[003] Anat And Relations Of Thyroid Flashcards
Function of thyroid gland
(What system is it part of?)
Important gland of endocrine system
Secretes hormonal production directly into cell interstitium and blood stream
Location of thyroid gland
Found directly beneath cricoid cartilage of larynx,
In midline of neck
Isthmus lies directly on trachea
Lateral lobes on lateral tracheal aspects
General anatomy of thyroid
Isthmus, lateral lobe
A pyramidal lobe can be discerned sometimes
What structures are posterior, medially-related to thyroid
Larynx, trachea
Oesophagus
What structure is lateral to thyroid gland
Carotid sheath
What structures are anteriorly related to thyroid
Pretracheal fascia
Infrahyoid muscles (Sternohyoid and Sternothyroid)
What is the extent of movement of thyroid?
Covered by Pretracheal fascia and infrahyoid musculature, it
Moves up and down with larynx but cannot move above it (tethered)
Parathyroid glands are part of which system?
Endocrine system
Function of parathyroid glands
Secrete parathyroid hormone, which plays an important role in:
regulation of low blood calcium, influencing the amount of calcium in blood and within the bones
Location of parathyroid glands
Four parathyroid glands : a superior and inferior pair
Parathyroid glands are embedded (mostly) on posterior aspect of thyroid gland but can vary considerably in position
Blood and nerve supply of parathyroid gland
Share blood supply and nerve supply with surrounding thyroid gland
Thyroid gland development: origins
Thyroid gland develops as an epithelial proliferation at the foramen caecum of developing tongue (embryonal week 4)
Which pharyngeal pouches do parathyroid glands develop from?
Develops from 3rd (inferior pair) and 4th (superior pair) pharyngeal pouch respectively
Thyroid and parathyroid development
By week 7, the thyroid will have migrated along the path of thyroglossal duct to its final position in relation to tracheal cartilages and cricoid cartilage
The inferior parathyroids will be pulled along with migration of thyroid and end below superior pair
Thyroglossal duct eventually regresses and obliterates (end of week 7)
Arterial blood supply to thyroid and parathyroid
- superior thyroid arteries branch from external carotid
- inferior thyroid arteries arise from thyrocervical trunk
What does the thyrocervical trunk supply
Shared supply to
- thyroid, parathyroid glands,
- scalene muscles
- parts of sternocleidomastoid and trapezius muscles
Identify the arteries
Variant of arterial blood supply to thyroid gland
Thyroid ima artery: supplies thyroid and trachea
In approximately 7-10% of population, an additional artery is found anterior to trachea, in midsagittal plane and at inferior aspect of thyroid isthmus
- originally an embryonic artery, arising from brachiocephalic trunk , or arch of aorta
- usually small or obliterated but can be substantial in variant to point where it is the main blood supply to thyroid
Venous drainage of thyroid gland
To internal jugular and brachiocephalic veins
Via superior, middle and inferior thyroid veins which also form extensive anastomoses
(Inferior thyroid vein variable in size, can be just a single inferior thyroid vein lying in middle of trachea)
Nerve supply to thyroid gland
Sympathetic trunk and branches of vagus nerve (superior laryngeal and recurrent laryngeal nerves)
What do the recurrent laryngeal nerves run in close proximity to?
What is the significance of this during surgery?
Inferior thyroid arteries
During thyroid surgery, inferior thyroid artery needs to be lighted and sometimes this results in damage to one or both recurrent laryngeal nerves
Lymphatic drainage of thyroid gland
Mostly to para-tracheal cervical and pre-tracheal lymph nodes
Lymphatics from gland usually pass to pre-laryngeal and tracheal nodes
May also pass directly into deep cervical nodes or into thoracic duct or right lymph duct
What are lumps in the mid-sagittal plane in neck, caused by migratory development of thyroid
- Thyroid cysts: persistent remnants of thyroglossal duct which fill with fluid and can produce fluctuate, pain-free midline swellings (soft to touch)
- Lingual thyroid: ectopic thyroid tissue can be located along the route of thyroglossal duct
What is an enlarged thyroid gland called
Goitre
