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MD1 Endocrine > Thyroid Function in Health and Disease > Flashcards

Thyroid Function in Health and Disease Flashcards

1
Q

What are the functions of the thyroid gland?

A

Secrete thyroid hormones > regulate metabolism

Secrete calcitonin > regulate Ca levels

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2
Q

What is the structure of the thyroid gland?

A

2 lobes joined by isthmus

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3
Q

What is the location of the thyroid gland?

A

Below larynx
Above trachea
Anterior in neck

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4
Q

What cells surround the colloid?

A

Follicular cells/thyrocytes

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5
Q

Where is thyroglobulin located?

A

In colloid

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6
Q

Where are the C cells?

A

In interstitial spaces

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7
Q

What is the function of C cells?

A

Secrete calcitonin

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8
Q

How are thyroid hormones synthesised?

A
  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
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9
Q

What is the role of thyroglobulin?

A

Stops iodine from diffusing out

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10
Q

Where do we get our iodine from?

A

Diet

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11
Q

What are the uses of iodine in the body?

A

Thyroid hormone synthesis

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12
Q

What are the structural components of thyroid hormone?

A

Iodine

Tyrosine derivative

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13
Q

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

A 
T3 = 10%
T4 = 90%
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14
Q

How much T3 is derived from T4?

A

80%

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15
Q

Why are thyroid hormones bound to plasma proteins?

A

Because lipophilic

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16
Q

Where is thyroid stimulating hormone (TSH) released from?

A

Anterior pituitary

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17
Q

What does TSH do?

A

Stimulates all steps in thyroid hormone synthesis

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18
Q

Where is thyroid releasing hormone (TRH) released from?

A

Hypothalamus

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19
Q

What increases levels of TRH secretion?

A

Cold in infants only known factor

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20
Q

What decreases levels of TRH secretion?

A

Stress

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21
Q

What is the half-life of T4?

A

6-7 days

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22
Q

What is the half-life of T3?

A

1 day

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23
Q

What are the factors affecting release of thyroid hormones?

A

Tonic release

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24
Q

What are the target tissues of thyroid hormones?

A

Most cells of body

25
Q

What are the actions of thyroid hormones?

A 
Increase basal metabolic rate and oxygen consumption
Modulate metabolism
Sympathomimetic effect
- Increases HR
- Increases CO
26
Q

Is thyroid hormone essential for life?

A

No, but essential for child growth and development

27
Q

How does thyroid hormone promote growth?

A

Foetal life

After birth, essential for GH and IGFs actions

28
Q

When is thyroid hormone needed for nervous system development?

A

Before and after birth

29
Q

When does goitre occur?

A

In both hypothyroidism and hyperthyroidism

30
Q

What is primary hypothyroidism?

A

Thyroid failure
Decreased T3 and T4
Increased TSH

31
Q

Do you get a goitre in primary hypothyroidism?

A

Yes, because of trophic effect of increased TSH

32
Q

What happens when you have low dietary iodine?

A

Decreased T3 and T4

Increased TSH

33
Q

Do you get a goitre in dietary iodine deficiency?

A

Yes, because of trophic effect of increased TSH

34
Q

What causes secondary hypothyroidism?

A

Hypothalamic/anterior pituitary failure/tumour

35
Q

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

A

Decreased T3 and T4
Decreased TSH
Decreased TRH

36
Q

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

A

Decreased T3 and T4
Decreased TSH
Increased TRH

37
Q

Do you get a goitre with secondary hypothyroidism?

A

No, because no trophic effect of TSH

38
Q

What causes cretinism?

A

Congenital deficiency of thyroid hormones

39
Q

What is the most common endocrine illness?

A

Hypothyroidism

40
Q

Who has hypothyroidism more: females or males?

A

Females

41
Q

What is the most common cause of hypothyroidism?

A

Iodine deficiency

42
Q

What are some causes of congenital hypothyroidism?

A

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

43
Q

How can congenital hypothyroidism be prevented?

A

Adequate iodine in diet during pregnancy

44
Q

Are newborns tested for thyroid deficiency?

A

Yes

45
Q

What are the physiological effects of hypothyroidism?

A

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
Q

What is the treatment for hypothyroidism?

A

Replace thyroid hormone

Adequate dietary iodine

47
Q

What are hormone levels in primary hyperthyroidism?

A

Increased T3 and T4
Decreased TSH
Decreased TRH

48
Q

Do you have a goitre with primary hyperthyroidism?

A

Yes

49
Q

What is Graves disease?

A

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

50
Q

Why do you get a goitre in Graves disease?

A

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

51
Q

What is the epidemiology of Graves disease?

A

60-80% of all cases of hyperthyroidism

More common in women

52
Q

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

A

Increased T3 and T4
Increased TSH
Increased TRH

53
Q

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

A

Increased T3 and T4
Increased TSH
Decreased TRH

54
Q

Do you get a goitre in secondary hyperthyroidism?

A

Yes, because of trophic effect of TSH

55
Q

What are hormone levels in a hypersecreting tumour?

A

Increased T3 and T4

Decreased TSH

56
Q

Do you get a goitre with a hypersecreting tumour?

A

No

57
Q

What are the physiological effects of hyperthyroidism?

A 
Increased
- Basal metabolic rate
- Oxygen consumption
- Appetite
- Weight loss
- Muscle weakness
- HR
- Alertness
Heat intolerance
Irritability
Hyperexcitability
58
Q

What is Graves disease exophthalmos?

A

Bulging eyes because of water retaining carbohydrates behind eyes

59
Q

What is the treatment for hypothyroidism?

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

MD1 Endocrine (18 decks)

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