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Endocrine > Thyroid Physiology and Pathophysiology > Flashcards

Thyroid Physiology and Pathophysiology Flashcards

1
Q

2 cell types in thyroid and their hormones

A

thyroid follicular cells (thyroid hormone) and parafollicular c-cells (calcitonin)

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2
Q

thyroglossal duct cyst

A

remnant of thyroid migration

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3
Q

goiter

A

enlarged thyroid gland

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4
Q

T/F goiters can be endemic or non-endemic

A

T

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5
Q

T/F goiter can be diffuse or nodular

A

T

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6
Q

T/F goiter can be toxic or non-toxic

A

T –> thyroid hormone production is toxic in a goiter

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7
Q

most common cause of goiter

A

iodine deficiency –> measurement of urinary iodine

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8
Q

iodine is crucial for _____ synthesis

A

thyroid hormone

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9
Q

Goitrogenesis

A

genetics + heterogeneity of follicular cells + iodine deficiency/environmental factors –> diffuse hyperplasia –> nodular non toxic/multinodular goiter (MNG) –> toxic goiter/toxic MNG

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10
Q

Thyroid hormone is derived from ___

A

tyrosine

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11
Q

Major intermediate precursor to thyroid hormone

A

thyroglobulin

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12
Q

MIT and DIT

A

Iodinated thyroglobulin that are the precursors to T3 and T4 (3 ioidine and 4 iodine)

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13
Q

I- is actively/passively transported into ____ cells for thyroid hormone synthesis

A

active transport across basement membrane of follicular cell

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14
Q

thyroid hormone is stored in ___

A

thyroid colloid as coupled iodotyrosine/Tg –> proteolyzed at time of need

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15
Q

What enzyme converts DIT/MIT/thyroglobulin to T3/T4/thyroglobulin?

A

peroxidase transaminase

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16
Q

T/F MIT/DIT are secreted with thyroid hormone

A

F –> recycled and deiodinated

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17
Q

HPT axis

A

hypothalamic TRH –> anterior pituitary TSH –>T3 and T4 –> T3 negative feedback

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18
Q

T3/T4 is the active hormone

A

T3

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19
Q

The process of converting T4 to T3 is called

A

extrathyroidal deiodination of T4

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20
Q

extrathyroidal deiodination of T4 takes place in

A

liver and skeletal muscle

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21
Q

T/F most thyroid hormone is free in the blood

A

F –> most binds to TBG, TBPA, and albumin

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22
Q

T4 half life

A

8 days

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23
Q

Increase in binding proteins results in decrease/increase in free hormone level

A

decrease

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24
Q

Conditions that increase TBG level

A

estrogen, increased hepatic release (hepatitis)

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25
Q

Conditions that decrease TBG level

A

androgens, decreased hepatic production, increased renal loss/nephrotic syndrome, congenital

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26
Q

thyroid hormone metabolism

A

diodinases:
type 1= hepatic, kidney, thyroid (inner and outer ring)
type 2= CNS, pituitary (outer ring)
type 3 = placenta (inner ring)

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27
Q

Conditions associated with decreased T4–>T3 conversion

A

caloric restriction, illness, hepatic disease, fetal life, drugs (propanolol, glucocorticoids, PTU), selenium deficiency

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28
Q

T/F TR can act as a transcriptional activator or repressor depending on target gene and presence of thyroid hormone

A

T

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29
Q

T3 increases/decreases O2 consumption in all tissues except _____

A

increases: except spleen and testes

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30
Q

What does it measure? TSH

A

pituitary secretion of TSH: normal = .5-5

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31
Q

What does it measure? Free T4

A

free unbound t4: normal = .8-1.8

32
Q

What does it measure? T4

A

total t4 (bound/unbound): normal = 5-12

33
Q

What does it measure? T3RU

A

of unoccupied serum protein bind sites (inversely proportional to # of free sites): normal = .85-1.1

34
Q

What does it measure? Free T4 index

A

concentration of free T4 //T4XT3RU: normal = 5-12

35
Q

The _____ is the optimal screening test in ambulatory healthy patients

A

TSH

36
Q

High TSH is hypo/hyperthyroid

A

hypothyroid

37
Q

When free T4 is higher, there is more/less TSH

A

less due to negative feedback

38
Q

Thyroid hormone levels in hypothyroidism

A

high TSH, low T4/T3

39
Q

Thyroid hormone levels in hyperthyroidism

A

low TSH, high T4/T3

40
Q

Causes of primary hypothyroidism

A

autoimmune/hashimotos –> measure via TPO Ab, thyroidectomy, dysgenesis of thyroid gland, biosynthetic defects

41
Q

Central hypothyroidism

A

pituitary/hypothalamic

42
Q

Transient hypothyroidism

A

hypothyroid phase of thyroiditis (subacute or autoimmune)

43
Q

Hashimoto’s

A

lymphocytic thyroiditis + follicular atrophy

44
Q

Why is TSH the optimal screening test?

A

change in TSH level comes before change in T3/T4 levels

45
Q

T/F there is an age and gender predilection for hypothyroidism

A

T –> older and female–> even out genderwise past age 65

46
Q

Signs of hypothyroidism

A

delayed relaxation of deep tendon reflexes, periorbital swelling, mild weight gain, queen anne’s eyebrows, elevated cholesterol, fetal death, atherosclerosis

47
Q

T/F high maternal tsh is associated with higher fetal death rate

A

T

48
Q

Myxedema coma

A

severe, life-threatening hypothyroidism –> elderly pts with preexisting hypothyroidism and acute illness/sepsis/MI –> hypothermia and coma

49
Q

Tx of hypothyroidism

A

levothyroxine sodium

50
Q

half life of LT4

A

7 days (levothryoxine sodium)

51
Q

Causes of thyroid hormone overproduction

A

graves, toxic solitary nodule, toxic multinodular goiter

52
Q

Leakage of thyroid hormone causes

A

autoimmune or viral/subacute thyroiditis

53
Q

Graves

A

TSH receptor stimulating antibody –> opthalmopathy, dermopathy, onycholysis/fingernail separation, general hyperthyroid findings

54
Q

Clinical symptoms of hyperthyroidism

A

heat intolerance, perspiration, headache, palpitations, tremor, weight change

55
Q

hyperthyroid eye disease

A

lid lag, lid retraction, and stare –> increased adrenergic tone stimulating the levator palpebral muscles

56
Q

True Graves Opthalmopathy

A

Proptosis, Diplopia, Inflammatory changes (conjunctival injection, periorbital edema, chemosis)

57
Q

How do you differentiate between graves’, toxic nodules, and thyroiditis?

A

radioiodine uptake I123

58
Q

I123 uptake/scan interpretation

A 
normal =15-35% over 24 hours
Graves: symmetric distribution of radioiodine
toxic nodule: singular node of tracer
multinodular: multiple nodes of tracer
thyroiditis: no/low tracer uptake
59
Q

Tx of graves

A

radioiodine ablation (I131), antithyroid drugs (propylthiouracil and methimazole), surgery

60
Q

Tx of choice for graves

A

propylthiouracil and methimazole: inhibit thyroid hormone synthesis and induce remission in 60%

61
Q

T/F I131 is associated with secondary cancers/congenital malformations

A

F –> not in treatment of graves b/c low dose

62
Q

Adverse effects of I131 for graves

A

may worsen opthalmopathy, especially in smokers, rare hyperthryoid exacerbation

63
Q

Adverse effects of propylthiouracil and methimazole for graves

A

rash, agranulocytosis, hepatitis, 40% relapse after 18 months

64
Q

Indications for thyroidectomy

A

subtotal –> become hypothyroid
large toxic nodular goiters with compression, pregnant women who would need high doses of drugs, people with severe drug effects

65
Q

Thyroid storm

A

severe, life threatening hyperthyroidism –> high fever, tachycardia, sweating, restlessness, AMS

66
Q

Thyroid nodules

A

palpable mass solitary/dominant –> distinct on imaging

67
Q

Diff Dx of thyroid nodules

A

cancers/mets, adenoma, thyroiditis

68
Q

Risk factors for thyroid nodules

A

history of neck irradiation, family hx, age 60, female, duration, local symptoms (hoarsness, etc), hx of coexistent benign thyroid disease

69
Q

Most common radiation induced thyroid cancers

A

mantle radiation for hodgkins

70
Q

Course of action if normal TSH with nodule

A

FNA

71
Q

Course of action if low TSH with nodule

A

scan –> malignancy unlikely so do not need to aspirate

72
Q

T/F all patients should have an ultrasound before/after FNA

A

T

73
Q

T/F”cold”/nonfunctional nodules should be aspirated

A

T –> more likely to be malignant

74
Q

What kinds of nodules are indeterminate?

A

follicular or hurthle cell neoplasm

75
Q

What kinds of nodules are benign?

A

nodular goiter, lymphocytic thyroiditis

76
Q

What % of FNA nodules are malignant?

A

5-10%

77
Q

___ % of patients with thyroid nodule malignant or indeterminate go to surgery with only ____ with cancer

A

30% and 1/3 –> majority of indeterminate are benign

Endocrine (26 decks)

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