thyroid gland Flashcards
what is the blood supply of the thyroid ?
superior thyroid artery branch of the external carotid for the upper part
inferior thyroid artery branch of the thyrocervical trunk for the bottom part
what is the connection between the thyroid and the tongue ?
the thyroglossal duct
what is the origin of the thyroid ?
the remanent of the thyroglossal duct which is the endoderm of the foramen cecum
what is the pathology of a thyroglossal duct cyst ?
persistence of the thyroglossal duct
what is the presentation of the thyroglossal duct cyst ?
it is a midline neck mass that is usually painless and moves up and down with swallowing or tongue protrusion
what is the most common location for ectopic thyroid tissue ?
base of the tongue
what is the presentation of ectopic thyroid ?
presents as a mass in the tongue
detected during puberty or during pregnancy
may be associated with hypothyroidism
increased TSH
what are thyroid follicular cells derived from ?
derived from endoderm
where do thyroid parafollicular cells arise from ?
arise form 4th pharyngealpouch
which cells of the thyroid are responsible for making the hormones ?
the follicular cells
what are the thyroid hormones and what are they made from ?
T3 T4 and TSh
made from tyrosine and iodine
what are the changes that iodine must go through to be taken by our body ?
uptake by follicular cells first
then oxidation
then organification
how does the iodine uptake by follicular cells happen ?
NIS - sodium iodine symporter , brings in iodine and sodium into the salt
what are the inhibitors of the NIS symporter?
perchlorate
pertechnetate
what is the enzyme responsible for the oxidation of iodine ?
thyroid peroxidase
from iodide to I2
what antibody is commonly seen in autoimmune thyroid disease ?
Anti TPO
what converts T4 into T3 ?
5 deiodinase ( peripheral conversion)
what drugs are used to inhibit TPO enzyme?
Methimazole
PTU
beta blocker and blocks 5 deiodenase ?
propanolol
what is the wolff chaikoff effect ?
prevention of the occurence of hyperthyroidism due to an excess in iodine consumption
where the organification process is inhibited by an excess of the iodide levels
what cardiac drug can cause hypothyroidism ?
amiodarone
via excess iodine
via the wolff chaikoff effect
mimics T4 and inhibits deiodinase enzyme
what are the thyroid hormone levels associated with the consumption of amiodarone ?
a decrease in T3
and a small rise in TSH
what is the carrier protein for T4 ?
TBG
thyroxine binding globulin
what is the result of less TBG in the plasma ?
less available T4/T3 to be used in tissues
what are the factors that can effect the levels of TBG ?
estrogen rises the levels of TBG
liver failure lowers the TBG levels
how do thyroid hormones exert their effect on cells ?
through thyroid hormone receptors
what is the main effect of thyroid hormones ?
major regulator of metabolic activity and growth
what are the metabolic effects in hypothyroid patients vs in hyperthyroid patients ?
hypothyroid : inc cholesterol
hyperthyroid : hyperglycemia, weight loss
what are the cardiac effects of thyroid hormones ?
increased cardiac contractility - hence the tachycardia
increase the number of B1 receptors
what is the effect of thyroid hormones on the CNS and bone effects ?
childhood hypothyroidism - cretinism
what is the most common cause of treatable mental retardation ?
cretinism
what is the thyroid hormone receptor regulator ?
TSH which is released by the anterior pitutary
what is the method of activation in which TSH works by ?
activated the cAMP/PKA 2nd messenger system
what is the order in which thyroid hormones are released from ?
TRH from the hypothalamus
then TSH from the anterior pituitary
then binds to TSH receptors on the thyroid gland
what is the effect of activation of PKA ?
stimulates the uptake of iodide ions and promotes the organification of Iodide
what is the effect of pregnancy on thyroid hormone production ?
due to the high levels of estrogen , more T3 and T4
hCG stimulates the thyroid
raises T$ and lowers the TSH
what other hormone is produced by the thyroid ?
calcitonin which is made by parafollicular cells
also called C cells
what is the physiologic effect of calcitonin ?
lowers serum calcium
used for hypercalcemia patients
