Endocrinology- thyroid gland Flashcards
Where is thryoid gland located and what nerve runs close to it?
BELOW thyroid cartilage
Label histopthology of a throid lobe?
Follicle -follicular cells, colloid
PARA(next to) follicular cells
Development of throid gland (beginning in tongue) from embryo until adult?
outpouching from floor of pharynx (base of tongue)
develops to thyroglossal duuct
then develop to 2 lobes
duct dissapear leaving leaving foramen caecum
Final position week 7 then thryoid gland develops
How does thyroid gland function in follicular cell (when TSH arrive from pit gland)?
TSH bind to TSH receptor on follicular cells.
stimulated: -production + release of thyroglobin into colloid
- also transport of I- from blood through cell to colloid
- production of enz TPO (cataylse both iodniation rxn with H202)
What happens to thyroglobin after in the colloid?
First iodide is oxides to iodine.
Binds to TG form MIT & DIT chains (that are still on TG)
then coupling reaction to form T3 and T4 chains (that are still on TG)
These are cleaved from thyroglobulin in the follicular cell cytoplasm (lysosomal enzymes) to yield T4 and T3
ENTER blood
on a molecular level of thyroglobin how does this occur?
TG (long peptide chain) has many Tyrosine (AA) residues x100
Tyrosine can be iodinated.
1 iodonation- MIT 2 iodonation- DIT
combine MITs and DITs (copling rxn)
PRODUCE- T3 and T4
What does this visually look like?
T3 is active but most thyroid hormones produced is T4 (inactive) how is this resolved?
In targeted tissues T4 is deiodinated to T3 by DEIONDINASE enz
What happens if you deiodinate in a different position?
Produce an inactive form of T3
How is it transported in blood ( 3 attached ways)?
1- 80% by TBG
2-Albumin
3-prealumin (transthyretin)
v little unbound
How does it have affect on gene expression?
enter nucleus + alter gene expression activ gene transciption
What is it overall purpose?
Essential for growth, development esp brain
disease if low in baby crentinism
tested in baby-heel prick measure TSH
What is T3/4 affects on systems and body?
increase BMR, increase metabolism, increasde cardiac output, maturation CNS, Catecholamines( hormones adrenal glands)
How is T3/4 production regulated?
T3/4 negative feedback to hypothalamus and anterior pituarity.
as well as high iodide prev production T3/4
Why are women suspectible to thyroid disease
Majority of T disease due to autoimmunity, antiobodies against T gland.
women more antibodies, more antibody variance due to giving birth.
What happens to blood levels in hypothyroidism (auto damage to cells)?
Thyroxine (T4) levels decline.
TSH levels increase due to negative feedback
Common disease associated of hypothyroidism?
Hashimoto’s thryoditis
immune attack T gland + inflammation leads to hypo
How is hypothyroidism diagnosed
enlarged thyroid glands
elevated thyroid stimulating hormone (TSH)
low thyroid hormone (Free thyroxine [Free T4]) levels
TPO antibody elevated
Symptoms of hypothyrodism?
Paresthesia hypo cause fluid retention resulting in swollen tissues that exert pressure on peripheral nerves.
shaggy hair + hair loss
fatigue+ memory lost
swollen gace
enlarged T gland due to inflammation
slower HR- bradycardia
Weight gain
rough skin
deepening voice
cold intolerance
What treatment usually given to hypothyroidism?
What is it?
Levothyroxine (T4)
How is that drug dosed?
adjust TSH to normal as usually too high
administered orally
When else can Levothyroxine be used?
For HYPERthyrodism- blocking and replacement regimen
- use iodine leads to T gland to underactive, prevent all T3/4
- Give levo for functioning in body
What are other alternatives?
Liothyronine (T3)
Has same effect but more expensive
Why is problem with combined T3/4 treatment?
Switch of hypothalamus cells as seeing much of T3/4 so supress TSH + toxicity
What levels changes are there in hyperthyoridism?
Thyroxine levels increase
TSH decrease
Examples of disease causing hyperthryoidism?
Graves disease- gland is enlarged
Toxic mutlinodular goitre- multiple nodules (fluid sacs) autonomically functioning
solitary toxic nodule (singular node)
what is pathophysiology of graves disease?
What does it look like?
Antibodies bind to and stimulate TSH receptor.
Looks smooth, enlarged and neck is fat (GOIRTE)
What are other symptoms of Graves disease?
Other antibodies bind to other places
(muscles beind eye lead to) Exopthalamos- buldging eye out of orbit
(soft tissue of shins) Pretibial myxoedema - ‘orange peal’
Symptoms of hyperthyroidism?
heat intolerance
weight loss
myopathy-muscle weakness
nervousness, insomia, depression
enlarged thyroid glands
increase HR
high BP
moist skin
irregular menstral cycle
