The thyroid gland Flashcards
The thyroid gland is the first
gland to develop in an embryo
the thyroid gland develops +/- ________ days after fertilization
24
The location of the development of the thyroid gland
Develops in the floor of the pharynx – at base of tongue
It then descends Infront of the pharyngeal gut, then over the next few weeks it migrates to the base of the neck.
During the migration, the thyroid remains connected to the tongue via a narrow channel = thyroglossal duct.
At end of the 5th week
the thyroglossal duct degenerates and over the following weeks, the detached thyroid migrates to its final position
Further embryology of the thyroid gland
- From endodermal thickening in primordial pharynx
- Which becomes an outpouching = thyroid primordium
- Descends before anterior 2⁄3 and posterior 1⁄3 of tongue fuse
- Remains connected to tongue via thyroglossal duct
- Attached to hyoid and to cartilages of larynx
The thyroid gland is located
in the anterior neck, spanning between the C5 and T1 vertebrae.
What type of gland is the thyroid gland?
Endocrine
The thyroid gland (said to have a butterfly shape) is divided into two lobes (L and R) which are
connected by an isthmus
which is anterolateral to the larynx and trachea
The relatively thin isthmus unites the lobes over the
trachea, usually anterior to the second and third tracheal rings
the isthmus may be
incomplete
The thyroid gland lies deep to what muscles
the sternohyoid and sternothyroid muscles, wrapping around the cricoid cartilage and superior tracheal rings. It is inferior to the thyroid cartilage of the larynx.
In which compartment is the gland found?
The gland is in the visceral compartment of the neck, along with the trachea, oesophagus and pharynx. The compartment is bound by pretracheal fascia.
Thyroid gland surrounded by thin fibrous capsule, which
sends a septa deep into the gland. The dense connective tissue attaches the capsule to the cricoid cartilage as well as the superior tracheal rings
arterial supply of the thyroid gland
- Mostly supplied by sup and inf thyroid artery
- These vessels lie between the fibrous capsule and loose fascial sheath
- Usually the first branches of external carotid artery (sup thyroid arteries) descends to the superior poles of the gland, piercing the pretracheal layer of deep cervical fascia and dividing into anterior and posterior branches, supplying mainly the anterior, superior aspect of the gland.
- The inferior thyroid artery, is a branch of the thyrocervical trunk (a branch of the subclavian artery)
- The inferior thyroid artery runs supramedially, posterior to the carotid sheeth to reach the posterior aspect of the thyroid gland
- They then divide into several branches that pierce the pretracheal layer of the deep cervical fascia and supply the posterior inferior aspect, including the inferior poles of the gland.
- The R and L inferior and superior thyroid arteries anastomose extensively within the gland
- Approx. in 10% of people, a small unpaired artery (thyroid ima artery) arises from the brachiocephalic trunk
- In about 3% it actually arises directly from the aorta. When present, this small artery ascends on the anterior surface of the trachea, supplying small branches to it. The artery then continues to the isthmus of the thyroid gland where it divides aswell as supplies it
Venous drainage:
- Takes place through 3 different veins;
- Superior thyroid vein, drains sup poles - into internal jugular vein and runs together with sup thyroid artery.
- Middle thyroid vein, drains middle areas - also drains into internal jugular vein, runs parallel to the superior thyroid artery and vein.
- Inferior thyroid veins, drains inferior portions of thyroid gland - drains into the brachiocephalic veins (which is posterior to the sternum)
