Thyroid - Pathology

Question 1

The thyroid gland develops from an invagination of what?

Answer 1

Pharyngeal epithelium

Question 2

Where does the thyroid gland descend to and from?

Answer 2

From the foramen caecum of the tongue to the thyroglossal duct

Question 3

What is known as when the thyroid gland fails to descend normally?

Answer 3

Lingual thyroid

Question 4

If there is excessive descent of the thyroid, where does it end up?

Answer 4

Retrosternal in the mediastinum

Question 5

What is the thyroid gland composed of?

Answer 5

Follicles

Question 6

What cell type are the thyroid follicles surrounded by?

Answer 6

Cuboidal follicular epithelial cells

Question 7

What is the area in the centre of each thyroid follicle known as?

Answer 7

Colloid

Question 8

What does the thyroid colloid contain? What is this?

Answer 8

Thyroglobulin- this is the protein on which T3 and T4 are synthesised

Question 9

What other cell type are found scattered among the thyroid follicles in the upper 2/3rds of the thyroid gland?

Answer 9

C-cells (parafollicular cells)

Question 10

What do C-cells produce?

Answer 10

Calcitonin

Question 11

What does calcitonin do?

Answer 11

Decrease serum calcium levels

Question 12

Calcitonin is a good marker for what?

Answer 12

Medullary thyroid cancer

Question 13

What three things does thyroid gland tissue secrete?

Answer 13

T3, T4 and calcitonin

Question 14

What is required for the synthesis of thyroid hormones?

Answer 14

Iodine

Question 15

What will happen if you live in an area where there is not enough iodine?

Answer 15

You won’t make enough thyroid hormones and hence will be hypothyroid

Question 16

What is the difference, chemically, between T3 and T4?

Answer 16

1 iodine

Question 17

Iodine is taken up by which cells?

Answer 17

Follicular cells

Question 18

What does iodine attach to once it has been taken up? What does this form?

Answer 18

Iodine attaches to tyrosine units on thyroglobulin to form MIT and DIT units

Question 19

How do carbimazole and PTU work?

Answer 19

They prevent iodination of tyrosine

Question 20

What units need to be combined to form T3?

Answer 20

1 MIT and 1 DIT

Question 21

What units need to be combined to form T4?

Answer 21

2 DITs

Question 22

What happens to T3 and T4 molecules once they have been synthesised?

Answer 22

They are stored in colloid thyroglobulin until they are required

Question 23

Which is the major biologically active thyroid hormone?

Answer 23

T3

Question 24

Which thyroid hormone is produced in greater amounts?

Answer 24

T4

Question 25

What happens to the majority of T4 produced?

Answer 25

It is converted to T3 in peripheral tissues

Question 26

What chemical process changes T4 to T3?

Answer 26

5-monodeiodination (removal of 1 iodine)

Question 27

What does 3-monodeiodination of T4 form?

Answer 27

rT3

Question 28

Which family of enzymes regulates the conversion of T4 to T3?

Answer 28

Deiodinase enzymes

Question 29

Where is deiodinase 1 found?

Answer 29

Liver and kidney

Question 30

Which deiosinase enzyme is the major determinant of generating T3 from T4?

Answer 30

D2

Question 31

Where is deiodinase 3 found?

Answer 31

Foetal tissue ad brain (except the pituitary gland)

Question 32

What is the first step in releasing thyroid hormones?

Answer 32

TSH binds to its receptor on the surface of thyroid epithelial cells

Question 33

What type of receptor is the TSH receptor?

Answer 33

GPCR

Question 34

What happens when TSH has bound to its receptor?

Answer 34

GTP is converted to GDP and cAMP is produced

Question 35

What allows T3 and T4 to be released from cells?

Answer 35

Increased cAMP

Question 36

Where is most T3 and T4 found in the plasma? Why?

Answer 36

Bound to hormone binding proteins, since they are hydrophobic and lipophilic

Question 37

What hormone binding protein is most of T3 and T4 bound to in the plasma?

Answer 37

Thyroxine binding globulin

Question 38

What are the less used hormone binding proteins?

Answer 38

Thyroid-binding pre-albumin Albumin

Question 39

Which thyroid hormone is bound less avidly to TBG?

Answer 39

T3

Question 40

What type of T3 and T4 should be measured in a thyroid function test?

Answer 40

Free

Question 41

What type of receptor is the T3 receptor?

Answer 41

Nuclear

Question 42

How are thyroid hormones taken into cells?

Answer 42

A transmembrane transporter

Question 43

What is the thyroid hormone receptor bound to?

Answer 43

Thyroid response element

Question 44

Where are TRalpha thyroid receptors found?

Answer 44

Peripheral tissues

Question 45

Where are TRbeta thyroid receptors found?

Answer 45

In the feedback loop

Question 46

Resistance to which type of thyroid receptor causes the biggest problem?

Answer 46

TRbeta

Question 47

What effect do thyroid hormones have on the basal metabolic rate?

Answer 47

Increase it

Question 48

What are 3 ways that thyroid hormones increase basal metabolic rate?

Answer 48

- Increase the number of mitochondria - Increase oxygen use and rate of ATP hydrolysis - Increase synthesis of respiratory chain enzymes

Question 49

What effect do thyroid hormones have on thermogenesis?

Answer 49

Increase it

Question 50

Name two effects that thyroid hormones have on carbohydrate metabolism?

Answer 50

- Increase plasma glucose due to stimulation of glycogenolysis and gluconeogenesis - Increase insulin dependent glucose uptake into cells

Question 51

Name two effects that thyroid hormones have on lipid metabolism?

Answer 51

- Mobilise fats from adipose tissue - Increase fatty acid oxidation in tissues

Question 52

What two effects do thyroid hormones have on protein metabolism?

Answer 52

- Increased protein synthesis - Decreased plasma amino acids

Question 53

What hormones relating to growth require thyroid hormones for their action?

Answer 53

GHRH and GH

Question 54

How do thyroid hormones help to develop the foetal and neonatal brain?

Answer 54

They allow myelinogenesis and axonal growth

Question 55

What can inadequately treated hypothyroidism in pregnancy cause?

Answer 55

Problems with cognitive development

Question 56

What effect do thyroid hormones have on the sympathetic nervous system? What effect does this have on the CV system?

Answer 56

They increase responsiveness to adrenaline and noradrenaline by increasing the number of receptors. This increases cardiac rate and force of contraction.

Question 57

What effect do low temperatures have on thyroid function in babies and young children?

Answer 57

Stimulate TRH release, hence TSH release, hence T3/4 release

Question 58

What effect does stress have on thyroid function?

Answer 58

Inhibits TRH and TSH release

Question 59

Describe the circadian rhythm of thyroid hormones?

Answer 59

Thyroid hormone levels are high at night and low in the morning