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Internal medicine (small) > Thyroid glands > Flashcards

Thyroid glands Flashcards

1
Q

what are the two types of endocrine cells found in the thyroid?

A

follicular
parafollicular (medullary/C) cells

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2
Q

what do follicular cells of the thyroid produce?

A

thyroid hormones

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3
Q

what do parafollicular/medullary cells of the thyroid produce?

A

calcitonin

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4
Q

what is thyroid hormone secretion regulated by?

A

hypothalamic-pituitary-thyroid axis

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5
Q

what does the hypothalamus release as part of the hypothalamic-pituitary-thyroid axis?

A

thyrotropin releasing hormone (TRH)

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6
Q

what does thyroid releasing hormone act on?

A

pituitary gland

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7
Q

what does the pituitary gland release as part of the hypothalamic-pituitary-thyroid axis?

A

thyroid stimulating hormone (TSH)

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8
Q

what does TSH act on?

A

thyroid gland

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9
Q

what does the thyroid gland produce as part of the hypothalamic-pituitary-thyroid axis?

A

T4 (thyroxine) and T3

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10
Q

what effect does T4 nd T3 have on the pituitary gland and hypothalamus?

A

negative feedback to prevent the release of TRH and TSH

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11
Q

what happens to T4 in peripheral tissue?

A

synthesised to T3

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12
Q

does the thyroid produce more T3 or T4?

A

T4

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13
Q

is T4 or T3 more biologically active?

A

T3

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14
Q

how is most T3 and T4 transported?

A

bound to plasma proteins (globulins)

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15
Q

what is the effect of thyroid hormones on metabolism?

A

increased metabolism

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16
Q

what are the functions of thyroid hormones?

A

increases metabolic rate of tissue
positive inotrope/chronotrope
increase number/affinity of beta-adrenergic receptor
enhance response to catecholamines
catabolic effect of muscle and adipose tissue
stimulate erythropoiesis
regulate cholesterol

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17
Q

what effect do thyroid hormones have on the heart?

A

positive inotrope and chronotrope

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18
Q

what is hypothyroidism?

A

clinical syndrome resulting from deficiency of T3 and T4

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19
Q

how does thyroid hormone increasing the number/affinity of beta-adrenergic receptors and enhancing their response to catecholamines effect the heart?

A

increases heart rate

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20
Q

what animals is hypothyroidism most commonly seen in?

A

middle/older aged dogs

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21
Q

what causes congenital hypothyroidism?

A

thyroid hypoplasia, aplasia or dyshormonogenesis

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22
Q

how can the pituitary gland cause congenital hypothyroidism?

A

panhypopituitarism causes TSH deficiency leading to thyroid hormone deficiency

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23
Q

what breed is panhypopituitarism seen in?

A

German shepherds

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24
Q

is acquired or congenital hypothyroidism more common?

A

acquired

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25
Q

what are the two types of acquired hypothyroidism?

A

primary (due to thyroid gland)
secondary (due to pituitary gland)
tertiary (due to hypothalamus)

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26
Q

what are some causes of primary hypothyroidism?

A

lymphocytic thyroiditis
idiopathic atrophy
thyroid neoplasia

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27
Q

what type of disease is lymphocytic thyroiditis?

A

immune-mediated

28
Q

what are the clinical signs of hypothyroidism?

A

metabolic - lethargy, obesity, exercise intolerance, cold intolerance
dermatological - thinning/alopecia, poor coat quality, skin hyperpigmentation, pyoderma
diarrhoea, bradycardia, altered oestrus cycle, neuropathy

29
Q

can haematology and biochemistry diagnose hypothyroidism?

A

no - may may point towards it or help to rule in/out other disease

30
Q

what will be the features on haematology of a dog with hypothyroidism?

A

mild normocytic normochromic non-regenerative anaemia

31
Q

what changes will be seen on biochemistry of a dog with hypothyroidism?

A

hypertriglyceridaemia
hypercholesterolaemia
mildly increased CK
mildly increased ALP and ALT
fructosamine increase

32
Q

how does the serum of a dog that has hypothyroidism appear?

A

milky colour due to hypertriglyceridaemia

33
Q

why are hypothyroidism dogs hypertriglyceridaemic?

A

because they have less lipid metabolism so it remains in the blood

34
Q

why does ALP and ALT mildly increase with hypothyroidism?

A

lipid storage in the liver due to decreased metabolism causing damage

35
Q

why does CK mildly increase in hypothyroidism cases?

A

muscle catabolism

36
Q

how is required to diagnose hypothyroidism?

A

thyroid hormone testing

37
Q

what ways can thyroid hormone be measured?

A

total T4
free T4
total T3
TSH

38
Q

what test results confirm hypothyroidism?

A

increased TSH and decreased total/free T4 (thyroxine)

39
Q

what dynamic function tests are available for thyroid hormone testing?

A

TRH or TSH stimulation

40
Q

what two things have to be measure to confirm hypothyroidism?

A

TSH and T4

41
Q

what is the most common test for hypothyroidism?

A

total T4

42
Q

what are some possible reasons for false positives when using total T4 to test for hypothyroidism?

A

can be low due to non-thyroidal illness
some drugs can cause it to be low
older dogs can have low T4

43
Q

what breeds have low-normal values of total T4?

A

greyhounds

44
Q

what happens to free T4 if the sample is left out?

A

concentration significantly increases if left at room temperature for prolonged periods

45
Q

what can cause a false increased in free T4?

A

severe lipaemia
samples stored at room temperature

46
Q

how will TSH be effected in hypothyroidism?

A

increased (sometimes normal)

47
Q

what can cause increases in TSH other than hypothyroidism?

A

recovery from non-thyroid illness
use of sulphonamides

48
Q

what should TSH always be measured with?

A

T4

49
Q

what can thyroid hormone autoantibodies be used to provide evidence for?

A

provide evidence of immune reaction to the thyroid gland (doesn’t diagnose hypothyroidism)

50
Q

how can thyroid hormone autoantibodies effect total T4/T3?

A

can cause increases in total T3 or T4 because tests can misinterpret the autoantibodies as T3 or T4

51
Q

how does prednisolone effect thyroid hormones?

A

causes decrease total and free T4
normal or decreased TSH

52
Q

how does phenobarbital effect thyroid hormones?

A

decrease total and free T4
increased TSH

53
Q

how does sulphonamide effect thyroid hormone?

A

decreased total and free T4
increased TSH

54
Q

what drugs cause hypothyroidism?

A

sulphonamides

55
Q

how do sulphonamides cause hypothyroidism?

A

inhibits thyroid peroxidase which is the enzyme used to release thyroid hormone from the thyroid

56
Q

how is hypothyroidism treated?

A

levothyroxine (thyroid hormone supplementation)

57
Q

how long is the treatment cause of levothyroxine for hypothyroidism?

A

life long

58
Q

why does care need to be taken when treating hypothyroidism in cases that have concurrent cardiac problems?

A

treating will cause increased heart rate which could compromise the heart

59
Q

how is the response to hypothyroidism treatment monitored?

A

look at clinical signs
measure total T4 (4-6 hours post treatment)

60
Q

how long should it take the metabolic signs of hypothyroidism to resolve after treatment?

A

couple of weeks

61
Q

what are some common complications of hypothyroidism?

A

neurological - generalised myopathy, megaoesophagus, laryngeal paralysis
hyperlipidaemia, atherosclerosis
myxoedema coma

62
Q

is hypothyroidism more common in cats or dogs?

A

dogs (rare in cats)

63
Q

what is the most common cause of hypothyroidism in cats?

A

iatrogenic - over treatment of hyperthyroidism, bilateral thyroidectomy, radioactive iodine treatment

64
Q

how is hypothyroidism of cats diagnosed?

A

canine TSH

65
Q

how do most cats present with hypothyroidism? (very uncommon)

A

goitre

66
Q
A

Internal medicine (small) (33 decks)

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