an overview of anatomy, development &clinical anatomy of thyroid gland

1. Dr. Kalpana Makhija
Assistant Professor, Anatomy
Govt. Medical College
Kota.

2. INTRODUCTION
DEVELOPMENT
GROSS ANATOMY
BLOOD SUPPLY
NERVE SUPPLY
LYMPHATIC DRAINAGE
HISTOLOGY
APPLIED ANATOMY

3. Introduction
 Thyroid is the largest
endocrine gland of the body.
 By its hormones T3, T4 &
calcitonin, it
- regulates BMR,
- Stimulates psychosomatic
growth,
- play an important role in
calcium metabolism.

4. Development  The gland begins to
develop as an
endodermal thickening
in the midline of floor of
pharynx, immediately
behind the tuberculum
impar during 3rd week of
intrauterine life.

5. Development
 This thickening depress
from the surface to form
thyroglossal duct.
 Grows downward across
tongue.
 Descends down in neck.

6. Development
 Then it descends below
the hyoid after passing in
front of it.
 Reaches its definitive
position by the end of 7th
week.
 This tract forms potential
site for aberrant thyroid
tissue or thyroglossal cyst.

7. Development
 Tip of duct bifurcates &
proliferates to form bilateral
swellings which enlarge to
form the thyroid gland.
 A portion of duct near its tip
may form pyramidal lobe.
 Remaining duct disappears.

8. Location
 It is the only endocrine
gland located superficially
in the body to be available
for physical examination.
 It lies in front of the neck
opp. C5,C6,C7 & T1
vertebrae (i.e. in front of
lower part of larynx & upper
part of trachea.)

9. General features
 Butterfly/H shaped
 Two Lobes 5×3×2 cm
 Isthmus 1.2×1.2cm
 Weight 25g
 Larger in females
 Enlarges in pregnancy &
menstruation

10. General features  Pyramidal lobe extend from
isthmus (left of midline.)
 May be connected by a
fibromuscular band, the
levator glandular thyroidae,
to the body of hyoid bone.
 Lobes extend up to the
oblique line of thyroid
cartilage above and to the
5th/6th tracheal ring below.
 Isthmus extends in front of
2nd,3rd & 4th tracheal rings.

11. Capsule  Invested by two capsules –
1. True capsule – formed by the
condensation of connective tissue
stroma of gland.
 Arteries and plexus of veins are
present deep to it
2. False capsule – derived from
splitting of pretracheal fascia.
 It is thin along posterior
border.
 On medial surface it thickens
to form Suspensory ligament
of Berry.
 Gland moves during deglutition
and speech

12. Relations
Anterior & Lateral surface of lobe is covered by sternothyroid,
sternohyoid & omohyoid muscle.
Anterior Border by sternocleidomastoid muscle.

13. Relations
Medial surface : 2tubes- trachea & oesophagus
2muscles – inferior constrictor & cricothyroid
2 cartilages – cricoid & thyroid
2 nerves - external and recurrent laryngeal N
Posterolateral surface : carotid sheath & contents.

14. Relation with parathyroid
 Parathyroid gland is
embedded in the
substance of the gland at
its posterior border
 Posterior border is also
related to the anastomosis
between superior &inferior
thyroid arteries.

15. Relations of isthmus
Anterior surface of isthmus is covered by sternohyoid,
sternothyroid muscles & ant. Jugular vein.
Post. Surface is related to 3rd,4th & 5th tracheal ring

16. Arterial Supply
• Thyroid gland is highly
vascular
• Supplied by
 superior thyroid artery
 inferior thyroid arteries
• Vessels lie between the
fibrous capsule and the
loose fascial sheath

17.  superior thyroid artery
(STA) The first branch of the
external carotid artery, then
descend to the superior
poles of the gland, pierce
the pretracheal layer of
deep cervical fascia.
 Divide into anterior and
posterior branches
supplying mainly the
anterosuperior aspect of
the gland

18. • Superior thyroid artery is
closely related to external
laryngeal nerve at its origin
• Nerve moves away from the
artery as artery approaches
the upper pole of the gland.
• In order to avoid injury of
external laryngeal nerve
the superior thyroid artery
is ligated just near the
superior pole of thyroid
gland, during surgery .
Superior
Thyroid Artery
and Vein
External Branch
Superior Laryngeal
Nerve
Thyroid gland
- Do not ligate here
- Do ligate here

19.  Inferior thyroid arteries
branches of thyrocervical
trunks arising from the
subclavian arteries, run
superomedially, posterior
to the carotid sheaths to
reach the posterior aspect
of the gland .
 Supply postero-inferior
aspect.

20.  Normally recurrent
laryngeal nerve passes
behind the ITA
 It is easy to damage this
nerve during ligation of
inferior thyroid artery
 So ligation of inferior
thyroid artery should be
as far away as possible
from thyroid gland.

21. Thyroid-ima artery
 ~10% of people .
 branch of brachiocephalic trunk
 Other possible sources of Ima
artery: arch of the aorta, right
common carotid, subclavian, or
internal thoracic arteries
 Ascends on the anterior surface
of the trachea and continues to
the thyroid isthmus
 The presence of this artery must
be considered before
tracheostomy (as a potential
source of bleeding.)

22. Venous drainage  Three pairs of thyroid veins
(superior, middle and inferior) form
thyroid plexus of veins on anterior
surface of the thyroid gland and
anterior to the trachea
 Superior thyroid veins accompany
the superior thyroid arteries
 Middle thyroid veins do not
accompany but run essentially
parallel courses with the inferior
thyroid arteries
 Inferior thyroid veins accompany the
thyroid -ima artery (if present)
 Superior and middle thyroid veins
drain into internal jugular veins
 Inferior thyroid veins drain into
brachio-cephalic veins posterior to
manubrium of sternum

23. Lymphatic drainage
 Extensive, multidirectional flow
 periglandular  prelaryngeal
(Delphian)  pretracheal 
paratracheal (along RLN) 
brachiocephalic (sup mediastinum) 
deep cervical  thoracic duct
 Upper lymphatics drain via
prelaryngeal LN to upper deep Cervical
lymph node.
 Lower lymphatics drain via
pretracheal and paratracheal LN to
lower deep Cervical
 regional metastasis of thyroid
carcinoma are superior and lateral,
along IJV i.e. invasion of the
pretracheal and paratracheal LNs and
obstruction of normal lymph flow

24. Innervation • Derived from the superior,
middle and inferior cervical
sympathetic ganglia
• Nerves reach the thyroid
through:
 Cardiac periarterial plexus
• Superior and inferior thyroid
plexus
• Only vasomotor fibers causing
constriction of blood vessels
• Endocrine secretion from the
thyroid gland is hormonally
regulated by the pituitary gland
through TSH.

25. Gland consist of Thyroid
follicles - follicular cells
and large pools of colloid
 Follicular cells produce
thyroid hormones and their
cell surfaces possess thyroid-
stimulating hormone
(TSH) receptors
 Thyroglobulin is an inactive
storage for the T4 and T3
hormones.
 Parafollicular cells (C cells)
along the periphery of the
thyroid follicles
secrete calcitonin
Histology

26. Applied Aspect
 Hypothyroidism
 Hyperthyroidism
 Goitre
 Ectopic thyroid
 Thyroglossal cyst
 Tumours