anatomy of thyroid gland

3. Introduction
Parts
Development
Situation & extent
Coverings
Relations
 Blood supply
 Lymphatic
drainage
 Nerve supply
 Applied

4. Introduction
The thyroid gland is the largest
endocrine gland of the body.
Hormones secreted by the thyroid
gland include:
 T3
 T4- thyroxine
 Calcitonin.

6. Shape & Parts :
H-shape
Right and Left lobes
Horizontal isthmus
connecting both the
Lobe in midline.
Weight: about 25 gm

7. Dimensions
Each lobe is 5 cm long, 3 cm wide, and
2 cm thick (5 × 3 × 2 cm).
The isthmus measures about 1.25 cm in
both, vertical and transverse diameters.

8. Location
Located in the front and side of the neck.
Deep to the floor of muscular triangle.
At C5, C6, C7, and T1 Vertebral level.
Extent: Each lobe – middle of thyroid
cartilage to 5th or 6th tracheal ring.
Isthmus – 2nd,3rd & 4th tracheal ring.

11. Coverings
2 capsules:
Outer false capsule – splitting of
pretracheal fascia.
Thick on medial surface of gland –
forms suspensory ligament of Berry
which connects the lobe with cricoid
cartilage.

13. Inner true capsule – condensation of
fibrous stroma of gland.
Deep to true capsule –capillary plexus.
During thyroidectomy
– remove the gland with
true capsule.

14. Shape & Parts
Roughly conical
Parts:
Apex
Base
3 Surfaces- lateral, medial, and
posterolateral
2 Borders- anterior and posterior

16. Apex
Extend up to Oblique line of thyroid
cartilage (C5).
Related to superior thyroid artery & external
laryngeal nerve.

17. Base
Extends 5th or 6th tracheal ring (T1)
Related to inferior thyroid artery &
recurrent laryngeal nerve.

18. Anterolateral (superficial) surface :
Overlapped by infrahyoid muscles
1) Sternothyroid
2) Sternohyoid
3) Superior belly of omohyoid
 SCM (partly)

19. Medial (deep) Surface
Related to - 2 tubes, 2 nerves & 2 muscles &
2 cartilages.
2 tubes –trachea & oesophagus
2 nerves- external & recurrent laryngeal
nerves
2 muscles- cricothyroid & inferior
constrictor
2 cartilages- cricoid and thyroid

21. Posterolateral surface
Related to carotid sheath & its contents
 Ansa cervicalis
Sympathetic chain
Carotid sheath Contents:
1. CCA
2. IJV
3. Vagus nerve

22. Anterior border
Thin and separates superficial and medial
surfaces.
Related to anterior branch of the superior
thyroid artery.

23. Posterior border
Thick and rounded.
Separates medial and the posterior
surfaces.
It is related to anastomosis between
superior and inferior thyroid arteries.
parathyroid glands.

26. ISTHMUS
Horizontal part
Two surfaces— anterior and
posterior
Two borders—superior and
inferior.

27. Isthmus
 Anterior surface:
 Skin
Superficial fascia & anterior jugular vein
Investing layer of deep cervical fascia
 Sternothyroid & sternohyoid

28. Posterior surface is related to
2nd, 3rd, and 4th tracheal rings.

29. Superior border
Related to anastomosis b/w the
anterior branches of two superior
thyroid arteries.

31. Inferior border
Along this border inferior thyroid vein
emerge and thyroidea ima artery (when
present) enters.

32. Arterial supply
 Superior thyroid artery:
Downwards and forwards in company
with the external laryngeal nerve.
Superior thyroid artery supplies the
upper one-third of the lobe and upper
half of the isthmus.

34. Inferior thyroid artery: supplies
lower two-third of the lobe and lower
half of the isthmus.
Accompanied by recurrent laryngeal
nerve.

35. Arteria thyroidea ima – occasionally
(from arch of aorta or brachiocephalic
trunk)- to lower part of istthmus.
Numerous accessory thyroid arteries.

36. Venous Drainage
Veins do not accompany the arteries.
 Arise from venous plexus.
1. Superior thyroid vein
2. Middle thyroid vein
3. Inferior thyroid vein
4. Occasionally fourth thyroid vein
(kocher’s vein) - IJV

39. Lymphatic drainage
Upper lateral part – upper deep cervical
nodes / jugulodigastric
 Lower lateral part – lower deep cervical
nodes / jugluo-omohyoid
 Upper medial part– prelaryngeal nodes
Lower medial part – pretracheal nodes

41. Nerve supply
1. Sympathetic nerves
2. Parasympathetic nerves
Sympathetic nerves: From superior,
middle & inferior cervical ganglion.
Vasoconstrictor in action.
Parasympathetic nerves: From vagus &
recurrent laryngeal nerves.

43. Congenital anomalies
 Agenesis
 One lobe or isthmus absent
Thyroglossal cyst/ fistula

44. Ectopic thyroid: Lingual thyroid,
suprahyoid, retrohyoid, or infrahyoid
thyroid.
Retrosternal thyroid: Descent of the
thyroglossal duct may go beyond the
definitive position in the neck to superior
mediastinum.
Accessory thyroid –on thymus/arise from
thyroglossal duct.

45. Movement of the gland with deglutition
Reasons:
1. Berry’s ligament connects the lobe of
thyroid to the cricoid cartilage.
2. Isthmus is attached to the trachea.
3. Pretracheal fascia surrounding the
gland is attached to the larynx &
hyoid bone.