thyroid gland Flashcards
how many lobes does the thyroid gland have
2
connected by
isthmus
what extra lobe do somepeoplpe have
pyramid
what is the thyroid made up of
follicles
describe the strcuture
follicular (circular) cells on outside
with colloid in midlle
what is colloid made up of
extracellular fluid
what other cell
parafollicular cells
function
secrete calcitonin
what 2 glands are embedded in thyroid
parathyroid glands (superior and inferiori)
which nerves runs vlose and supplies vocal cords
left recurrent laryngeal nerve
what do the para thyroid glands secrete
hormone importnat for calcium metabolism
in embryo where does the thyroid start of
base of tongue develop of thyroglossal duct divide in 2 lobes Duct disappears leaving foramen caecum Final position by week 7 Thyroid gland then develops
how are blood vessels shown in histology
red
what are the White line/dot-
where the thyroid hormone is made
how is t3/t4 sythesised
TSH- arrives via blood, binds to TSH R
Na+ and I-, enter by sodium iodine co transporter then iodide transported via another receptor to colloid
Become oxidesed called iodination to become iodine
TG (thyroglobulin) is made as a result of TSH R being bound(?) ]
TG binds to iodine
to produce MIT and DIT
coupling reaction to produce t3 t4
TPO and h2o2 catalysis the reaction
TG prohormone
which amino acid residue is iodinated in the TG
tyrosine
structure
aromatic ring
only one iodine added
3 monoiodotyrosine (MIT)
2 iodine
3,5-DIIODOTYROSINE
3-MONOIODOTYROSINE +
3,5-DIIODOTYROSINE
MIT + DIT
T3
3,5-DIIODOTYROSINE
+
3,5-DIIODOTYROSINE
DIT + DIT
t4
which is the active hormone
t3
how is t4 converted to active t3
Deiodinated to triiodothyronine (T3), its bioactive form, in target tissues
if deiodinated in different position
Also deiodinated in a different position to produce reverse T3 (inactive)
which enzyme deiodinates
deiodinase enzyme
so t4 is a what sort of hormone
prohormone
how are t3 t4 transported in blood
Mostly bound to plasma proteins
is it active when bound
no
what affect does t4/t3 have on a gene
Target tissue have the diodinase enzyme
T3 enters nucleus
T3 binds to thyoid receptor
Altered gene expression
what is cretinism
severe deficiency of thyroid hormone in newborn
how is it tested at birth
TSH measured in new-born infant’s heel-prick test
what does thyroid hormone do
↑Basal metabolic rate
Protein, carbohydrate & fat metabolism
Potentiate actions of catecholamines (e.g. tachycardia, lipolysis)
Effects on the GI, CNS, Reproductive systems
↑glucose absorption ↑gylcogenolysis Gluconeogenesis ↑lipolysis ↑protein synthesis & degradation
↑cardiac output
how is homostasis achieved when TRH causes TSH causing T3/T4 in posistive cylce
inhibited by negative feedback by increase in T3 T4 ((Wolff-Chaikoff effect)
Iodine can inhbit production of t3 t4 in large amounts
Large amount of potassium iodine given to stop production
which hormone can also inhibt
omatostatin- inhibit production of TSH
Are thyroid disorders more common in men or women, or the same?
Women (4:1 ratio)
why
???? Over time, evolved to carry baby, baby has lots of other antigesn, so women immune system is diffrenent
Is an overactive thyroid gland or an underactive thyroid gland more common?
The same
what causes Primary hypothyroidism
autoimmune
surgery- removal of thyroid
what happens in Primary hypothyroidism to thyroxine and TSH levels
Thyroxine levels decline
TSH levels climb
what are 2 diseases associated with hypo
Graves can cause hypo but more rare mostly hyper
Hashimoto’s thyroiditis
signs ans symptoms of hypo in hair brain thyroid face voice skin weight bowel heart cold/hot
hair- hair loss, receding, thin brain- fatigue, memory impairment, depression thyroid- enlarge face-swollen, voice-deep weight-increase with reduced appetite bowel-Constipation heart- Bradycardia cold intolernace- always hot
Affects sypmathtic nervous system- everything slows down
drug to treat hypo
Levothyroxine
what is it similar to
Levothyroxine- similar to t4
Deiodinated in the same way to give you t3
can it treat hyper
Hyper- high anti thyroid hormone, and give back what they need to survive
why not give t3
Expensive t3
T4 cheap
No evidence it works better than t4
what haooens to thyroxine and TSH levels in hyper
Thyroxine levels rise
TSH levels drop
disease
Graves’ disease – whole gland smoothly enlarged and whole gland overactive
Toxic multinodular goitre
Solitary toxic nodule
sign and symptoms
nervousness,irritability, insomnia, depression
broken hair/hairloss enlarge thyroid weight loss tachycardia Heat intolerance Weight loss with increased appetite Myopathy Mood swings Diarrhoea Tremor of hands Palpitations Sore eyes, goitre eye- Exophthalmos- problem gritty, dry, don’t close at night
what causes enlarged thyroid
Antibodies bind to and stimulate TSH receptor in the thyroid
Smooth goitre
