Thyroid Hormones (Lec 16) Flashcards
___ mg of Iodine are required each year
50
Iodine is absorbed from gut tract in same manner as what?
chlorides
What symporter is in the basal membrane of thyroid cell?
sodium-iodide
Where does energy for sodium-iodide pump come from?
sodium-potassium ATPase pump
Iodide can be concentrated inside the cell ____ X plasma concentration
30-250
Iodide is transported across apical membrane of cell into follicle via what?
chloride-iodide counter-transporter = pendrin
Thyroid cells secrete ___ into follicle
thyroglobulin
Each thyroglobulin molecule has about ___ tyrosine amino acids which bind iodine to form thyroid hormones
70
Iodide ions are converted to what?
an oxidized form of iodine: either nascent iodine or I3-
note: these can bind directly to tyrosine
The major hormonal product of iodine metabolism is what?
thyroxine (T4)
How is thyroxine formed?
when two molecules of diiodotyrosine are joined together or one monoiodotyrosine may combine with one diiodotyrosine to form triiodothyronine (T3)
Each thyroglobulin contains about ___ molecules of thyroxine
30
The thyroid can store several months supply of what?
thyroid hormones
In regards to the release of thyroid hormones, the apical surface of thyroid cells pinch off small portions of the ___ ___ to form pinocytic vesicles
follicular colloid
In regards to the release of thyroid hormones, lysosomes fuse with vesicles and digest thyroglobulin molecules to release what?
thyroxine and triodothyronine (thyroid hormones)
In regards to the release of thyroid hormones, they diffuse where?
into blood
In regards to the release of thyroid hormones, most of the iodinated tyrosine in the thyroglobulin does not become thyroid hormones but is recycled using what?
a deiodinase enzyme
In regards to the release of thyroid hormones, most of released thyroid hormone is thyroxine which then is slowly deiodinated to from what?
triiodothyronine
In regards to the release of thyroid hormones, most thyroid hormones entering blood are immediately bound to plasma proteins synthesized where?
in the liver
True or false?
In regards to the release of thyroid hormones, plasma proteins have a high affinity for thyroid hormones so the hormones are released rapidly to tissue cells
false; slowly to tissue cells
Increased transcription of a large number of genes, increased cellular metabolic activity, effect on growth, effects on specific bodily mechanisms are all physiological functions caused by what?
thyroid hormones
List some of the specific bodily mechanisms thyroid hormones provoke
stimulation of carbohydrate metabolism, stimulation of fat metabolism, effect on plasma and liver fats, increased requirement for vitamins, increased BMR, decreased body weight
What are thyroid hormone’s effects on the cardiovascular system?
increased blood flow and cardiac output, increased heart rate, normal arterial pressure, increased respiration
What do thyroid hormones do to the GI system?
increase GI motility
What are thyroid hormone’s effects on CNS
excitatory
True or false?
Thryoid hormones can cause muscle tremor
true
In regards to sleep, endocrine, glands, and sexual function; do thyroid hormones have a positive or negative effect on these three things?
negative
TSH has what effect on thyroid hormone?
increases release of thyroid hormone
TRH has what effect on on thyroid hormone secretion?
stimulates release of TSH
Grave’s disease and Adenoma are two causes of what?
hyperthyroidism
What are the symptoms of hyperthyroidism?
high state of excitability, intolerance to heat, increased sweating, mild to extreme weight loss, varying degrees of diarrhea, muscle weakness, nervousness, extreme fatigue, inability to sleep, tremor in hands, exophthalmos (eyes bulging out)
How is hyperthyroidism treated?
surgical removal of most of thyroid gland; treatment with radioactive iodine
what is the major issue with removal of thyroid gland?
removal of parathyroid glands = death
What are the causes of hypothyroidism?
hashimoto disease (autoimmunity), endemic goiter, cretinism
Myexdema and atherosclerosis are symptoms of what?
hypothyroidism
How is hypothyroidism treated?
oral medication
In regards to antithyroid drugs, what do thiocyanate ions do?
inhibit iodine uptake
In regards to antithyroid drugs, what does propylthiouracil do?
inhibits peroxidase
In regards to antithyroid drugs, what do iodides do?
decrease thyroid activity when present in very high concentrations
