Flashcards in case 9 anatomy Deck (23):
Which vertebral level is the suprasternal notch located?
Which vertebral level is the thyroid notch located?
Which vertebral level is the lower border of cricoid cartilage located?
Which vertebral level is the hyoid bone located?
lobes of thyroid gland
The thyroid gland is made up of an isthmus and two lateral lobes; in some cases a pyramidal lobe is also present.
The apex extends up to the oblique line of the thyroid cartilage and the base to the level of the fourth or fifth tracheal ring.
Crosses anterior to the 2nd, 3rd and 4th tracheal ring.
Projects upwards from the isthmus to the left of the midline
sheath of thyroid gland
The thyroid gland is enclosed by a thin connective tissue capsule, from which, septa project into the gland. A loose connective tissue sheath surrounds the gland and the capsule. Its derived from the pretracheal fascia
relations to the lateral lobes
anterolateral: superior belly of omohyoid, sternohyoid, ant border SCM, sternothyroid,
posterolateral: common carotid artery, vagus, internal jugular vein, carotid sheath
Medial: oesophagus, recurrent laryngeal nerve, external laryngeal nerve, trachea, cricothyroid, pharynx, larynx
relations to the isthmus
anterior: ant jugular vein, sternohyoid, sternothyroid
posterior: 2nd, 3rd, 4th rings of tracheal cartilages
arterial supply of thyroid gland
As it is an endocrine organ the thyroid gland has to receive a rich blood supply. The blood vessels of lie between the capsule and the fascial sheath.
Arterial blood is supplied by the superior and inferior thyroid arteries; the superior thyroid artery supplies the upper pole of each lobe whilst the inferior thyroid artery supplies the posteroinferior aspect. There is considerable anastomosis between vessels.
The superior thyroid artery arises from the external carotid artery. the superior laryngeal nerve runs alongside the artery. ITA arises from thyrocervical trunk, which arises from subclavian artery. the recurrent laryngeal crosses the ITA. 4In 10% of the population a third artery also contributes. This vessel is termed the thyroid ima artery and it may arise from the brachiocephalic trunk or arch of aorta, less commonly it has been seen to arise from the right common carotid, subclavian or internal thoracic arteries.
venous drainage of the thyroid gland
Three pairs of veins, the superior, middle and inferior thyroid veins drain the superior, middle and inferior parts of the thyroid gland respectively. These vessels form a plexus of nerves on the anterior aspect of the gland. the superior and middle drain into the IJV. the inferior drains into the brachiocephalic vein.
A rich lymphatic network is found within the connective tissue septa of the thyroid gland. These vessels drain into the prelaryngeal, pretracheal and paratracheal nodes. Efferent vessels from these nodes go to the deep cervical nodes.
The thyroid gland receives sympathetic innervation. Post ganglionic sympathetic fibres arise in the superior, middle and inferior cervical ganglia and pass through the cardiac, superior and inferior thyroid plexuses to reach the gland. it transmits vasomotor information.
which direction can the thyroid gland not enlarge in a goitre
A thyroid goitre is an enlargement of the thyroid gland which may occur due to over activity or underactivity of the gland. it cant grow superiorly due to the superior attachments of sternothyroid and sternohyoid muscles.
which structures may be compressed by a thyroid goitre
oesophagus, recurrent laryngeal nerve and the trachea
development of the thyroid gland
The thyroid gland develops from a thickening on the floor of the embryonic pharynx in the developing tongue. A diverticulum develops from this thickening forming the thyroglossal duct. The thyroglossal duct elongates and its distal end becomes bi-lobed and proliferates into the thyroid gland. The thyroid gland descends through the neck anterior to the hyoid bone. At seven weeks the gland reaches its adult position. The thyroglossal duct subsequently degenerates but a pit remains on the dorsum of the tongue marking its site of origin.-foramen cecum.
failure of the gland to desend
Ectopic thyroid glands occur when the gland fails to descend. In incomplete descent the gland will be located high in the neck. Rarely, the gland may fail to leave the tongue and a lingual thyroid develops. Pyramidal lobes are present in approximately 50% of the population. These lobes extend upwards from the isthmus usually to the left of the median plane. They develop from the remnants of the epithelium and connective tissue of the thyroglossal duct. Accessory thyroid tissue may present anywhere along the route of descent of the thyroglossal duct. It occurs when isolated pockets of glandular tissue of the thyroglossal duct fails to degenerate. Thyroglossal duct cysts occur when the duct fails to degenerate leaving a persistent connection between the back of the tongue and the thyroid gland. They can be asymptomatic but fluid may accumulate in small pockets and infection may occur. The cysts are often located close to the hyoid bone. Their position in the neck will rise if the patient sticks their tongue out.
The parathyroid glands secrete parathyroid hormone. There are usually four glands; two superior and two inferior. Each gland is ovoid and approximately 6mm long. The parathyroid glands are embedded into the posterior aspect of the thyroid gland, they lie deep to the fascial sheath. The superior parathyroid glands usually lie below the point where the superior thyroid vessels enter the thyroid gland.The inferior parathyroid glands may be located in the superior mediastinum. The parathyroid glands are most commonly supplied by the inferior thyroid artery. The parathyroid glands are innervated by postganglionic sympathetic fibres from the superior or middle cervical ganglia.
inc basal metabolic rate
reduces plasma Ca levels