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Hugh's MD1 Endo > Iodine Metabolism and Thyroid Hormone > Flashcards

Iodine Metabolism and Thyroid Hormone Flashcards

1
Q

Which hormone regulates the release of TSH from the pituitary?

A

Thyrotropin releasing hormone (TRH)

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1
Q

What is the function of leptin?

A

Fat controller - signals how much fat is present

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1
Q

What is TSI?

A

Thyroid-stimulating immunoglobulin

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2
Q

What is the ratio of T4 to T3 production by the thyroid?

A

80% T4

20% T3

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2
Q

Binding of T3 to its nuclear receptor usually causes what?

A

The receptors stop inhibition of transcription and acts as a transcription factor

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3
Q

What type of iodine is carcinogenic?

A

I-131

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4
Q

Most T3 is created where?

A

In the liver and kidney, by the action of deiodinase

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4
Q

Why don’t you get goiter in secondary thyroid disorders?

A

Problem with hypothalamus & ant. pituitary gland > Low TRH or TSH > No growth stimulation

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5
Q

What are the physiological effects of thyroid hormones?

A

Increase mental alertness

Increase basal metabolic rate

Increase the no. of catecholamine (adrenaline) receptors - enhancing catecholamine effects

Stim. differentiation and function of brown adipsoe tissue to generate heat

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6
Q

Are thyroid hormones lipophilic or lipophobic?

A

Lipophilic

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7
Q

What is the mechanism of anti-septic action used by iodine?

A

I2 is a potent oxidiser that disrupts the respiratory chain

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7
Q

Where in the thyroid is hormone made?

A

The colloid

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8
Q

What is the name of the best iodine anti-septic?

A

Betadine

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9
Q

Where is iodine more abundant, in the sea or on land?

A

In the sea

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9
Q

Which is more likely iodine deficiency or excess?

A

Deficiency

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10
Q

What is the most common cause of hyperthyroidism?

A

Grave’s disease: 60-80%

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11
Q

Do you get goiter with secondary causes of hyperthyroidism?

A

Yes - Due to overproduction of TRH or TSH

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12
Q

What causes cretinism?

A

Maternal iodine deficiency

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14
Q

What are the physiological effects of thyroid hormones?

A

Increase BMR and O2 consumption - heat production

Modulate metabolism

Sympathomimetic effects - Increase HR and CO

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15
Q

What are 4 treatment options for hyperthyroidism?

A

Radioactive I

Antithyroid drug therapy (propylthiouracil and methimazole typically)

Surgery

Thyroid arterial embolisation

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15
Q

What aspect of growth are controlled by thyroid growth?

A

Growth promoting

Nervous system development

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16
Q

What is the RDI of iodine for the production of T3 and T4?

A

150ug

18
Q

In which population of people is iodine excess most concerning?

A

Pregnant women

19
Q

What carrier proteins carry thyroid hormones?

A

Thyroxine-binding protein

Albumin

Transthyretin

21
Q

Why does goitre form?

A

TSH induces thyroid cells to proliferate in response to their deficient production due to iodine deficiency

22
Q

Where is thyroglobulin produced?

A

Follicular cells

23
Q

Why do you get goiter in Grave’s disease?

A

TSI has the some trophic effect as TSH

25
Q

What are the precursors for MIT?

A

Iodine and tyrosine

26
Q

How is the secretion of TRH and TSH regulated?

A

Via negative feedback from thyroid hormones

27
Q

What are the physiological effects of hypothyroidism?

A

Low BMR and O2 consumption

Increase weight

Decrease energy

Cold intolerance

Decrease HR

Decrease protein synthesis: myxedema (puffy eyes)

28
Q

What is the precursor to T4 and T3?

A

Tyrosine

29
Q

Do you get goiter in iodine deficiency?

A

Yes

30
Q

What does calcitonin regulate?

A

Ca levels

32
Q

What food has the highest concentration of iodine on the planet?

A

Kelp

33
Q

To what is most circulating thyroid hormone bound?

A

Thyroine-binding globulin

34
Q

Which enzyme catalyses the condensation of precursors into T4 and T3?

A

Thyroperoxidase

35
Q

What is the name of the membrane channel used to transport I into the thyroid cells?

A

NIS (Na iodide symport)

36
Q

T/F Goitre is can be present in iodine deficiency and excess

A

True

37
Q

What has lead to a resurgence of iodine deficiency in Australia?

A

Change in milk processing technique

39
Q

What is the activity of thyroid hormones at a cellular level?

A

Increase activity of enzymes

Increase Na-K ATPase

40
Q

What are thyroid hormones main action?

A

Master controller of metabolic rate

41
Q

What do C cells produce?

A

Calcitonin

42
Q

The activity of NIS increases in response to what?

A

Binding of TSH

43
Q

What is the cause of exophthalmos in Grave’s disease?

A

Water retaining carbohydrates behind the eye

45
Q

When is reverse T3 synthesised?

A

When there is excess I in order to “dump” it

46
Q

What is the function of thyroglobulin?

A

Acts as a backbone for thyroxine production

47
Q

What are the physiological effects of hyperthyroidism?

A

Increase BMR

Heat insensitivity

Decrease weight

Increase HR

Increase appetite

Increase alertness, excitability, irritability

Exophthalmos - bulging of the eyes

48
Q

Why do you get goiter in primary thyroid failure?

A

Low T3 & T4 > High TSH > Stimulates growth of the thyroid

49
Q

What are goitrogens?

A

Substances that inhibit iodine uptake in the thyroid to magnify the severity of any iodine deficiency

50
Q

How does thyroid hormone levels change in response to starvation?

A

Output is greatly reduced

51
Q

What enzymes converted T4 to T3?

A

Deiodinase

52
Q

Name some goitrogens

A

Soy

Cabbage

Kale

Brussel sprouts

53
Q

What percentage of thyroid hormone produced is T4?

A

90%

54
Q

In which parts of the world are iodine deficiencies must common?

A

At high altitudes

Hugh's MD1 Endo (14 decks)

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