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Human Physiology 2 - Unit 3 - Zach H. > Lecture 21: Thyroid Hormones > Flashcards

Lecture 21: Thyroid Hormones Flashcards

1
Q

How many mg of iodine (iodides such as sodium iodide) are required each year?

A

50 mg

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2
Q

True or False:

Iodine is absorbed from the gut tract in the same manner as chlorides.

A

True

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3
Q

Is the sodium-Iodide symporter (2:1) located on the basal or apical membrane of the thyroid cell?

A

Basal membrane

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4
Q

Where does the energy to drive the sodium-iodide symporter come from?

A

sodium-potassium ATPase pump

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5
Q

How much more concentrated can iodide be inside the cell compared to its concentration in the plasma?

A

30-250x plasma

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6
Q

What is the chloride-iodide counter-transporter also known as?

A

pendrin

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7
Q

What transporter pumps iodide across the apical membrane of the thyroid cell into the follicle?

A

Chloride-Iodide counter-transporter

aka - Pendrin

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8
Q

What membrane bound enzyme catalyzes the conversion of iodide into iodine (I2)?

A

peroxidase

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9
Q

What enzyme catalyses the combing of iodide with thyrosine on thyroglobulin?

A

peroxidase

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10
Q

What does the combining of iodine with tyrosine on thyroglobulin result in?

A
  • Monoiodotyrosine (MIT)
  • Diiodotyrosine (DIT)

catalyzed by peroxidase - which is a membrane enzyme

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11
Q

What thyroid hormone is produced by the recombination of DIT + DIT?

A

thyrosxine (T4)

more T4 is formed than T3

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12
Q

What thyroid hormone is produced by the recombination of DIT + MIT?

A

triiodothyronine (T3)

more active than T4 - but more T4 is formed

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13
Q

What is attached to a thyroglobulin molecule when it is stored in the colloid until needed?

A
  • MIT
  • DIT
  • T3
  • T4
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14
Q

Study and know figure 77-2 well for the exam.

A

Iodine transport.

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15
Q

What does thyroid cells secrete into the follicle?

A

thyroglobulin (MW=335,000)

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16
Q

How many tyrosine amino acids does each thyroglobulin molecule have that binds iodine to form thyroid hormones?

A

70 tyrosine amino acids

17
Q

What form are iodide ions converted to so that they can directly bind to tyrosine amino acids on thyroglobulin molecules to form thyroid hormones

A

Iodide ions are converted to an oxidized form of iodine to directly bind to tyrosine.

> nascent iodine (I2) or
I3-

18
Q

What is the major hormonal product formed during iodine metabolism to produce thyroid hormones?

A

thyroxine (T4)

19
Q

How many molecules of thyroxine does each thyroglobulin molecule contain?

A

30 molecules of thyroxine.

20
Q

True or False:

The thyroid can store several months supply of thyroid hormones.

21
Q

Go through the mechanism of the release of thyroid hormones.

A

> Apical surface of thyroid cells pinch off small portions of the follicular colloid to form pinocytic vesicles.

> Lysosomes fuse with vesicles and digest thyroglobulin molecules to release thyroxine and triiodothyronine (thyroid hormones).

> Thyroid hormones diffuse into blood.

> Most of the iodinated tyrosine in the thyroglobulin does not become thyroid hormones but is recycled using a deiodinase enzyme (deficiency mimics iodine deficiency).

> Most of released thyroid hormone is thyroxine which then is slowly deiodinated to form triiodothyronine.

> Conversion from T4 to T3 requires 5’-iodinase

> T3 is more active than T4.

> Most thyroid hormones entering blood are immediately bound to plasma proteins synthesized in the liver.

  • thyroxine-binding globulin (TBG):
    • produced by liver
    • hepatic failure - decreased total thyroid hormone level but normal free hormone levels.

> Plasma proteins have a high affinity for thyroid hormones, so the hormones are released slowly to tissue cells.

22
Q

What enzyme is required for the conversion of T4 to T3?

A

5’-iodinase

23
Q

What happens to most of the iodinated tyrosine in the thyroglobulin molecule?

A

Most of the iodinated tyrosine in the thyroglobulin does not become thyroid hormones but is recycled using a deiodinase enzyme.

a deficiency of deiodinase enzyme mimics iodine deficiency

24
Q

What are most thyroid hormones that enter the blood stream immediately bound to?

A

Plasma proteins (thyroxine-binding globulin (TBG)) that are synthesized in the liver.

plasma proteins have a high affinity for thyroid hormones, so the hormones are released slowly to tissue cells

25
Q

What signaling mechanism does TSH act on follicular cells via?

A

Adenylate cyclase - cAMP mechanism.

26
Q

What is the regulation of thyroid hormone secretion starting in the hypothalamus?

A

> hypothalamus -> TRH (thyrotropin-releasing hormone)
TRH -> anterior pituitary -> TSH
TSH -> thyroid gland -> thyroxine
thyroxine -> increased cellular metabolism

*increased cellular metabolism provides an inhibitory feedback to the hypothalamus and the anterior pituitary**

27
Q

What are the causes of hyperthyroidism?

A
  • Graves’ disease
  • high concentration of circulating thyroid-stimulating immunoglobulins:
    • IgG components
    • Mimic TSH and bind to TSH receptors.
    • REsult in high concentrations of circulating thyroxine and low levels of TSH.
  • Adenoma
28
Q

What are the symptoms of hyperthyroidism?

A
  • high state of excitability
  • intolerance to heat
  • increased sweating
  • mild to extreme weight loss
  • varying degrees of diarrhea
  • muscle weakness
  • nervousness or other psychic disorders
  • extreme fatigue
  • inability to sleep
  • tremor in hands
  • exophthalmos
29
Q

What are the treatments for hyperthyroidism?

A
  • Surgical removal of most of thyroid gland.

- Treatment with radioactive iodine.

30
Q

What are the causes of hypothyroidism?

A
  • Hashimoto disease (autoimmunity)
  • Endemic goiter
  • Cretinism (caused by extreme early hypothyroidism)
31
Q

What are the symptoms of hypothyroidism?

A
  • Generally opposite those of hyperthyroidism.
  • Myxedema
  • Atherosclerosis
32
Q

What are the treatments of hypothyroidism?

A

oral medication

33
Q

What do the antithyroid drugs thiocyanate and perchlorate anions do?

A

Inhibit iodine uptake (inhibit I-Na cotransport).

34
Q

What does the antithyroid drug propylthiouracil do?

A
  • inhibits peroxidase

- can be used to treat for hyperthyroidism

35
Q

What does the antithyroid drug iodides do?

A

Decrease thyroid activity when present in very high concentrations.

36
Q

use your test for details of the following general functions.

A 
> Increased transcription of a large number of genes. 
> Increased cellular metabolic activity. 
> Effect on growth. 
> Effects on specific bodily mechanisms:
- stimulation of carbohydrate metabolism
- stimulation of fat metabolism 
- effect on plasma and liver fats 
- increased requirement for vitamins 
- increased BMR
- decreased body weight

> Effects on cardiovascular system:

  • increased blood flow and cardiac output
  • increased heart rate
  • normal arterial pressure
  • increased respiration
> Increased GI motility. 
> Excitatory effect on CNS. 
> Effects on muscle function. 
> Muscle Tremor. 
> Effect on sleep. 
> Effect on other endocrine glands. 
> Effect on sexual function.

Human Physiology 2 - Unit 3 - Zach H. (9 decks)

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