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Thyroid Gland Flashcards

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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
In hyperthyroidism T3 resin uptake is Increased or decreased?
Increased
26
In hypothyroidism T3 resin uptake is increased or decreased?
Decreased
27
T/F: even though levels of TBG are elevated during pregnancy, levels of free, physiologically active thyroid hormones are normal.
True ("clinically euthyroid")
28
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 _______ __________.
Negative feedback
29
Percentage of T3 bound to TBG vs percentage of T4 bound to TBG
T3: 99.5% T4: 99.98%
30
How are T3 and T4 transported from blood into cytosol in thyroid or periphery?
MCT8/10 transporters
31
How many types of deiodinases are there?
Two: type 1 & 2 (different tissue distributions and affinities)
32
T/F: T3 receptors are in cytosol
False: in nucleus
33
Effect of TH on Growth
Growth | Bone maturation
34
Effect of TH on Nervous System
CNS maturation
35
Effect of TH on BMR
Increase Na+/K+ ATPase Increase O2 consuption Increase Heat production Increase BMR
36
Effect of TH on Metabolism
``` Increase glucose absorption Increase Gluconeogenesis Increase Glycogenolysis Increase Lipolysis Increase Protein Synthesis and degradation (net catabolic) ```
37
Effect of TH on Cardiovascular System
Increase cardiac output | Up regulation of beta-adrenergic receptors
38
Effect of TH on GI
Increase motility
39
Proteins whose synthesis is unregulated by TH
- Na+/K+ ATPase - Transport proteins - betta-1 adrenergic receptors (cardiac muscle) - Myosin (cardiac muscle) - Ca2+ ATPase - Lysosomal enzymes - Proteolytic enzymes - Structural proteins
40
T/F: Cholesterol and TG levels in blood are inversely correlated with TH levels
True (higher TH, lower cholesterol)
41
TH is required for conversion of carotene to vitamin A, therefore hypothyroidism can lead to ________.
Blindness
42
____days before activity of T4 begins ____days before activity of T4 reaches maximum Activity of T4 persists _____wk
2-3 10-12 6-8
43
Are actions of T3 slower or more rapid than that of T4?
more rapid
44
_____ hr before activity of T3 begins | _____ days before activity of T3 reaches maximum
6-12 | 2-3
45
Is Thyroid Hormone more sensitive to stimulation by parasympathetic or sympathetic nervous system?
Sympathetic
46
High levels of TH increases the number of _-__________ receptors in cardiac muscle cells.
beta1-adrenergic
47
Effects of excess TH on skin
Sweating
48
Effect of TH deficiency on skin
Dry | Mixedema
49
Effect of excess TH on CNS
Agitation Anxiety Difficulty concentrating Hyperreflexia
50
Effect of TH deficiency on CNS
``` Cretinism (congenital) In adults: listlessness slowed movement somnolence impaired memory decreased mental capacity ```
51
Which disease is an example of primary hyperthyroidism?
Graves disease
52
Example of secondary hyperthyroidism
TSH-secreting pituitary tumor
53
Presence of what in the serum helps distinguish Graves Disease from adenoma of pituitary thyrotrophs (TSH-secreting tumors)?
TSI (thyroid-stimulating immunoglobulins)
54
How do TSIs cause hyperthyroidism in Graves disease (increase of T3 and T4 in the blood)?
They bind to TSH receptors in the absence of TSH and so TSH receptor is ON all the time.
55
TSH levels in Graves disease high or low?
Low (negative feedback)
56
Which disease is an example of hypothyroidism?
Hashimoto's thyroiditis
57
Effect of excess TH on bone
Osteoporosis
58
Effect of TH deficiency on bone
Stunted growth
59
In Hashimoto's Disease TH synthesis is impaired by antibodies against _________, leading to decreased T3 and T4 secretion.
Thyroglobulin or TPO
60
In Hashimoto's Thyroiditis TSH levels are _____ due to loss of negative feedback. This has trophic effect and leads to _____.
high; Goiter
61
Possible causes of Cretinism (example of hypothyroidism)
- Iodine deficiency - Maternal intake of anti-thyroid medications - Impaired development of thyroid gland - Inherent deficit in synthesis of thyroid hormones
62
Hypothyroidism due to iodine deficiency results in what processes?
- Transient decrease in synthesis of T3 and T4 - TSH levels elevated - Goiter

Endo/Repro (8 decks)

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