Thyroid Flashcards
from where is the thyroid innervated?
the middle/inferior of cervical ganglia or SNS
which artery vascularizes the thyroid?
the thyroid artery
what is the functional unit of the thyroid?
thryoid follicle
colloid
a thich fluid that fills follicular cells and stores TH. it contains iodinated thryoglobulin TG
role of follicular cells
synthesize hormones
thyroglobulin
large glycoprotein scaffold with tyrosines
TH is made up of ____ and ____
iodide and tryosine
what are the two TH’s
T3 and T4
how is iodide moved around the body?
absorbed in GI tract
taken up by thryroid
removed by kidneys
transported by Na+/I- symporters
how is TH made?
- tyrosines are iodinated with thyroglobulin via thyroperoxidase(ox rxn).
- Then these are coupled via thryoperoxidase to form T2 or T4
- Epithelial cells endocytose colloid
- endosomes fuse with lysosomes
- lysosomes digest TG to release T3/T4
- this free TH (T3 or T4) diffuses into the blood
what is the main type of TH secreted?
T4
which TH is active and why?
T3 is active, T4 is inactive due to its very high affinity for the TH receptor over T3
circulating TH is bound to _____, or _____ or _____
- thyroid binding globulin
- transthyretin
- albumin
T4 is converted to T3 via ______
deiodinases
rT3
reverse T3, this is inactive and is made by removing iodides from an inner ring
which deiodinase is responsible for removing an iodide from an inner ring?
D3
where is the TRH receptor?
cell membrane, gpcr
what are 2 factors that regulate TH?
- diet (high carbs)
2. conditions that increase body energy requirements
how does TBG regulate TH?
They are directly correlated, as TBG increases, so does TH
wolff-chaikoff effect
the autoregulatory inhibition of the organification of iodine as there is an increase in circulating iodine. helps regulate T3/T4 production
factors that contribute to TH synthesis
nutrients such as
iron, iodine, tyrosine, zince, and vitamins
factors that inhibit TH synthesis
stress, infection, trauma, fluroide, toxins, diseases
how is transcription initiated by TH?
TH passes through the transporters and enters the nucleus where it binds to factors on TRE sequence of DNA.
what are the effects of TH?
- increase metabolism
- burn calories
- heat production
- metabolize substrates
