2 - Thyroid Hormone Flashcards
(40 cards)
Thyroid Hormones (3)
T3
T4
Calcitonin
Regulation of Thyroid Hormone Synthesis
Hypothal stimulates Ant. Pit via TRH, which —> releases TSH that acts on thyroid to release T4 and T3
Regulation of Thyroid Hormone Synthesis: Feedback Inhibition
T4 inhibits anterior pituitary
T3 inhibits hypothalamus
Thyroid Hormone Synthesis
- Uptake of Iodide (iodide trapping(
- Iodide organification (oxidation and iodination)
- Coupling of MIT and DIT
- Secretion of thyroid hormones
- Conversion of T4 and T3
What enzyme performs oxidation and organification of iodine?
Thyroid peroxidase
T4 and T4 in plasma are reversibly bound to what protein?
Thyroxine-binding globulin (TBG)
Does T3 or T4 have 3x metabolic activity?
T3
What percent of T4 is made in the thyroid?
100%
What’s the percentage of T3 synthesis (2 values)
20% made in thyroid
80% peripherally
Thyroid Function Tests (6)
Free T4 (FT4) - direct measurement of free T4
Free T3
Total T4 (Free AND protein-bound T4)
Total T3 (free AND protein bound T3)
TSH
Radioactive Iodine Uptake Test (RAIU)
Preparations of Thyroid Hormones (3)
Levothyroxine (T4, Synthroid)
Liothyronine (T3)
Liotrix
Uses of Thyroid Hormones: Hypothyroidism - Infancy and?
Infancy Cretinism (congenital hypothyroidism)
Childhood hypothyroidism
Uses of Thyroid Hormones: Hypothyroidism - Adult Type (Name, MOA, and Rx)
Hashimoto’s thyroiditis
AI destruction of the thyroid gland
Rx. Levothyroxin
Uses of Thyroid Hormones: Hypothyroidism - Myxedema Coma (Defined and Sxs - 9)
End state of untreated hypothyroidism
Progressive weakness, stupor, hypothermia, hypoventilation, hypoglycemia, hyponatremia, water intoxication, shock, and death
Uses of Thyroid Hormones: Hypothyroidism - Treatment for Myxedema Coma (5)
Intubation and mechanical ventilation
Control hypothermia
Infection or heart failure must be treated by appropriate therapy
- Levothyroxine IV
- Liothyronine IV
Antithyroid Drugs: Thioamides (3)
Propylthiouracil (PTU)
Methimazole
Carbimazole
Antithyroid Drugs: Thioamides Overall MOA (3)
Inhibit thyroid peroxidase
- Block iodine oxidation
- Coupling of MIT and DIT
Antithyroid Drugs: Thioamides MOA of Propylthiouracil (2)
Inhibit peripheral conversion of T4 to T3
- Block synthesis of T3 and T4 not release, therefore slow onset of action
Antithyroid Drugs: Toxicity (5)
Maculopapular Pruritic Rash
Agranulocytosis (Granulocyte count < 500 cells/mm3 )
Propylthiouracil - hepatitis
Cross the placental barrier and are concentrate by the fetal thyroid
Propylthiouracil is preferable in pregnancy
Anion Inhibitors (3)
Perchlorate (ClO4-)
Pertechnetate (TCO4-)
Thiocyanate (SCN-)
Anion Inhibitors: MOA and What does it cause?
Block uptake of iodide by the gland through competitive inhibtion of the iodide transport mechanism
Causes aplastic anemia
Iodine and Iodides: MOA (4)
Wolff-Chaikoff Effect
Inhibit hormone release
Decrease the vascularity, size, and fragility, of a hyperplastic gland, making the drugs valuable as preoperative preparation for surgery
Improvement in thyrotoxic symptoms occurs rapidly - within 2-7 days
Iodine and Iodides: Preparations
Lugol’s Iodine (I2 + KI), NaIodide, KIodide
Iodine and Iodides: Thyroid Escape
Gland escapes from the iodide block in 2-8 weeks
