Thyroid Gland Flashcards
(25 cards)
Which hormone, T3 or T4 is active?
T3
Which thyroid hormone is the main secretory product?
T4 (90%)
What is the secretory product of the thyroid gland?
Iodothyronines
How is T4 converted to T3?
Peripheral conversion w/ deiodinase
enzyme = 5’ - iodinase
Iodide =
I-
Inside follicular cell
Iodine =
I2
In apical lumen
What is a treatment for hyperthyroidsm?
PTU –> Inhibits peroxidase + NIS
Wolff-Chiakoff Effect –> increased levels of I- (iodide) prevents the synthesis of thyroid hormones cause you need decreased iodide for deiodinase to convert
T4 –> T3 and get them out of storage form and into blood stream
How is iodine stored?
It is stored in follicular colloids iodinated as tyrosines attached to thyrogobulin (need to use deiodinase to break them apart)
How can you assess the activity of the thyroid gland?
By radioactive iodine uptake
Which thyroid hormone has a longer half life?
T4 –> 6 days
vs. 1 day for T3
thats why T4 = most circulating hormone
How can we assess circulating levels of TBG?
With a resin uptake test
Thyroid function involves the interaction of many hormones, including triiodothyronine (T3) and thyroxine (T4). Both of these hormones exist in two forms in the blood. The more abundant forms are bound to a carrier protein called thyroxin-binding globulin (TBG), which helps transport the hormones through the body. The less abundant forms circulate unattached or “free.” Only the free forms of the thyroid hormones (free T4 and free T3) are available to affect body processes.
The T3 resin uptake is used by doctors to estimate the amount of TBG in the blood, and how much T4 and T3 in the blood is free form and available to affect the body.
Explain what happens to TBG, T4, and T3 in these disorders during the resin uptake test:
Hyperthyroidism
Hypothyroidism
High TBG
Low TBG
Hepatic Failure
Preganancy
What enzyme converts Iodide to Iodine?
Thyroid Peroxidase (via pendrin transporter)
What factors stimulate thyroid hormone secretion?
TSH
Thyroid stimulating immunogobulins
Increased TBG levels –> ex = pregnancy
What factors inhibit thyroid hormone secretion?
I- deficiency –> can’t make T3
Deiodinase deficiency
Excessive I- intake (Wolff-Chaikoff effect)
Perchlorate + thiocyanate –> inhibit Na + I- cotransport
Propylthiouracil (PTU) –> inhibits peroxidase enzyme
Decreased TBG levels –> ex = liver disease
What do people with hypothyrodism take?
Thyroxine (T4) injection, increases BMR
Review this chart (good things to look for in stem)
Are TSH levels low or high in hyperthyroidism?
Low
Are TSH levels low or high in hypothyroidism?
High
What is the other name for hyperthyroidism?
Thyrotoxicosis
What is primary hyperthyroidism?
Grave’s Disease
What causes Grave’s disease?
Thyroid stimulating immunogobulins (TSI’s) stimulate the TSH receptor without actually having the TSH hormone.
Soooo TSH receptor is being constantly stimulated!
But, you still have low TSH hormone cause all the high T3 + T4 hormones are stopping it from making more through negative feedback.
Remember main symptom = exophthalmos
What causes Hashimoto’s Thyroiditis?
Usually thyroid gland destrction –> causing impaired thyroid hormone synthesis and decreased T3 + T4 levels
TSH = high –> causes trophic effect (Goiter)
What is caused by untreated postnatal hypothyroidism?
Cretinism
