Thyroid and Diabetes intro Flashcards
What is the chemical name for the hormone T3?
Liothyronine
Which is more pharmacologically active, T4 or T3? Which is more abundant?
T3 is more active, T4 is more abundant
Outline the synthesis of thyroid hormone from peroxidase
Peroxidase – oxidation of dietary iodine – iodination of tyrosine – thyroid hormone
What is thyroid hormone stored as?
Thyroglobulin
What releases TRH and TSH?
TRH – hypothalamus
TSH – pituitary
What is thyroid binding globulin?
The plasma protein that binds the majority of circulating T3 and T4
Name two common increasers of TBG
Pregnancy and oral contraceptives
Name a common decreaser of TBG
Anabolic steroids
List three functions of thyroid hormone
Stimulates protein synthesis, increases metabolic rate, increases sensitivity to catecholamines
How long does it take T4 (levothyroxine) to reach max efficacy?
10 days
How long does it take T3 (Liothyronine) to reach max efficacy?
24 hours
Which is “slower on and slower off”, T3 or T4?
T4
How does the thyroid hormone dose change in pregnant individuals?
Pregnant females require nearly 50% more thyroid hormone due to increased TBG production
What is a typical initial dose of Synthroid?
50 to 100 µg adjusted every 30 days until TSH is normal
Why should thyroid hormone be taken on an empty stomach?
It sticks to food and is excreted
In which case should T3 be administered?
In thyroid emergencies (myxedema coma), T3 can be given IV
What is the effect of administering too much thyroid hormone?
Pseudo-hyperthyroidism causing a fib
How is pseudohyperthyroidism treated?
Discontinue medicine for seven days then recommence at lower dose
Why is Synthroid the preferred treatment for hypothyroidism?
Generic thyroid hormone may be significantly less biologically active
What is the chemical name for T4 hormone?
L – thyroxine
What are the hyperthyroid medications (Methimazole and PTU) method of action? How do they differ?
Inhibits the oxidation (activation) of thyroid hormone
Methimazole does not affect peripheral conversion of T4 to T3, while PTU cannot take effect until preformed T4 -T3 is exhausted
Which of the two hyperthyroid medications is taken 1 x a day and which is taken 3 x a day?
Methimazole – 1x a day
Propylthiouracil- 3x a day
Which hyperthyroid medication can be used to treat thyroid storm in high doses?
PTU – inhibits peripheral conversion of T4 to T3
What are the most common adverse effects of PTU?
Rash, dysphasia, agranulocytosis
When is iodine used?
Before thyroid surgery to firm up thyroid (negative feedback loop within thyroid causes involution)
What is the typical dose of iodine given preop?
Potassium iodide 60 mg Q8 hours for 10 to 14 days
When and how is radioactive iodine used?
Can be used to treat graves disease: selectively up taken by thyroid tissue, slowly destroys tissue, often induces hypothyroidism
How is thyroid storm most effectively treated?
With a nonselective beta blocker (Propanolol) IV or PO
How is thyroid storm treated (other than beta blocker)?
High-dose dexamethasone steroid will inhibit T4 conversion to T3
What is a risk of using dexamethasone to treat thyroid storm?
Can cause hyperglycemia due to steroid effect on blood glucose
What is hyperinsulinemia?
Increased production of insulin in people who consume excessive amounts of sugar (leads to hyperglycemia from down regulation)
Which cells secrete in store insulin?
Beta islet cells of pancreas
How is synthetic insulin made?
Either enzymatic modification of porcine insulin or recombinant technology
What bacteria is used in recombinant technology to produce insulin?
E. coli
Describe the 3 biological effects of insulin
Activates glucokinase and glucose phosphatase
Causes conversion of glucose to glycogen
Enhances arachidonic acid and K+ entry into cells
What is the general dosage rule for insulin?
One unit of insulin per kilogram of body weight per day
