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Endocrinology > Week 4 - Thyroid A/P > Flashcards

Week 4 - Thyroid A/P Flashcards

1
Q

What is the anatomical location of the thyroid gland?

A

Straddling the trachea at the level of C5-T1, just below the laryngeal prominence

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2
Q

Thyroid first becomes functional in _____ _____ _____

A

Early fetal life

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3
Q

The thyroid gland is comprised of numerous _________

A

Follicles

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4
Q

What do follicular cells secrete?

A

Thyroid hormones

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5
Q

Follicular cells have transporters for which mineral? What is this transporter and what does it do?

A

Iodine
Na/I symporter
Traps iodine from the plasma and concentrates it within the thyroid follicle (iodine in follicle 30-40x more concentrated than in plasma

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6
Q

What do parafollicular cells (C-cells) secrete? What does this do?

A

Secretes calcitonin: inhibits bone resorption.

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7
Q

T/F: Calcitonin is clinically important as a tumor marker produced by medullary thyroid cancer

A

True

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8
Q

What is mostly composed of thyroglobulin: an iodine-protein secreted by the follicular cells into the lumen of the follicle?

A

Colloid

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9
Q

Thyroid follicular cells arise from _______ _______ _________

A

Midline thyroid diverticulum

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10
Q

Parafollicular cells arise from _________ _____ ______

A

Neural crest cells

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11
Q

Follicular cells descend via the ____________ duct to the anterior trachea and bifurcates forming 2 lobes.

A

Thyroglossal duct

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12
Q

Thyroglossal duct may give rise to what pathology? What are possible consequences?

A

Midline cysts lined by squamous epithelium.

May become infected or give rise to thyroid tumors

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13
Q

Which nerve courses behind the thyroid?

A

Recurrent laryngeal nerve

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14
Q

Which glands lie behind the upper and middle portions of the thyroid lobes? How many pairs are there?

A

Parathyroid glands; 2 pair

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15
Q

Which structure does the thyroid wrap around?

A

Trachea

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16
Q

What is the cause of bruits or thrills in the thyroid?

A

Rich blood supply increased in hyperthyroidism

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17
Q

What are the 5 iodine-containing hormones? From which amino acid are they all derived?

A
  1. Thyroxine (LT4)
  2. Triiodothyronine
  3. T2 (DIT)
  4. T1 (MIT)
  5. rT3 (Reverse T3)
    Derived from tyrosine
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18
Q

Which thyroid hormone is known pharmaceutically as Synthroid?

A

Thyroxine (LT4)

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19
Q

Which thyroid hormone contains 4 iodine atoms, levels reach significant amount at 18-20 weeks gestation and plasma half-life is 7 days?

A

Thyroxine (LT4)

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20
Q

Which thyroid hormone is pharmaceutically known as “Liothyronine” - Cytomel?

A

Triiodothyronine (T3)

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21
Q

Which thyroid hormone contains 3 iodine atoms, about 15% of the total body’s release of this hormone comes from the thyroid gland, and levels remain low until 30 weeks gestation?

A

Triiodothyronine (T3)

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22
Q

Where is T4 converted to T3?

A

Peripheral tissues

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23
Q

Which enzyme converts T4 to T3?

A

Deiodinases

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24
Q

Which thyroid hormone binds and activates thyroid hormone receptors?

A

T3

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25
Q

Which thyroid hormone is considered inactive and may stimulate mitochondria?

A

T2 (DIT)

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26
Q

Which 3 thyroid hormones are considered inactive?

A

T2, T1, and rT3

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27
Q

Which hormone is released by the parafollicular cells in the thyroid?

A

Calcitonin

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28
Q

Calcitonin opposes effects of which other hormone?

A

Parathyroid hormone

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29
Q

Calcitonin serves as a marker for which type of cancer?

A

Medullary thyroid cancer

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30
Q

What is the process where an iodine ion (I-) is brought into follicular cells (co-transported with Na+)?

A

Iodination

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31
Q

What is the enzyme that oxides iodine ion to iodide (I2)?

A

Thyroperoxidase (TPO)

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32
Q

What is the term for TSH from the anterior pituitary binding to TSH-receptors on the surfaces of follicular cells and stimulating the endocytosis of the colloid?

A

TSH binding

33
Q

TSH increases the production of thyroglobulin and the number of follicular cells: high TSH levels may lead to which issues with they thyroid?

A

Excessive synthesis of thyroglobulin and follicular cell hypertrophy, causing an enlarged thyroid (goiter)

34
Q

The release of T4 occurs with endocytosed vesicles fusing with ________ of the follicular cell? Lysosomal enzymes cleave the T4 from the ________ _____________

A

lysosomes

iodinated thyroglobulin

35
Q

Iodine is found as iodide (I-) or iodate (IO3-) in food/water. It is converted to iodide in which organ?

A

stomach

36
Q

World Health Organization (WHO) daily dietary iodine intake:
____ mcg for adults (1100 mcg/max = 1.1 mg)
____ mcg for pregnant/lactating women
___-____ mcg for children

A

150 mcg for adults
200 mcg for pregnant/lactating women
50-250 mcg for children

37
Q

Intake < ____ mcg/day: gland can’t maintain normal hormone production & enlarges (goiter, hypothyroidism)

A

50 mcg/day

38
Q

Thyroid stores ___-___mg of iodine (thyroid hormones & iodinated tyrosines)

A

8-10 mg of iodine

39
Q

What are the main sources of iodine?

A
  • Seafood: fish, shellfish, kelp, etc.
  • Dairy products: milk, cheese, eggs
  • Plants grown on iodine-rich soils
  • Iodized salt: fortified with iodine
  • Excess may induce hyperthyroidism: Jod-Basedown phenomena
  • Supersaturated potassium iodide (SSKI)
40
Q

Iodine may be displaced from body tissues by which other halogens?

A
  • Bromine: found in baked goods, plastics, soft drinks, medications, pesticides
  • Fluorine: fluoridated drinking water
  • Perchlorate (rocket fuel) contamination in food
41
Q

Which 2 conditions can be associated with iodine deficiency?

A
  1. Fibrocystic breasts/Breast cancer

2. Stomach cancer

42
Q

What is a radioactive isotope of iodine

that is a component of nuclear fallout: that becomes concentrated in the thyroid? What is the treatment?

A

Iodine-131

High dose non-radioactive iodine given as treatment: 130 mg/24 hours (supplies 100 mg of iodine)

43
Q

Secretion of TSH is primarily regulated by what?

A

Levels of T4 & T3

44
Q

Thyroid-releasing hormone (TRH) from the

hypothalamus stimulates the release of _____.

A

TSH

45
Q

TRH also found in which 7 other areas of the body?

A
  1. pancreatic islet cells
  2. GI tract
  3. placenta
  4. heart
  5. prostate
  6. testes
  7. ovaries (role is unknown in these tissues)
46
Q

Which 3 factors increase TSH release?

A
  1. Cold
  2. Alpha-adrenergic agonists
  3. Hypothyroidism
47
Q

Which 4 factors decrease TSH release?

A
  1. Hyperthyroidism
  2. Somatostatin
  3. Dopamine, dopamine agonists (bromocriptine)
  4. Glucocorticoids/cortisol
48
Q

What are 6 effects of TSH on the thyroid cell?

A
  1. Upregulates sodium-iodide symporter
  2. Stimulates iodination of thyroglobulin
  3. Stimulates conjugation of iodinated tyrosine residues
  4. Increases endocytosis of iodinated thyroglobulin
  5. Stimulates proteolysis of iodinated thyroglobulin to form
    T4 & T3
  6. Secretion of T4 & T3 into blood
49
Q

TSH has which 3 trophic effects?

A
  1. Causes hypertrophy & hyperplasia of follicular cells
  2. Increases vascularity of thyroid gland
  3. Excess TSH may lead to goiter
50
Q

TSH Circadian Rhythm - TRH-stimulated TSH secretion is pulsatile: mean TSH pulse amplitude of _____ mU/L every ___ hours.
Normal individuals have a circadian rhythm in TSH release: peak between _____ and ____.

A

0.6 mU/L every 2 hours;

midnight and 4am

51
Q

T/F: Thyroid hormones are lipid-like and poorly soluble in water, requiring transport proteins

A

True

52
Q

_____% of T4 & T3 are non-covalently bound to carrier proteins. The remainder of free thyroid hormone can move into tissues (fT4, fT3)

A

~99.9%

53
Q

Binding globulins are synthesized in the ______.

A

liver

54
Q

What are the 3 carrier proteins in the transport of thyroid hormones in plasma?

A
  1. Thyroxine-binding globulin (TBG) (70%)
    Increased in: pregnancy, high estrogen states (OCP use), liver disease
  2. Transthyretin (Thyroxine-binding prealbumin) (10-15%)
  3. Albumin (15-20%)
55
Q

The plasma half-life of T4 is _____ days.

A

7

56
Q

What % of T4 is metabolized by deiodination? Some is converted to T3 & rT3, and the remainder is removed via which 2 processes?

A

80%

liver glucuronidation & sulfation

57
Q

Plasma half-life of T3 is ____ day(s). Half-life of rT3 is _____ day(s).

A

1 day; 0.2 days

58
Q

Deiodinase enzymes either:
Activate thyroid hormone (T4 —> T3), which means…
-or-
Inactivate thyroid hormone (T4 —> reverse T3 (rT3)), which means…

A

Outer ring of T4 is 5’ deiodinated to produce T3

Inner ring of T4 is deiodinated to produce rT3. T3 can also be converted to T2.

59
Q

Deiodinases are which type of proteins (uses which mineral as a cofactor)?

A

Selenoprotiens - uses selenium as a co-factor

60
Q

Once inside the cell, T4 —> T3 via the action of ___ or ___. T3 then enters the nucleus, where it binds to a ____

A

DI or DII; Thyroid hormone receptor

61
Q

Thyroid hormone receptors regulate gene expression by binding to ______ _____ ______ in DNA (several types exist,
but the most common are retinoid X receptors (RXR)) —->
once bound the TR/RXR initiates gene
transcription/protein synthesis.

A

hormone response elements (HREs)

62
Q

T3 is [more/less] actively bound to TR than T4?

A

MORE

63
Q

What are 3 isoforms of the thyroid hormone receptor?

A
  1. alpha-1
  2. beta-1
  3. beta-2
64
Q 
How and where are the following expressed? 
TR-alpha1:  
TR-alpha2:  
TR-beta1: 
TR-beta2:
A

TR-alpha1: widely expressed, especially in cardiac & skeletal muscle
TR-alpha2: widely expressed, but unable to bind hormone
TR-beta1: mostly expressed in brain, liver, kidney
TR-beta2: mostly expressed in pituitary & hypothalamus

65
Q

Thyroid hormone (TH) receptors are located in the _____ of most of the body’s cells

A

nuclei

66
Q

By ___-___ weeks of development, fetus is largely dependent on it’s own production of thyroid hormones

A

15-18

67
Q

What is the absence of thyroid hormone during fetal life resulting in a poorly developed nervous system and a form of mental retardation?

A

Cretinism

68
Q

What is the most common cause of cretinism worldwide?

A

iodine deficiency

69
Q

T/F: The nervous system may develop normally if iodine is given to the child starting at birth, although mental function may not be totally restored.

A

True

70
Q

What is the primary action of T3? What is the result?

A

Stimulation of Na/K-ATPases throughout the body and increases O2 consumption.
Results in a net increase in metabolic rate with an increase in the amount of body heat produced.

71
Q

T/F: The calorigenic action of thyroid hormone accounts for a large portion of the total heat produced by a person each day

A

True

72
Q

Thyroid hormone stimulates carbohydrate absorption from the SI resulting in increases in hepatic ______ and _______.

A

Gluconeogenesis and glycogenolysis

73
Q

T/F: Thyroid hormones decrease fatty acid release from adipocytes

A

FALSE! TH increases fatty acid release

74
Q

TH up-regulates which receptors in tissues like the heart and nervous system

A

Beta-adrenergic

75
Q

Unlike the sympathetic nervous system, how do thyroid hormones impact gut motility and blood pressure?

A

Increase GI motility
Induce vasodilation
Lower blood pressure

76
Q

What are 5 cardiovascular effects of TH?

A
  1. Stimulates transcription of sarcoplasmic reticulum Ca2+ ATPase: increases rate of myocardial diastolic relaxation
  2. Increases expression of myosin: enhances systolic function
  3. Increases expression of alpha-adrenergic receptors
  4. Increases rates of depolarization & repolarization of the SA node (increases heart rate)
  5. Decreases peripheral vascular resistance, diastolic function & ventricular filling
77
Q

T3 [decreases/increases] production of erythropoietin: [decreases/increases] erythropoiesis.

A

Increases; increases

78
Q

What are the musculoskeletal responses to Hyperthyroidism:

Hypothyroidism:

A

Hyperthyroidism: increased bone loss, muscle turnover, hyperreflexia, fine distal hand tremor
Hypothyroidism: hyporeflexia (delayed deep tendon reflex relaxation)

79
Q

Which endocrine hormones are stimulated to be released by TH?

A
  1. Growth hormone
  2. Hypothyroidism: hyperprolactinemia
  3. Response of HPA axis to stress is blunted in hypothyroidism

Endocrinology (13 decks)

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