Thyroid Hormone

Question 1

How is thyroid hormone produced?

Answer 1

• Produced by vesicles, colloids are made up of a large complex glycoprotein called thyroglobulin.
• Hormones will remain bound to thyroglobulin until they are secreted from the gland.
• Upon release colloid is ingested by the thyroid cells where the peptide bonds are hydrolysed.
• Free T3 and T4 are released into the capillaries.
• Release of both these hormones from thyroglobulin is controlled by TSH.

Question 2

What is the mechanism of action of thyroid action

Answer 2

• Iodide trapping results in the uptake of iodide ion by the thyroid gland.
• Oxidised by peroxidase enzymes to form nascent iodine.
• This nascent iodine binds to tyrosine to form mono and di-iodotyrosine within the thyroglobulin.
• 2 di= T4 while mono + di = T3.
• T3 is also formed from the deiodination of thyroxin in tissues (T4).

Question 3

Calcitonin

Answer 3

• Synthesised in parafollicular C cells present in the connective tissue around thyroid follicular cells.
• Causes transfer of blood into bone by increased calcification of the bones or by diminished decalcification.

Question 4

What are the functions of thyroid hormone?

Answer 4

• Increased metabolic activity, it increases the amount of oxygen consumed in oxidative phosphorylation.
• Has an important role in growth and development of cells, in the absence of thyroid hormone GH secretion is depressed.
• Increases the rate of endocrine secretion of most glands.
  -Calcitonin reduces blood calcium ion concentration (opposite function of parathyroid).