Thyroid

Question 1

describe the signalling pathway of TRH

Answer 1

IP3 and DAG increase the release of TSH

Question 2

describe the signalling pathway of TSH

Answer 2

cAMP

Question 3

describe the daily requirements of iodine

Answer 3

• 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

Question 4

describe the location and amounts of iodine in the body

Answer 4

Question 5

describe structure of thyroglobulin

Answer 5

• large glycoproteins
• contains ~70 tyrosine molecules

Question 6

describe synthesis of thyroglobulin

Answer 6

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

Question 7

list the 8 steps in TH synthesis

Answer 7

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

Question 8

describe the effect of T3/T4 at the target tissue

Answer 8

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

Question 9

describe the locations of T3 and T4 in the body

Answer 9

• 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

Question 10

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

Answer 10

T3

• T4 doesn’t regulate thyroid hormones

Question 11

describe hyperthyroidism diseases

Answer 11

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

Question 12

describe Grave’s disease

Answer 12

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

Question 13

describe the signs of Grave’s disease

Answer 13

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

Question 14

describe causes of hypothyroidism

Answer 14

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

Question 15

describe hypothyroidism in newborns

Answer 15

• 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

Question 16

describe amenorrhea in hypothyroidism

Answer 16

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