Laboratory Investigation of Endocrine Disorders

Question 1

Describe the hypothalamic-pituitary-thyroid-axis

Answer 1

• Neurosecretory cells of the hypothalamus will secrete TRH via portal circulation
• This will stimulate anterior pituitary cells to secrete TSH
• This will stimulate the thyroid gland to produce large amounts of T4 and smaller amounts of T3

Question 2

What is the biologically active thyroid hormone?

Answer 2

T3

• This is mainly formed by the peripheral conversion of T4 through deiodinase enzymes

Question 3

What is the function of the thyroid hormone

Answer 3

• Essential for normal growth and development
• Increase basal metabolic rate (BMR) and affect many metabolic processes

Question 4

How are thyroid hormones synthesised?

Answer 4

Synthesised in the thyroid via a series of enzyme catalysed reactions

Iodine is taken up into the gland, follicular cells will export iodine into the colloid where the thyroid hormone wil be synthesised via multiple enzymes such as TPO

Synthesis will be controlled via TSH