Thyroid Function in Health and Disease Flashcards Preview

MD1 Endocrine > Thyroid Function in Health and Disease > Flashcards

Flashcards in Thyroid Function in Health and Disease Deck (59):
1

What are the functions of the thyroid gland?

Secrete thyroid hormones > regulate metabolism
Secrete calcitonin > regulate Ca levels

2

What is the structure of the thyroid gland?

2 lobes joined by isthmus

3

What is the location of the thyroid gland?

Below larynx
Above trachea
Anterior in neck

4

What cells surround the colloid?

Follicular cells/thyrocytes

5

Where is thyroglobulin located?

In colloid

6

Where are the C cells?

In interstitial spaces

7

What is the function of C cells?

Secrete calcitonin

8

How are thyroid hormones synthesised?

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

9

What is the role of thyroglobulin?

Stops iodine from diffusing out

10

Where do we get our iodine from?

Diet

11

What are the uses of iodine in the body?

Thyroid hormone synthesis

12

What are the structural components of thyroid hormone?

Iodine
Tyrosine derivative

13

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

T3 = 10%
T4 = 90%

14

How much T3 is derived from T4?

80%

15

Why are thyroid hormones bound to plasma proteins?

Because lipophilic

16

Where is thyroid stimulating hormone (TSH) released from?

Anterior pituitary

17

What does TSH do?

Stimulates all steps in thyroid hormone synthesis

18

Where is thyroid releasing hormone (TRH) released from?

Hypothalamus

19

What increases levels of TRH secretion?

Cold in infants only known factor

20

What decreases levels of TRH secretion?

Stress

21

What is the half-life of T4?

6-7 days

22

What is the half-life of T3?

1 day

23

What are the factors affecting release of thyroid hormones?

Tonic release

24

What are the target tissues of thyroid hormones?

Most cells of body

25

What are the actions of thyroid hormones?

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

26

Is thyroid hormone essential for life?

No, but essential for child growth and development

27

How does thyroid hormone promote growth?

Foetal life
After birth, essential for GH and IGFs actions

28

When is thyroid hormone needed for nervous system development?

Before and after birth

29

When does goitre occur?

In both hypothyroidism and hyperthyroidism

30

What is primary hypothyroidism?

Thyroid failure
Decreased T3 and T4
Increased TSH

31

Do you get a goitre in primary hypothyroidism?

Yes, because of trophic effect of increased TSH

32

What happens when you have low dietary iodine?

Decreased T3 and T4
Increased TSH

33

Do you get a goitre in dietary iodine deficiency?

Yes, because of trophic effect of increased TSH

34

What causes secondary hypothyroidism?

Hypothalamic/anterior pituitary failure/tumour

35

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

Decreased T3 and T4
Decreased TSH
Decreased TRH

36

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

Decreased T3 and T4
Decreased TSH
Increased TRH

37

Do you get a goitre with secondary hypothyroidism?

No, because no trophic effect of TSH

38

What causes cretinism?

Congenital deficiency of thyroid hormones

39

What is the most common endocrine illness?

Hypothyroidism

40

Who has hypothyroidism more: females or males?

Females

41

What is the most common cause of hypothyroidism?

Iodine deficiency

42

What are some causes of congenital hypothyroidism?

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

43

How can congenital hypothyroidism be prevented?

Adequate iodine in diet during pregnancy

44

Are newborns tested for thyroid deficiency?

Yes

45

What are the physiological effects of hypothyroidism?

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

46

What is the treatment for hypothyroidism?

Replace thyroid hormone
Adequate dietary iodine

47

What are hormone levels in primary hyperthyroidism?

Increased T3 and T4
Decreased TSH
Decreased TRH

48

Do you have a goitre with primary hyperthyroidism?

Yes

49

What is Graves disease?

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

50

Why do you get a goitre in Graves disease?

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

51

What is the epidemiology of Graves disease?

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

52

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

Increased T3 and T4
Increased TSH
Increased TRH

53

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

Increased T3 and T4
Increased TSH
Decreased TRH

54

Do you get a goitre in secondary hyperthyroidism?

Yes, because of trophic effect of TSH

55

What are hormone levels in a hypersecreting tumour?

Increased T3 and T4
Decreased TSH

56

Do you get a goitre with a hypersecreting tumour?

No

57

What are the physiological effects of hyperthyroidism?

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

58

What is Graves disease exophthalmos?

Bulging eyes because of water retaining carbohydrates behind eyes

59

What is the treatment for hypothyroidism?

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