Thyroid physiology and anatomy 2 (read)

Question 1

Describe how thyroid hormones are transported in the blood

Answer 1

• They are hydrophobic/lipophilic so mainly transported in bound form to plasma proteins
• Note only unbound thyroid hormone is biologically active

Question 2

What is the main plasma protein which transports thyroid hormones ?

Answer 2

Thyroxine binding globulin

Question 3

What are the major biological effects of thyroid hormones ?

Answer 3

Affect virtually everything

Profound effects on:

• Metabolism
• Growth and development
• Reproduction
• Behaviour

Question 4

What are the effects of thyroid hormones on metabolism ?

Answer 4

• Increase BMR
• Increase thermogenesis
• Increase carbohydrate metabolism - Increase BG, also increase insulin-dependant glucose uptake into cells
• Incease lipid metabolism
• Increase proetin metabolism

Question 5

What are the thyroid hormone effects on growth ?

Answer 5

Required for:

• Growth hormone releasing hormone (GHRH) production and secretion
• GH/somatomedins require presence of thyroid hormone for activity

Question 6

What are the effects of thyroid on development ?

Answer 6

• Required for development of foetal and neonatal brain e.g. for mylinogenesis
• Required for normal CNS activity

Question 7

What effects does the thyroid hormone have on sympathetic action ?

Answer 7

Increases responsiveness to adrenaline and noradrenaline by increasing the no. of receptors

CV responsiveness also increases due to this effect (hence why B-blocker used in hyperthyroidism)

Question 8

Describe thyroid hormone regulation

Answer 8

1. TRH (thyroid releasing hormone) from hypothalamus released
2. Stimulates TSH release from anterior pituitary
3. TSH stimulates T3 and T4 release from thyroid
4. T3 and T4 exert negative feedback on release fo TRH and TSH

Question 9

Go over this

Answer 9