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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
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

Endocrine (26 decks)

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