Thyroid Flashcards
thyroid hormone
produced in follicular cells of thyroide
-requires iodine
(+) TSH
(-) T3/T4
thyroxine
T4
triiodothyronine
T3
higher action and affinity than T4
D1
deiodinates outer ring T4 - T3
-plasma membrane of peripheral tissue
D2
deiodinates outer ring of T4
-in ER in pituitary, brown fat, brain
D3
deiodinate inner ring T4 to produce rT3
- inactivating
- plasma memra eon skin, placenta, brain
thyroid hormone in blood
on thyroid-binding globulin
long half life
action of thyroid hormone
increase metabolism carbs, protein, lipid
necessary for growth and mental development
also increase beta-adrenergic receptor sensitivity
-increased HR, tremors, sweating
thyroid follicle
thyroid hormone synthesis in follicular epithelial cells
basal membrane - blood
apical - lumen
lumen has colloid - thyroid hormones attached to thyroiglobulin
thyroid hormone storage
extracellularly in lumen
thyroglobulin
synthesized on rER and golgi of follicle cells
-transported to lumen
I trap
Na/I cotransport
active transport of I from blood into follicle cells
low I- = increased Na/I pump activity
thiocyanate and perchlorate
block I- uptake into follicular cells
oxidation of I-
to I2
thyroid peroxidase at apical membrane
thyroid peroxidase
oxidation of I- to I2
organification I2 to tyrosines of thyroblobulin
coupling of DIT and MIT
two DIT = T4
MIT + DIT = T3
PTU
propylthyouracil - inhibits thyroid peroxidase
lumen rxns
organification and coupling
endocytosis of thyroglobulin
thyroid gland stimulation
- iodinated thyroglbulin endocytosed to follicile cells from lumen
- hydrolysis of T4 and T3 from thyroglobulin occurs
- MIT and DIT are deiodinated in follicle cell (thyroid deiodinase) - recycled
thyroid in circulation
T4 and T3 bound to TBG
provides large reservoir
hepatic failure
low TBG - decreased hepatic protein synthesis
increased free thyroid levels
-negative feedback on thyroid synthesis
pregnancy
high estrogen inhibits breakdown of TBG
- more bound thyroid
- more production of thyroid hormones
total levels increased, free thyroid stays same
-“clinically euthyroid”
T3 resin uptake test
measure for circulating levels of TBG
major product of thyroid gland
T4 - not most active form
5’-iodinase
converts T4 to T3 intissue
tissues also convert to rT3 - inactive
TRH
released from paraventricular nuclei of hypothalamus
acts on thyrotropes of anterior pituitary to increase TSH secretion
TSH
from anterior pituitary
-increased growth thyroid gland
(-) thyroid hormones (free T3)
TSH action on thyroid gland
increases synthesis of thyroid hormones
- I uptake, oxidation, organification, coupling, endocytosis, proteolysis
- trophic affect on gland itself
graves disease
hyperthyroidism
-thyroid-stimulating immunoglobuins
low TSH, but high circulating thyroid hormones
decreased converstion of T4 to T3
pregnancy, fasting, stress, hepatic and renal failure, beta-adrenergic blocking agents
affects of T3
increased O2 consumption
-increased in BMR and body temperature
- increased metabolism
- catabolic - decreased muscle mass
increased cardiac output
- upregulate beta-1 adrenergic receptors
- increased heart rate and contractility
- increased growth
- essential for maturation of CNS
hyperthyroid treatment
beta-adrenergic blocking agents
-propanolol
graves disease
autoimmune
-increased thyroid-stimulating Igs
bulging eyes**
causes of hyperthyroidism
graves disease
thyroid neoplasm
excessive of TRH or TSH
exogenous thyroid hormones
low TSH levels?
hyperthyroidism due to:
- graves
- neoplasm
- exogenous thyroid (factitious hyperthyroidism)
high TSH levels?
hyperthyroidism due to:
-excess TSH or TRH
symptoms of hyperthyroidism
weight loss - with increased food intake
- excessive heat production
- rapid heart rate (beta-1)
- weakness
increased activity may lead to goiter
Tx hyperthyroidism
propylthiouracil (PTU) - inhibits thyroid hormone synthesis
surgical removal of gland
radioactive ablation of gland w/ 131- I-
hypothyroidism
most common - autoimmune destruction
-thyroditis
also due to:
- surgical removal gland
- I- deficiency
- hypothalamic / pituitary failure
thyroiditis
TSH will be increased
defect in hypothalamus or pituitary
TSH decreased
symptoms of hypothyroidism
decreased metabolism, weight gain
- cold intolerance
- myxedema - swelling around eyes
- goiter
cretinism
hypothyroidism in perinatal period
-growth and mental retardation
Tx of hypothyroidism
TH replacement - usually T4
serum TSH
most valid and useful assessment of thyroid function
hot nodule
toxic adenoma
- low TSH and gland atrophy surrounding nodule**
- nodule products too much thyroid hormones
toxic nodular goiter
multiple nodules producing thyroid
subacute thyroiditis
granulomatous
-hyperthyroidism
painful gland **
viral
hyperthyroid > euthyroid > hypothyroid > euthyroid
silent thyroiditis
subacute lymphocytic
-non-tender gland**
-autoimmune
transient
ex/ postpartum thyroiditis - after delivery
euthyroid
normal
hashimotos
primary hypothyroidism
-T-cell mediated
pituitary insufficiency
secondary hypothyroidism
tertiary hypothyroidism
hypothalamic disease
hashimotos thyroiditis
T cell mediate autoantibodies
- against thyroiglobulin and thyroid peroxidase
- gradual thyroid failure
goiter, peripheral edema, constipation, HA, fatigue
- high TSH/TRH
- low T3/T4
Tx: levothyroxine (T4) therapy
absence of iodine for extended period of time
high TSH
low T4
low T3
TH administration
decreased TSH
- decreased iodide uptake
- decreased thyroglobulin levels
- gland atrophy
radioactive iodine scan
to see if thyroid hormones are being made
don’t do if breastfeeding
sheehans syndrome
hypopituitarism caused by ischemic necrosis due to blood loss and hypovolemic shock during and after childbirth
TRH
stimulate TSH and prolactin release
hard to sample the release hormone levels - too invasive to brain arterial capillary plexus
euthyroid sick syndrome
critically ill patients
thyroid hormone decrease
decrease in T3
increase in rT3 - inactive
adaptive to protect body during illness
estrogen
from contraceptive
- may cause increased TBG
- transient hyperthyroidism
mechanism of thyroxine
binds cytoplasm receptor
- complex diffuses to nucleus
- affects transcription
hypothyroidism
bradycardia constipation peripheral edema muscle weakness small thyroid periorbital edema puffy face hair loss
hyperthyroid
bulging eyes- exopthalmos tachycardia weight loss diarrhea hyperreflexia
