4. *Hypothyroid disorders

Question 1

What causes thyroxine to be produced from the thyroid gland?

Answer 1

TSH from pituitary gland (adenohypophysis) causes thyroxine to be produced from the thyroid

Question 2

What would happen if T4 production increased?

Answer 2

TSH levels would fall as a result of negative feedback

Question 3

Which form of thyroid hormone is active?

Answer 3

T3

Question 4

Why do you feel tired when your thyroid hormones fall?

Answer 4

T3 controls basal metabolic rate

Your metabolic rate would decrease if T3 fell and less energy would be available for the body

Question 5

Outline the structure of a thyroid follicle

Answer 5

Has a colloid in the middle and cells around the edge.

Question 6

What is found in thyroid follicles?

Answer 6

Thyroglobulin

Question 7

Outline the production of thyroxine in the thyroid follicles

Answer 7

• Pituitary gland makes TSH
  
  • TSH causes the trapping of iodide. Iodide goes into the cell where it is converted into iodine
  • Iodine binds to the amino acid tyrosine which is converted to monoiodotyrosine and then thyroxine. The follicles store the thyroxine. When thyroxine is needed TSH turns on an enzyme which causes the release of the thyroxine and metabolic effects can be caused.

Question 8

What would white bits in the colloid indicate on a histology?

Answer 8

Stored thyroxine has been released into the blood stream

Question 9

What form of thyroxine is secreted by the thyroid gland?

Answer 9

Both T3 (triiodothyronine) and T4 (tetraiodothyronine)

Question 10

How is T4 converted into T3?

Answer 10

T4 is converted to T3 bydeiodinase

Question 11

What are the two ways that T3 is produced by the body?

Answer 11

80% - deiodination of T4
20% - direct thyroidal secretion
T3 providesalmost allthe thyroid hormone activity in the target cells

Question 12

What is primary hypothyroidism?

Answer 12

Also known as myxoedema

It is when the immune system destroys the thyroid gland

Question 13

How would you test primary hypopituitarism? What would the results be if the test was positive?

Answer 13

Carry out a thyroid function test
If there is primary hypopituitarism then levels of T3/T4 would be very low and TSH would be high to try and stimulate the thyroid to produce more T4

Question 14

What are the symptoms of primary hypopituitarism?

Answer 14

○ Tongue gets thick 
	○ Speech slows down
	○ Deepening of the voice 
	○ BMR falls 
	○ Bradycardia 
	○ General weakness 
	○ Depression
	○ Cold intolerance 
	○ Weight gain and reduced appetite 
	○ Constipation 
	○ Confusion as brain metabolic rate has also slowed down and eventual myxoedema coma