7 - General thyroid disorders

Question 1

Where is the thyroid located and what shape is it?

Answer 1

located in the neck and shield-shaped

Question 2

What are the lobes of the thyroid?

Answer 2

left and right lobe and an isthmus (and some people have a pyramidal lobe - which is a part oft he extension from the back of the tongue from which the thyroid originated)

Question 3

Where are the parathyroid glands found?

Answer 3

at the four corners of the thyroid

Question 4

What are the parathyroid glands involved in?

Answer 4

the control of calcium (but functionally, they have nothing to do with the thyroid)

Question 5

What is the origin of the thyroid?

Answer 5

back of the tongue

Question 6

What is the foramen caecum?

Answer 6

simple at the back of the tongue (left by the disappearing thyroglossal duct)

Question 7

What is the average thyroid weight?

Answer 7

20g

Question 8

What important neve runs close thyroid gland and what does it supply?

Answer 8

recurrent laryngeal nerve

it innervates the larynx (voice box), allowing speech

Question 9

What is the origin of the thyroid gland?

Answer 9

• midline outpouching of the floor of the pharynx (tube with no function that connects the tongue and the thyroid)
• the outpouching form a duct which elongates down: THE THYROGLOSSAL DUCT
• it migrates down the neck and splits into 2
• by week 7, it is in its final position
• the thryoglosaal duct disappears (leaving a dimple at the back of the tongue)

Question 10

What does aberrant mean?

Answer 10

in the wrong place

Question 11

What is a lingual thyroid?

Answer 11

where the thyroid tissue barely descends and can cause problems with breathing

Question 12

Where os thyroxine produced and what is it essential for?

Answer 12

in thy thyroid

essential for normal brain development

Question 13

What is usually the cause of cretinism?

Answer 13

low iodine levels

Question 14

What cells are the site of thyroxine synthesis?

Answer 14

thyroid follicular cells

Question 15

What is the effect of thyroxine?

Answer 15

affects the basal metabolic weight (affects every cell)

Question 16

What is the difference between thyroglobulin and thyroxine binding globulin?

Answer 16

Thyroglobulin - not in the circulation
TBG - in the circulation

Thyroglobulin - stores thyroxine
TBG - binds to thyroxine

Question 17

What do thyroid hormones do?

Answer 17

regulate growth, development and basal metabolic rate (general)

Question 18

What is myxoedema?

Answer 18

primary hypothyroidism/ primary thyroid failure

Question 19

What is the most common causes of myxoedema?

Answer 19

autoimmune damage to the thyroid

thyroidectomy (since thyroid tissue is removed)

Question 20

What happens to the hormones levels in myxoedema?

Answer 20

• Thyroxine levels decrease
• TSH levels rise (to try and stimulate the production of more thyroxine)
• Eventually, TSH levels will fall because It becomes exhausted
• TRH levels will also increase, but only TSH is measured because TRH is undetectable in the blood

Question 21

What is the negative feedback mechanism for of thyroxine on the pituitary and the hypothalamus?

Answer 21

• direct negative feedback effect on the pituitary to inhibit production of more TSH
• also affects the hypothalamus, where it inhibits the production of TRH (thyrotrophs)

Question 22

What is hyperthyroidism (thyrotoxicosis)?

What happens to the levels of hormones?

Answer 22

overactive thyroid gland

over production of of thyroxine
TSH falls to zero

Question 23

What is pretibial myxoedema?

What is it caused by?

Answer 23

(non pitting oedema) swelling on the shins pf patients with graves disease
caused by the growth of soft tissue

Question 24

What is the different between myxoedema and pretibial myxoedema?

Answer 24

myxoedema - primary hypothyroidism

pretibial myxoedema - a feature of graves disease, which causes hyperthyroidism