Thyroid Flashcards
Embryology of thyroid
Develops from foramen cecum (base of tongue)
Descends to anterior neck forming thyroglossal duct
Position of the thyroid
Wrapped around cricoid cartilage and superior rings of trachea C5-T1
Within visceral compartment of the neck, surrounded by pre-tracheal fascia
Two lobes
Position of the thyroid
Tow lobes
Overlying cricoid cartilage and superior rings of trachea
C5-T1
Visceral compartment of neck, bound by pretracheal fascia
Blood supply to thyroid
Superior thyroid artery (1st branch of external carotid)
Inferior thyroid artery (thyrocervical trunk, branch of subclavian)
Thyroid ima artery (in 10%, from brachiocephalic trunk)
Venous drainage of the thyroid
Venous plexus Drains into Superior thyroid vein (drains into IJV) Middle thyroid vein (drains into IJV) Inferior thyroid vein (brachiocephalic)
Lymphatic drainage of thyroid
Paratracheal nodes
Deep cervical nodes
Innervation of the thyroid
Sympathetic trunk
Anatomical relations of the thyroid
Right & left recurrent laryngeal nerves run through tracheoesophageal groove passing deep to thyroid to innervate larynx
Type of thyroid cells
Follicular cells: thyroid epithelium: simple cuboidal. Form follicles filled with colloid.
Parafollicular cells.
Function of the thyroid
Endocrine gland
Produces: T3/T4 and calcitonin
Hypothalamic-pituitary-thyroid axis
Hypothalamus detects low T3/T4 conc and releases thyrotrophin-releasing hormone (TRH) into hypophyseal portal system
TRH binds to receptors on thyrotrophic cells of ant pituitary causing them to release TSH
TSH binds to receptors on basolateral membrane of thyroid and induces synthesis and release of thyroid hormone from follicular cells
Functions of follicular cells
Effects of T3/T4
increases BMR Gluconeogenesis Glycogenolysis Lipogenesis Thermogenesis Increases expression of B receptors of cardiac tissue
Functions of parafollicular cells
Produce calcitonin
Effects of calcitonin
Inhibits Osteoclasts, reducing bone resorption
Inhibits renal tubular reabsorption of calcium and phosphate
Opposes effect of PTH
Net effect: reducing Ca2+