Hypothalamus - Pituitary - Thyroid axis Flashcards
what stimulates the hypothalamus to release thyrotropin-releasing hormone (TRH)?
The hypothalamus detects low levels of T3 or T4
how does the hypothalamus signal to the anterior pituitary gland to release thyroid-stimulating hormone (TSH)?
hypothalamus releases thyrotropin-releasing hormone through the hypophyseal portal system to the anterior pituitary which stimulates the synthesis and release of TSH
what happens once TSH reaches the thyroid?
thyroid starts synthesizing T3 and T4 (predominantly T4)
walk me through the basics of T3/T4 synthesis
- stimulation from TSH
- iodine trapping into the follicular cell via ATP transporters
- thyroglobulins are also formed in the follicular cells
- thyroglobulins are iodized via thyroid peroxidase
- creates T3 and T4 to be released, thyroglobulin is recycled to be used again
T3 and T4 can travel in the circulatory system w/o being bound to a serum protein? T/F
F! they require serum proteins for transport
very little T3 and T4 are free, if they are free its typically cause they’re at their end location
where do T3 and T4 lose an iodine?
in the liver and kidney
for T3, it is deactivated, for T4, the removal of an iodine transformed it to T3
the thyroid produces more T4 vs T3, T/F?
True! however, most T4 is later converted into T3
where does the deiodization of T4 occur to convert to T3?
mainly the liver
can also occur in kidneys, muscles, CNS, brown adipose fat
tell me about T4 and T3 characteristics
T4: less potent vs T3 but has a longer half life
T3: more potent and has shorter half life ➔ is considered the “active” thyroid hormone cause it binds to cells’ thyroid hormone receptor a lot better vs T4
How does T4/T3 impact/regulate metabolism on a cellular level?
increases gene expression of ATPases in tissues so cells are able to have more energy to complete functions
how does T4/T3 impact the heart, lungs, and muscles?
heart - increases HR and contractility
lungs - increases oxygenation and perfusion
muscle - aids in the development of muscle fibers for better contraction
why is thyroid hormone important in developing children? what relationships does it have with other hormones?
works synergistically with cortisol to stimulate more growth hormone release to improve bone and CNS development
what happens when there is either not enough or too much thyroid hormone in children/during developemnt?
hypo - growth retardation w/ delayed skeletal development
hyper - accelerated bone maturation
