Which cells of the thyroid produce thyroid hormones?
Follicular cells (aka thyrocytes)
Thyroid hormones are attached to ____ and stored in the extracellular fluid known as _____
Thyroglobulin
Colloid
Which cells produce calcitonin?
Parafollicular C cells
What is the trace element required by thyroid hormone that is unique to them?
Iodine
Formation of thyroid hormone requiring presence of what substance in the colloid?
Iodide
How is iodide transported from the blood into thyrocytes?
Sodium-iodide symporter moves iodide from blood into the thyrocyte
Sodium-iodide symporter transport iodide _____ the concentration gradient.
Against
Needing energy from Na/K ATPase
T/F: sodium-iodide symporter pumps both sodium and iodide from blood into the thyrocyte, but the sodium gets pumped out through Na/K ATPase in order to generate the energy required for the symporter
True
How is iodide transported from the thyrocyte into the colloid?
Cl-/ I- antiporter called pendrin
What is pendrin?
The Cl-/I- antiporter that transports iodide from the thyrocyte into the colloid in exchange of a Cl- from colloid into thyrocyte
Dietary intake of 500 iodide, and the thyroid gland takes up ____ of it
120 , 80 of it is used to produce T3 and T4
T/F: body takes in more iodide than it excretes out
False; body takes in 500 and excretes out 500 (480 through pee and 20 in stool)
What is organificiation?
Oxidizing iodide via peroxidase, first step
What happens after iodide is oxidized?
It combines with tyrosine within the thyroglobulin
T/F: rT3 is most biologically active
False; rT3 has no known biological activity; T3 is the most active
T4, T3 and rT3 are all products of the coupling of two ________ derivatives
Iodinated tyrosine = MIT and DIT= monoiodotyrosine, diiodotyrosine
i.e. mono + di = T3, di + di = T4
rT3 is formed by two ____ molecules with _____ iodine being removed from the inner benzyl ring of ____
DIT
One
T4
The activity of Na/I pump is regulated by _____ levels, low level of it would ____ the pump
Iodide
Stimulate
High levels of ___ inhibits organification and synthesis of thyroid hormone, this is the ______ effect
Iodide
Wolff-chaikoff
What is the enzyme that recycles iodide and tyrosine?
Iodotyrosine Deiodinase
Congenital absence of this enzyme would have MIT and DIT appear in the urine and contribute to symptoms of iodine deficiency
What are the plasma proteins that bind thyroid hormones to maintain a large poo of hormone ready for mobilization?
Albumin
Transthyretin
Thyroxine-binding globulin
T/F: most of the T4 and T3 found in plasma are in free form
False; they are mostly bound to thyroxine-binding globulin or albumin (T3), low amounts are in free form
Human thyroid secretes mostly _____
T4
Most of the T3 and rT3 are formed from T4 deiodination in the tissues
T/F: TSH is hydrophobic so it can diffuse through cell membrane and bind nuclear receptors
False; TSH binds GPR and stimulate G alpha which raises cAMP and stimulates the synthesis of T4 and T3. T4 and T3 are hydrophobic so they can diffuse through cell membrane and bind intracellular receptors
Increased TBG (thyroxine binding globulin) levels, such as in pregnancy, can _____ thyroid hormone secretion
Stimulate
Thyroid hormones ____ metabolism, so would _____ glucose absorption, glycogenolysis, gluconeogenesis, lipolysis and protein synthesis and degradation
Increase
Increase metabolic pathways
Thyroid hormones effect on CNS:
Maturation of CNS
(in hyperthyroidism, there is increased DTRs)
In the nucleus, T3 interacts with the thyroid hormone receptor, which is bound as _____ with a ______ receptor
Heterodimer
Retinoid X
T/F: patients with elevated or decreased concentrations of binding proteins, particularly TBG, are typically euthyroid
True
When there is an increased in the concentration of TBG proteins in the plasma, what happens to the concentration of free thyroid hormones?
Falls , but this is a temporary change because would then stimulate TSH production
Conditions in which concentrations of thyroxine binding proteins increases:
Estrogens,
Methadone
Heroin,
Major tranquilizers,
Clofibrate
Conditions in which concentrations of thyroxine binding protein decreases:
