Thyroid gland Flashcards
Describe the anatomy of the thyroid - no. lobes, names etc
Two lobes, left and right.
Isthmus = thin band of tissue between lobes
sometimes pyramidal lobe above isthmus
Describe the anatomy of the thyroid - blood supply to thyroid
via superior + inferior thyroid arteries
superior thyroid = 1st branch of external carotid artery
inferior thyroid = thyrocervical trunk off subclavian
describe thyroid embryology
forms from floor of pharynx, consists of epithelial cells
thyroid diverticulum descends into neck from base of the tongue. initially maintains connection to tongue (thyroglossal duct which later disappears)
what are the 2 remnants of the thyroglossal duct in child/adult
foramen caecum in tongue
pyramidal lobe of thyroid
Thyroglossal duct cyst
- what is it
- features
- cell type
persistent remnant of thyroglossal duct
midline neck mass, usually painless
discovered usually in childhood
classically moves up with swallowing or tongue protrusion
may contain thyroid cells
what is an ectopic thyroid?
how does it present?
what is a complication?
functioning thyroid tissue outside of gland, most commonly at base of tongue
presents as a mass in the tongue commonly detected during increased demand for hormones eg puberty + pregnancy
may be the only functioning thyroid tissue. may under produce thyroid hormone leading to hypothyroidism, increasing TSH production and growth of ectopic tissue
What element of thyroid hormones contain?
why is it not a deficiency in western world?
contain iodine
table salt mixed with small amount of iodine to prevent deficiency
describe thyroid histology
thyroid gland contains follicles filled with colloid (protein material)
single layer of epithelial cells lines each follicle “follicular cells”
hormone is synthesised by follicular cells
what are the thyroid hormones?
what are they synthesised from?
T3 and T4
synthesised from tyrosine and iodine
what is thyroglobulin?
large protein produced by thyroid follicular cells
contains numerous tyrosine molecules
what is the role of iodine in diet/thyroid hormone?
taken up by follicular cells
oxidised to I2 ie undergoes oxidation
added to organic/carbon structures ie organification
describe iodine uptake by cells of the thyroid
sodium iodine symporter (NIS pump) brings iodine into the follicular cell
sodium iodine symporter also brings in perchlorate and pertechnetate which compete with iodine (inhibitors of NIS pump)
describe iodine oxidation by cells of the thyroid
thyroid peroxidase catalyses oxidation of iodine to I2
describe iodine organification by cells of the thyroid
thyroid peroxidase catalyses organification of I2 where i2 added to tyrosine
adding 1 molecule of iodine = MIT
adding 2 molecules of iodine = DIT
describe coupling reactions by cells of the thyroid
MIT + DIT = T3, catalysed by thyroid peroxidase
DIT + DIT = T4 , catalysed by thyroid peroxidase
what is the role of thyroid peroxidase?
compare T3 with T4
describe the effects of hyperthyroid medications on thyroid hormones
what is the Wolff-Chaikoff effect?
what is the impact of amiodarone on thyroid function?
what is the action of amiodarone?
What is radioactive iodine?
how does it work?
what are its uses?
what is thyroxine binding globulin (TBG)?
what impacts TBG levels?
what are the effects of thyroid hormone? general
what are the effects of thyroid hormone? metabolic 1
what are the effects of thyroid hormone? metabolic 2
what are the effects of thyroid hormone? cardiac
what are the effects of thyroid hormone? CNS + bone
what is cretinism?
features
screening
mental retardation, coarse facial features, short stature, umbilical hernia, enlarged tongue
describe thyroid hormon regulation
describe TSH regulation
what are the impacts of pregnancy on thyroid hormones?
What is calcitonin?
what does calcitonin do?
