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Endocrine intro...hormones > 3.5 Thyroid > Flashcards

3.5 Thyroid Flashcards

1
Q

What hormone is released from the hypothalamus that eventually leads to thyroid hormone release? What kind of hormone is it?

A

Thyrotropin Releasing Hormone (TRH) is released from the hypothalamus (–> TSH release from anterior pituitary)

TRH is a tripeptide

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2
Q

What kind of receptor does TRH bind to to illicit TSH release?

A

TRH binds to GPCR –> IP3 –> Ca++ –> vesicular/membrane fusion and TSH release

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3
Q

TSH is composed of two chains (alpha and beta). Which chain is common to other pituitary hormones?

A

Alpha chain is common to TSH, LH, FSH, and hCG (placental hormone)

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4
Q

TSH is composed of two chains (alpha and beta). Which chain distinguishes TSH from other pituitary hormones?

A

Beta chain…significant for specific TSH events

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5
Q

What kind of receptor does TSH bind to?

A

TSH binds to a GPCR

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6
Q

What is the effect of TSH binding to its GPCR?

A

Secretion of mature thyroid hormones

Production of new thyroid hormone batch

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7
Q

What needs to be unregulated by TSH in order to synthesize more thyroid hormones?

A

Thyroid peroxidase synthesis
Thyroglobulin tsx
Na+/I+ symporter

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8
Q

There are ~7 steps to thyroid hormone synthesis. What is necessary to happen I in order for it to be used?

A

Iodide (I-) has to be oxidized to Iodine (I)

This is called organification

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9
Q

There are ~7 steps to thyroid hormone synthesis. What are the possible products of Iodine binding to tyrosine?

A

Monoiodothyronine (MIT)

Diiodothryonine (DIT)

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10
Q

There are ~7 steps to thyroid hormone synthesis. What happens after MIT and DIT are formed?

A

Conjugation of MIT/DIT or DIT/DIT occurs…forming T3 or T4 respectively

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11
Q

Which thyroid hormone, T3 or T4, has the shorter half-life?

A

T3 has the shorter half-life (~1 day)

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12
Q

Which thyroid hormone, T3 or T4, is more active?

A

T3 is more active…T4 can also bind to Thyroid Hormone Receptor, but it is often converted to T3

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13
Q

So basically, just short of all T3/T4 is circulating BOUND to a protein. Which proteins bind to thyroid hormones?

A

Thyroxine binding globulin (75% of each)
Transthyretin (20% T4; 5% T3)
Albumin (5%T4; 20% T3)

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14
Q

When are thyroid hormone binding proteins increased?

A

During pregnancy

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15
Q

What decreases thyroid hormone binding proteins?

A

Androgens
Hyperthyroidism
Malnutrition
Nephritic syndrome (causes protein loss)

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16
Q

Deiodinase I, II, and III all metabolize thyroid hormones to some extent. Which one is most prevalent in the liver and kidneys? What is the result of this enzymes activity?

A

Deiodinase I is primarily in the liver/kidneys

Deiodinase I converts T4 to either active T3 or inactive rT3

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17
Q

Deiodinase II is present in the brain, pituitary, skeletal and cardiac muscles. What are the results of its enzymatic activity?

A

Deiodinase II works with deiodinase I to convert T4 to active T3

I + II = active T3

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18
Q

Deiodinase III is present in the brain, skin, and placenta. What are the results of its enzymatic activity?

A

Deiodinase III works with deiodinase I to inactivate hormone…makes rT3

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19
Q

Where is the thyroid hormone receptor?

A

Pretty sure that TH binds to THR in the cytoplasm, enters the nucleus, and dimerizes with RXR

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20
Q

How does thyroid hormone enter a cell?

A

Either carrier-mediated transport (protein bound form?)

Diffusion (free form)

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21
Q

What are the main actions of thyroid hormone?

A

Regulation of BMR
Heat production
Glucose utilization, uptake, and synthesis
Permissive sympathetic effects (increase HR and contractility)

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22
Q

Why do most states mandate that all newborns get tested for thyroid function?

A

Because if hormone replacement is started early enough the child will grow/develop normally

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23
Q

What is cretinism?

A

Hypothyroid in infants

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24
Q

What are some signs of cretinism?

A

Profound mental/growth/motor/sexual retardation
Coarse hair
Protuberant abdomens

25
Q

What are two potential causes of cretinism?

A

Congenital lack of thyroid hormone in infants

Maternal hypothyroidism

26
Q

What can cause maternal hypothyroidism?

A

Lack of iodine in diet (rare)
Hashimoto’s thyroiditis (makes TSH receptor antibodies)
Exposure to radioactive iodine or antithyroid drugs during pregnancy

27
Q

What are the symptoms of low thyroid hormone in adults?

A

Lethargy/somnolence
Slowed intellectual functions (including speech)
Stiffness/aching muscles
Cold intolerance
Delayed deep tendon reflex and relaxation
Menorrhagia and anovulation

28
Q

Excess thyroid hormone in adults has a lot of down stream effects. What is a general rule to apply?

A

Excess thyroid hormone speeds things up (increased HR, increased bone resorption, increased GI motility, increased liver function…)

29
Q

What is thyrotoxicosis? What is thyroid storm?

A

Thyrotoxicosis is any cause of excess thyroid hormone concentration

Thyroid storm is the extreme version of thyrotoxicosis

30
Q

Knowing that excess thyroid hormone increases many basic functions, what drugs should be given to people with severe thyrotoxicosis?

A 
Beta blockers (there are increased receptors)
Thinamides (antithyroids)
Corticosteroids (for functional hypoadrenalism)
31
Q

What is the likelihood of a patient with severe thyrotoxicosis progresses to thyroid storm? What is the likelihood that a thyroid storm will end in death?

A

10% progress to thyroid storm

20-30% with thyroid storm die d/t disease

32
Q

What are some causes of primary hypothyroidism?

A

Congenital defects
Gland destruction
Iodine deficiency
Hashimoto’s thyroiditis or chronic lymphocytic thyroiditis (autoimmune disorders)

33
Q

What causes secondary hypothyroidism? Tertiary hypothyroidism?

A

Pituitary gland disorder causes secondary hypothyroidism

Hypothalamus disorder causes tertiary hypothyroidism

34
Q

What is Graves’ disease?

A

Production of Thyroid Stimulating Immunoglobulins (TSIs)

35
Q

If a Graves’ patient becomes pregnant, can the baby be effected by the TSIs?

A

Yes…IgG can cross the placental membranes

36
Q

What is a goiter?

A

Enlarged thyroid gland

37
Q

What can cause the formation of a goiter?

A

Hypo or hyperthyroidism

Iodine deficiency

38
Q

How can Iodine deficiency cause a goiter?

A

Iodine deficiency → low T3/T4 → increased anterior pituitary production of TSH → thyroid gland enlarges

39
Q

How can Graves’ disease cause a goiter?

A

Thyroid stimulating immunoglobulins activates thyroid gland enlargement regardless of the negative feedback

40
Q

What are three diagnostic tests for thyroid function?

A

TSH test
T3 and T4 test
TSI test

41
Q

What does a low TSH indicate? High TSH?

A

Low TSH –> hyperthyroidism

High TSH –> hypothyroidism

42
Q

What does high T3 and T4 indicate?

A

Hyperthyroidism…self explanatory

43
Q

When is the only time a TSI test is effective?

A

Graves’ disease

44
Q

Levothyroxine is a T4 drug. How many times does it have to be taken per day? Is it safe? Does it have a long or short half-life?

A

Levothyroxine should be taken once daily…it is safe at that dose, but has a narrow TI

Levothyroxine’s half-life is 7 days…reaches steady state in 6-8 weeks

45
Q

What dietary substances can decrease absorption of levothyroxine?

A

Iron, calcium, AlOH, and soy

46
Q

What conditions require a smaller dose of levothyroxine? What conditions require a higher dose of levothyroxine?

A

Old age and cardiac disease require a decreased dose

Pregnancy requires a 30-50% higher dose

47
Q

Liothyronine is a T3 drug. When would this drug be administered?

A

When quick onset is desirable

48
Q

What are three kinds of thioamides (thionamides)?

A

Propylthioruacil (PTU)
Methimazole
KI

49
Q

How does PTU work?

A

PTU inhibits deiodinase I and thyroid peroxidase

50
Q

How does methimazole work?

A

Methimazole only inhibits thyroid peroxidase

51
Q

Does PTU or methimazole have a longer duration of action?

A

Methimazole lasts 24hr…PTU only 12hr

52
Q

How long does it take for methimazole or PTU to be effective?

A

2 weeks

53
Q

What is a concern with PTU?

A

Liver injury

54
Q

When can KI be used?

A

Prep for thyroidectomy
thyroid storm
Protection from radioactive iodine

55
Q

How does KI work?

A

Basically, iodine flooding inhibits almost all aspects of iodine metabolism

56
Q

What are some side effects to KI use?

A

Allergic RXN
Sore teeth/gums
Excess salivation

57
Q

What is (131)Iodine used for?

A

Ablation of thyroid

58
Q

What is (123)Iodine used for?

A

Imaging of thyroid

59
Q

What hormones are negative regulators of thyroid hormone release?

A

Somatostatin
Dopamine
Glucocorticoids

Endocrine intro...hormones (4 decks)

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