Thyroid

Question 1

general functions of thyroid hormoens

Answer 1

growth

development

body temp

energy metabolism

Question 2

describe the thyroid hormone synthesis

Answer 2

1. iodide uptake into thyroid gland by soidum/iodide symporter (NIS)
2. peroxidase mediated oxidation of iodide to iodine
3. iodination of tyrosine residues within thyroglobulin molecule –> iodide organification (MIT and DIT formed)
4. Molecules of MIT and DIT are combined to form thyroid hormones

Question 3

describe secretion and transport of thyroid hormones

Answer 3

• ratio of T4 to T3 = 5:1 (more T4)
• majority bound to thyroxine-binding globulin (TBG) in the blood
  
  • active form is free

Question 4

how to thyroid hormone exert its effect

Answer 4

• Absence of thyroid hormones
  
  • corepressor inhbits gene transcription
• Presence of thyroid hormone
  
  • T4 needs to be converted to T3 by 5’-deiodinase
  • co-repressor and a TR monomer dissociate and increases gene transcription

Question 5

describe teh regulation of secretion

Answer 5

• Hypothalamus releases Thyroid releasing hormone (TRH)
• TRH promotes release of thyroid stimulating hormone (TSH) by pitutary
• TSH promotes syntheiss of T4 and T3
  
  • thyroid homrones regulate secretion by negative feedback at the level of HYPOTHALAMUS and PITUITARY
• ALSO REGULATED BY IODIDE
  
  • HIGH iodide inhibits (short term)
  • Low iodide promotes thyroid hormone syntheisis at the thyroid

Question 6

Conditions that cause Hypothyroidism

Answer 6

• Congential defect
  
  • lack of thyroid development, lack of TSH receptor responsiveness, lack of thyroid hormone synthesis
• Autoimmune thyroiditis (Hasimoto’s disease)
  
  • infiltration of lymphocytes in the thyroid gland leading to decrease function (TSH LEVELS ELEVATED)
• Iodide deficiency
  
  • dietary deficeincy leading to IMPAIREd HORMONE PRODUCTION

Question 7

Conditions of Hyperthyroidism

Answer 7

• Graves disease
  
  • autoantibodies stimulate TSH receptors and increase T3 and T4 (TSH LEVELS WILL BE LOW)
• Thyroid adenoma/carcinoma
  
  • hyperfunction of a single adenoma or multiple toxic nodules
• Thyroid storm
  
  • acute episode of thyroid activity brought on by stress (surgery, infection, DKA, MI, embolism) in a patient with undiagnosed/untreated hyperthryoidism
• Excess Iodide
  
  • too much or excess Iodide