THYROID GLAND

THYROID GLAND

INTRODUCTION:-

It is the largest endocrine gland of the body.

It produces, stores and secrete hormones triiodothyronine, tetraiodothyronine and calcitonin.

LOCATION:-

Lower part of the front and side of the neck opposite to the C5,C6,C7,C8 and T1 vertebrae clasping the upper part of trachea.

PARTS AND FEATURES:-

1. It is H shaped and consisting of vertical right and left lateral lobes and horizontal isthmus connecting them.  Sometimes a small pyramidal lobe projects upwards from the isthmus.

2. It is connected to the body of the hyoid by a fibromuscular band called LEVATOR GLANDULAE THYROIDAE.

3. The isthmus extends across the midline in front of the 2nd, 3rd, 4th tracheal rings.

WEIGHT; 25g

DIMENSIONS; 

Length; 5cm

Breath; 3cm

Thickness; 2cm

Isthmus: 1.25cm

CAPSULE OF THE THYROID GLAND:-

Invested by two capsules - True and False

TRUE - Condensation of fibrous tissue

FALSE - splitting of pretracheal fascia

ATTACHMENT

ABOVE - To hyoid bone

SIDES - Thyroid cartilage

BELOW - Blends with fibrous pericardium

VENOUS PLEXUS lies deep to true capsule

RELATIONS OF THYROID LOBE:-

-APEX 

-BASE 

-THREE SURFACES

-TWO BORDERS

APEX

Extends up to the oblique line of thyroid cartilage.

Sandwiched between inferior constrictor medially and sternothyroid laterally.

Related to superior thyroid artery and external laryngeal nerve.

BASE

Extends up to the 5th or 6th tracheal ring.

Related to loop of inferior thyroid artery and recurrent laryngeal nerve.

LATERAL/SUPERFICIAL SURFACE:-

It is convex

Sternothyroid, sternohyoid, superior belly of omohyoid and anterior border of sternocleidomastoid.

MEDIAL SURFACE:-

TWO TUBES - Trachea, oesophagus

TWO MUSCLES - Inferior constrictor and cricothyroid

TWO CARTILAGES - Cricoid and thyroid

POSTEROLATERAL SURFACE:-

Related to carotid sheath and its contents.

ANTERIOR BORDER:-

Related to anterior border of superior thyroid artery.

POSTERIOR BORDER:-

Longitudinal arterial anastomosis

Parathyroid gland

RELATIONS OF ISTHMUS:-

ANTERIOR SURFACE:-

Anterior jugular veins

Sternohyoid, sternothyroid muscles

POSTERIOR SURFACE:-

2nd, 3rd, 4th tracheal rings.

SUPERIOR BORDER:-

Anastomosis between the anterior branches of two superior thyroid arteries

INFERIOR BORDER:-

Inferior thyroid vein

Thyroid ima artery

ARTERIAL SUPPLY:-

1. SUPERIOR THYROID ARTERY

-Branch of external carotid artery

-Downwards with the external laryngeal nerve

-At the apex 

   -Anterior branches

   -Posterior branches

-Anterior branch anastamose with its fellows of opposite at the superior border of isthmus

-Posterior branch anastamose with ascending branch of the inferior thyroid artery along the posterior border of the lobe.

-Supplies - Upper 1/3rd lobe & upper 1/2 of isthmus

2. INFERIOR THYROID ARTERY

-Branch of thyrocervical trunk from 1st part of the subclavian artery.

-Intimately related to recurrent laryngeal nerve at the back of the lobe.

-SUPPLY - lower2/3rd lobe and lower 1/2 of isthmus.

3. THYOIDAE IMA ARTERY

-Brachiocephalic or arch of aorta

4. ACCESSORY THYROID ARTERIES

-Tracheal and oesophageal arteries.

VENOUS DRAINAGE:-

Superior thyroid vein - internal jugular vein

Middle thyroid vein - internal jugular vein

Inferior thyroid vein - left brachiocephalic vein

Thyroid vein of koucher - internal jugular vein

LYMPHATIC DRAINAGE:-

Upper group 

 

Prelaryngeal lymph nodes 

Upper deep cervical lymph nodes

Jugulodigastric lymph nodes

Lower group

Pretracheal

Lower deep cervical along the recurrent laryngeal nerve

Isthmus

Retrosternal/Brachiocephalic nodes

NERVE SUPPLY:-

Parasympathetic 

Vagus through EXTERNAL and RECURRENT laryngeal nerves

Sympathetic

Superior, middle and inferior cervical sympathetic ganglia.

Stimulates T3 synthesis and secretion.

CLINICAL CORRELATION:-

- To avoid hemorrhage during thyroidectomy, the thyroid gland is removed along with the true capsule.

- The portion of the fascia stretching between cricoid cartilage and thyroid gland posterior surface is thickened - suspensory ligament of berry.

- Structures between true and false capsule - Parathyroid gland.