Thyroid Flashcards
Thyroid Hormone Forms
Triiodothyronine (T3) - Active
Thyroxine (T4) - Inactive
T3 more potent than T4
Hypothalamus
Secretes thyrotropin-releasing hormone (TRH)
Stimulates the anterior pituitary
Anterior Pituitary Gland
Stimulation of thyrotropic cells secretes the release of thyroid stimulating hormone (TSH)
Thyroid Gland
Stimulates 2 effects:
Synthesis and secretion of thyroid hormones
Trophic effect - increases thyroid gland growth
Negative Feedback Loop
High amounts of thyroid hormone in the bloodstream inhibit the secretion of both TRH and TSH

Hypothyroidism
Endocrine gland hyposecretion results in hormone deficiency
- Hashimoto’s thyroiditis
- Severe iodine deficiency
- Congenital hypothyroidism
Hyperthyroidism
Endocrine gland hypersecretion results in hormone excess
- Graves’ disease
- Thyroid nodules
- Postpartum thyroiditis
Hypothyroidism Symptoms
Weight gain
Cold intolerance
Weakness
Fatigue
Hair loss
Decreased libido
Constipation
Myxedema coma
Hyperthyroidism Symptoms
Weight loss
Heat intolerance
Sweating
Increase heart rate (tachycardia)
Irritability
Nervousness
Exopthalmos (Graves’ Disease)
Hypothyroidism Treatment
Thyroid hormone replacement therapy
Levothyroxine Brand Name
Synthroid
Levoxyl
Levothroid
Unithroid
Levothyroxine MOA
Acts as synthetic thyroid hormone of thyroxine (T4)
Levothyroxine Initial Dosing
Full replacement dose
- 1.6 mcg/kg/day using IBW
- Healthy, <50 yo adult
Partial replacement dose
- Start low 25-50 mcg daily
- Elderly, comorbidities (coronary artery disease)
Levothyroxine Administration
- Take in the morning on an empty stomach
- 30-60 minutes before first meal of the day
- Take with a full glass of water
- Separate from other medications by 4 hours
- Antacids
- Iron supplements
- Multivitamins
Levothyroxine Side Effects
Tachycardia
Palpitations
Sweating
Weight loss
Arrhythmias
Irritability
Decreased bone mineral dansity