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Gabe's Endocrinology > Iodine Metabolism and Thyroid Hormones > Flashcards

Iodine Metabolism and Thyroid Hormones Flashcards

1
Q

What is the recommended daily intake for iodine?

A

150µg/day

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2
Q

What does iodine deficiency give rise to?

A

Goitre, when high production of TSH induces thyroid cells to proliferate.

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3
Q

What is cretinism?

A

A congenital condition caused by maternal iodine deficiency

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4
Q

What therapy can be used to destroy an overactive thyroid?

A

Radiation from 131I-

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5
Q

What are thyroid hormones?

A
  • Master controller of metabolic rate.
  • They operate via membrane receptors and direct activation of genes in DNA.
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6
Q

What is the advantage of iodine antiseptics?

A

They have a wide scope of antimicrobial activity, killing all principal pathogens and even spores.

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7
Q

What is the microbial action of iodine due to?

A
  • I2 is a potent oxidizer.
  • It reacts in electrophilic reactions with enzymes of the respiratory chain as well as with amino acids located in cell membrane and cell wall proteins.
  • It also inactivates the proton pump.
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8
Q

Why is organic iodine not toxic?

A

Because it does not dissociate to free I2.

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9
Q

What is goitre caused by?

A

A combination of iodine deficiency and goitrogens

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10
Q

What do goitrogens do?

A

Inhibit iodide uptake in the thyroid and magnify the severity of any iodine deficiency.

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11
Q

Where are goitrogens found?

A

In soy, cabbage, kale, brussel sprouts and other cuciferous vegetables in the genus Brassica.

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12
Q

What are cretins?

A

Children born from iodine deficient mothers, causing goitre, mental retardation and deafness, all of which are irreversible.

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13
Q

What does thyroid hormone alter?

A
  1. Energy level. Elevates ATP, acetyl-CoA, NADH and NADPH.
  2. Synthesis of enzymes.
  3. Increase mental alertness and BMR - elevate the number of catecholamine receptors, enhance catecholamine effects and stimulate differentiation and function of brown adipose tissue to generate heat.
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14
Q

What does the normal thyroid produce?

A

80% T4 and 20% T3.

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15
Q

How are T3 and T4 synthesised?

A

Peroxidase convertes 2I- to I2, which is then attached to tyrosine in thyroglobulin to make MIT or DIT, which then undergo condensation to make T3 or T4. See image.

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16
Q

What catalyses the condenstion of DIT+DIT to T3 or T4?

A

Thyroperoxidase.

17
Q

What is the half-life of T4?

A

6-9 days

18
Q

What is the half-life of T3?

A

24-36 hours

19
Q

What is reverse T3?

A

Inactive T3

20
Q

What is the use of reverse T3?

A

Dumping of excess iodine as an inactive product.

21
Q

What converts T4 to T3?

A

Di-iodinase

22
Q

How are T3 and T4 released into the bloodstream?

A

See image

23
Q

How is iodide taken up by the thyroid?

A

By the NIS symporter.

24
Q

What drives the NIS symporter?

A

A Na+ gradient maintained by a 3Na+/2K+ ATPase.

25
Q

What is Grave’s disease also known as?

A

Hyperthyroidism

26
Q

What are the treatment options for Grave’s disease?

A
  1. Radioactive iodide
  2. Antithyroid drug therapy (ATD)
  3. Surgery/Thyroidectomy
  4. Thyroid arterial embolization
27
Q

Which drugs are used in antithyroid drug therapy?

A

Propylthiouracil and methimazole .

28
Q

What is the action of antithyroid drug therapy?

A

Inhibition of thyroperoxidase.

29
Q

How is the majority of T3 and T4 carried in the plasma?

A

Bound to thyroid binding globulin (TBG). The remainder is divided between transthyretin and serum albumin.

30
Q

Which is more abundant, plasma T3 or T4?

A

T4

31
Q

What is most T3 in the circulation created by?

A
  • Type I deiodinase activity in the liver and kidney.
  • Type II deiodinases in the brain, brown adipose tissue and pituitary produce T3 within cells.
32
Q

What is the function of the thyroid hormone receptor in the absence of thyroid hormone?

A

Binds DNA, leading to transcriptional repression.

33
Q

What happens to the thyroid hormone receptor when thyroid hormone binds?

A

Undergoes conformation change in the nuclear receptor that causes it to function as a transcriptional activator.

34
Q

What is the function of the thyroid hormone receptor in the presence of thyroid hormone?

A
  • Thyroid hormone sets the rate of synthesis of many proteins.
  • The proteins of oxidative phosphorylation are upregulated so more ATP is made.
35
Q

What are symptoms of hyperthyroidism (Grave’s disease)?

A
  • Difficulty sleeping
  • Heat intolerance
  • Infertility
  • Irritability
  • Muscle weakness
  • Nervousness
  • Scant menstrual periods.
36
Q

What are the symptoms of hypothyroidism (Hashimoto’s disease)?

A
  • Arthritis
  • Cold intolerance
  • Depression
  • Dry skin
  • Fatigue
  • Forgetfulness
  • Heavy menstrual periods
  • Infertility
  • Muscle aches

Gabe's Endocrinology (17 decks)

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