Thyroid Function in Health and Disease

Question 1

What are the functions of the thyroid gland?

Answer 1

Secrete thyroid hormones > regulate metabolism

Secrete calcitonin > regulate Ca levels

Question 2

What is the structure of the thyroid gland?

Answer 2

2 lobes joined by isthmus

Question 3

What is the location of the thyroid gland?

Answer 3

Below larynx
Above trachea
Anterior in neck

Question 4

What cells surround the colloid?

Answer 4

Follicular cells/thyrocytes

Question 5

Where is thyroglobulin located?

Answer 5

In colloid

Question 6

Where are the C cells?

Answer 6

In interstitial spaces

Question 7

What is the function of C cells?

Answer 7

Secrete calcitonin

Question 8

How are thyroid hormones synthesised?

Answer 8

1. Follicular cell synthesises enzymes and thyroglobulin for colloid
2. Na/I symporter brings iodide into cell > pendrin transporter moves iodide into colloid
3. Enzymes add iodine to tyrosine > make T3 and T4
4. Thyroglobulin taken back into cell in vesicles
5. Intracellular enzymes separate T3 and T4 from protein
6. Free T3 and T4 enter circulation

Question 9

What is the role of thyroglobulin?

Answer 9

Stops iodine from diffusing out

Question 10

Where do we get our iodine from?

Answer 10

Diet

Question 11

What are the uses of iodine in the body?

Answer 11

Thyroid hormone synthesis

Question 12

What are the structural components of thyroid hormone?

Answer 12

Iodine

Tyrosine derivative

Question 13

What are the proportions of T3 and T4 made by the thyroid gland?

Answer 13

T3 = 10%
T4 = 90%

Question 14

How much T3 is derived from T4?

Answer 14

80%

Question 15

Why are thyroid hormones bound to plasma proteins?

Answer 15

Because lipophilic

Question 16

Where is thyroid stimulating hormone (TSH) released from?

Answer 16

Anterior pituitary

Question 17

What does TSH do?

Answer 17

Stimulates all steps in thyroid hormone synthesis

Question 18

Where is thyroid releasing hormone (TRH) released from?

Answer 18

Hypothalamus

Question 19

What increases levels of TRH secretion?

Answer 19

Cold in infants only known factor

Question 20

What decreases levels of TRH secretion?

Answer 20

Stress

Question 21

What is the half-life of T4?

Answer 21

6-7 days

Question 22

What is the half-life of T3?

Answer 22

1 day

Question 23

What are the factors affecting release of thyroid hormones?

Answer 23

Tonic release

Question 24

What are the target tissues of thyroid hormones?

Answer 24

Most cells of body

Question 25

What are the actions of thyroid hormones?

Answer 25

``` Increase basal metabolic rate and oxygen consumption Modulate metabolism Sympathomimetic effect - Increases HR - Increases CO ```

Question 26

Is thyroid hormone essential for life?

Answer 26

No, but essential for child growth and development

Question 27

How does thyroid hormone promote growth?

Answer 27

Foetal life | After birth, essential for GH and IGFs actions

Question 28

When is thyroid hormone needed for nervous system development?

Answer 28

Before and after birth

Question 29

When does goitre occur?

Answer 29

In both hypothyroidism and hyperthyroidism

Question 30

What is primary hypothyroidism?

Answer 30

Thyroid failure Decreased T3 and T4 Increased TSH

Question 31

Do you get a goitre in primary hypothyroidism?

Answer 31

Yes, because of trophic effect of increased TSH

Question 32

What happens when you have low dietary iodine?

Answer 32

Decreased T3 and T4 | Increased TSH

Question 33

Do you get a goitre in dietary iodine deficiency?

Answer 33

Yes, because of trophic effect of increased TSH

Question 34

What causes secondary hypothyroidism?

Answer 34

Hypothalamic/anterior pituitary failure/tumour

Question 35

What are hormone levels with secondary hypothyroidism when it's a hypothalamic cause?

Answer 35

Decreased T3 and T4 Decreased TSH Decreased TRH

Question 36

What are hormone levels with secondary hypothyroidism when it's an anterior pituitary cause?

Answer 36

Decreased T3 and T4 Decreased TSH Increased TRH

Question 37

Do you get a goitre with secondary hypothyroidism?

Answer 37

No, because no trophic effect of TSH

Question 38

What causes cretinism?

Answer 38

Congenital deficiency of thyroid hormones

Question 39

What is the most common endocrine illness?

Answer 39

Hypothyroidism

Question 40

Who has hypothyroidism more: females or males?

Answer 40

Females

Question 41

What is the most common cause of hypothyroidism?

Answer 41

Iodine deficiency

Question 42

What are some causes of congenital hypothyroidism?

Answer 42

Maternal iodine deficiency Foetal thyroid dysgenesis Inborn errors of thyroid hormone synthesis Maternal antithyroid Abs > cross placenta Foetal hypopituitary hypothyroidism

Question 43

How can congenital hypothyroidism be prevented?

Answer 43

Adequate iodine in diet during pregnancy

Question 44

Are newborns tested for thyroid deficiency?

Answer 44

Yes

Question 45

What are the physiological effects of hypothyroidism?

Answer 45

Decreased basal metabolic rate and oxygen consumption Decreased energy Increased weight Cold intolerance Decreased HR Decreased mentation, reflexes, and fatigue Decreased protein synthesis > accumulate mucopolysaccharides under skin = puffy appearance of myxedema

Question 46

What is the treatment for hypothyroidism?

Answer 46

Replace thyroid hormone | Adequate dietary iodine

Question 47

What are hormone levels in primary hyperthyroidism?

Answer 47

Increased T3 and T4 Decreased TSH Decreased TRH

Question 48

Do you have a goitre with primary hyperthyroidism?

Answer 48

Yes

Question 49

What is Graves disease?

Answer 49

Autoimmune hyperthyroidism Thyroid-stimulating Ig - Targets TSH receptors - Acts as TSH

Question 50

Why do you get a goitre in Graves disease?

Answer 50

AutoAbs acting as TSH by stimulating TSH receptor drive gland to enlarge

Question 51

What is the epidemiology of Graves disease?

Answer 51

60-80% of all cases of hyperthyroidism | More common in women

Question 52

What are the hormone levels in secondary hyperthyroidism, when it's caused by a hypothalamus excess?

Answer 52

Increased T3 and T4 Increased TSH Increased TRH

Question 53

What are the hormone levels in secondary hyperthyroidism, when it's caused by an anterior pituitary excess?

Answer 53

Increased T3 and T4 Increased TSH Decreased TRH

Question 54

Do you get a goitre in secondary hyperthyroidism?

Answer 54

Yes, because of trophic effect of TSH

Question 55

What are hormone levels in a hypersecreting tumour?

Answer 55

Increased T3 and T4 | Decreased TSH

Question 56

Do you get a goitre with a hypersecreting tumour?

Answer 56

No

Question 57

What are the physiological effects of hyperthyroidism?

Answer 57

``` Increased - Basal metabolic rate - Oxygen consumption - Appetite - Weight loss - Muscle weakness - HR - Alertness Heat intolerance Irritability Hyperexcitability ```

Question 58

What is Graves disease exophthalmos?

Answer 58

Bulging eyes because of water retaining carbohydrates behind eyes

Question 59

What is the treatment for hypothyroidism?

Answer 59

``` Remove thyroid/tumour Use radioactive iodine > destroy gland Antithyroid drugs - Block thyroid hormone synthesis - Block conversion of T4 to T3 ```