Thyroid Metabolic Hormones Flashcards
thyroid gland 2 main hormones
T4 93%
T3 7%
also produces calcitonine
calcitonine
minor role in maintaining Ca2+ and phosphate
chronic lack of TH
decrease BMR to 40-50% below normal
will feel cold and gain weight possibly
chronic excess TH
increase BMR to 60-100% above normal
feel hot and lose bw possibly
iodine
chemical element
turn into ion iodide
have to consume iodiDe
only thyroid gland needs iodide in the body
iodide pump
actively transport the iodides from the blood into the thyroid gland
iodide trapping
iodide trapping
not very effective
20% of iodide in blood is taken by thyroid gland
rest is excreted by kidney
colloid
in follicles of the thyroid gland
mainly composed of glycoprotein called thyroglobulin
thyroglobulin
contains TH and secretes into follicular colloid to be stored
prehormone
contains 70 tyrosine amino acids
reservoir of TH hormones
formation of TH
peroxidase is needed to add 3-4 iodide molecules to 2 tyrosines
TH stored in body for 2-3 months so takes time to observe effects of deficiency
what happens to thyroglobulin once TH is synthesized
TH remains attached to it
how is T3 and T4 released from thyroid gland
proteinases digest thyroglobulin and releases the hormones
diffuse from the thyroid cells into the blood
what can cause iodide deficency
lack of deiodinase enzyme because can’t recycle iodide
how does T3 and T4 get transported to the tissues
combine with several plasma binding proteins :
thyroxine-binding globullin (mainly
Thyroxine-binding prealbumin
albumin
what is the rate of release of T3 and T4 to the tissues
T3: one day
T4: 6 days because plasma binding protein has higher affinity for T4
general effect of TH
cause nuclear transcription of genes for synthesizing large number of substances
what 4 substances are synthesized by TH
enzymes
structural proteins
transport proteins
other
what hormones binds the most to receptors
T3 (more than 90%)