Rat 1 Flashcards
(34 cards)
Thyroid gland
- Butterfly shaped
- Secretes thyroid hormones
Thyroid hormones
Influence functions of virtually all organ systems. *Children- normal growth + development. Adults- Maintain metabolic stability and homeostasis. (metabolic effects, cardiovascular effects and thermogenic effects)
What does the thyroid gland do with iodine?
Iodine can be found in regular diet (iodize salt). Uses iodine to make thyroid hormones
What makes T4 different from T3?
Unlike T4, T3 is 4x biologically potent, receptor affinity is 10-15x more, and is mainly produced from broken down T4 once in the peripheral tissue (20% produced in thyroid)
What are target tissues for T3?
Heart, nerves, bone, liver, muscle and glands
Describe the Hypothalamic- Pituitary- Thyroid (HPT) Axis
The hypothalamus releases (TRH: thyrotropin-releasing hormone) triggering the pituitary to release (TSH: thyroid- stimulating hormone). The thyroid gland is triggered by TSH to produce T4 and T3. T4 goes into the peripheral tissues to be converted to T3 as well.
What happens in hyperthyroidism? (Primary)
The thyroid produces large amounts of T3 and T4, which, through negative feedback inhibition, suppress TSH secretion from the anterior pituitary
What happens in hypothyroidism?
The thyroid produces insufficient amounts of T3 and T4, which leads to loss of negative feedback inhibition, and increased production of TSH from the anterior pituitary
What is usually screened for patients suspected of thyroid problems?
TSH
What happens in hyperthyroidism? (Secondary)
The anterior pituitary produces large amounts of TSH, which, in turn, stimulate the thyroid follicular cells to secrete thyroid hormones in excessive amounts
Define thyrotoxicosis
Excessive level of thyroid hormone by any cause. (Hyperthyroidism is a potential cause)
Define hyperthyroidism
Overproduction of thyroid hormone by thyroid gland
Define thyroid storm
Sudden release of thyroid hormone by thyroid gland
Life threatening emergency
Who gets affected by hyperthyroidism?
More women get it than men and it affects 0.5% of population
Etiology of hyperthyroidism
- Graves’ disease: Most common cause, auto immune disease
- Thyroid adenoma
- Excess TSH production
- Drug induced: amiodarone, iodinated contrast, lithium
- Interacts with Biotin (lab assay)
How can patients present hyperthyroidism?
- Heating intolerance
- Increased HR: palpitations
- Increased BP
- Bulging eyes (exophthalmos)
- Goiter
- Unintentional weight loss
- Amenorrhea
- Anxiety/ nervousness
- Diarrhea
- Fatigue
- Menstrual disturbances
- Fine hair
Define the normal ranges for TSH, T4, and T3
TSH: 0.5 - 4.7 mIU/L
T4: total: 4.5 - 10.9 mcg/dL free: 0.8 - 2.7
T3: total: 60 - 181 ng/dL
free: 2.3 - 4.2 pg/mL
Laboratory findings for hyperthyroidism
Decreased TSH and increased T4, T3
Laboratory findings for hypothyroidism
Increased TSH and decreased T4, T3
What are goals of therapy for hyperthyroidism?
- Eliminate excess thyroid hormone
- Provide symptomatic relief
- Minimize long-term consequences of hyperthyroidism
How do you approach treatment for hyperthyroidism?
Treatment is individualized and is based on disease severity, gender, age and response to previous therapy
Antithyroid Drugs (ATD): Thionamides
- Drug of Choice: Methimazole (MMI)
- Place in therapy: 1st line option for hyperthyroidism
- Goal of therapy: Achieve normal thyroid hormone levels
- MOA: Prevents synthesis and release of thyroid hormones
Name another thionamide
Propylthiouracil (PTU) which is dosed 300-600 mg/day divided 3-4 doses. Maintenance: 100-150 mg/day divided into 3 doses
How is methimazole dosed?
Dosed based on free T4 levels (generally 10-30mg/day) Free T4 1-1.5x ULN: 5-10mg once daily—
Free T4 >1.5 – 2x ULN: 10-20mg once daily—
Free T4 >2x ULN: 20-40mg/day
Maintenance: 5-10 mg/day PO QD
