Flashcards in Tuesday - Thyroid Phys - Trachte Deck (25):
What causes a release of TSH
TRH (made in the hypothalamus)
Effects of Thyroid hormone
similar to sympathetic stimulation - increase BMR, heat production, glucose utilization, heart rate, contractility
Negative regulators of TSH
Somatostatin, Dopamine, glucocorticoids
Receptor for TRH mechanism
on thyrotrophs of the anterior pituitary
works through Phosholipase C (g protein Q)--> IP3 --> Ca2+ stores --> secretion of TSH
Receptor for TSH mechanism
Gs --> cAMP --> export T3 and T4
(tSh = gS)
also causes thyroglobulin transcription
How many Iodine does thyroxine have?
T3 = triodothyroxine
Difference between T3 and T4
T3 is more active but has a shorter half life (~ 1 day vs. T4 ~ 6 days)
3 transporters for thyroid homones
how many binding sites?
Thyroxine binding hormone (TBH) - 1 site. 75%
Transthyretin - 2 sites - mostly T4
Albumin - many binding sites - mostly T3
How does T4 get broken down?
Deiodination by deiodinase (outer ring --> T3, inner ring --> reverse T3)
T3 --> T2 (inactive)
T3 and T4 go in cell via transporters. What happens next?
act on most cells in body - in the nucleus, bind to Thyroid Hormone Receptor THR --> transcriptional regulation
What happens if a baby doesn't have thyroid hormone?
It's called cretinism - low brain development.
What are some things that can cause thyroid deficiency?
lack of iodine
Hashimotos's thyroiditis - anti TSH receptor antibodies
radioactive iodine or antithyroid drugs
Hypothyroid symptoms in babies
Bone maturation is delayed
cyanosis, jaundice, poor feeding, umbilical hernia
Symptoms of low thyroid in adults
lethargy, somnolence, stiffness, cold intolerance, delayed tendon relaxation
sx of hyper thyroidism
bone turnover --> hypercalciuria
increased gluconeogenesis - bad in diabetics
(basically increases your metabolic rate)
too much thyroid emergency is called
Thyrotoxicosis. can lead to thyroid storm!
3 spots in cascade that can lead to hypotyroidism
primary - thyroid problem - low TH, high TRH and TSH.
(iodine deficiency, autoimmune (hashimoto), gland destruction)
Secondary - pituitary problem - low TH and TSH but TRH is high
Thyroid hormone resistance - all levels are high.
What happens in graves disease
what happens to TSH TRH and TH?
you make antibodies that can mimic TSH.
TH is super high, causes feed back inhibition of TRH and TSH
can cross placenta -->hyperthyroid in baby too
Is that a goiter in your throat, or are you just excited to see me?
Why can a goiter be from hyper and hypo thyroid?
Idodine deficiency --> no TH --> more TRH --> stimulates thyroid.
Graves disease - constant stimulation by antibody
Test for Graves Disease
Thyroid Stimulating Immunoglobulin (TSI) test
If TSH is high or low, next test to do is?
T3 and T4
Radioactive iodine is uptaken a lot, what might that mean?
Grave disease, because you're taking up a lot of iodine to be used for TH
What's a thyroid scan good for?
actually, shows where the iodine is. Can show irregularities
3 drugs for treating hyperthyroidism
Methimazole - inhibits peroxidase
- inhibit thyroid peroxidase and de-iodinase
- don't know why it works