Thyroid Hormone Function

Question 1

What are thyroid follicles?

Answer 1

Structural units of the thyroid gland made up of follicular cells creating a ring

Question 2

What are colloids?

Answer 2

A glycoprotein in the centre of the thyroid follicles

Question 3

What are follicular cells?

Answer 3

The cells which secrete thyroid hormone and form the ring of thyroid follicles

Question 4

What are thyroid hormones?

Answer 4

Iodine containing hormones derived from two tyrosine amino acids linked with iodine

Question 5

What are the three types of thyroid hormones produced?

Answer 5

T3, T4 and rT3

Question 6

What does T4 stand for?

Answer 6

Thyroxine

Question 7

What is thyroxine (T4)?

Answer 7

The precursor hormone that follicular cells produce

Question 8

What happens to thyroxine (T4)?

Answer 8

It is converted to triiodothyronine (T3) or rT3

Question 9

What is triiodothryonine?

Answer 9

The biologically active thyroid hormone

Question 10

What is the more uncommon way of synthesising T3?

Answer 10

DIT+MIT

Question 11

What is the more common way of synthesising T3?

Answer 11

DIT+DIT which form T4 which is then converted into T3 or rT3

Question 12

What is rT3?

Answer 12

It is an isomer of T3 which is not very common and is unhelpful

Question 13

What is the steps for the synthesis of thyroid hormones?

Answer 13

• Follicular cells produce enzymes and thyroglobulin for colloid
• I- is co-transported with Na+ into the colloid
• Enzymes add iodine to thyroglobulin to make T3 and T4
• Thyroglobulin is taken back into the cell and enzymes seperate T3 and T4 from protein
• Free T3 and T4 enter the circulation

Question 14

What type of T3 and T4 are biologically active?

Answer 14

Free or unbound T3 and T4

Question 15

How do T3 cells act?

Answer 15

By binding to thyroid receptors that regulate expression of thyroid responsive genes

Question 16

What do thyroid hormones do?

Answer 16

• Increase mitochondrial activity and glucose oxidation
• Increase basal metabolic rate and heat production

Question 17

What three thing stimulate thyroid hormone production?

Answer 17

• Low levels of thyroid hormones
• Low metabolic rate
• Decreased body temp

Question 18

What is hyperthyroidism?

Answer 18

Too much thyroid hormones secreted

Question 19

What is the most common disease associated to hyperthyroidism?

Answer 19

Grave’s disease

Question 20

What causes Grave’s disease?

Answer 20

When the body produces thyroid stimulating immunoglobins which mimic the action of TSH resulting in too much T3 and T4

Question 21

What are signs and symptoms of Grave’s disease?

Answer 21

• Muscle weakness
• Muscle tremor
• Rapid heartbeat
• Enlarged thyroid gland

Question 22

What is primary hypothyroidism?

Answer 22

When the thyroid gland does not make enough thyroid hormones due to iodine deficiency

Question 23

What is secondary hypothyroidism?

Answer 23

When the body does not produce enough TSH due to a tumour of the anterior pituitary

Question 24

What is tertiary hypothyroidism?

Answer 24

When the hypothalamus does not make enough TRH

Question 25

What are the signs and symptoms of hypothyroidism?

Answer 25

- Slow oxygen consumption - Slow speech - Slow heartbeat

Question 26

What is the most common disease associated with hypothyroidism?

Answer 26

Goiter