Endocrine Day 4- Thyroid and Pancreas Flashcards Preview

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Flashcards in Endocrine Day 4- Thyroid and Pancreas Deck (56)
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Hormones involved in thyroid HPA axis

  • TRH- released from anterior hypothalamic area
  • TSH released from thyrotrophs in anterior pituitary
  • TH released from thyroid
    • T4- 10x more secreted then T3
    • T3- less secreted, more potent
  • SOmatostatin can inhibit thyrotrophs as well


TSH is similar in structure to which hormones?

  • LH
  • FSH
  • HCG

All have same alpha subunit


What is the functional unit of the thyroid gland? How does it appear with activation of TSH and unstimulated?


  • Without activation of TSH, T3/t4 thyroglobulin matrix is stored inside colloid
  • With activation of TSH, invaginations appear on colloid membrane to reabsorb T3/T4


What is the biosynthesis of T3/T4?

  • Tyrosine (AA) converts to monoidotyrosine or diiodotyrosin in the presence of iodinase
  • Monoido and di iodo can combine to make T3
  • 2 diiodotyrosine can combine to make T4


What causes T3/T4 to be synthesized inside thyroid cell?

  • Binding of TSH causes activation of Na-I transport (secondary active transport) (Na/K ATPase dependent)
    • this brings iodide into cell
  • Organification of Iodide via peroxidases inside cell
  • "Coupling" of MIT and DIT to itself makes T3/T4
  • Attaches to thyroglobulin backbone (all stored together in colloid)


What occurs to cause secretion of T3/T4?

  • With continued TSH production, apical membrane of thyroid cell develops invaginations to pinch off colloid and bring it into cell
  • Inside cell, lysosomes have proteolytic and hydrolytic enzymes
    • liberates MIT, DIT, T3, T4 from thyroglobulin
  • T3/T4 aromatase ring allows it to freely leave plasma membrane into blood
  • MIT, DIT stays inside thyroid cell to be reused


TSH acts to increase ___ inside cell


  • important to remember because cAMP can be stimulated by other things and this will also increase thyroid hormone production


What are 2 major end effects of TSH on the cell?

  • Stimulates thyroid gland hormone production
  • increases thyroid cell size and cellular proliferation by increase cAMP levels


When T4 binds to cell, it is converted to ____ by _____.

T3; 5'-deiodinase


What actions does T3 have once inside target cell? (at normal physiologic levels)

  • Stimulates Na-K ATPase
  • Increases mitochondria and respiratory enzymes
  • increases other enzymes, proteins such as growth hormone
  • proteins for growth and maturation

At normal physiologic levels, TH is anabolic


What whole body effects does high level of TH have on body?

At high physiologic levels, TH is catabolic

  • increased O2 consumption causes
    • increased CO
    • Increased ventilation
  • Increased upatke of substrates
    • increase food uptake
    • increased mobilization of endogenous carbs, protein, fat
  • Increased metabolic rate
    • increase CO2, heat
    • increase urea
    • decrease muscle mass
    • decrease adipose tissue
    • increase thermogenesis
    • increase sweating
    • increase insensible loss



What whole body effects does TH have on metabolic rate?

  • Increase CO2, increase urea, 
  • increase muscle mass
  • decrease adipose tissue


How is TSH production affected in cold environment?


Increase in TH then maintains body temperature


What is TSH production in warm environment?

  • Inhibit TRH-TSH-TH levels


What are TSH levels like in hypothyroidism?

Very high due to lack of negative feedback from TH


What are TSH levels like in hyperthyroidism?

Very low due to increased negative feedback from thyroid hormone


What are TSH levels like in hypopituitarism?

  • Very low d/t inability to make TSH


What happens when you inject TRH into patient with hypothyroidism?

HUGE increase in TSH 

  • With loss of TH, TRH receptors are upregulated on thyrotrophs
  • so, when TRH injected, get exaggerated release of TSH


What happens when you inject TRH into hyperthyroid patient?

No change in TSH production

  • With increase TH production, get downregulation of receptors, so no response from injected TRH


What is grave's disease?

  • Autoimmune diseaes caused by production of autoantibody called thyroid stimulating immunoglobulin
    • antibody binds to TSH receptor, elevates cAMP and stimulates excess TH production
  • Symptoms
    • exophthalmus
    • rasies BMR
    • accerlerates organ activity
    • increases beta adrenergic receptors on CV tissue
      • more sensitive to catecholamines
    • hyperphagia
    • increase body temp
    • smooth, velvety skin


What is goiter?

  • Increased proliferation of thyroid cells d/t excessive TSH secretion from lack of TH
  • Occurs with iodine deficiency, no iodine to make TH 


What is cretinism? (congenital hypothyroidism)

  • Arises from perinatal deficiency of thyroid hormone
  • lack of TH results in slowing of mentation d/t failure of
    • dendritic branching of neurons
    • reduction in synapses
    • reduced myeline formation
  • Avoided by admin of TH to newborn if TH found to be low


What is Myxedema?

  • Adult hypothyroidism
  • lacks TH, results in accumulation of mucopolysaccharides
    • causes osmotic effect and edematous appearance
  • leads to incrase fat accumulation and impair wound healing
  • slow metabolism, constipation, cold intolerance and dry skin


Why is KI given before thyroid surgery?

  • decreases proliferation of TH
  • May cause less of a problem at surgery if pt is pretrated with KI


What is thyroid storm?

  • d/t increased TH, increased beta adrenergic receptors, when hyperthyroid patient goes into surgery, they can release a lot of catecholamines
  • with extra beta adrenergic receptors, this can result in VF, MI
  • To prevent thyroid storm, can give KI preop or treat HR during sx with propranolol


What is the Wolf-Chaikoff effect?

decrease in TH caused by excess iodine admin with KI


What do beta cells in pancreas secrete?



What do alpha cells in pancreas secrete?



What do delta cells in pancreas secrete?



All hormones inside pancreas exhibit ____ response