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Physiology II > Thyroid Hormones (L12) > Flashcards

Thyroid Hormones (L12) Flashcards

1
Q

Thyroid hormone controls BMR, which stands for ____

A

basal metabolic rate

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2
Q

The thyroid is composed of follicles. Follicles are composed of ___ and ____

A

follicular (thyroid) cells and colloid cells

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3
Q

Colloid (protein) solution contains
____ and stored _____

A

thyroglobulin (TG) ; thyroid hormone

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4
Q

Thyroid Hormone Synthesis requires adequate intake of ____

A

Iodine

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5
Q

Where does iodide trapping occur? Via what transporter?

A

Iodide trapping occurs within follicular cells via NIS (Na/Iodide Symporter)

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6
Q

What is the ‘backbone’ for thyroid
hormone synthesis?

A

Thyroglobulin (TG)

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7
Q

What cell type produces thyroglobulin?
Where is TG release into?

A

Follicular cells
TG is released into colloid

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8
Q

True or False: TG contains large numbers of amino acid serines

A

False - TG contains large numbers of amino acid tyrosines

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9
Q

What are two ways that thyroid hormones are made?

A

1) Incorporating iodine onto tyrosines
2) Coupling iodinated tyrosines

Note: In both cases, it occurs while tyrosine is part of thyroglobulin

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10
Q

What does this image display?

A

Coupling of Iodinated Tyrosines

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11
Q

What does this image display?

A

Incorporating Iodine onto Tyrosine

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12
Q

What molecule moves I2 from the follicular cell into the colloid?

A

Pendrin

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13
Q

Which enzyme incorporates iodine onto tyrosines, causing TG to have just tyrosines to having MIT and DIT and, eventually, T4 and T3?

A

TP (Thyroperoxidase)

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14
Q

What is mostly made in the thyroid gland: T3 or T4?

A

T4

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15
Q

What are the three roles of TP (thyroperoxidase)?

A

1) oxidation of iodide
2) iodination of tyrosine
3) coupling of iodotyrosines

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16
Q

_____ allows for conversion of I- to I2

A

Thyroperoxidase

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17
Q

Large amount of thyroid hormones are stored in the ___, which enhances one’s ability to survive acute iodine deficiency

A

colloid

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18
Q

Which trophic hormone stimulates the synthesis and secretion of thyroid hormone?

A

TSH

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19
Q

True or False: TSH promotes gland growth and cell integrity

A

True

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20
Q

Endocytosis will be facilitated by ___

A

TSH

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21
Q

As 2nd messengers are generated, it promotes ____ of thyroid hormone and TF molecule, which leads to T3/4

A

As 2nd messengers are generated, it promotes endocytosis of thyroid hormone and TF molecule, which leads to T3/4 secretion

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22
Q

When thyroid hormone is secreted, iodide from any MIT/DIT is ___

A

recycled

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23
Q

Once T4 and T3 are made, they enter into ___

A

circulation

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24
Q
A

Delete

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25
Q

Stress (physical, starvation, and infection) inhibits ___

A

TRH (thyroid-releasing hormone)

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26
Q

What two factors increase TRH?

A

1) Diurnal Rhythm
2) Temperature

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27
Q

If an excess of thyroid hormones is made, what two molecules are inhibited?

A

TRH and TSH

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28
Q

True or False: TSH is made in the hypothalamus while TRH is made in the anterior pituitary

A

True

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29
Q

True or False: Thyroid hormone is an amino acid derivative hormone with steroid-like characteristics

A

True

30
Q

What is the half life of T3 and T4?

A

T3 = 1.0 days
T4 = 6.2 days

31
Q

Most T3 is produced at the tissue level by de-iodination of ___

A

T4

32
Q

Type 1 and Type 2 Deiodinase produces ___

A

T3

33
Q

Which type of deiodinase produces rT3?

A

Type 3 Deiodinase

34
Q

Where are Type 1 Deiodinases found?
Where are Type 2 Deiodinases found?

A

Type I: Liver and Kidney
Type II: Muscle and Brain

35
Q

Most T3 is produced at the tissue level by de-iodination of T4 by which types of deiodinases?
How?

A

Type 1 and Type 2 Deiodinases
Via: removal of outer iodide

36
Q

Which is more potent: T3 or T4

A

T3

37
Q

At the tissue level, T4 can also be deiodinate by which type of deiodinase to make rT3 (inactive)?

A

Type 3 Deiodinate (removes innher iodide)

38
Q

Equal amounts of what two molecules are made in the peripheral tissues?

Why might this be advantageous?

A

T3 and rT3
-Allow for maximal increase and maximal decrease in T3 and rT3

39
Q

T4 is converted to T3 via Type ___ Deiodinase
T4 is converted to rT3 via Type __ Deiodinase

A

T4 is converted to T3 via Type 1 Deiodinase
T4 is converted to rT3 via Type 3 Deiodinase

40
Q

True or False: The activity of Type 1 Deiodinase can be altered at the tissue level

A

True

41
Q

What inhibits Type 1 Deiodinase?

A

1) Starvation
2) Cancer
3) Renal failure
4) Burns
5) Trauma

42
Q

Prolonged stressors can increase the secretion of what two molecules?

A

1) Epinephrine - increases adipose tissue lipolysis
2) Cortisol - increases protein breakdown

43
Q

If Type 1 Deiodinase is inhibited, T3 levels ___ while inactive rT3 levels ___

Why might this be helpful during severe illness or starvation?

A

decrease; increase

  • LIMITS T3 induced substrate breakdown in tissues
44
Q

True or False: Prolonged stressors can increase the secretion of thyroid hormones

A

False - prolonged stressors can decrease the secretion of thyroid hormones

(T4>T3)

45
Q

T4 is converted to ___ at the tissue level

A

rT3

46
Q

True or False: Brain, spleen, and gonads have few receptors for thyroid hormones so their BMR and temperature do not change

A

True

47
Q

Which thyroid receptor isoforms is more prevalent in the brain (alpha or beta)?

Which thyroid receptor isoform is more prevalent in the liver, muscle, and pituitary gland?

A

Brain = Alpha
Liver, muscle, and pituitary = Beta

48
Q

What are the overall roles of thyroid hormone in body metabolism?

A

1) Energy
2) ATP synthesis
3) Heat production
4) Calorie supply
5) O2 consumption

49
Q

True or False: Thyroid hormone involves protein synthesis

A

True

50
Q

What are two intracellular effects of thyroid hormone?

A

1) Increase BMR
2) Increase synthesis and activity of Na/K ATPase

51
Q

What are three systemic effects of thyroid hormone?

A

1) Mobilization of substrates for ATP generation by cells
2) Increased delivery of substrate to cells
3) Increased delivery of O2 to cells; CO2 removal from cells

52
Q

Intracellular effects of thyroid hormone?

A

Increased synthesis of:
- metabolic enzymes
- mitochondrial enzymes
- substrate transporters
- Na/K ATPase

Increased metabolism of susbtrates:
- heat and ATP production
- O2 consumption

Increased activity of Na/K ATPase
- heat production

53
Q

True or False: Once T4 is converted to T3, T3 enters the nucleus and increases synthesis of
- metabolic enzymes
- mitochondrial enzymes
- substrate transporters
- Na/K ATPase

A

True

54
Q

True or False: thyroid decreases availability of substrate for cells

A

False - Thyroid hormone increases the availability of substrates for cells

55
Q

___ substrates increases food intake while ___ substrates store

A

Exogenous substrates; endogenous

56
Q

How do thyroid hormones increase HR and SV?

A

Increase number of beta-adrenergic receptors in the heart

57
Q

True or False: Thyroid hormones decrease CO

A

False - thyroid hormones increase CO

58
Q

True or False: Thyroid hormones increase delivery of substrates to cells

A

True

59
Q

Thyroid hormones increase respiratory rate. How does this affect O2 delivery and removal of CO2?

A

Increase O2 delivery and removal of CO2

60
Q

Thyroid hormone is permissive for full physiological effects of:
______
______
______

A

Epinephrine
Insulin
GH

61
Q

True or False: Thyroid hormone is required for normal in utero brain development

A

True

62
Q

How do you evaluate thyroid abnormalities?

A

TSH, T3/T4
Evaluate symptoms

63
Q

Symptoms associated with hyperthyroidism?
Symptoms associated with hypothyroidism?

A

Hyperthyroidism: weight loss, tachy, sweating, and diarrhea

Hypothyroidism: weight gain, brady, cold intolerance, and constipation

64
Q

Graves’ Disease is associated with _____

A

hyperthyroidism

65
Q

____: TSH receptor antibodies that activate TSH receptor

A

Graves’ Disease: TSH receptor antibodies that activate TSH receptor

66
Q

True or False: Hyperthyroidism can be due to tumor of follicular cells or abnormal TRH/TSH secretion

A

True

67
Q

Four ways to treat hyperthyroidism?

A

1) Inhibit iodide trap using thiocynate or perchlorate
2) Inhibit TP activity
3) Surgically remove some thyroid gland
4) Thyroid gland ablation

68
Q

Hasimoto’s Disease is an autoimmune disease, which results in ___

A

hypothyroidism

69
Q

Cause of Hypothyroidism?

A

1) Hashimoto’s
2) Surgical removal
3) Hypothalamic/pituitary failure
4) Low iodine in diet

70
Q

Treatment for Hypothyroidism?

A

Exogenous thyroid hormone (synthetic T4)

Physiology II (23 decks)

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