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Endo/Repro > Thyroid Gland > Flashcards

Thyroid Gland Flashcards

1
Q

What enzyme converts T4 into T3?

__% converted in periphery
__% directly secreted as T3 from the Thyroid Gland

A

Deiodinase
90
10

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2
Q

Functional unit of parathyroid gland

A

Thyroid follicle

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3
Q

Parafolicular cells that produce Calcitonin

A

C cells

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4
Q

Colloid is composed of newly synthesized thyroid hormones-attached to ________.

A

Thyroglobulin

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5
Q

Clinical states associated with reduced conversion of T4 to T3.

A

Fasting
Medical and Surgical stress
Catabolic Disease

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6
Q

Process of binding Iodine to Thyroglobulin

A

Organification

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7
Q

Steps of Thyroid Hormone synthesis catalyzed by peroxidase

A 
Transport of I- into follicular lumen and oxidation to I2
Organification of I2 (I2+TG=MIT; DIT) 
Coupling Reaction (DIT+DIT=T4; DIT+MIT=T3)
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8
Q

Inhibitor of peroxidase

A

PTU (Propylthiouracil)

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9
Q

Inhibitors of Na+/I- symporter (NIS)

A

Perchlorate

Thiocynate

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10
Q

Inhibition of which step of thyroid hormone synthesis results in Wolff-Chaikoff effect?

A

Organification of Iodine

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11
Q

What can result in inhibition of organification and therefore in Wolff-Chaikoff effect?

A

High levels of I-

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12
Q

Iodine is stored iodinated as tyrosine of ___.

A

TG

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13
Q

Enough hormone is stored in the follicular colloid as iodinated TG to last for ____.

A

2-3 months

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14
Q

What is used to assess the activity of thyroid gland?

A

Radioactive Thyroid uptake

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15
Q

Normal Iodine uptake

A

15% at 6 hr, 25% at 25hr

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16
Q

Hyperthyroid Iodine uptake

A

> 60% at 24 hr

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17
Q

Hypothyroid Iodine uptake

A

<5% at 24 hr

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18
Q

Thyroid hormones circulate in the bloodstream either bound to proteins (__%), or free (__%).

A

99; 1

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19
Q

Thyroid hormone binding proteins

A

Thyroxin-binding globulin (TBG)-70%
Transthyretin (TTR)- 10-15%
Albumin - 15-20%

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20
Q

Where is TBG synthesized?

A

Liver

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21
Q

T/F: TBG has higher affinity to T4 that to T3.

A

True

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22
Q

What test is used to indirectly assess the circulating levels of TBG?

A

T3 Resin Uptake Test

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23
Q

If T3 resin uptake is high that means levels of TBG is ____.

A

Low

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24
Q

If T3 resin uptake is low that means levels of TBG is ____.

A

High

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25
Q

In hyperthyroidism T3 resin uptake is Increased or decreased?

A

Increased

26
Q

In hypothyroidism T3 resin uptake is increased or decreased?

A

Decreased

27
Q

T/F: even though levels of TBG are elevated during pregnancy, levels of free, physiologically active thyroid hormones are normal.

A

True (“clinically euthyroid”)

28
Q

Hepatic failure leads to hyperthyroidism at first because unbound T3 and T4 levels go up, but later it leads to hypothyroidism due to decreased synthesis of T3 and T4 via _______ __________.

A

Negative feedback

29
Q

Percentage of T3 bound to TBG vs percentage of T4 bound to TBG

A

T3: 99.5%
T4: 99.98%

30
Q

How are T3 and T4 transported from blood into cytosol in thyroid or periphery?

A

MCT8/10 transporters

31
Q

How many types of deiodinases are there?

A

Two: type 1 & 2 (different tissue distributions and affinities)

32
Q

T/F: T3 receptors are in cytosol

A

False: in nucleus

33
Q

Effect of TH on Growth

A

Growth

Bone maturation

34
Q

Effect of TH on Nervous System

A

CNS maturation

35
Q

Effect of TH on BMR

A

Increase Na+/K+ ATPase
Increase O2 consuption
Increase Heat production
Increase BMR

36
Q

Effect of TH on Metabolism

A 
Increase glucose absorption
Increase Gluconeogenesis
Increase Glycogenolysis
Increase Lipolysis 
Increase Protein Synthesis and degradation (net catabolic)
37
Q

Effect of TH on Cardiovascular System

A

Increase cardiac output

Up regulation of beta-adrenergic receptors

38
Q

Effect of TH on GI

A

Increase motility

39
Q

Proteins whose synthesis is unregulated by TH

A
  • Na+/K+ ATPase
  • Transport proteins
  • betta-1 adrenergic receptors (cardiac muscle)
  • Myosin (cardiac muscle)
  • Ca2+ ATPase
  • Lysosomal enzymes
  • Proteolytic enzymes
  • Structural proteins
40
Q

T/F: Cholesterol and TG levels in blood are inversely correlated with TH levels

A

True (higher TH, lower cholesterol)

41
Q

TH is required for conversion of carotene to vitamin A, therefore hypothyroidism can lead to ________.

A

Blindness

42
Q

____days before activity of T4 begins
____days before activity of T4 reaches maximum
Activity of T4 persists _____wk

A

2-3
10-12
6-8

43
Q

Are actions of T3 slower or more rapid than that of T4?

A

more rapid

44
Q

_____ hr before activity of T3 begins

_____ days before activity of T3 reaches maximum

A

6-12

2-3

45
Q

Is Thyroid Hormone more sensitive to stimulation by parasympathetic or sympathetic nervous system?

A

Sympathetic

46
Q

High levels of TH increases the number of _-__________ receptors in cardiac muscle cells.

A

beta1-adrenergic

47
Q

Effects of excess TH on skin

A

Sweating

48
Q

Effect of TH deficiency on skin

A

Dry

Mixedema

49
Q

Effect of excess TH on CNS

A

Agitation
Anxiety
Difficulty concentrating
Hyperreflexia

50
Q

Effect of TH deficiency on CNS

A 
Cretinism (congenital)
In adults:
listlessness
slowed movement 
somnolence 
impaired memory
decreased mental capacity
51
Q

Which disease is an example of primary hyperthyroidism?

A

Graves disease

52
Q

Example of secondary hyperthyroidism

A

TSH-secreting pituitary tumor

53
Q

Presence of what in the serum helps distinguish Graves Disease from adenoma of pituitary thyrotrophs (TSH-secreting tumors)?

A

TSI (thyroid-stimulating immunoglobulins)

54
Q

How do TSIs cause hyperthyroidism in Graves disease (increase of T3 and T4 in the blood)?

A

They bind to TSH receptors in the absence of TSH and so TSH receptor is ON all the time.

55
Q

TSH levels in Graves disease high or low?

A

Low (negative feedback)

56
Q

Which disease is an example of hypothyroidism?

A

Hashimoto’s thyroiditis

57
Q

Effect of excess TH on bone

A

Osteoporosis

58
Q

Effect of TH deficiency on bone

A

Stunted growth

59
Q

In Hashimoto’s Disease TH synthesis is impaired by antibodies against _________, leading to decreased T3 and T4 secretion.

A

Thyroglobulin or TPO

60
Q

In Hashimoto’s Thyroiditis TSH levels are _____ due to loss of negative feedback. This has trophic effect and leads to _____.

A

high; Goiter

61
Q

Possible causes of Cretinism (example of hypothyroidism)

A
  • Iodine deficiency
  • Maternal intake of anti-thyroid medications
  • Impaired development of thyroid gland
  • Inherent deficit in synthesis of thyroid hormones
62
Q

Hypothyroidism due to iodine deficiency results in what processes?

A
  • Transient decrease in synthesis of T3 and T4
  • TSH levels elevated
  • Goiter

Endo/Repro (8 decks)

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