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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?

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
Why does goitre form?
TSH induces thyroid cells to proliferate in response to their deficient production due to iodine deficiency
22
Where is thyroglobulin produced?
Follicular cells
23
Why do you get goiter in Grave's disease?
TSI has the some trophic effect as TSH
25
What are the precursors for MIT?
Iodine and tyrosine
26
How is the secretion of TRH and TSH regulated?
Via negative feedback from thyroid hormones
27
What are the physiological effects of hypothyroidism?
Low BMR and O2 consumption Increase weight Decrease energy Cold intolerance Decrease HR Decrease protein synthesis: myxedema (puffy eyes)
28
What is the precursor to T4 and T3?
Tyrosine
29
Do you get goiter in iodine deficiency?
Yes
30
What does calcitonin regulate?
Ca levels
32
What food has the highest concentration of iodine on the planet?
Kelp
33
To what is most circulating thyroid hormone bound?
Thyroine-binding globulin
34
Which enzyme catalyses the condensation of precursors into T4 and T3?
Thyroperoxidase
35
What is the name of the membrane channel used to transport I into the thyroid cells?
NIS (Na iodide symport)
36
T/F Goitre is can be present in iodine deficiency and excess
True
37
What has lead to a resurgence of iodine deficiency in Australia?
Change in milk processing technique
39
What is the activity of thyroid hormones at a cellular level?
Increase activity of enzymes Increase Na-K ATPase
40
What are thyroid hormones main action?
Master controller of metabolic rate
41
What do C cells produce?
Calcitonin
42
The activity of NIS increases in response to what?
Binding of TSH
43
What is the cause of exophthalmos in Grave's disease?
Water retaining carbohydrates behind the eye
45
When is reverse T3 synthesised?
When there is excess I in order to "dump" it
46
What is the function of thyroglobulin?
Acts as a backbone for thyroxine production
47
What are the physiological effects of hyperthyroidism?
Increase BMR Heat insensitivity Decrease weight Increase HR Increase appetite Increase alertness, excitability, irritability Exophthalmos - bulging of the eyes
48
Why do you get goiter in primary thyroid failure?
Low T3 & T4 \> High TSH \> Stimulates growth of the thyroid
49
What are goitrogens?
Substances that inhibit iodine uptake in the thyroid to magnify the severity of any iodine deficiency
50
How does thyroid hormone levels change in response to starvation?
Output is greatly reduced
51
What enzymes converted T4 to T3?
Deiodinase
52
Name some goitrogens
Soy Cabbage Kale Brussel sprouts
53
What percentage of thyroid hormone produced is T4?
90%
54
In which parts of the world are iodine deficiencies must common?
At high altitudes

Hugh's MD1 Endo (14 decks)

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