Physiology of thyroid gland Flashcards
3 parts of thyroid gland
left, right branch, isthmus
Things released by thyroid gland
thyroxin, triiodothyronine, calcitonin
____ cells surround colloid
follicular
____ bring iodide to follicular cells
blood vessels
______ release calcitonin
parafollicular cells
____ contains thyroglobulin.
Colloid
Iodide uptake occurs on the _____ side of the ______ cell via what mechanims?
Basolateral, follicular, Na/I symporter
What transport brings iodide into the basolateral side of the follicular cell and what transport brings it out the apical side?
Basolateral: Na/I Symporter
Apical: Pendrin
What is iodide trapping?
The process of intracellular accumulation
What does iodide do in the colloidal lumen?
It binds tyrosine residues on thryoglobulin
____ is a large protein with few tyrosine residues
Thryoglobulin
Where is thyroglobulin synthesized?
follicular cells
What is thyroid peroxidase and what does it do?
It is on the luminal side of of secretory vescicles (secreteing thyroglobulin). It oxidizes iodide to Io, which is unstable, so that it reacts with thyroglobulin
Only ____ tyrosine residues on thyroglobulin are iodinated.
20%
What happens after endocytosis of iodinated thyroglobulin?
Hydrolysis forms T3 and T4 in lyso-endosome, iodide is recycled
What is the ration of T4 to T3 produced in lyso-endosome?
10:1
What percent of T4 is bound? T3?
99.98%; 99.5%
Formed T3 and T4 are released into the blood where they immediately ____.
Bind to binding protein, mostly TBG
What conditions increase TBG? What does this to do total and free T3 and T4?
Pregnancy, hepatitis, heroin abuse - increases total T3 and T4, but NOT free hormone
What conditions decrease TBG? What does this do to total T3 and T4?
Steroids- decreases total but NOT free hormone
Compare the half lives of T3 and T4
bound T4- 8 days
bound T3- 24 hrs
What is structurally required for active hormone?
2 iodide needed on inner ring and at least 1 on the outside
What enzyme catalyzes T4–> T3?
5’/3’mondeoiodinase
What enzyme catalyzes T4 to rT3?
5/3 monodeiodinase
Metabolism of T3 and rT3?
T2–> T1–> Thyronine
What is type 1 deiodinase?
5’/3’: T4–> T3–> Liver, Kidney, Thyroid, Primarily responsible for free hormone in the blood
What is type 2 deiodinase?
5’/3’: T4–> T3–> pituitary (presents T3 to pituitary, a TH regulator, no regulation here during starvation, CNS, placenta
What does 5/3 Deiodinase do?
T4–> rT3–> All tissues
Where is the thyroid receptor?
nucleus
Describe the action of thyroid hormone on target cells
T3 or T4 enter cell–> nuclear target–> THR which dimerizes with RXR and acts direly on DNA to both increase and decrease production
____ is the major hormone secreted by the thyroid and carried in the circulation. ____ is the physiologically active form of hormone.
T4; T3
Effect of hyperthyroid on basal metabolic rate
Increase (increase O2 consumption and thermogenesis)
Effect of hyperthyroid on carb metabolism
increase with no change in glucose in someone with a NORMAL pancreas
Effect of hyperthyroid on lipid metabolism
increase
Effect of hyperthyroid on serum cholerterol
decrease
Effect of hyperthyroid on thermogenesis
increase
Effect of hypothyroid on basal metabolic rate
decrease
Effect of hypothyroid on carb metabolism
decrease; no change in blood glucose
Effect of hypothyroid on protein metabolism
decrease
Effect of hypothyroid on lipid metabolism
decrease
Effect of hypothyroid on serum cholesterol
increase
Effect of hypothyroid on thermogenesis
decrease
Describe what happens to Na/K ATPase pump and actin with T3?
Increase, actin–> tachycardia
Increase in TRH stimulates what?
thyrotrophs in ant. pit. to increase release of TSH –> T3, T4
What role does somatostatin play in regulation of thyroid?
Negative regulation at level of thyrotrophs in ant. pituitary
Role of dopamine in thryoid regulation
Negative regulation at level of thyrotrophs in ant pit
Role of T3 and T4 in thyroid regulation
Negative regulation on Thyrotrophs and TRH
How does TSH increase thyroid secretion?
Increases activity of NIS (iodide uptake), stimulates iodination of thyroglobulin in follicular lumen, stimulates conjugation of iodinated tyrosines to generate T3 and 4, increase endocytosis of iodinated tyrosines to generate T3 and 4, stimulate proteolysis of iodinated thyroglobuin in lysoendosomes, increase secretion of T4 and T4 into circulation, exerts growth factor effects on the thyroid cells increasing their size and number
Is TH important in development?
Yes- no sure why but low levels can be seen in dwarfism
LOOK OVER LAST FEW SLIDES IF PATHO NOT COVERED IN FUTURE LECTURES
do it
