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Endocrinology > Physiology of thyroid gland > Flashcards

Physiology of thyroid gland Flashcards

1
Q

3 parts of thyroid gland

A

left, right branch, isthmus

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2
Q

Things released by thyroid gland

A

thyroxin, triiodothyronine, calcitonin

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3
Q

____ cells surround colloid

A

follicular

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4
Q

____ bring iodide to follicular cells

A

blood vessels

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5
Q

______ release calcitonin

A

parafollicular cells

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6
Q

____ contains thyroglobulin.

A

Colloid

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7
Q

Iodide uptake occurs on the _____ side of the ______ cell via what mechanims?

A

Basolateral, follicular, Na/I symporter

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8
Q

What transport brings iodide into the basolateral side of the follicular cell and what transport brings it out the apical side?

A

Basolateral: Na/I Symporter
Apical: Pendrin

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9
Q

What is iodide trapping?

A

The process of intracellular accumulation

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10
Q

What does iodide do in the colloidal lumen?

A

It binds tyrosine residues on thryoglobulin

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11
Q

____ is a large protein with few tyrosine residues

A

Thryoglobulin

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12
Q

Where is thyroglobulin synthesized?

A

follicular cells

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13
Q

What is thyroid peroxidase and what does it do?

A

It is on the luminal side of of secretory vescicles (secreteing thyroglobulin). It oxidizes iodide to Io, which is unstable, so that it reacts with thyroglobulin

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14
Q

Only ____ tyrosine residues on thyroglobulin are iodinated.

A

20%

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15
Q

What happens after endocytosis of iodinated thyroglobulin?

A

Hydrolysis forms T3 and T4 in lyso-endosome, iodide is recycled

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16
Q

What is the ration of T4 to T3 produced in lyso-endosome?

A

10:1

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17
Q

What percent of T4 is bound? T3?

A

99.98%; 99.5%

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18
Q

Formed T3 and T4 are released into the blood where they immediately ____.

A

Bind to binding protein, mostly TBG

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19
Q

What conditions increase TBG? What does this to do total and free T3 and T4?

A

Pregnancy, hepatitis, heroin abuse - increases total T3 and T4, but NOT free hormone

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20
Q

What conditions decrease TBG? What does this do to total T3 and T4?

A

Steroids- decreases total but NOT free hormone

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21
Q

Compare the half lives of T3 and T4

A

bound T4- 8 days

bound T3- 24 hrs

22
Q

What is structurally required for active hormone?

A

2 iodide needed on inner ring and at least 1 on the outside

23
Q

What enzyme catalyzes T4–> T3?

A

5’/3’mondeoiodinase

24
Q

What enzyme catalyzes T4 to rT3?

A

5/3 monodeiodinase

25
Q

Metabolism of T3 and rT3?

A

T2–> T1–> Thyronine

26
Q

What is type 1 deiodinase?

A

5’/3’: T4–> T3–> Liver, Kidney, Thyroid, Primarily responsible for free hormone in the blood

27
Q

What is type 2 deiodinase?

A

5’/3’: T4–> T3–> pituitary (presents T3 to pituitary, a TH regulator, no regulation here during starvation, CNS, placenta

28
Q

What does 5/3 Deiodinase do?

A

T4–> rT3–> All tissues

29
Q

Where is the thyroid receptor?

A

nucleus

30
Q

Describe the action of thyroid hormone on target cells

A

T3 or T4 enter cell–> nuclear target–> THR which dimerizes with RXR and acts direly on DNA to both increase and decrease production

31
Q

____ is the major hormone secreted by the thyroid and carried in the circulation. ____ is the physiologically active form of hormone.

A

T4; T3

32
Q

Effect of hyperthyroid on basal metabolic rate

A

Increase (increase O2 consumption and thermogenesis)

33
Q

Effect of hyperthyroid on carb metabolism

A

increase with no change in glucose in someone with a NORMAL pancreas

34
Q

Effect of hyperthyroid on lipid metabolism

A

increase

35
Q

Effect of hyperthyroid on serum cholerterol

A

decrease

36
Q

Effect of hyperthyroid on thermogenesis

A

increase

37
Q

Effect of hypothyroid on basal metabolic rate

A

decrease

38
Q

Effect of hypothyroid on carb metabolism

A

decrease; no change in blood glucose

39
Q

Effect of hypothyroid on protein metabolism

A

decrease

40
Q

Effect of hypothyroid on lipid metabolism

A

decrease

41
Q

Effect of hypothyroid on serum cholesterol

A

increase

42
Q

Effect of hypothyroid on thermogenesis

A

decrease

43
Q

Describe what happens to Na/K ATPase pump and actin with T3?

A

Increase, actin–> tachycardia

44
Q

Increase in TRH stimulates what?

A

thyrotrophs in ant. pit. to increase release of TSH –> T3, T4

45
Q

What role does somatostatin play in regulation of thyroid?

A

Negative regulation at level of thyrotrophs in ant. pituitary

46
Q

Role of dopamine in thryoid regulation

A

Negative regulation at level of thyrotrophs in ant pit

47
Q

Role of T3 and T4 in thyroid regulation

A

Negative regulation on Thyrotrophs and TRH

48
Q

How does TSH increase thyroid secretion?

A

Increases activity of NIS (iodide uptake), stimulates iodination of thyroglobulin in follicular lumen, stimulates conjugation of iodinated tyrosines to generate T3 and 4, increase endocytosis of iodinated tyrosines to generate T3 and 4, stimulate proteolysis of iodinated thyroglobuin in lysoendosomes, increase secretion of T4 and T4 into circulation, exerts growth factor effects on the thyroid cells increasing their size and number

49
Q

Is TH important in development?

A

Yes- no sure why but low levels can be seen in dwarfism

50
Q

LOOK OVER LAST FEW SLIDES IF PATHO NOT COVERED IN FUTURE LECTURES

A

do it

Endocrinology (31 decks)

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