Thyroid Physiology and Pathophysiology Flashcards Preview

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Flashcards in Thyroid Physiology and Pathophysiology Deck (77):
1

2 cell types in thyroid and their hormones

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

2

thyroglossal duct cyst

remnant of thyroid migration

3

goiter

enlarged thyroid gland

4

T/F goiters can be endemic or non-endemic

T

5

T/F goiter can be diffuse or nodular

T

6

T/F goiter can be toxic or non-toxic

T --> thyroid hormone production is toxic in a goiter

7

most common cause of goiter

iodine deficiency --> measurement of urinary iodine

8

iodine is crucial for _____ synthesis

thyroid hormone

9

Goitrogenesis

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

10

Thyroid hormone is derived from ___

tyrosine

11

Major intermediate precursor to thyroid hormone

thyroglobulin

12

MIT and DIT

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

13

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

active transport across basement membrane of follicular cell

14

thyroid hormone is stored in ___

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

15

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

peroxidase transaminase

16

T/F MIT/DIT are secreted with thyroid hormone

F --> recycled and deiodinated

17

HPT axis

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

18

T3/T4 is the active hormone

T3

19

The process of converting T4 to T3 is called

extrathyroidal deiodination of T4

20

extrathyroidal deiodination of T4 takes place in

liver and skeletal muscle

21

T/F most thyroid hormone is free in the blood

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

22

T4 half life

8 days

23

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

decrease

24

Conditions that increase TBG level

estrogen, increased hepatic release (hepatitis)

25

Conditions that decrease TBG level

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

26

thyroid hormone metabolism

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

27

Conditions associated with decreased T4-->T3 conversion

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

28

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

T

29

T3 increases/decreases O2 consumption in all tissues except _____

increases: except spleen and testes

30

What does it measure? TSH

pituitary secretion of TSH: normal = .5-5

31

What does it measure? Free T4

free unbound t4: normal = .8-1.8

32

What does it measure? T4

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

33

What does it measure? T3RU

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

34

What does it measure? Free T4 index

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

35

The _____ is the optimal screening test in ambulatory healthy patients

TSH

36

High TSH is hypo/hyperthyroid

hypothyroid

37

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

less due to negative feedback

38

Thyroid hormone levels in hypothyroidism

high TSH, low T4/T3

39

Thyroid hormone levels in hyperthyroidism

low TSH, high T4/T3

40

Causes of primary hypothyroidism

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

41

Central hypothyroidism

pituitary/hypothalamic

42

Transient hypothyroidism

hypothyroid phase of thyroiditis (subacute or autoimmune)

43

Hashimoto's

lymphocytic thyroiditis + follicular atrophy

44

Why is TSH the optimal screening test?

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

45

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

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

46

Signs of hypothyroidism

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

47

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

T

48

Myxedema coma

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

49

Tx of hypothyroidism

levothyroxine sodium

50

half life of LT4

7 days (levothryoxine sodium)

51

Causes of thyroid hormone overproduction

graves, toxic solitary nodule, toxic multinodular goiter

52

Leakage of thyroid hormone causes

autoimmune or viral/subacute thyroiditis

53

Graves

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

54

Clinical symptoms of hyperthyroidism

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

55

hyperthyroid eye disease

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

56

True Graves Opthalmopathy

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

57

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

radioiodine uptake I123

58

I123 uptake/scan interpretation

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

Tx of graves

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

60

Tx of choice for graves

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

61

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

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

62

Adverse effects of I131 for graves

may worsen opthalmopathy, especially in smokers, rare hyperthryoid exacerbation

63

Adverse effects of propylthiouracil and methimazole for graves

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

64

Indications for thyroidectomy

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

65

Thyroid storm

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

66

Thyroid nodules

palpable mass solitary/dominant --> distinct on imaging

67

Diff Dx of thyroid nodules

cancers/mets, adenoma, thyroiditis

68

Risk factors for thyroid nodules

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

69

Most common radiation induced thyroid cancers

mantle radiation for hodgkins

70

Course of action if normal TSH with nodule

FNA

71

Course of action if low TSH with nodule

scan --> malignancy unlikely so do not need to aspirate

72

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

T

73

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

T --> more likely to be malignant

74

What kinds of nodules are indeterminate?

follicular or hurthle cell neoplasm

75

What kinds of nodules are benign?

nodular goiter, lymphocytic thyroiditis

76

What % of FNA nodules are malignant?

5-10%

77

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

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