Part 16: Thyroid Disorders Flashcards
thyroid hormones are involved in what physiologic processes (6)?
- metabolism
- energy expenditure
- body temp
- promote growth and differentiation of cells
- bone remodelling
- protein synthesis and degradation
higher levels of thyroid hormones tends to cause ____ (increased or decreased) metabolism
increased
t/f thyroid hormones can be increased to a pathologic level which can cause overactive cellular processes
t
by increasing energy expenditure & metabolism, thyroid hormones increase ____ utilization and _____ oxidation
glucose; fatty acid
thyroid hormones have ___ (sympatholytic or parasympatholytic) effects
sympath
what is the effect of thyroid hormones on heart rate
raise hr
thyroid hormone secretion is regulated by the ___ and ___ glands
hypothalamus & pituitary
thyroid hormones are typically secreted in parallel with ____ rhythms
circadian
at what time of day is the highest amount of thyrotropin released from the hypothalamus?
2-4 am, when most people are sleeping
TRH stimulates the pitutary gland to secrete ____
TSH
the release of TSH from the pituitary causes the release of 2 thyroid hormones ___ & ___
T3 & T4
TRH stands for
thyrotropin releasing hormone
what are 2 positive regulators of TRH?
psychosis & cold temperature
what is a negative regulator of TRH?
stress
what is a negative regulator of TSH?
cortisol (stress)
what is the only structural difference between T3 & T4?
one iodine group
which thyroid hormone has higher affinity for the thyroid hormone receptors?
T3
the majority of thyroid-related physiologic effects are the result of thyroid hormone receptors being activated by which hormone?
T 3
what enzyme in the follicular cells of the thyroid is responsible for thyroid hormone synthesis and storage of the hormones as thyroglobulin comblexes?
thyroid peroxidase
once the thyroid hormones are made, they are stored as ___
thyroglobulin complexes
thyroid hormones are made from dietary ___
iodine
t/f the thyroid gland is the only human organ that uses iodine
t
does the thyroid gland create small amounts of hormone PRN or does it makes lots and store it?
makes lots and stores it
when stimulated by TSH, the ____ is cleaved and thyroid hormones are released into circulation
thyroglobulin
which of the 2 thyroid hormones is secreted in greater amount?
t4
how does thyroid peroxidase make thyroid hormones?
adds iodine groups to tyrosine residues and groups 2 iodinated tyrosine together
thyroid hormones circulate in the blood, primarily bound to ____ protein
thyroid-binding globulin
T4 is taken up by target cells via _____ transporters
organis anionic (OAT)
when T4 is taken up by OATS into target cells, it is converted into ___ by
T3
what enzymes are responsible for turning T4 into T3
cellular deiodinases
T3 binds to thyroid hormone receptors in the ____ of target cells
nucleus
activation of nuclear thyroid hormone receptors alters gene ___, which results in increasded cellular ___ and ____
transcription; metabolism & activity
nuclear receptors are classed with intracellular receptors and are sometimes called _____
ligand-activated transcription factprs
T4 has a ____ (long or short) half-life
long
what is the rate limiting step in the process of thyroid causing physiologic effects?
the converesion of T4 to T3
T4 is almost like an endogenous _____drug
pro
what is the half-life of T4?
6-7 days
hyperthyroidism presents as symptoms associated with ___ metabolic rate
increased
hypothyroidism presents as symptoms associated with ___ metabolic rate
decreased
the circulating thyroid hormones impose ____ feedback loops on the release of TSH and TRH
negative
the 2 most common thyroid disorders are autoimmune diseases and are :
- graves (hyper)
2. hashimoto’s (hypo)
graves disease is the most common clinical presentation of _____
hyperthyroidism
in Grave’s disease, a stimulatory anti-body called _____ is made by the immune system and it will stimulate ____ receptors to promote thyroid hormone release
thyroid-stimulation immunoglobulin; TSH
why can the thyroid-stimulating IG continue to cause the release of thyroid hormones even when a negative feedback loop is present?
it is not sensitive to the negative feedback loop
Case: a patient presents with high levels of T4, but low levels of TSH, what is the likely diagnosis?
likely graves disease hyperthyroidism bc the IG would bind to the TSH receptor to promote more T4 even though there is a negative feedback loop to reduct the amount of TSH made
in Grave’s disease ____ hormone is high and ___ and ___ hormones are low
T4; TRH and TSH
what are some clinical symptosm of Grave’s disease/ hyperthyroidism?
fast heart rate, weight loss (despite eating more) , elevated body temp. Extreme cases can have bulging eyes, goiter, and tremour
what causes a goiter?
increased production of thyroid hormone
what causes bulging eyes in Grave’s disease?
inflammation & edema
what are some long-term consequences of untreated hyperthyroidism?
osetoporosis, peridontal disease, increased risk for “thyroid storm” and thyrotoxic risk
what is thyroid storm?
a life-threatening situation where there is a sudden onset of systemic symptoms such as sweating, raised body temp, increased HR , dyspnea, muscle weakness, and cognitive changes
thyroid storm can be triggered by ____ during a prolonged period of uncontrolled hyperthyroidism
systemic triggers like an infection
what is methimazole?
a thyroid hormone antagonist
t/f there is typically a delay in onset of thyroid antagonsists and they are not always 100% successful in managing hyperthyroidism, but do reduce the production of thyroid hormones
t
methimazole is an antagonist of _____ (enzyme)
thyroid peroxidase
is methimazole a competitive or non-competitive inhibitor?
competitive
methimazole reduces the ____ synthesis of thyroid hormones
de novo
why do the effects of methimazole take several weeks to kick in?
bc the thyroid gland has a lot of thyroid hormones already stored and ready to go, so you need to wait until that supply has been depleted
methimazole is part of the ___. class
thioamide
thioamides like methimazole have what important consideration in pregnancy?
they may interfere with fetal thyroid hormone synthesis and can cause hypothyroidism in the fetus
what is the typical approach to methimazole use in pregancy?
it is also risky to have too high thyroid hormone, so methimazole may be used in pregnancy, but doses and serum level of thyroid hormones will be closely monitored
t/f thioamides cross the placemta
t
what are some of the pregancy risks associated with hyperthyroidims?
spontaneous abortion, low birth weight, stillbirth, preeclampsia, and heart failure
list 2 examples of more complete methods of reducing thyroid hormones?
destruction of the thyroid gland with radioactive iodine or surgical removal
why is systemic radioactive iodine not Thatttt unsafe?
bc the thyroid gland is the only organ that takes it up and uses it, so only the thyroid will be destroyed
is the treatment with radioactive iodine immediate for reducing thyroid hormone?
no, because there is still the stored hormone
t/f radioactive iodine treatment results in a dose-dependent irreversible termination of thyroid hormone productio
t
t/f most patients treated with radioactive iodine will need surgical removal later bc it is difficult to know the exact dose needed of the iodine to completely inhibit the thyroid
t
t/f the removal of the thyroid gland puts patients in a hypothyroid state and will require supplementation
t
what is hypothyroidism?
thyroid hormone levels are too low to properly maintain metabolic and cellular functions
what is Hashimoto’s thyroditis?
a form of hypothyroidim caused by an autoimmune disorder in which the autoantibody destroys the thyroid gland
t/f Hashimoto’s results in low thyroid hormone levels despite the hypothalamus and pituitary calling for more release
t
Case: patient is persistently cold and tired, gaining weight despite eating well, her T4 is low and TSH is high
she has hyperthyroidism
which sex has higher rates of hypothyroidism?
female
is hypothyroidism more common in younger or older people/
older
hypothyroidism during development will have what effect on growth?
slowed growth
the heart rate and BP of hypothyroid patients will be ____ (higher/lower) than normal
lower
edema and enlarged tongue are symptoms of what type of thyroid disorder?
hypo
what is a common drug used to treat hypothyroidism?
levothyroxine (synthroid)
what is levothyroxine?
a synthetic T4 hormone
t/f the doses of synthroid need to be titrated over time
t
is the GI absorption os synthroid affected by food?
yes
which has a longer half-life, synthroid, T4, or liothyroxine
synthroid
the TH effects of synthroid are controlled by the physiological conversion to ____-
T3
what is Liothyroxine and why is it not preferred?
a synthetic T3 hormone, not preferred bc it has higher risk for hyperthyroidism
why is the risk for hyperthyroidism higher in liothyronine than synthroid?
bc liothyronine skips the rate limiting step of converting T4 to T3
do patients continue thyroid medications for life?
yes
can lifestyle changes affect the dose of thyroid drugs needed?
yes
the biovailabilty of synthroid is increased on a full or empty stomach?
empty
the demand for thyroid hormones is ofetn ___ (higher or lower) during pregnancy
higher
people on any type of thyroid medication need routine ____
blood wrk
