Physiology 3120 Lecture Notes - Lecture 3: Calcitriol, Bone, Biomineralization

11 views6 pages
Hardy Lec 3
Hypothalamo-pituitary-thyroid axis (regulate metabolism)
-hypothalamus releases TRH and SRIF  TRH stimulates anterior pituitary to release TSH  TSH
goes to thyroid follicles through bloodstream to stimulate T3/T4 release
-thyroid hormones act over long periods of time to regulate metabolism and HR (more next
TRH = thyrotropin releasing hormone
TSH = thyroid stimulating hormone
-if too much T3/T4, negative feedback regulation where receptors on hypothalamus and
anterior pituitary binds to T3/T4 to inhibit further TRH/TSH release
-on top of that, also have SRIF released by hypothalamus into anterior pituitary to inhibit
further TSH release (less common mechanism)
SRIF = somatostatin release inhibiting peptide
NOTE: somatostatin = somatotropin same thing
-TPO has two functions: iodinates and couples
TPO = thyroid peroxidase
1. TPO adds one iodine to tyrosine to give monoiodotyrosine or two iodines to tyrosine to give
diiodotyrosine  randomly occurs
2. TPO then couples either a monoiodotyrosine with diiodotyrosine to give T3 or couples two
diiodotyrosines to give T4
-need to bring in iodine from basolateral side  apical side where TPO is
-Na-I symporter uses Na gradient to drive Na and I transport from blood on basolateral side to
colloid on apical side
-pendrin is symporter on apical side that transports I from parafollicular cell to colloid where
TPO couples TG to I to get Tg-T3/T4
-Tg-T3/T4 complex goes back into cell via pinocytosis
-in parafollicular cell, intracellular enzymes separate T3/T4 from Tg
-T3/T4 leaves via basolateral side to enter bloodstream and bind to thyroid target tissues
TSH Stimulation
-so TSH binds to its receptor on basolateral side to:
find more resources at
find more resources at
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 6 pages and 3 million more documents.

Already have an account? Log in
1. Stimulate Na/I symporter activity to bring in more iodine into cell
2. Stimulates thyroglobulin production
3. Stimulates TPO activity to get more Tg iodination
-even though T3/T4 are not steroid hormones, they are not very soluble due to aromatic ring
thus more lipid-loving
-need binding proteins (carrier proteins) to take them to target tissues
-regulate bioavailability because without them, hormones would be able to get to target tissues
-also provide mobility to hormones as they go from tissue to tissue
-thyroid gland secretes more T4 BUT in plasma, there is more T3
-this is because T3 less stable but more potent ie: active  live fast die young
-T4 more stable but less potent ie: active
RMR talked about changing message of hormones en route
-similarly, T4 converted to T3 in cell when needed using deiodinases
-T3/T4 lipid-loving so can easily go through PM
-D2 converts T4 into T3 that enters nucleus to bind to TR (T3-receptor)
-T3-TR complex acts like transcription factor that turns on/off T3-responsive gene
-D2 can also convert T4 into rT3 which is inactive reverse T3
-D3 can also convert T3 into T2 which is a weaker thyroid hormone
 Do not need to worry about above two points just appreciate that T4 can also be converted
into two other weaker thyroid hormones
-TR bound to co-repressors thus no transcription factor thus no transcription of thyroid genes
-T3 binds to TR to displace corepressors to act as transcription factor to allow transcription of
thyroid genes
-T3 recruits coactivators to completely activate transcription of thyroid genes
-cretinism = impaired mental capacity
-increase O2 demand as in more oxygen available when needed
find more resources at
find more resources at
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 6 pages and 3 million more documents.

Already have an account? Log in

Get OneClass Notes+

Unlimited access to class notes and textbook notes.

YearlyBest Value
75% OFF
$8 USD/m
$30 USD/m
You will be charged $96 USD upfront and auto renewed at the end of each cycle. You may cancel anytime under Payment Settings. For more information, see our Terms and Privacy.
Payments are encrypted using 256-bit SSL. Powered by Stripe.