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Flashcards in Thyroid Hormones Deck (38)
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1

triiodothyronine

T3

2

thyroxine

T4

3

Thyroid hormone preparation of T4

Levothyroxine (given orally, long half life)

4

T3 aka

triiodothyronine

5

T4 aka

thyroxine

6

Thyroid hormone preparation of T3

Liothyronine (more potent, faster acting but short half life, injectable)

7

When do you give T3?

T3 given only when an immediate response is needed (E.g. in myxodema coma)

8

MOA of thyroid hormones

➢ Thyroid hormones are attached to plasma carrier proteins.
• Hormones dissociate from carrier proteins enter the cell by active transport

➢ Within the cell T4 converted to T3 – enters nucleus- bind to thyroid hormone receptor - localized in the nucleus --> Stimulates transcription of particular genes

9

Levothyroxine

T4 hormone prep

10

Effects of Thyroid hormones on growth & development

• Essential for normal physical & mental growth, hence cretinism - mental retardation

11

caloric effects of thyroid hormones

• ↑ BMR and
• ↑ manitain body temperature

12

Liothyronine

T3 hormone prep

13

cardiovascular effects of thyroid hormones

• ↑ HR and
• ↑ peripheral resistance

14

metabolic effects of thyroid hormones

• ↑ blood sugar,
• ↑ synthesis of fatty acids and
• decrease plasma CH and TG levels

15

Use of thyroid hormones

➢ Hypothyroidism caused by:

• Hashimoto’s disease
• Myxedema
• Following surgical ablation of thyroid gland

16

hypothyroidism signs and symptoms

• anemia;
• hyponatremia,
• galactorrhea,
• goiter;
• hard, pitting edema of the lower extremities
• delayed return of deep tendon reflexes

• Any combination of a few or many signs and symptoms may occur at any given time.
• Some signs and symptoms, such as galactorrhea, anemia, and skin changes are seen in individuals in later stages of hypothyroidism.

17

Thyroid Inhibitors:

• Perchlorate,
• thiocyanate,
• goitrin

18

Thyroid Hormone Synthesis

1. Uptake of Iodide (iodide trapping)

2. Iodide organification
• (oxidation and iodination)

3. Coupling of MIT and DIT

4. Secretion of thyroid hormones

5. Conversion of T4 to T3

19

Ionic Inhibitors

Affects uptake of Iodine

• Perchlorate (ClO4- )
• thiocyanate (SCN- )

➢ No Therapeutic use: only Diagnostic

20

Monovalent anions

Affects uptake of Iodine

• Resemble Iodide
• Inhibit transport of iodide into thyroid

➢ No Therapeutic use: only Diagnostic

21

Thyroid peroxidase

Oxidizes iodide to iodine

22

Thioamides

Antithyroid drug!

➢ Iodine rapidly iodinates tyrosine residues in thyroglobulin forming MIT (mono-iodotyrosine) and DIT (di-iodotyrosine)

• Inhibited by: Thioamides

23

Coupling of MIT and DIT

➢ Coupling reaction involves oxidation by:
• Thyroid peroxidase

1. MIT + DIT --> T3
2. DIT + DIT --> T4

➢ Stored in thyroglobulin in colloid matrix
• Inhibited by thioamides -

examples:
• Methimazole
• Propylthiouracil

24

Thioamides MOA

➢ Inhibit thyroid peroxidase :
• Block iodine oxidation
• Coupling of MIT and DIT

25

Propylthiouracil MOA

Inhibit peripheral conversion of T4 to T3

• Block synthesis T3 and T4 not release, therefore slow onset of action

26

Thioamides A/E

➢ Relatively low incidence (3 – 12%)
• Maculopapular pruritic rash
• Hypothyroidism
• Gastrointestinal intolerance
• Agranulocytosis (

27

Secretion of T4 and T3 Inhibited by:

Iodine and Iodides

28

Secretion of T4 and T3

➢ Proteolysis - release of T4 and T3 stored within thyroglobulin (TG)
• MIT and DIT deiodinated; iodine reutilized
➢ Inhibited by Iodine and Iodides

29

Iodides

➢ Inhibit TH release - thyroid constipation
➢ Decreased size & vascularity of gland
➢ Improvement of thyrotoxic symptoms occurs rapidly – used in thyroid storm

30

Conversion of T4 to T3 Inhibited by

• Propranolol
• Propylthiouracil
• Glucocorticoids (prednisolone)