Iodine Metabolism and Thyroid Hormones Flashcards Preview

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

Flashcards in Iodine Metabolism and Thyroid Hormones Deck (36):
1

What is the recommended daily intake for iodine?

150µg/day

2

What does iodine deficiency give rise to?

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

3

What is cretinism?

A congenital condition caused by maternal iodine deficiency

4

What therapy can be used to destroy an overactive thyroid?

Radiation from 131I-

5

What are thyroid hormones?

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

6

What is the advantage of iodine antiseptics?

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

7

What is the microbial action of iodine due to?

  • 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.

8

Why is organic iodine not toxic?

Because it does not dissociate to free I2.

9

What is goitre caused by?

A combination of iodine deficiency and goitrogens

10

What do goitrogens do?

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

11

Where are goitrogens found?

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

12

What are cretins?

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

13

What does thyroid hormone alter?

  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.

14

What does the normal thyroid produce?

80% T4 and 20% T3.

15

How are T3 and T4 synthesised?

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.

16

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

Thyroperoxidase.

17

What is the half-life of T4?

6-9 days

18

What is the half-life of T3?

24-36 hours

19

What is reverse T3?

Inactive T3

20

What is the use of reverse T3?

Dumping of excess iodine as an inactive product.

21

What converts T4 to T3?

Di-iodinase

22

How are T3 and T4 released into the bloodstream?

See image

23

How is iodide taken up by the thyroid?

By the NIS symporter.

24

What drives the NIS symporter?

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

25

What is Grave's disease also known as?

Hyperthyroidism

26

What are the treatment options for Grave's disease?

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

27

Which drugs are used in antithyroid drug therapy?

Propylthiouracil and methimazole .

28

What is the action of antithyroid drug therapy?

Inhibition of thyroperoxidase.

29

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

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

30

Which is more abundant, plasma T3 or T4?

T4

31

What is most T3 in the circulation created by?

  • 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

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

Binds DNA, leading to transcriptional repression.

33

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

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

34

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

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

35

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

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

36

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

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