thyroglossal cysts– Remnants of thyroglossal ducts
at anypoint in the wayof
descent,(midline nearhyoid)
• Pyramidal lobe and presenceof levator glandulae
thyroidae

75. • Ectopic thyroid glands–lingual/higher placed
• Non neoplastic, noninflammatory enlargement –
goiter
• pressuresymptoms and nerve involvments are
common in goiter and carcinoma

76. THANK YOU!