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endocrine - thyroid Flashcards

0
Q

DIT plus DIT

A

Tetraiodithyronine or T4

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1
Q

Biosynthesis of T3 and T4

A
  1. Dietary iodide ingestion by follicular cells
  2. Active transport and uptake of iodide into colloid by thyroid gland
  3. Oxidation of I and iodination of Tg tyrosine residues
  4. Coupling of Iodotyrosine residues (MIT & DIT) to form T3 and T4
  5. Proteolytic of Tg with release of T3 and t4 into circulation
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2
Q

DIT plus MIT

A

Triiodothyronine T3

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3
Q

Indispensable component of thyroid hormone comprising 65% of T4 and 58% of T3’s weight.

A

Iodine

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4
Q

Required daily intake of iodine in 0-7y/o.

A

90 ug/d

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5
Q

Required daily intake of iodine in 7-12y/o.

A

120 ug/d

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6
Q

Required daily intake of iodine in teenager and adults

A

150 ug/d

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7
Q

Required daily intake of iodine in pregnant and lactating women

A

25o ug/d

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8
Q

Iodine intake not more than

A

1100 ug/d

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9
Q

Excess iodine

A

Wolff chaikoff effect

Jodbasedow phenomenon

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10
Q

Excess iodine with transient shut down of thyroid hormone production (normally).
When increasing doses of iodide inhibit organification and hormonogenesis of thyroid hormone.

A

Wolff chaikoff effect

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11
Q

In some pts with HAshimoto’s thyroiditis, they may stay hypothyroid because of inability to escape this effect

A

Wolff-chaikoff effect

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12
Q

Thyroid hyperfunction induced by excess iodine ingestion in pts with various thyroid disorder (grave’s disease)

A

Jod-basedow phenomenon

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13
Q

Dietary iodine reaches the circulation as

A

Iodide anion

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14
Q

Iodide active transport by thyroid Is mediated by this membrane protein

A

Sodium-iodide symporter or NIS

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15
Q

It functions as iodide concentrating mechanism that enables iodide to enter the thyroid for hormone biosynthesis

A

NIS

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16
Q

Iodide trapping by the aid of

A

NIS

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17
Q

Iodide must be first ___ to be able to iodinate tyro sly residues of Tg

A

Oxidized

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18
Q

Iodination of tyrosyl residues then forms monoiodotyrosine and diiodotyrosine which are then coupled to form either T3 or T4. Both reactions are catalyzed by

A

Thyroperoxidase

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19
Q

Thyroperoxidase Catalyzes oxidation steps involved in:

A

I- activation
Iodination of Tg tyrosyl residues
Coupling of iodotyrosyl residues

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20
Q

TPO uses ___ as the oxidant to activate I- to hypoiodate the iodination species

A

H2O2

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21
Q

To liberate t3 and t4, Tg is resorted into follicular cells in the form of ___ which fuse with lysosomes to form phagolysosome

A

colloid droplets

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22
Q

Primary secretory product of thyroid gland

A

T4

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23
Q

Thyroid secretes approximately how many grams of thyroxine daily

A

70-90 ug/d

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24
Q

Total daily production rate of t3

A

15-30 ug/d

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25
Q

T3 is derived from 2 processes

A
  1. 80% of circulating T3 comes from deiodination of T4 on peripheral cells
  2. 20% comes directly from thyroid secretion.
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26
Q

Pro hormone for T3

A

T4

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27
Q

T4 is biologically inactive in target tissues

A

True. Until converted to T3

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28
Q

T4 is converted to T3 by

A

5-deiodination of outer ring of T4

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29
Q

T3/T4 which is biologically active responsible for the majority of thyroid hormone effects

A

T3

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30
Q

Major extrathyroidal T4 conversion site for production of T3

A

Liver

Some occurs in kidney and other tissue

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31
Q

Normal disposition of T4

A

41% is converter to T3
38% is converter to rT3
21% is metabolized via other pathways (conjugation on liver and excretion in bile)

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32
Q

Normal circulating concentration of t4

A

4.5-11 ug/dl

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33
Q

Normal circulating concentration of t3

A

60-180 ng/dl

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34
Q

T3/4: Produced only in thyroid gland

A

T4

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35
Q

T3/4: 80% are from peripheral conversion

A

T3

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36
Q

Half life of t4

A

7 days

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37
Q

Half life of t3

A

One day

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38
Q

T3/4: only free hormones are active

A

T4

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39
Q

3-8x more potent

A

T3

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40
Q

More than 99% of circulating T3 and t4 is bound to plasma protein Carrier proteins which are

A

TBG 75%
Transthyretin TTR / thyroxine-binding prealbumin TBPA 10-15%
Albumin 7%
HDL 3%

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41
Q

Decrease or increase TBG effects on total serum T3 and T4 level and free T3 and T4.

A

Decrease or increase TBG will decrease/increase total serum T3 and T4 level.
While free T3 and T4 remain unchanged

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42
Q

Drugs that increase TBG

A 
Oral contraceptives
Methadone
Clofibrate
5-fluorouracil
Heroin 
Tamoxifen
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43
Q

Conditions that increase TBG

A 
Pregnancy
Infectious/chronic active hepatitis
HIV infection 
Biliary cirrhosis
Acute intermittent porphyria 
Genetic factors
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44
Q

Drugs that decrease serum t3 and t4 by decreasing TBG conc

A 
Glucocorticoids 
Androgens 
L-asparaginase
Mefenamic acid
Furosemide
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45
Q

Drugs that decrease serum t3 and t4 by decreasing binding

A

Antiseizure medications

Salicylates

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46
Q

Decreased thyroid hormone concentration may lead to alteration of ___. May develop impairment of attention, slowed motor function, and poor memory

A

cognitive function.

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47
Q

Thyroid hormone influences cv hemodynamics by

A 
Increase HR and decrease systemic vascular resistance thus increase CO = improve cardiac performance 
Elevate blood volume 
Local vasodilators 
Decrease diastolic blood pressure 
Cardiac chronotropy and inotropy
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48
Q

Thyroid hormone is critical for normal bone Growth and development

A

T3 regulates sk maturation at growth plate.
T3 participates in osteoblasts differentiation and proliferation and chondrocytes maturation loading to bone ossification.

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49
Q

Major regulator of mitochondrial activity

A

T3

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50
Q

Thyroid hormone is a major regulator of mitochondria activity

A

T3 induces early transcription and increases TFA expression.
T3 stimulates O2 consumption.

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51
Q

Thyroid hormone stimulates mitochondrial activity in most tissue

A

T3 increases basal metabolic rate, body heat production and O2 consumption.

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52
Q

Metabolic effects of T3

A
  1. Lipolysis- FA + glycerol
  2. expression of lipogenic enzymes
  3. cholesterol catabolism into BA
  4. Rapid removal of LDL from plasma
  5. Carbohydrate and protein catabolism
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53
Q

Thyroid hormone influences the female repro system

A

Hypothyroidism may be asso with menstrual disorder, infertility, risk of miscarriage and other complications of pregnancy.

54
Q

AOG when fetus is completely dependent on maternal thyroid hormones

A

First 3 mos

55
Q

AOG when fetal thyroid begins to conc iodine and synthesize Iodothyronines

56
Q

AOG when fetal pituitary gland differentiates

57
Q

Thyroid hormones that appear in fetal serum

58
Q

Placental transfer without difficulty

A

Iodide
Thionamides
Thyroid ab
TRH

59
Q

Some placental transfer

60
Q

Little or no placental transfer

61
Q

Increased thyroid hormone requirements during pregnancy

A

Increase free TH binding to TBG - marked fall in serum free T4 - if no compensatory increase in thyroid secretion leads to hypo.
Transplacental transfer of T4 - placental degradation of T4 - if no compensatory increase in thyroid secretion leads to hypo.

62
Q

During first trimester, ___ is at its highest conc and can stimulate thyroid cells to produce new thyroid hormones.

63
Q

There is transient low TSH during 1st trimester due to increased thyroid hormone production.

64
Q

During pregnancy, there is an increased Renal iodine clearance, therefore..

A

Increased 24-hr RAIU

65
Q

During pregnancy, there is an decreased plasma iodine and placental iodine transport to the fetus, therefore..

A

In deficient women, decreased T4, increases TSH then leads to goiter formation

66
Q

During pregnancy, there is an increased O2 consumption, therefore..

A

Increased BMR

67
Q

During 1st tri in pregnancy, there is an increased HCG, therefore

A

Increased free T4 and T3

Decreased basal TSH

68
Q

During pregnancy, there is an increased serum TBG, therefore..

A

Increased total T3 and T4

69
Q

During pregnancy, there is an increased plasma volume, therefore..

A

Increased T3 and T4 pool size

70
Q

During pregnancy, there is an increased plasma type 3 deiodinase, therefore..

A

Accelerates rates of t3 and T4 degradation and production.

71
Q

Refers to classic physiologic manifestations if excessive quantities of the thyroid hormones

A

Thyrotoxicosis

72
Q

RAIU level in thyrotoxicosis

73
Q

Most common cause of thyrotoxicosis

A

Thyroiditis

74
Q

Reserved for disorders that results from sustained overproduction of hormone by the thyroid gland itself

A

Hyperthyroidism

75
Q

Most common cause of hyperthyroidism

A

Graves disease

76
Q

Lab diagnosis for thyrotoxicosis and hyperthyroidism

A

Suppressed TSH <0.1 mU/L
Elevated T4
RAIU

77
Q

Lab diagnosis to differentiate thyrotoxicosis and hyperthyroidism

78
Q 
TSH level and RAIU level of:
Graves disease 
Toxic multinodular goiter
Toxic adenoma
Gestational hyperthyroidism
A

Low TSH

High RAIU

79
Q 
TSH level and RAIU level of:
Iodine induced hyperthyroidism 
Amiodarone- induced hyperthyroidism 
Struma ovarii 
Metastatic thyroid Ca 
Thyroiditis
A

Low TSH

Low RAIU

80
Q

TSH level and RAIU level of:
TSH-secreting pituitary tumor
TH hormone resistance

A

Elevated or normal TSH

81
Q

TSH level and free T4 level of:

Secondary or central hypothyroidism

A

Low TSH

Low T4

82
Q

TSH level and T4 level of:

Sick euthyroid syndrome

A

Low TSH

Low T4

83
Q

TSH level and T4 level of:
T3 thyrotoxicosis
Sub clinical hyperthyroidism

A

Low TSH

Normal T4

84
Q

TSH level and T4 level of:

True hyperthyroidism

A

Low TSH

High T4

85
Q

TSH level and T4 level of:

Graves disease

A

Low TSH

High T4

86
Q

Graves disease is a syndrome characterized by

A

Hyperthyroidism
Ophthalmopathy
Dermopathy
Pretibial myxedema

87
Q

Graves disease is an autoimmune disease with a strong familial disposition more common in male/female.

88
Q

Environmental triggers of graves disease

A

Stress
Tobacco use
Infection
Iodine exposure

89
Q

Most frequent cause thyrotoxicosis in iodine-sufficient countries

A

Graves disease

90
Q

Main ag in graves disease

91
Q

Circulating ab in graves disease

92
Q

Dermopathy in graves disease

A 
Plummer's nail
Hyperpigmentation
Hyperhidrosis
Alopecia 
Acropachy (triad of digital clubbing, soft tissue swelling of hands and feet and periosteal new bone formation)
93
Q

Signs and symptoms of hyperthyroidism

A 
Freq bowel movement
Bulging eyes
Sudden paralysis
Weigh loss / gain
Tachycardia
Heat intolerance 
Warm, moist palm
Light period

Increase sweating
Insomnia
Nervousness, tremors

Goiter
Hoarseness 
Infertility
Irritability
Dry/sore throat
Dysphagia
94
Q

Signs and symptoms in hypothyroidism

A 
Constipation
Puffy eyes
Muscle weakness
Weigh loss gain
Bradycardia
Cold intolerance 
Dry, patchy skin
Heavy period 
Hairloss
Tiredness
Forgetfulness
Depression
Elevated cholesterol 
Goiter
Hoarseness 
Infertility
Irritability
Dry/sore throat
Dysphagia
95
Q

Atrial fibrillation is characteristically manifested in what thyroid disorder

A

Graves disease

96
Q

First line therapy for hyperthyroidism or graves disease

A

Radioactive iodine

97
Q

Mechanism of action do radioactive iodine

A

Destroys the thyroid and stops the excess production of hormone

98
Q

Indication for radioactive iodine treatment

A

Female planning a pregnancy in the future
Pts with increase ping surgical risk
Pts previously operated or externally irradiated neck
Pts with CI to ATD

99
Q

Treatment of choice for recurrent hyperthyroidism after ATD therapy

100
Q

RAI is used by elderly and cardiac pts

101
Q

RAI has no effect on fertility, no increased incidence of congenital malformation and no increased risk of cancer

102
Q

RAI is contraindicated during

A

Lactation and pregnancy

103
Q

Pregnancy must be postponed for at least ____ after RAI therapy

104
Q

RAI therapy or RAI ablation:

To destroy some thyroid tissue in graves disease or toxic nodules.

A

RAI therapy

105
Q

RAI therapy or RAI ablation:

Low dose

A

RAI therapy

106
Q

RAI therapy or RAI ablation:

With intention to destroy all thyroid remnant and metastasis in well diff Ca

A

RAI ablation

107
Q

Indications for thyroidectomy

A 
Planning for pregnancy (<4-6 mos)
Thyroid malignancy
Large goiter (>80gms)
Low RAIU
Coexisting hyperparathyroidism
108
Q

Patients undergoing surgery (thyroidectomy) should be rendered

109
Q

What would be given in immediate preop period in thyroidectomy

A

Potassium iodide
To diminish vascularity to suppress the thyroid hormone production becoz patients undergoing surgery should be rendered euthyroid.

110
Q

Potential complication of thyroidectomy

A

Hypoparathyroidism
Hypothyroidism
Vocal cord paralysis

111
Q

Anti thyroid drugs

A

Methimazole
Propylthiouracil
Carbimazole
Thiamazole

112
Q

PTU / MMI:

Blocks thyroid hormone production and secretion

113
Q

PTU / MMI:

Blocks peripheral conversion of T4 to T3

A

Porpylthiouracil

114
Q

PTU / MMI:

Long half life

115
Q

PTU / MMI:

More binding to albumin

116
Q

PTU / MMI:

Less placental passage

117
Q

PTU / MMI:

Lower conc in breast milk

118
Q

PTU / MMI:

With peculiar toxicity - aplastic cutis embryopathy

119
Q

Mechanism of action of ATDs

A

Inhibition of organification (iodine binding to Tg)
Inhibition of coupling of Iodothyronines
Inhibition of T4 to T 3 conversion (PTU)
Possible immunosuppressive effects (MMI)

120
Q

ATD that is used in all patients

A

MMI

Except those in 1st tri in pregnancy, treatment for thyroid storm

121
Q

Myxedema is due to

A

Accumulation of hyaluronic acid which alter the composition of the subs of the dermis and other tissue

122
Q

Life threatening clinical condi in pts with long standing severe untreated hypothyroidism

A

Myxedema coma

123
Q

Severe hypothyroidism in infancy with irreversible mental and growth retardation

124
Q

TSH level, T3 or t4 level in subclinical hyperthyroidism

A

Low TSH
Normal t4 and t3
Asymptomatic

125
Q

TSH level, T3 or t4 level in subclinical hypothyroidism

A

High TSH

Normal t4 and t3

126
Q

Thyroxine therapy must be considered in subj (age) if TSH is ___ and/or TPO ab is (present/absent)

A

<65 yrs old if TSH >10mU/L and/or TPO ab is present

127
Q

In cases wherein TSH <10mU/L and/or TPO ab is absent, thyroxine therapy still might be warranted in individual with high background for

A

Cv risk, pregnancy and infertility

128
Q

Most common case of hypothyroidism in areas wherein dietary iodine is sufficient

A

HAshimoto’s thyroiditis

129
Q

Pathologic feature of HAshimoto’s thyroiditis

A

Presence of both mononuclear cells and thyroid follicle destruction

130
Q

Hallmark of classic HAshimoto’s disease

131
Q

Treatment of choice in HAshimoto’s disease and /or large goiter

A

Levothyroxine

132
Q

Self limited anti-inflammatory disorder of thyroid and the most common cause of pain from thyroid origin

A

Subacute thyroiditis

133
Q

Rare disorder of chronic sclerosing thyroiditis

A

Riedel’s thyroiditis

Med Prep (52 decks)

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