Thyroid Flashcards
Thyroid is a
2-lobed gland
Thryoid follicular cells oxidize iodide in process of
producing triiodothyronine (T3) and thyroxine (T4)
Pituitary gland secretes
thyroid-stimulating hormone (TSH) which
controls rate and release of T3 and T4
Hypothalamus secretes
thyrotropin- releasing hormone which
regulates the release of TSH
Low levels of serum thyroid hormones cause
increased secretion of
TSH, and subsequently T3, T4
Most of T3 and T4 is
bound, free T3 and T4 regulate metabolism
Hypothyroidism is a deficiency of
T4 usually. or a deficiency of iodine
Autoimmune or Hashimoto’s thyroiditis
- Infiltration of thyroid by lymphocytes
- Leads to fibrosis and decreased function of the gland
- May present with goiter, be euthyroid or hypothyroid
- Anti-thyroid antibodies serum titers are high
Primary hypothyroidism labs
High TSH (usually
≥ 10mlU/L
Low T4
Secondary
(central) hypothyroidism labs
Low T4
Do not see inverse
appropriate
elevation in TSH
Subclinical (early
hypothyroidism,
pre-clinical
hypothyroidism) labs
Normal T4
Elevation TSH
Transient hypothyroidism labs
phas of subacute thyroidits
Hypothyroidism S/S
• Symptoms
• Fatigue, constipation, weight gain, changes in menses
• Elderly: more subtle signs; ataxia, parasthesia, carpal tunnel,
psychiatric changes
• P.E.
• Thyromegaly, bradycardia, peripheral edema
Hypothyroidism LAB tests to do
- TSH (most widely used screening test), free T4
* Total cholesterol and LDL elevated
Hypothyroidism goal of treatment
• Restore patient to euthyroid state
Hypothyroidism products
- Natural thyroid extract
- T3 replacement (liothyronine)
- Liotrix (T3 and T4 combination product)
- Levothyroxine (T4), most common
Hypothyroidism when to initiate therapy
• TSH ≥ 10mlU/L
• TSH levels 5 -10 μIU/mL with goiter or positive antithyroid peroxidase
antibodies (or both).
Synthetic Levothyroxine
(Synthroid) Fast Facts
- Preparation of choice for thyroid replacement and suppression
- Stable compound
- Uniform content
- Low cost
- Lack of allergenic foreign protein
- Easy lab measurement of serum levels
• Generic form has comparable efficacy to brand and is more
cost-effective, but don’t alternate (DO NOT ALTERNATE)
Levothyroxine is easily
Easily absorbed from GI tract but erratic absorption
Levothyroxine is what exactly
Synthetic T4
Levothyroxine how does it work
T4 is converted to T3 so replaces both
• Peak T4 serum level in 2-4 hours
• Peak T3 slower because of time needed for conversion
Levothyroxine has a
Long half-life allows once-daily dosing
Levothyroxine elimination
Elimination: bile/feces
Levothyroxine requires
Requires 1 month to reach steady state
