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Flashcards in Thyroid Deck (16):

describe the signalling pathway of TRH

IP3 and DAG increase the release of TSH


describe the signalling pathway of TSH



describe the daily requirements of iodine

  • daily requirements = 150 micrograms from diet
    • ingested in form of idodide (I-) or iodate (IO3)
  • pregnant women and lactating females have higher iodine requirements
  • deficiency will initially compensate by increased TSH levels which leads to goiter
  • if intake is < than 50 micrograms, compensation will fail


describe the location and amounts of iodine in the body

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describe structure of thyroglobulin

  • large glycoproteins
  • contains ~70 tyrosine molecules


describe synthesis of thyroglobulin

  • made in epithelial cells
    • synthesized in ribosomes
    • transport to Golgi
    • discharged into follicle lumen
  • synthesis and storage of TH remains here


list the 8 steps in TH synthesis 

  1.  synthesis and extrusion of TG into the lumen
  2. Na/I symporter on the basal membrane
  3. oxidation of I- to I0 to fuse with TG via TPO (inhibited by PTU)
  4. Organification of I2 to MIT and DIT via TPO (inhibited by PTU)
  5. Coupling MIT and DIT via TPO
  6. endocytosis of TG that contain DIT, MIT, T3, T4
  7. hydrolysis of T3, T4 off the TG via proteolyase 
  8. Deiodination of MIT and DIT via deiodinase


describe the effect of T3/T4 at the target tissue

  • 5' deiodinase converts T4 into T3 (10x more potent)
    • T3 enters the nucleus and modulates gene expression
  • increases basal metabolic rate


describe the locations of T3 and T4 in the body

  • 70% of T3 and T4 bound to thyroxine-binding globulin (TBG)
    • pregnancy and estrogen increase levels of TBG
    • liver disease decreases levels of TBG
  • rest bound to blood proteins


increase in ___ negatively feedbacks thyrotrophs (TSH) and hypothalamus (TRH)


  • T4 doesn't regulate thyroid hormones


describe hyperthyroidism diseases

  • thyroid enlargement (Grave's disease)
  • overactive lump (Plummer's disease)


describe Grave's disease

  • antibody for TSH receptor upregulates production of T3/T4
    • decreases TRH and TSH since T3 negative feedback


describe the signs of Grave's disease

  • thyroid enlargement
  • opthalmopathy
  • pretibial myxedema
    • non-pitting edema
  • untreated can lead to thyroid storm
  • bulging eyes


describe causes of hypothyroidism

  • due to low levels of TH in blood
    • Hashimoto's thyroiditis
    • thyroidectomy
    • iodide deficiency
  • secondary
    • insufficient pituitary action
    • resistance of organs to TH


describe hypothyroidism in newborns

  • may be due to
    • iodide deficiency (not common in 1st world)
    • placental transfer of TSH antibodies
  • symptoms
    • respiratory problems, jaundice, poor feeding, umbilical hernia, reduction of bone development


describe amenorrhea in hypothyroidism

  • decrease in thyroid hormone increases TRH levels which stimulates prolactin
    • prolactin inhibits GnRH, which leads to amennorhea