Thyroid physiology Flashcards
what 3 parts make up the thyroid gland?
2 lateral lobes, connected by isthmus
where does the thyroid gland embryologically originate from?
base of tongue
Between what vertebral levels does the thyroid lie?
C5-T1
What does the thyroid gland consist of?
follicles lined by cuboidal epithelium
What do the follicular cells make?
the colloid
Which hormones does the thyroid secrete?
triiodothyronine (T3)
L-thyroxine (T4)
Calcitonin
How many parathyroid glands are there?
4
What hormone does the parathyroid hormone secrete?
Parathyroid hormone (PTH)
What 2 cartilages lie above the thyroid gland?
Cricoid cartilage
Thyroid cartilage
T3 is produced more than T4.
true or false
false
more T4 is produced
what is T4 converted into in peripheral tissues?
active T3
Is it free or unbound hormones that are active?
free
What hormone stimulates the pituitary to secrete thyroid stimulating hormone?
Thyrotrophin-releasing hormone (TRH)
What dietary requirement is necessary for thyroid hormone synthesis?
iodine
Which hormone stimulates the release of thyroid hormones?
Thyroid-stimulating hormone (TSH)
What 3 hormones are measured in thyroid function tests?
TSH
T4
T3
What results of a thyroid function test would be expected in thyrotoxicosis?
suppressed TSH
Increased free T4
Increased free T3
What results of a thyroid function test would be expected in primary hypothyroidism?
increased TSH
low free T4
normal/low free T3
What results of a thyroid function test would be expected in TSH deficiency?
low-normal TSH
low-normal free T4
normal/low free T3
Is it the free or unbound hormone measured in thyroid function tests?
free
How does T3 complete the negative feedback loop for thyroid hormones?
T3 suppresses TRH and TSH production
What serum proteins do thyroid hormones bind to for transport?
TBG
TBPA
Thyroid hormones can enter a cell when bound to a serum protein
True or false
False
only the unbound form can enter cells
List some causes of increased TBG
Pregnancy
Hep A
Acute intermittent porphyria
List some causes of decreased TBG
Acromegaly
large doses of glucocorticoids
chronic liver disease
genetics
List some effects that thyroid hormones have on the body…
Increased metabolic rate
increased thermogenesis
increased HR
increased RR
What enzyme is needed to degrade T3 and T4?
de-iodinase
