the thyroid Flashcards
(48 cards)
what type of protein is thyroid hormone?
a glycoprotein (a basophil)
what does an over-active thyroid look like?
tall columnar epithelium with very little colloid
what does an under-active thyroid look like?
flattened epithelium with excess colloid
what can occur if the thryoglossal duct does not atrophy?
if the upper portion does not atrophy (this can lead to a midline thryoglossal cyst) this is clinically distinguishable because it can move when the tongue is protruded.
some patients have a pyramidal lobe, this is the lower portion of the thyroglossal duct
what is an under-migrated thyroid?
lingual thyroid
what is an over migrated thyroid?
retro-sternal thryoid
what is a mutation that can cause congenital hypothyroidism?
PAX-8 mutation
what is a bruit an auscultation evident off?
this is evident of an over active thyroid, recall the thyroid has a very high blood supply from the superior and inferior thyroid arteries
what are the two main actions of thyroid perioxidase?
this causes organification:
- oxidises the iodide
- then adds this iodide to tyrosine residues exposed on the thyroglobulin.
causes coupling:
- di-iodo-tryosine + di-iodo-tyrosine = T4
- di-iodo-tyrosine + mono-iodo-tyrosine = T3
where is thyroid perioxidase synthesised?
this is synthesised in the follicular cell and packaged into a vesicle by the Golgi, it then becomes activated at the apical plasma membrane
where is thryoglobulin synthesised?
this is transcribed, translated and post translation mofiied and packaged into vesicles at the Golgi
where does iodine for thyroid hormone synthesis come from? and how does it reach the follicular lumen?
this comes from dietary supplied. it is concentrated in the follicular epithelial cells via the sodium/ iodide transporter and then transported into the lumen via pendrin
what can mutations in pendrin cause?
this can cause pendrin syndrome, which is a congenital form of hypothyroidism.
what are the effects of TSH on thyroid hormone secretion?
it causes an increase in the amount of the fresh thryoglobulin and thyroid hormone secretion. the secreted thyroid hormone is more active because it has higher proportion of T3:T4
what are the usual concentrations of free thyroid hormone within circulation
in picomolar and this is because 99.9% of the thyroid hormone is bound to plasma proteins
what are the physiological actions of thyroid hormone
- positive chronotropic and ionotropic effects
- increases BMR
- is a CNS stimulant
- promotes growth and development with GH
synergies with adrenaline to: - increase lipolysis -increase glycogenolysis - increase heart rate antagonises insulin
its secretion is reduced by GHRH
why can selenium deficiency cause a rare form of hypothyroidism
because selenium is required to deiodinate the outer ring of T4 to form T3
this is because T4 is the precursor for T3
there are several forms of De-iodinating enzymes:
what is the function of D1:
D1 is responsible for making most of the T3 in the body (found in the liver, kidney and muscle)
what is the function of D2?
this is responsible for negative feedback mechanisms and is found in the brain and pituitary
what is the function of D3
This ensures that once cells have taken up all the T3 they require they’re not under influence by circulating T3
they de-iodinate the inner ring of T4 to make inactive T3, or de-idoinate the inner ring of T3 to make T2 which is hormonally inactive and rapidly cleared from circulation
what are long acting thyroid stimulators?
those are the type of antibodies produces in Grave’s disease:
- they have prolonged action on the TSH-R
- although the action of the auto-antibodies may take longer to manifest
what are the specific symptoms associated with Grave’s disease
orbital pathology e.g. proptosis
pretibial myooxedema
thyroid acropachy
what are the acute causes of hyperthyroid status?
Hashimoto’s disease and De Quervain’s
- those are thryoditis, initially may manifest as hyperthyroid but with time, there is glandular dysfunction and this leads to a hypothyroid status
why does Grave’s disease sometimes have a relapsing-remiting disease course
because the auto-antibodies produced in Grave’s are not only stimulatory,TSI
but sometimes antibodies produced can be inhibitory; TBII
