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Drew 921 > 4_Thyroid > Flashcards

4_Thyroid Flashcards

1
Q

Describe the location of the thyroid gland.

A

below larynx of either side, anterior to trachea in an H-shape

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2
Q

What percentage of thyroid hormone does T3 make up?

A

7%

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3
Q

t1/2 of T3

A

1 day

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4
Q

t12 of T4

A

6 days

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5
Q

Describe the relative potencies of T3 & T4.

A

T3 4x more potent

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6
Q

Describe the cell structure of the thyroid gland.

A

follicles of cuboidal epithelium surrounded by colloid

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7
Q

How is iodine trapped?

A

Na/K ATPase & TSH-linked NIS (Na/I symporter)

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8
Q

Where is TRH synthesized?

A

PVN of hypothalamus (affected by emotion, temp, etc)

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9
Q

Where is TSH secreted?

A

anterior pituitary

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10
Q

Other name for TSH?

A

thyrotropin

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11
Q

Describe the receptor pathway for TSH.

A

G-alpha-S

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12
Q

What is the effect of TSH binding its receptor in the thyroid?

A

increased activity of NIS, iodination of Tyr, Tg proteolysis; thyroid hyperplasia

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13
Q

What is the feedback circuit for TSH?

A

T3 & T4 only

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14
Q

Describe the steps in the formation of thyroid hormones.

A

1) TSH-dependent I trapping, 2) peroxidase oxidation, 3) Tg precursor secretion, 4) peroxidase iodization, 5) Tg auto-coupling, 5) pinocytosis, 6) proteolysis and secretion

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15
Q

Where is peroxidase located in the thyroid cuboidal cell?

A

at the apical membrane (colloid side)

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16
Q

Describe the action of peroxidase in the thyroid?

A

1) oxidizes iodide to yield I2 or I3-, 2) iodizes Tyr

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17
Q

What are the products of Tg auto-coupling?

A

1) MIT + DIT = T3; 2) DIT + MIT = RT3; 3) DIT + DIT = T4

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18
Q

What is the chemical numbering name for T3?

A

3,5,3’-T3

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19
Q

What is the chemical numbering name for RT3?

A

3,3’,5-T3

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20
Q

What is the physiologic function of RT3?

A

none known

21
Q

Describe the structure of Tg precursor.

A

chain of Tyr

22
Q

How is Tg proteolyzed after reuptake via pinocytosis?

A

fusion with a lysosome

23
Q

Describe the relative concentrations of T3 and T4 in the plasma.

A

T4 much greater than T3

24
Q

How are T3 & T4 transported in the plasma?

A

thyroxine-binding globulin

25
Q

How are T3 & T4 imported?

A

via AA transporters

26
Q

Describe the storage of T3 & T4.

A

stored for days-week intracellularly

27
Q

Why is T3 more potent?

A

T4 binds stronger intracellularly

28
Q

What are the adverse effects brought about by the T3/T4 receptor?

A

CV: increased HR, contractility, tissue flow, CO

29
Q

What is the function of T3/T4 via its receptor?

A

increase BMR (via increased Na/K-ATPase, increased plasma glucose, increased protein turnover, increased mitochondria)

30
Q

Describe the receptor action of T3/T4.

A

nuclear hormone receptor forms a homodimer or heterodimer with RXR at specific thryoid HREs

31
Q

What is graves disease?

A

a toxic goiter

32
Q

What is TSI?

A

thyroid-stimulating immunoglobulin, an antibody that mimics TSH

33
Q

How is hyperthyroidism caused?

A

by a toxic goiter (Graves Disease)

34
Q

How is hyperthyroidism diagnosed?

A

1) increased T3 or T4, 2) TSI, 3) BMR +30 to +60

35
Q

How is hyperthyroidism treated?

A

surgery or propylthiouracil

36
Q

How does propylthiouracil work?

A

blocks MIT/DIT coupling and iodination via inhibiting peroxidase

37
Q

What is a side effect of propylthiouracil?

A

can increase TSH and cause a goiter

38
Q

What are non-obvious symptoms of hyperthyroidism?

A

sweating, fatigue, fine hand tremor, diarrhea, exophthalmos

39
Q

What is exophthalmos?

A

protrusion of eyeball caused by swelling of retro-orbital tissues and degeneration of extra-ocular muscles

40
Q

How is an endemic nontoxic colloid goiter caused?

A

iodine deficiency

41
Q

How is an endemic nontoxic colloid goiter treated?

A

iodine

42
Q

What causes an idiopathic nontoxic colloid goiter?

A

thyroiditis: inflammation causes hypothyroidism, which increases TSH; or T3/T4 synthetic enzyme defects

43
Q

What is myxedema?

A

facial swelling due to increased proteoglycans and hyaluronic acid

44
Q

What are the effects of hypothyroidism?

A

failure of trophic functions (less hair, scaly skin, husky voice), myxedema, arteriosclerosis, altered lipid metabolism, less bile/cholesterol secretion

45
Q

What is cretinism?

A

extreme hypothyroidism in infance or early childhood leading to growth failure

46
Q

What are the various forms of cretinism?

A

1) congenital, 2) genetic, 3) endemic

47
Q

What causes congenital cretinism?

A

no thyroid

48
Q

What causes genetic cretinism?

A

no T3/T4 production

49
Q

What causes endemic cretinism?

A

inadequate dietary iodine

Drew 921 (33 decks)

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