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*Neuroendocrine Exam 3 > 16. Thyroid Gland > Flashcards

16. Thyroid Gland Flashcards

1
Q

What is the anatomy of the thyroid follicle (the functional unit of the thyroid)?

A

Surrounded by a layer of epithelial cells and the lumen is filled w/ colloid.

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2
Q

What are C cells? What do they secrete?

A

Parafollicular cells.

Secrete calcitonin.

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3
Q

Can the epithelial cell size and amount of colloid change?

A

Yes, with activity.

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4
Q

What synthesizes thyroid hormone?

A

Follicular epithelial cells

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5
Q

What is colloid composed of?

A

Newly synthesized thyroid H attached to thyroglobulin.

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6
Q

What is produced in more quantity: T4 or T3?

A

10x more T4 is produced than T3

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7
Q

What element is rich in thyroid H?

A

Iodine

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8
Q

What catalyze the conversion of T4 to T3? Where does it happen?

A

Deiodinase.
80-90% in the periphery.
About 10-20% is secreted from the thyroid.

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9
Q

What can reduce the conversion of T4 to T3? (3)

A

Fasting
Medical/surgical stress
Catabolic diseases.

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10
Q

Deficiency of deiodinase mimics a dietary deficiency of what?

A

Iodine deficiency

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11
Q

What is favored favored when iodine levels are low?

A

T3 formation is favored when Iodide is low.

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12
Q

What is an effective treatment for hyperthyroidism?

A

PTU

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13
Q

What is the Wolff-Chaikoff effect?

A

When high levels of I- inhibit organification and synthesis of thyroid H.

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14
Q

How much of iodide is “trapped” in the thyroid?

How much is leaked from thyroid to the ECF?

A

120 ug is trapped.

60 ug is leaked.

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15
Q

How is iodine stored?

A

Iodinated as tyrosines of thyroglobulin.

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16
Q

How much thyroid H is secreted daily from a follicular cell?

A

60 ug

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17
Q

How can radioactive iodine be helpful?

A

It can help assess the activity of the thyroid.

-ex: hyperthyroidism, high uptake of radioactive iodine b/c high thyroid hormone production

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18
Q

The majority (99%) of thyroid H circulates in the bloodstream how?

A

Bound to plasma proteins (TBG, albumin, transthyretin)

1% is free.

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19
Q

What are the 3 main thyroid hormone binding proteins? (3)

A

Thyroid binding protein (TBG) - 70%
Transthyretin (TTR) - 10-15%
Albumin - 15-20%

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20
Q

Half life of T4 and T3

A

T4 - 6 days

T3 - 1 day

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21
Q

Most circulating thyroid H is:

A

T4

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22
Q

What does the T3 resin uptake test examine?

A

Tests circulating levels of TBG.

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23
Q

Hyperthyroidism and T4/T3 resin uptake levels

A

Increase in T4

Increase in T3 resin uptake

24
Q

Hypothyroidism and T4/T3 resin uptake levels

A

Decreased T4

Decreased T3 resin uptake

25
Q

Hepatic failure and TBG and T3 resin uptake levels

A

Decreased TBG

Increased T3 resin uptake

26
Q

Pregnancy and TGB and T3 resin uptake levels

A

Increase in TBG

Decrease in T3 resin uptake

27
Q

Hepatic failure causes a ________ in levels of TBG. How does that effect FREE T3, T4 levels?

A

Decrease.

Increases free T3/4, followed by inhibition of synthesis (neg feedback).

28
Q

Pregnancy causes an ________ in TBG levels.

How does that effect levels of bound T3/4, free T3/4 and synthesis of T3/4?

A

Increase in TBG.

Increases bound T3/4.
Decreases free T3/4.
Increases synthesis of T3/4.

29
Q

What does “clinically euthyroid” mean?

A

In pregnancy when there is a increased levels of T3/4, but active (free levels) of TH is normal.

30
Q

What 2 things does TSH regulate?

A

Growth of the thyroid.

Secretion of THs.

31
Q

What regulates TSH? (2)

A

TRH and free T3

32
Q

At what rate does TSH secretion occur?

A

Steadily

33
Q

What organ does T3/4 inhibit?

A

Ant pit and hypothalamus if levels are high

34
Q

What’s the second messenger for TSH at the thyroid?

A

Cyclic AMP

35
Q

Thyroid hormones can cause the synthesis of new:

A

Proteins. (Nak atpase, receptors, enzymes, myosin, Ca atpase)

36
Q

What is the effect of TH on BMR? How does it do that?

A

Increases basal metabolic rate.

Increases activity of NaK ATPase —> increased O2 consumption.

37
Q

What is the correlation of cholesterol/TAG plasma concentration w/ TH?

A

Inversely.

High cholesterol —> low thyroid.

38
Q

How do hypothyroid patients suffer from blindness/yellow skin?

A

Thyroid h is necessary for conversion of carotene to vit A

39
Q

What is the effect of TH on the mobilization of fats?

A

Increases fat mobilization.

40
Q

Whats the effect of TH on carb metabolism?

A

Increases GNG and glycogenolysis to free glucose..

Enhances insulin dependent entry of glucose into cells.

41
Q

How does T3 increase cardiac output?

A

Activates RAAS —> Increase preload —> increases CO

42
Q

What receptors do thyroid hormones stimulate the synthesis of?

A

Cardiac B1 adrenergic —> chronograph and inotropy.

Myocardium is more sensitive to SNS when TH is high.

43
Q

Low TH in perinatal development can lead to:

A

Abn synapsing.

Decreased dendritic branching/myelination.

44
Q

Primary hyperthyroidism is known as:

A

Graves’ disease

45
Q

What is an example of secondary hyperthyroidism?

A

TSH-secreting pituitary

46
Q

What happens to TSH levels in hyperthyroidism?

A

Decrease due to negative feedback of T3 on the ant pit.

IF the defect is in the ant pit, then TSH will in crease.

47
Q

What do thyroid-stimulating immunoglobulins do?

A

Stimulate the TSH receptor without TSH around. (Graves’ disease).

48
Q

How does thyroid-stimulating immunoglobulin effect TSH levels?

A

TSH levels decrease because high TH inhibits TSH secretion.

49
Q

Clinical signs of Graves’ disease

A

Exophthalamos (protrusion of eyes), periorbital edema.

50
Q

How is Graves’ disease diagnosed?

A

Elevated serum free and total T3/4 and clinical signs of goiter and ophthalmophaty.

51
Q

Primary causes of hypothyroidism

A

Agenesis
Gland destruction
Inhibiting TH synthesis/release.
Pituitary disease.

52
Q

How is hypothyroidism treated? How does is change with pt age?

A

Replacement doses of T4.

Younger patients need higher doses because they metabolize it quicker.

53
Q

Overprescribing T4 in postmenopausal women can cause:

A

Osteoporosis

54
Q

Hashimoto’s thyroiditis

A

TH synthesis is inhibited by thyroglobulin or TPO ABs —> low T3/4.
TSH is high.

55
Q

Cretinism is caused by:

A

Untreated postnatal hypothyroidism.

56
Q

Hypothyroidism and iodine deficiency

A

Iodine deficiency leads to decrease in synthesis of TH.
TSH levels increase.
Can have a goiter.

57
Q

Goiter develops in response to both:

A

Hyperthyroidism and primary hypothyroidism.

*Neuroendocrine Exam 3 (27 decks)

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