Thyroid Physiology

Question 1

Which hormones does the thyroid gland secrete?

Answer 1

Triiodothronine (T3)
L-thyroxine (T4)
Calcitonin

Question 2

Which hormone does the parathyroid gland secrete?

Answer 2

Parathyroid hormone

Question 3

What is the name of the basic functional unit of the thyroid gland?

Answer 3

Follicle

Question 4

Which cells produce calcitonin?

Answer 4

Parafollicular cells

Question 5

How does the majority of T3 and T4 exist in the blood?

Answer 5

It is bound to hormone-binding proteins.

Question 6

What is the function of free thyroid hormones?

Answer 6

It is available for action at target tissues

Question 7

What is the negative feedback system in place in the thyroid?

Answer 7

1. The HYPOTHALAMUS secretes TRH.
2. This causes the PITUITARY to secrete TSH.
3. This causes the THYROID to secrete T4 and T3.
4. T3 and T4 have a negative feedback mechanism

Question 8

What happens to T4 in the peripheral tissues?

Answer 8

It is converted to T3

Question 9

What are the 6 steps to thyroid hormone synthesis?

Answer 9

1. Thyroglobulin synthesis
2. Uptake and concentration of Iodine I-
3. Oxidation of I- to Iodine
4. Iodination of thyroglobulin
5. Formation of MIT and DIT
6. Secretions

Question 10

Where is T3 and T4 stored?

Answer 10

Colloid thyroglobulin

Question 11

What is combined to form T3?

Answer 11

One monoiodotyrosine and one diiodotyrosine

MIT + DIT

Question 12

What is combined to form T4?

Answer 12

2 Diiodotyrosine

2 DITs

Question 13

Which thyroid hormone is the most potent?

Answer 13

T3 is 4 times more potent than T4

Question 14

What is the major biologically active thyroid hormone?

Answer 14

T3

Question 15

What should we measure in order to determine thyroid function?

Answer 15

free T3 and T4

Question 16

Which states increase the number of thyroid binding globulins?

Answer 16

Pregnancy
New Born
Hepatitis A
Biliary Cirrhosis
Genetically Determined

Question 17

Which states decrease the number of thyroid binding globulins?

Answer 17

Androgens
Severe systemic illness
Chronic liver disease
Genetically determined

Question 18

What are the effects of the thyroid hormones?

Answer 18

They have the overall effect of increasing the basal metabolic rate.
Increase net glucose release
Increase lipolysis
Decrease fat formation
Increase heart rate
Increase heart contractility
Increase breathing
Increase protein synthesis

Question 19

How do the thyroid hormones increase the BMR within the cells?

Answer 19

Increase the number and size of mitochondria
Increase O2 use and rates of ATP hydrolysis
Increase synthesis of respiratory chain enzymes

Question 20

What are the effects of thyroid hormone on growth and development?

Answer 20

Growth hormone releasing hormone production and secretion requires thyroid hormones

Question 21

What is the sympathetic action of thyroid hormones?

Answer 21

They increase responsiveness to adrenaline and noradrenaline by increasing the numbers of receptors

Question 22

Why can beta blockers be used to treat the initial symptoms of hyperthyroidism?

Answer 22

Because of its nervous action

Question 23

Where are the three types of de-iodinases located?

Answer 23

Type 1 - commonly found in the liver and kidney
Type 2 - found in the heart, skeletal muscle, CNS, fat, thyroid, and pituitary
Type 3 - found in foetal tissue, placenta and brain

Question 24

How are thyroid hormones degraded?

Answer 24

Inactivation of thyroid hormones occurs by removal of an iodine atom on the inner ring, which converts thyroxine to the inactive reverse triiodothyronine (rT3), or which converts the active triiodothyronine to diiodothyronine (T2).

Question 25

What is the difference between thyroid disease and thyroid syndrome?

Answer 25

In thyroid syndrome there is excess cortisol in secretion but no underlying pituitary abnormalities