The thyroid gland is butterfly-shaped and located in the front of the lower neck. It consists of two lobes connected by an isthmus. The basic functional unit is the follicle, composed of epithelial cells surrounding a colloid-filled cavity. The gland receives arterial blood supply from the superior and inferior thyroid arteries and drains into thyroid veins. It is innervated by both parasympathetic and sympathetic fibers and secretes three key hormones: T3, T4, and calcitonin. Disorders include hypothyroidism, goiter, and hyperthyroidism.

1. THYROID
GLAND
M . S C C L I N I C A L E M B R Y O L O G Y
S U B J E C T: A N AT O M Y
B Y – P R A C H I N A I K

2. INDRODUCTION
• It is the largest endocrine gland.
• It is like a butterfly shape.
• Location : It lies in front of the lower part of the
neck, between C5 to C7 and T1 against vertebrae.
Below thyroid cartilage just above the trachea.
It consists of two lateral lobes and connected by
Isthmus.
• Size and weigh : It is brownish red in colour and
weighs 20 – 40 g.
The lobe measures in 5 x 2.5 x 2.5 cm, and the
Isthmus measures 1.2 x 1.2cm.

3. STRUCTURE
The unit structure of thyroid gland is called
follicle which consist of a layer of cuboidal
epithelial cells enclosing a cavity filled with
colloid substance.
The Parafollicular cells are found in a delicate
network of connective tissue between the
follicles and amongst the cells that comprise the
wall of follicles.
The cells of thyroid gland develop from two
different sources:
1. Follicular cells develop from endodermal
cells of thyroglossal duct.
2. Parafollicular cells develop from neural
crest.

4. TRUE AND
FALSE CAPSULE
• True capsule: contains peripheral
condension of the connective tissue
of the gland.
The dense venous plexus unlike that
of the prostate gland lies deep to true
deep. Therefore to avoid hemorrhage.
• False capsule: is derived from the
pretracheal layer of the deep cervical
fascia.

5. RELATION
• Lateral or superficial surface is
convex and is covered by
1. Sternohyoid muscle.
2. Omohyoid muscle.
3. Sternothyroid muscle.
4. Sternocleidomastoid muscle.

6. LOBE
• Each lobe of thyroid gland is pyramidal in shape and has
1. Apex
2. Base
• Apex is related to superior thyroid artery and the external
laryngeal nerve.
• Base is at the level with the 4th or 5th tracheal ring, related to
inferior artery and recurrent laryngeal nerve.
• Three surfaces:
1. Lateral (superficial)
2. Medial
3. Posterolateral
• Two borders:
1. Anterior
2. posterior

7. ARTERIAL
SUPPLY
• The thyroid gland is profusely
supplied by the blood. The
arteries supplying the thyroid
gland are:
1. Superior thyroid artery: a
branch of external carotid
artery.
2. Inferior thyroid artery: a
branch of thyrocervical
trunk of subclavian artery.

8. VENOUS DRAINAGE
• The venous blood from the
thyroid gland is drained by
following veins:
1. Superior and middle thyroid
veins: into the internal jugular
vein
2. Inferior thyroid veins: into the
brachio-cephalic vein

9. LYMPHATIC SUPPLY
• The lymphatic of the gland drain
into:
1. Prelaryngeal: infront of
cricothyroid membrane.
2. Pretracheal: infront of trachea.
3. Paratracheal: alongside the
trachea.
4. Upper and Lower deep cervical:
along the internal jugular vein.

10. NERVE SUPPLY
• Parasympathetic supply: derived
from vagus and recurrent laryngeal
nerves.
• Sympathetic supply: derived from
the superior, middle and inferior
cervical sympathetic ganglia but
mainly from the middle one.

11. HORMONES SECRETED BY
THYROID GLAND
• Three hormones are secreted by the thyroid gland are:
1. T3 (triiodothyronine or thyroxine) secreted by cuboidal cells of the
thyroid follicles.
2. T4 (tetraiodothyronine) secreted by cuboidal cells of thyroid follicles.
3. Calcitonin (thyrocalcitonin) secreted by parafollicular cells.

12. CINICAL CORRELATION
• Hypothyroidism: the hyposecretion of the thyroid hormone, decrease
the rate of metabolism.
• Goiter: an enlargement of the thyroid gland is called goiter.
• Hyperthyroidism: the hypersecretion of the thyroid hormone, increases
the rate of metabolism.

13. THANK YOU