endocrine 4

Question 1

name 2 thyroid hormones

Answer 1

T3 and T4

Question 2

follicular cells of thyroid gland:

first step occurs in ___, when the preprohormone is synthesized as a peptide called ____ –> its packaged in vesicles and secreted into lumen of follicular cells –> a same time, ___ is being taken up by follicular cell form blood, transported into follicular cell by ____ –> transported into lumen by protein ___ –> ___ gets oxidized to ___ ….

Answer 2

ER
thyroglobulin (lots of tyrosine residues)
iodide (I-)
cotransporter
pendrin
iodide oxidized to iodine
…iodine gets attached to tyrosine residues of thyroglobulin –> thyroglobulin + iodine retaken up into follicular cell via endocytosis –> proteolytic enzymes cleave off tyrosines –> resulting in T3 & T4 –> secreted into blood

Question 3

tyrosine is ___, so it does not have good solubility in blood…

Answer 3

nonpolar
has to be carried in blood by a series of carrier proteins ( serum albumin, TTR, TBG)

Question 4

what are the distributions for the thyroid hormone carriers

Answer 4

TBG most abundant
TBG has higher affinity for T4 –> so more free T3 in blood then T4

have long biological life spans (days), can exist in blood stream for a while

Question 5

how do T3 & T4 get into cells?

Answer 5

enter target cell as free T3 & T4 b/c dissociate from carriers

-tyrosine hormones are hydrophobic, so in many cases, can just diffuse thru cell membrane, also transporters to take hormones across membrane (exception: amine-based residues)

Question 6

once inside a cell, what do T3 and T4 do?

Answer 6

T3 is the active form & has regulatory effect (inside cell, T4 converted to T3)

T3 then binds a chaperone protein (not t3 receptor), T3 binding complex is just to get the T3 chaperone into the nucleus –> once in nucleus, actual binding to receptor takes place –> hormone-receptor complex binds to GREs to typically turn on genes

Question 7

how are thyroid hormones regulated?

Answer 7

short and long negative feedback systems

Question 8

thyroid hormones control metabolic rate to produce ___

Answer 8

heat of metabolism (metabolism produces and splits ATP, everytime you split ATP, some of that energy going to be released in unusable form of heat –> called heat of metabolism)

Question 9

describe feedback loops and RF/hormones involved with regulating thyroid hormones

Answer 9

stimulus for thyroid hormone production is cold temp (temp sensors on skin & spinal cord) –> send signals to hypothalamus (which constantly monitoring internal & external core temps) –> produces TRH (TSH-releasing hormone) –> TRH travels down portal system to stimulate anterior pituitary –> anterior pituitary releases TSH –> TSH stimulates thyroid gland to release t3 and t4 –> TSH also travels back to hypothalamus to cut off production of TRH (short loop) –> thyroid hormones also travel back (long loop)

Question 10

T3 and T4 increase ___ and ___ and lots of other things to…

Answer 10

metabolism (ATP synthesis & turnover)
fatty acid mobilization

produce more heat

Question 11

T3 and T4 also affects the heart…

Answer 11

increases synthesis of beta1 receptors –> results in increased sensitivity to nor/epinephrine –> increased heart rate and strength of contraction –> inhibits expression of Na/Ca antiporter in cardiac muscle membrane –> results in higher intracellular calcium & increased force of contraction

Question 12

name 5 other effects of thyroid hormones

Answer 12

increased O2 consumption
increased resting respiratory rate
increased sensitivity to ventilation to CO2 & O2
increased production of Epo –> higher hematocrit
promotes growth & maturation