Thyroid Gland Flashcards
(44 cards)
Hormones secreted by thyroid gland:
Hormones secreted by the gland include: triiodothyronine (T3)
tetraiodothyronine (T4 or thyroxine) calcitonin
Function of thyroid gland hormones :
- Its secretion regulate the basal metabolic rate
- Stimulates the psychosomatic growth of the
body - Calcitonin plays an important role in calcium metabolism
What occurs during a thryroidectomy :
During thyroidectomy to avoid much haemorrhage, the thyroid is removed along with the true capsule
Each Lobe of thyroid consists of:
- Apex
- Base
- 3 surfaces:
-antero-lateral or superficial
-medial
-postero-lateral - 2 borders:
-anterior
-posterior
Thyroid gland : Relations of Apex:
- directed upwards and laterally
- upward extension is limited by the attachment of sterno-thyroid to the oblique line of the thyroid cartilage
- hence the thyroid enlargement cannot extend above
- the superior thyroid artery and external laryngeal nerve diverge from each other close to the apex
- artery runs superficial and the nerve passes deep to the apex
Thyroid gland : Relations of The base:
- extends up to 4th or 5th tracheal ring
- related to inferior thyroid artery and recurrent laryngeal nerve
Thyroid gland : Relations of Superficial surface or antero-lateral surface:
Overlapped from within outwards by:
- sternothyroid
- sternohyoid
- superior belly of omohyoid
- anterior border of sternocleidomastoid
Thyroid gland : Relations of Postero-lateral or posterior surface:
Related to carotid sheath and its contents:
- common carotid artery
- internal jugular vein
- vagus nerve
Thyroid gland : Relations of Medial or deep surface:
Related to 2 tubes, 2 muscles and 2 nerves
2 tubes – trachea and oesophagus
2 muscles – inferior constrictor and cricothyroid muscle
2 nerves – external laryngeal nerve and recurrent laryngeal nerve
The recurrent laryngeal nerve passes upwards in the tracheo-oesophageal groove and usually lies behind the ligament of Berry. Sometimes it may pass through or in front of the ligament
Thyroid gland : Relation of Anterior border:
- separates the superficial surface from the medial surface
- related to anterior branch of superior thyroid artery
Thyroid gland : Relation of Posterior border:
- separates the medial surface from the postero-lateral surface
Thyroid gland : Relation of both posterior and anterior border:
- inferior thyroid artery
- anastomosis between superior and inferior
thyroid arteries - superior and inferior parathyroid glands - thoracic duct on the left side
Isthmus consists of 2 surfaces and 2 borders :
Anterior and Posterior Surface
Upper and Lower Border
Isthmus: relation of
Anterior surface or in front it is related to:
- skin
- superficial fascia
- anterior jugular vein
- investing layer of deep cervical fascia - sternohyoid and sternothyroid muscle
Isthmus: relation of
Posterior surface or behind it is related to:
- 2nd to 4th rings of trachea
Isthmus: relation of
Upper border:
Related to anastomosis between the anterior branches of two superior thyroid arteries
The striated muscle fibres of this band is supplied by external laryngeal nerve or C2, C3 via ansa cervicalis
Isthmus: relation of Lower Border
- Inferior thyroidal veins leave the gland at this border
- Thyroidea ima artery, when present is related to this border
Blood supply of thyroid gland: Arterial supply:
-Superior thyroid artery :
* First ventral branch of external carotid
* Runs downwards and forwards to reach the upper pole of the gland with external laryngeal nerve
* Close to the gland the nerve deviates from the artery
* At the upper pole it divides into anterior and posterior branches
-Inferior thyroid artery:
* Branch of thyrocervical trunk of subclavian artery
* Runs upwards, medially and then downwards to reach the lower pole of the gland
Venous drainage of thyroid gland:
-Superior thyroid vein – run the lateral border of superior belly of omohyoid and
opens into internal jugular vein
-Middle thyroid vein – follows the medial border of superior belly of omohyoid and opens into internal jugular vein
-Inferior thyroid veins – emerge from the lower border of isthmus and open into left brachiocephalic vein
-Fourth thyroid vein (Kocher’s vein) – emerge near the lower pole and drain into internal jugular vein
Lymphatic drainage of thyroid gland:
- From the upper part drains into upper deep cervical lymph nodes through prelaryngeal and jugulo-digastric lymph nodes
- From the lower part drains directly into lower deep cervical lymph nodes and also through pretracheal and paratracheal nodes
Nerve supply of thyroid gland:
-Parasympathetic nerves are derived from vagus and recurrent laryngeal nerve.
- Sympathetic nerves are derived mainly from middle cervical sympathetic ganglion and partly from superior and inferior cervical sympathetic ganglion
(They are vasoconstrictor in function)
What are colloid :
The cavity of the follicle contains the stored iodine containing hormones called the colloid.
Colloid is an inactive precursor of T3 and T4. It is made up of a glycoprotein called thyroglobulin, made by the epithelial cells, which is bound to iodine.
Function of clear cells or parafollicular cells:
Secrete calcitonin - which regulates blood calcium levels. Secretion of calcitonin causes blood calcium levels to drop, and its secretion is directly dependent on blood calcium levels.
The parathyroid gland contains 2 cells: what are the function :
Chief cells: secrete parathyroid hormone (PTH)
-Parathyroid hormone acts on osteoclasts, and on the epithelial cells of the renal tubule, to increase plasma calcium by
promoting bone resorption and increasing renal calcium resorption.
Para Follicular cells:
* secrete thyrocalcitonin.
* Regulates the calcium metabolism
* It tends to withdraw the serum calcium level by depositing it in the bone
- Development – neural crest cells and ultimobranchial body (5th pharyngeal pouch) become incorporated secondarily into the thyroid gland and form the parafollicular cells or C cells.
