WEEK 2: THYROID GLAND Flashcards
State anatomical position of the thyroid gland
It lies posterior to the sternothyroid and sternohyoid muscles , wrapping around cricoid cartilage and tracheal rings.it is inferior to the larynx and located on the anterior neck.
Describe nervous supply to the thyroid gland
*Parasympathetic stimulation
Vagus nerve giving left and right recurrent laryngeal nerves
*Sympathetic stimulation: superior, middle drain and inferior cervical ganglia forming
What are the parts of the thyroid gland that gives it it’s butterfly shape?
*right lobe, left lobe and isthmus of thyroid gland
What ligament attaches the thyroid to the trachea?
Berry’s ligament ( Lateral suspensory ligament)
What is the zuckerkandl tubercle?
a lateral projection from lateral thyroid lobe which is a constant landmark for finding the recurrent laryngeal nerve during thyroid surgery
At what vertebral level is the thyroid gland found?
C5 to T1
Describe the blood supply to the thyroid gland
- Superior thyroid artery which is a branch of the external carotid artery
*Inferior thyroid artery which is a branch of the thyrocevical trunk which is a branch from the right subclavian artery coming from the brachiocephalic trunk
*Thyroid I’ma artery: supplies the isthmus and the anterior aspect of the thyroid gland.found in 10% of the population.
-It is a branch of the brachiocephalic trunk.
Describe the venous drainage of the thyroid gland
*Superior, middle and inferior thyroid veins which forms a venous plexus.
Superior and the middle thyroid veins drain into the Internal Jugular Vein
Inferior thyroid veins drains into the brachiocephalic vein
Describe the lymphatic system supply to the thyroid gland
Pre laryngeal drains into superior deep cervical LN
Pre-tracheal drains into the inferior deep cervical LN
Para-tracheal drains into the thoracic duct
How much does an adult thyroid weight?
25g
The thyroid lobules are each made up of follicles.State the cell types found in a thyroid follicle
- follicular cells
*Para follicular cells
What are the functions of the cell types of the thyroid gland?
Follicular cells: produce T3 and T4 ( Triiodothyronine and Tetraidothyronine)
What is the other name for T4?
Thyroxine
What are the para follicular cells of the thyroid gland also called?
C cells/ clear cells
Whare is the colloid found in the follicle?
In the lumen of the follicle surrounded by the follicular cells
What are the functional units of a thyroid gland called?
Follicles
Which cells of the thyroid gland are not dependant on TSH from the anterior pituitary gland?
Para follicular cells
How can one define the activity of a thyroid follicle?
*Look at the lumen size( amount of colloid)
* Look out for the surrounding epithelial cells
Where are the para follicular cells found?
Located in the basal lamina as clusters within follicular cells
Briefly describe the embryology of the thyroid gland
*It appears as an epithelial proliferation between in the floor of the pharynx between the tuberculum impar and the copula at a point later indicated by the foramen cecum
*It is at the 1st pharyngeal arch between the anterior and posterior of the tongue
*The thyroid descends in front of the pharyngeal gut as a bilobed diverticulum
*It is connected to the tongue by the thyroglossal duct during this movement
*Which further development, the thyroid gland descends in front of the hyoid bone and the laryngeal cartilages
- It reaches its final destination in front of the trachea in the 7th week, NY then it would have developed the lateral lobes and the isthmus
*The thyroglossal duct degenerates leaving it’s cranial end as the foramen cecum
*It’s caudal end might also end up being connected to the isthmus forming a third lobe called a PYRAMIDAL LOBE which is found in 50% population
*The thyroid starts functioning at the end of third month (3 months)
*The para follicular cells are derived from the Ultimobranchial Body
What is a foramen cecum?
An embryological remnant of the upper end of the thyroglossal duct.
Where are the para follicular cells derived from?
The para follicular cells of the thyroid gland are of neural crest origin.They are formed from the migration of cells from the neural crest to the Ultimobranchial Body. The UBB then fuses with the thyroid gland and disseminates it’s cells into it
Describe the anomalies associated with the embryology of the thyroid gland
- Thyroglossal cyst:it is a persistence of a part of the thyroglossal duct along the migratory pathway
*Thyroglossal fistula: May occur when the cyst is connected to the outside by a fistulous canal.It opens to the skin - Ectopic thyroid: failure of thyroid descend
Lingual thyroid and Prelaryngeal thyroid are examples - Abberant ( retrosternal goiter): over descent of the thyroid gland in the thorax
- Thyroid aganesis: failure of the thyroid gland to form
Where do thyroglossal cyst usually occur?
Near or in the midline of the neck
The para follicular cells of the thyroid gland are of neural crest origin.They are formed from the migration of cells from the neural crest to the Ultimobranchial Body The UBB then fuses with the thyroid gland and disseminates it’s cells into it
What structure do the C cells migrate to from the neural crest which fuses with the thyroid gland and disseminates it’s cells into it?
Ultimo brachial body
What two structures does the thyroid diverticulum form in between?
Tuberculum impar and the copula
At what pharyngeal arch does the thyroid diverticulum form?
Between 1st and 2nd
What epithelium is found on the wall of follicles?
Cuboidal epithelium
What are the 3 anatomical features that the thyroid diverticulum passes as it goes to it’s final destination in front of the trachea?
Pharyngeal gut, hyoid bone and laryngeal cartilages (cricoid)
Account for the movement of the thyroid gland with the larynx during swallowing.Confirm this on yourself or colleague
Because it is attached to the cartilage of the larynx by suspensory ligament of Berry
Describe an active follicle
Simple columnar to low cuboidal epithelium
Few coloid
Smaller in size
Describe an inactive Follicle
Simple squamous epithelium
Abundant coloid
Larger in size
