glands - thyroid Flashcards
where is the thyroid gland found?
In the anterior neck
In front of 2nd and 4th rings of trachea cartilage
Wraps around cricoid cartilage and
Just below thyroid cartilage of larynx
what is the role of the thyroid gland
Site of production and secretion of hormones that control metabolism
gross structure of the thyroid gland
Consists of a left and right lobe that are joined by central isthmus
blood supply to the thyroid
Blood supply: superior and inferior thyroid arteries
venous drainage of the thyroid
Venous drainage:
superior and middle thyroid veins to internal jugular
inferior thyroid vein to brachiocephalic
where does thyroid lymphatics go?
Lymphatic: to deep cervical nodes
describe the histology of the thyroid gland
Contains 2 types of cells:
Cuboidal follicular epithelial cells that are arranged into follicles - these follicles surround a lumen filled with colloid
C cells/parafollicular cells - at the base of the follicle epithelium
what hormone is made from the follicular and parafollicular cells?
follicular = T3/4 > T3
parafollicular = calcitonin
how do the follicular cells make T3/4?
Follicular cells trap and pump iodide from the plasma so it can be used to produce T3/T4
Iodine is combined with tyrosine in the colloid to make T3/4
Newly synthesised T3/4 are attached to thyroglobulin in the colloid = this makes them inactive
TSH from anterior pituitary will stimulate thyroid follicular cells for the endocytosis of colloid from follicular lumen into the follicular cells where it is digested by lysosomes
This releases T3/T4
what is the role of the liver in making thyroid hormone?
T4 is the inactive form = metabolised by liver to make T3
what is the role of T3?
T3 acts to increase the basal metabolic rate Increase HR Increase gut motility Increase speed of muscle contraction Increase temperature
What does calcitonin do?
Parafollicular cells/C cells release calcitonin = lowers calcium levels in the blood by
- inhibiting osteoclasts
- decreasing calcium reabsorption in the kidneys
what inhibits calcitonin secretion?
calcitonin Secretion is inhibited by somatostatin
what germ layer does the thyroid develop from?
endoderm - (think metabolism = gut lining???)
how does the thyroid develop embryologically?
Originates from diverticulum located in medial, ventral wall of pharynx
Week 4: endoderm thickening appears in midline floor of primitive pharynx (between 1st and 2nd pharyngeal pouches
Thickening grows into underlying mesoderm
Thyroid develops from this diverticulum
Thyroid becomes spherical and then lobulated
Descends to be anterior to trachea
