003 anatomy and relations of the thyroid Flashcards
where is the thyroid gland found?
- anterior neck, between C5-T1
- found beneath cricoid cartilage of larynx, inferior to thyroid cartilage
- isthmus lies directly on trachea
- lateral lobes on lateral lobes on the lateral trachea aspects
- bound by pretracheal fascia
what fascia is the thyroid gland bound by?
- pretracheal fascia
what is the role of the thyroid gland (overview)?
- important gland of the endocrine system, plays an important role in metabolism, homeostasis and growth
- secretes hormones directly into the cell interstitium
what is the structure/shape of the thyroid gland?
- 2 lateral lobes
- an isthmus (midline)
- sometimes an extra pyramidal lobe (remains of thyroglossal duct)
- butterfly shape
what structures is the thyroid gland closely associated to?
- trachea, larynx (thyroid and cricoid cartilage) and oesophagus = posterior, medial
- carotid sheath = lateral
- pretracheal fascia and infrahyoid muscles = anterior
- it moves up and dow with the larynx but cannot move above it due to the fascia holding it tightly in place
what are parathyroid glands?
- endocrine glands that secrete parathyroid hormone, which regulates low blood calcium
what is the location and structure of parathyroid glands?
- 4 glands in superior and inferior pairs embedded on the posterior lateral lobes of the thyroid gland
what is the blood supply/drainage and nerve innervation of the parathyroid glands?
- shared with thyroid gland
- thyroid arteries, thyroid veins/plexus into internal jugular vein and brachiocephalic vein + parathyroid vein
- sympathetic trunk branches innervate
when does the thyroid gland start to develop in the embryo?
- week 4
what does the thyroid gland develop from?
- as an epithelial proliferation at the foramen caecum of the developing tongue
where does the parathyroid glands develop from?
- from the 3rd (inferior pair) and 4th (superior pair) pharyngeal pouch respectively
describe the development and migration of the thyroid and parathyroid glands
- by week 7, the thyroid has migrated along the path of the thyroglossal duct to its final position (from the tongue , pass the hyoid bone to beneath the thyroid cartilage )
- the inferior parathyroid glands are pulled along with the thyroid migration to below the superior pair
- the thyroglossal duct degenerates end of week 7
what is the blood supply to the thyroid gland?
- superior thyroid arteries from external carotids
- inferior thyroid from the thyrocervical trunk (branch off the subclavian arteries)
- thyroid ima = additional artery in 10% of people, found anterior to the thyroid in the midsagittal plane and at the inferior aspect of the isthmus (also supplies trachea)
- ima is an embryonic artery from the brachiocephalic trunk, which is usually obliterated in development
what is special about the thyroid ima artery
- in 10% of people
- embryonic artery from the brachiocephalic trunk which Is usually obliterated in development
- supplies thyroid and trachea
what is the venous drainage of the thyroid gland?
- superior, middle and inferior thyroid veins form thyroid venous plexus
- superior and middle drain into internal jugular vein
- inferior drains into brachiocephalic vein
what is the innervation of the thyroid gland?
- sympathetic trunk branches and branches of vagus nerve (parasympathetic)
- superior and recurrent laryngeal nerves
describe the pathway of the recurrent laryngeal nerves
- right = vagus nerve runs down medially behind of brachiocephalic trunk and loops underneath and in front up to larynx and thyroid
- left = vagus nerve runs down medially behind and under aortic arch and then loops back up to thyroid and larynx
what is the clinical relevance of the recurrent laryngeal nerves?
- run very close to inferior thyroid arteries
- during thyroid surgery the inferior thyroid artery needs to be ligated and this could damage the recurrent laryngeal nerves = effect control of voice
describe the lymphatic drainage of the thyroid gland
- drain into cervical, pre-tracheal and pre-laryngeal lymphatic nodes
- may even drain directly into deep cervical nodes or left thoracic duct / right lymphatic duct
what are thyroid cysts?
- persistent remains of the thyroglossal duct which fill with fluid and can produce asymptomatic moveable swellings (unless infected)
what is a lingual thyroid?
- ectopic thyroid tissue that is located on the route of the thyroglossal duct ( most often at base of tongue)
- lump of thyroid that breaks off on its way down during development
what is goitre?
- an enlarged thyroid gland (usually due to iodine deficiency)
- does not rise above thyroid cartilage
- moves up and down with larynx
- also caused by congenital hypothyroidism, autoimmune diseases affecting the thyroid, cancers of the thyroid and disorders of the hormonal system
what is lymphadenopathy?
- enlarged lymph nodes, often sue to chronic illnesses, e.g. chronic tonsillitis, tuberculosis, cancer, HIV
- usually solid, painful neck swellings
- can be uni or bi-lateral
what are branchial cysts and fistulae?
- located in the lateral neck and are usually asymptomatic one-sided lateral swellings (no medical implications)
- they occur when brachial clefts do not obliterate, or when brachial arches do not fuse properly during embryonal development
- the cysts develop along the anterior border of the sternocleidomastoid
