Thyroid

Question 1

What is the name of an enlarged thyroid gland?

Answer 1

Goiter.

Question 2

Describe the structure of the thyroid gland.

Answer 2

There are areas called colloid which are surrounded by simple cuboidal epithelial cells called follicular cells. The basolateral membrane is on the side outside of the colloid. The other membrane is the apical membrane.

Question 3

What is the function of the thyroid gland?

Answer 3

Its main function is to synthesise and secrete Thyroid Hormone.

Question 4

What precursor molecule is a major constituent of thyroid follicle?

Answer 4

Thyroglobulin.

Question 5

What can be said about the blood supply in the thyroid gland?

Answer 5

It is very large and comes from both inferior and superior thyroid arteries.

Question 6

What is the effect of the sympathetic nervous system on the thyroid gland?

Answer 6

This increases secretion of thyroid hormones.

Question 7

What is the effect of TRH on the pituitary gland?

Answer 7

TRH binds to receptors and this increases calcium which causes exocytosis of TSH.

Question 8

Where in the thyroid gland does TSH bind?

Answer 8

It binds to the basolateral membrane of the follicular cells.

Question 9

Name three things which activation of a TSH receptor leads to.

Answer 9

Iodine uptake, production of Idothyrines, promotion of thyroid growth.

Question 10

What does chronically high TSH lead to?

Answer 10

This stimulates thyroid growth and division of follicular cells leading to an enlarged gland.

Question 11

Where is iodine for thyroid hormone synthesis derived from?

Answer 11

The diet.

Question 12

What enzyme activates iodine so that it can combine with thyroglobulin?

Answer 12

Perioxidase enzyme.

Question 13

Where is thyroglobulin produced?

Answer 13

This is produced by ribosomes in the follicular cells. It is then transported through the Golgi where it is glycosylated and packaged into vesicles before it is stored in the colloid.

Question 14

What are thyroid hormones synthesised from?

Answer 14

Tyrosine residues on thyroglobulin.

Question 15

What two substances do thyroid hormones bind to for transport in the blood?

Answer 15

Thyronine binding globulin (TBG) and also to albumin or pre albumin.

Question 16

What is the effect of oestrogen in pregnancy on TBG?

Answer 16

Oestrogen increases synthesis of TBG which leads to less active T3 and T4 in circulation. Negative feedback allows these to increase and so overall there is more T3 T4 in circulation despite the fact that the same amount of the active form is present.

Question 17

What happens to T4 at peripheral tissues?

Answer 17

It undergoes deiodination which leads to T3. Thyroid hormones pass cell membranes, produce a response and are then broken down.

Question 18

Where are T3 and T4 deactivated?

Answer 18

In the liver and kidney due to removal of iodine.

Question 19

Why is T4 used to treat hypothyroidism?

Answer 19

This is more protected than T3 because it binds more tightly to TBG.

Question 20

What effects do thyroid hormones have on the body?

Answer 20

They increase the BMR by increasing mitochondria size and number which increases oxygen usage and heat production. There is also increased nutrient production. They also promote normal growth and tissue development.

Question 21

How do thyroid hormones affect the responsiveness of tissues?

Answer 21

Thyroid hormones make tissues more responsive to the sympathetic nervous system, and also other metabolic and reproductive hormones.

Question 22

Why do people with hypothyroidism have saggy skin?

Answer 22

Thyroid hormones stimulate turnover of proteins and glycoproteins in the skin.

Question 23

How does thyroid hormone affect the nervous system?

Answer 23

Thyroid hormone stimulates myelination of nerve fibres and neuron development. It also causes increase in reflex speed, and an increase in mental activity.

Question 24

What are the consequences of untreated hypothyroidism in newborns?

Answer 24

Mental retardation, delayed sexual development, coarse features and diminished linear growth.

Question 25

What are some of the symptoms of hyperthyroidism?

Answer 25

Heat intolerance leading to increased perspiration, weightloss, tachycardia (high pulse), increased bowel movements and appetite, nervousness and hyperreflexive (tremors)

Question 26

What is Graves’ disease?

Answer 26

This is an autoimmune disease where an antibody is produced which stimulates the TSH receptor on thyroid follicular cells.

Question 27

What is the action of carbimazole?

Answer 27

This inhibits incorporation of iodine with thyroglobulin. It thus reduces thyroid hormone levels.

Question 28

What are the treatment options for hyperthyroidism?

Answer 28

Radioactive iodine, carbimazole and surgical removal of thyroid gland.

Question 29

What is Hashimotos disease?

Answer 29

This is autoimmune destruction of thyroid follicles and production of an antibody which blocks TSH receptors on follicular cells.

Question 30

What is the treatment for hypothyroidism?

Answer 30

Oral T4. This is controlled until all symptoms of hypothyroidism disappear and there are no symptoms of hyperthyroidism.

Question 31

State some of the symptoms of hypothyroidism.

Answer 31

Fell cold, weight gain, low pulse, constipation, poor concentration, mood swings, dry skin, brittle nails and hair loss.

Question 32

What is the embryonic origin of the thyroid gland?

Answer 32

The thyroid gland is initially found positioned at the back of the tongue and rarely it can remain here. Usually it is under active due to poor vascular supply. Ovarian tumours can also be a source of thyroid tissue.

Question 33

In what condition can a goiter be present?

Answer 33

Hypothyroidism

Question 34

Where is the thyroid gland found?

Answer 34

The thyroid gland is a butterfly shaped gland in the neck.