7/21/2019 Pulsenotes | Thyroid anatomy notes

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ENDOCRINOLOGY (/ENDOCRINOLOGY/NOTES)

Thyroid anatomy

OTES

Gross structure

The thyroid is located in the mid-line of the neck, anterior to the trachea and inferior to

the larynx.

he thyroid gland comprises of  two lateral lobes and a central isthmus. It is surrounded by a

brous capsule and located at the level of vertebrae C5-T1 .

he pyramidal lobe, an embryological remnant from the descent of the thyroid, typically

roject upwards from the isthmus, however, there is a wide degree of variation between

ndividuals.

s primary function is to produce thyroid hormones T3 and T4 following stimulation by TSH.

urrounding structures

The thyroid gland is surrounded by a number of important structures.

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hyroid cartilage

s superior border is at the level of vertebrae C4. It forms a median projection, termed

he adams apple. Superior to this projection is the superior thyroid notch. The cartilage has

oth superior and inferior horns.

ricoid cartilage

he cricoid cartilage sits at the level of vertebrae C6. It is the only complete ring of cartilage in

he trachea.

is composed of a posterior component termed the lamina and an anterior component termed

he arch. It attaches to first tracheal ring by the cricotracheal ligament.

Medium cricothyroid ligament

his ligament connects the inferior border of the thyroid cartilage with the superior border of he cricoid cartilage.

n incision is made through the medium cricothyroid ligament to establish an emergency

rway - a cricothyroidotomy .

arathyroid gland

he parathyroid glands (typically four) are located posterior to the thyroid gland. It ismportant to note there is a great deal of variety in both the location and number of glands.

hey are responsible for the release of  parathyroid hormone, a key part of the calcium

omeostasis pathways. Due to their location they are frequently removed during

hyroidectomy, typically resulting in a transient hypocalcaemia.

Arterial supply

A rich blood supply is received from the external carotid artery and the thyrocervical

trunk.

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uperior thyroid veins

Drains from: Superior poles of the thyroid gland

Drains to: Internal jugular vein

Middle thyroid veins

Drains from: Middle poles of the thyroid gland

Drains to: Internal jugular vein

nferior thyroid veins

Drains from: Lower poles of the thyroid gland

Drains to: Brachiocephalic vein

Recurrent laryngeal nerve

The recurrent laryngeal nerve is a branch of the vagus nerve (CN X).

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he right and left recurrent laryngeal nerves branch o!  at di! erent levels on the right and leftdes. The right side branches of at the level of the subclavian artery whilst the left side

ranches from at arch of the aorta.

hey follow a ‘recurrent’ path upwards through a groove between the trachea and oesophagus.

his brings them close to the thyroid gland. The nerve may be damaged during thyroid

urgery, typically resulting in a hoarse voice.

he recurrent laryngeal nerve has a number of functions:

Motor:

Intrinsic muscles of the larynx (except cricothyroid muscle).

Sensory and secretomotor:

Glottis

Subglottis

Trachea

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