The Thyroid Gland Flashcards
What is the thyroid gland and where is it located
located in the anterior neck, spanning between the C5 and T1 vertebrae. It is an endocrine gland, divided into two lobes which are connected by an isthmus. It is said to have a butterfly shape.
Which levels does the thyroid gland span between
C5 and T1 vertebrae
It lies behind which muscles?
the sternohyoid and sternothyroid
The thyroid gland wraps around which cartilage
cricoid cartilage and superior tracheal rings
it is inferior to the thyroid cartilage of the
larynx.
The gland is in the WHAT of the neck, along with the trachea, oesophagus and pharynx.
visceral compartment
The compartment is bound by
pretracheal fascia
During development, the thyroid gland initially forms in the
floor of the primitive pharynx, near the base of the tongue
It descends down the neck to lie in its adult anatomical position
The thyroid gland secretes hormones directly into the blood. Therefore it needs to be highly vascularised
What does this mean?
to supply (an organ or tissue) with blood vessels.
Blood supply to the thyroid gland is achieved by two main arteries;
the superior and inferior thyroid arteries.
These are paired arteries arising on both the left and right.
The superior thyroid artery is the first branch of the external carotid artery. After arising, the artery descends toward the thyroid gland. As a generalisation, it supplies the
superior and anterior portions of the gland.
The superior thyroid artery is the first branch of the
external carotid artery
The inferior thyroid artery arises from the
thyrocervical trunk (which in turn is a branch of the subclavian artery).
Where does The inferior thyroid artery run and supply
The artery travels superomedially to reach the inferior pole of the thyroid. It tends to supply the postero-inferior aspect.
In a small proportion of people (around 10%), there is an additional artery present;
the thyroid ima artery
Where does the the thyroid ima artery come from and what does it supply
It comes from the brachiocephalic trunk of the arch of aorta, supplying the anterior surface and isthmus.
Venous drainage is carried out by the
superior, middle and inferior thyroid veins, which form a venous plexus
he superior and middle veins drain into the
internal jugular veins,
whereas the inferior drains into
the brachiocephalic vein.
The thyroid gland is innervated by branches derived from the sympathetic trunk. However, these nerves do not control endocrine secretion – release of hormones is regulated by
pituitary gland.
The are two recurrent laryngeal nerves; one left and one right. They arise from their respective
vagus nerves, and descend into the chest.
In the chest, they hook around the subclavian artery (right RL nerve), or the arch of aorta (left RL nerve). The nerves then ascend back up the neck, running between the trachea and oesophagus. They pass underneath the thyroid gland to innervate the larynx.
What nerves do this
The two recurrent laryngeal nerves
What is the function of the extrinsic laryngeal muscles (sternothyroid, thyrohyoid etc.)?
They move the larynx up and down the neck and support its central positon, this is particularly important for swallowing.
Where may you create an emergency airway?
Between the thyroid and cricoid cartilage, through the cricothyroid membrane.
Why does the thyroid gland have such a good blood supply?
Iodine is present in very low concentration in the blood so the gland needs a
high blood flow to ensure adequate delivery of iodine.
Which structure may be compressed by an enlarged thyroid gland?
The trachea
What is the location of the parathyroid glands and how many are there?
They are positioned on the posterior surface of the thyroid gland, there are
four.
What is the only complete cartilage ring around the airway?
The cricoid cartilage.
A patient may develop hypocalcaemia after thyroid surgery, why?
The parathyroid glands may be (accidentally or deliberately) removed during
thyroid surgery which will cause acute (sudden) hypoparathyroidism.
