The thyroid gland is the largest endocrine gland located in the neck. It produces important hormones including T3, T4, and calcitonin. The thyroid gland has two lobes connected by an isthmus and may have a pyramidal lobe. It is located in the anterior neck against vertebrae C5-T1 and is invested by inner and outer capsules. The lobes have apexes, bases, and surfaces related to surrounding structures. The isthmus lies at the level of tracheal rings 2-4 and connects the upper borders of the lobes.

1. Thyroid Gland
Parts, Relations & Coverings
- Jatin Yadav

2. Contents
1. Introduction
2. Parts and Extents
3. Capsules
4. External Features
a. Lateral lobe
b. Isthmus
5. Cadaveric image of Thyroid Gland

3. Thyroid Gland
● The Thyroid gland is the largest
endocrine gland.
● Highly vascular.
● The hormones secreted by the
thyroid gland include :
A. Triiodothyronine (T3),
B. Tetraiodothyronine (T4;
commonly called thyroxine)
C. Calcitonin

4. Fig. Location of the thyroid gland
Dimensions
Lobe: 5cm X 3cm X 2cm
Isthmus: 1.2cm X 1.2cm
Weight: 25g
The thyroid gland is usually larger in
females and further increases in size
during menstruation and pregnancy.
Source: Textbook of Anatomy by Vishram Singh

5. Source: Textbook of Anatomy by Vishram Singh
Parts and
Extents
of the
Thyroid Gland

6. Parts and Features:
● It presents two lobes connected by an isthmus.
● H-shaped.
● An extension from the upper margin of isthmus on the
left side is called as the Pyramidal lobe.
● Pyramidal lobe is connected to the body of the hyoid
bone by a fibrous or fibromuscular band called levator
glandulae thyroideae.

7. Above: Oblique line of Thyroid Cartilage
Below: 5th or 6th Tracheal Ring
Isthmus: over the second to fourth tracheal
rings
In the anterior cervical region lying against
the C5-T1 vertebrae, protected by the
infrahyoid muscles
Extent:
Source: BD Chaurasia’s Human Anatomy
Location and subdivisions of the thyroid gland

8. Factors keeping the Gland in Position
● Attachment of the pretracheal fascia to the hyoid
bone and thyroid cartilage.
● Ligament of Berry to the cricoid cartilage.
● Levator Glandulae thyreoideae.

9. Capsules of the thyroid gland
The thyroid gland is invested by two
capsules: an inner true capsule and an
outer false capsule.
1. True capsule: It is formed by the
peripheral condensation of the fibrous
stroma of the gland.
2. False capsule: It is derived from the
splitting of the pretracheal fascia.
Source: Textbook of Anatomy by Vishram Singh
Fig. Capsules of the thyroid gland

10. Relationship of the venous plexuses
related to:
(a) The Thyroid gland
(b) The Prostate
Source: BD Chaurasia’s Human Anatomy

11. Space between Two Capsules
The contents of this space are
the following:
● Trunks of blood vessels
supplying the gland
● Superior parathyroid
gland- often
● Inferior parathyroid gland-
sometimes
Fig. Thyroid Gland: pretracheal fascia and relations
Source: MedOne Thieme

12. External Features: Lateral Lobe
Presenting Parts:
● Apex/superior Pole
● Base/inferior pole
● Three surfaces: anterolateral, medial, and
posterolateral
● Two borders: anterior and posterior

13. ● Apex:
Directed upwards and slightly
laterally.
Limited superiorly by the
attachment of the
sternothyroid muscle to the
oblique line of thyroid
cartilage.
Related to superior thyroid
artery and the external
laryngeal nerve.
Fig. Relations of the lateral lobe of the thyroid gland:
A. Upward extension of the thyroid lobe
B. The apex Source: Textbook of Anatomy by Vishram Singh

14. ● Base:
At the level with 4th or 5th tracheal
ring.
It is related to inferior thyroid artery
and recurrent laryngeal nerve.
Source: Textbook of Anatomy by Vishram Singh

15. 1. Lateral (superficial) surfaces:
Convex and covered by:
(a) three strap muscles
(b) anterior border of sternocleidomastoid
1. Posterolateral (posterior) surface:
Carotid sheath and its contents
Three Surfaces

16. 3. Medial Surface:
(a) Two tubes: trachea and esophagus
(b) Two muscles: inferior constrictor
and cricothyroid
(c) Two cartilages: cricoid and thyroid
Fig. Medial relations of the lateral lobe of the thyroid
gland.
Source: Textbook of Anatomy by Vishram Singh

17. Two Borders
Anterior border:
Thin
Separates superficial and medial surfaces.
Related to anterior branch of the superior thyroid artery.
Posterior border:
Thick and round.
It separates the medial and the posterior surfaces.
It is related to
(a) longitudinal arterial anastomosis between superior and inferior thyroid arteries
(b) parathyroid gland

18. External Features: Isthmus
Shape: Quadrilateral
Measurements: 1.25 X 1.25 cm
Presenting Features:
● Two surfaces (anterior and posterior)
● Two borders (upper and lower)

19. Fig. Transverse section through the anterior part of the neck at the level of the
isthmus of the thyroid gland
Source: BD Chaurasia’s Human Anatomy

20. Relations:
Anterior Surface (from inside to outward):
Pretracheal fascia
Sternothyroid and Sternohyoid muscles.
Investing layer of deep cervical fascia
Anterior Jugular Vein
Superficial Fascia and skin
Posterior Surface:
Second to fourth tracheal rings.

21. Source: Clinically Oriented Anatomy ( Keith L. Moore)

22. Upper Border:
Anastomosis between the anterior branches of two superior thyroid
arteries.
Pyramidal lobe
Levator glandulae thyreoideae
Lower Border:
Inferior Thyroid Vein
Thyroidea ima artery (if present)

23. Source: MedOne Thieme

24. Dissectional view
of Thyroid Gland
Source: Anatomical Society,
HIMS

25. Take Away
Points

26. SUMMARY