Thyroid Function

Question 1

Where is the thyroid gland located?

Answer 1

Lower anterior neck, in front of the trachea

Question 2

What shape is the thyroid gland?

Answer 2

Butterfly-shaped

Question 3

What structures make up the thyroid gland?

Answer 3

Two lobes connected by an isthmus

Question 4

What are thyroid follicles?

Answer 4

Structural and functional units of the thyroid

Question 5

What fills the center of thyroid follicles?

Answer 5

Colloid

Question 6

What is the main component of colloid?

Answer 6

Thyroglobulin

Question 7

What cells produce thyroid hormones?

Answer 7

Follicular cells

Question 8

What cells produce calcitonin?

Answer 8

Parafollicular (C) cells

Question 9

Where do parathyroid glands lie?

Answer 9

Posterior to the thyroid

Question 10

When does the fetal thyroid begin hormone production?

Answer 10

Around week 11 of gestation

Question 11

What are the two main thyroid hormones?

Answer 11

T3 and T4

Question 12

What does T3 stand for?

Answer 12

Triiodothyronine

Question 13

What does T4 stand for?

Answer 13

Thyroxine (tetraiodothyronine)

Question 14

Which hormone is biologically active?

Answer 14

T3

Question 15

Which hormone is produced in greater quantity?

Answer 15

T4

Question 16

What is the approximate T4:T3 ratio?

Answer 16

20:1

Question 17

How long is T4’s half-life?

Answer 17

About 1 week

Question 18

How long is T3’s half-life?

Answer 18

About 1 day

Question 19

What two elements are required for thyroid hormone synthesis?

Answer 19

Iodine and tyrosine

Question 20

Where does iodine come from?

Answer 20

Diet

Question 21

What enzyme is essential for hormone synthesis?

Answer 21

Thyroid peroxidase (TPO)

Question 22

What are MIT and DIT?

Answer 22

Iodinated tyrosine residues

Question 23

MIT + DIT produces what hormone?

Answer 23

T3

Question 24

DIT + DIT produces what hormone?

Answer 24

T4

Question 25

Where are thyroid hormones stored?

Answer 25

In colloid bound to thyroglobulin

Question 26

Where does most T3 come from?

Answer 26

Peripheral deiodination of T4 (liver)

Question 27

Are most thyroid hormones free or bound?

Answer 27

Bound

Question 28

Name the main binding proteins.

Answer 28

TBG, prealbumin, albumin

Question 29

Are protein-bound hormones biologically active?

Answer 29

no

Question 30

Which hormone form is measured for activity?

Answer 30

Free T3 and Free T4

Question 31

What hormone does the hypothalamus release?

Answer 31

TRH

Question 32

What hormone does the anterior pituitary release?

Answer 32

TSH

Question 33

What does TSH stimulate?

Answer 33

Thyroid hormone production and release

Question 34

What feedback mechanism regulates thyroid hormones?

Answer 34

Negative feedback

Question 35

High T3/T4 causes what change in TSH?

Answer 35

Decrease

Question 36

Low T3/T4 causes what change in TSH?

Answer 36

Increase

Question 37

What major process do thyroid hormones increase?

Answer 37

Basal metabolic rate

Question 38

How do thyroid hormones affect cholesterol?

Answer 38

Inversely related

Question 39

What happens to cholesterol in hypothyroidism?

Answer 39

Increased

Question 40

How do thyroid hormones affect the heart?

Answer 40

Increase heart rate and contractility

Question 41

What system is affected during development?

Answer 41

Central nervous system

Question 42

Best screening test for thyroid disease?

Answer 42

TSH

Question 43

What does high TSH usually indicate?

Answer 43

Hypothyroidism

Question 44

What does low TSH usually indicate?

Answer 44

Hyperthyroidism

Question 45

What does total T4 measure?

Answer 45

Bound + free T4

Question 46

Why is free T4 preferred over total T4?

Answer 46

Not affected by binding proteins

Question 47

What is reverse T3?

Answer 47

Inactive form of T3

Question 48

TPO antibodies are associated with what disease?

Answer 48

Hashimoto’s thyroiditis

Question 49

TSH receptor antibodies indicate what disease?

Answer 49

Graves’ disease

Question 50

What antibody is used to confirm autoimmune hyperthyroidism?

Answer 50

TSI / TRAb

Question 51

What is thyroglobulin used for clinically?

Answer 51

Tumor marker for thyroid cancer

Question 52

Most common cause of hypothyroidism in the US?

Answer 52

Hashimoto’s disease

Question 53

Typical lab pattern in primary hypothyroidism?

Answer 53

↑ TSH, ↓ FT4

Question 54

Common symptoms of hypothyroidism?

Answer 54

Fatigue, cold intolerance, weight gain

Question 55

Standard treatment for hypothyroidism?

Answer 55

Levothyroxine (T4)

Question 56

What is thyrotoxicosis?

Answer 56

Excess thyroid hormone effect on tissues

Question 57

Most common cause of hyperthyroidism?

Answer 57

Graves’ disease

Question 58

Graves’ disease is caused by what mechanism?

Answer 58

TSH receptor–stimulating antibodies

Question 59

Lab pattern in hyperthyroidism?

Answer 59

↓ TSH, ↑ FT4/T3

Question 60

What eye finding is associated with Graves’?

Answer 60

Ophthalmopathy

Question 61

What is a toxic adenoma?

Answer 61

Single autonomously functioning nodule

Question 62

What is toxic multinodular goiter?

Answer 62

Multiple autonomous nodules

Question 63

How do toxic nodules appear on thyroid scan?

Answer 63

“Hot” nodules

Question 64

What does radioactive iodine uptake measure?

Answer 64

Thyroid metabolic activity

Question 65

High RAIU suggests what?

Answer 65

Graves’ or toxic nodules

Question 66

Low RAIU suggests what?

Answer 66

Thyroiditis or exogenous hormone

Question 67

Best test to evaluate thyroid nodules?

Answer 67

Fine-needle aspiration (FNA)

Question 68

Primary hypothyroidism originates where?

Answer 68

Thyroid gland

Question 69

Secondary hypothyroidism originates where?

Answer 69

Pituitary gland

Question 70

Primary hyperthyroidism lab pattern?

Answer 70

↓ TSH, ↑ FT4/T3

Question 71

Secondary hyperthyroidism lab pattern?

Answer 71

Normal or ↑ TSH with ↑ FT4/T3