Thyroid Flashcards
Which are the active and which are the inactive forms of thyroid hormone?
Active: T3 (triiodothyronine)
Inactive: T4 (thyroxine), Reverse T3
How is iodide moved from the blood into the colloid?
- first, iodide enters epithelial cells via a sodium-iodide symporter
- the symporter is driven by the high extracellular Na and low intracellular Na
- the iodide can then diffuse into the colloid
- symporter gene mutations or Hashimoto’s thyroiditis can lead to a defective pump
What are the two steps in synthesis of thyroid hormones and what enzyme is responsible for them?
1) iodination of tyrosine to diiodotyrosine
2) coupling of iodinated tyrosine to form thyroxine (T4)
- both steps carried out by thyroid peroxidase
How does T4 reach its target tissue?
- endocytosed out of colloid and hitches a ride on thyroxin-binding globulin
What common symptoms should clue you in to hypothyroidism? (These can be from disease or from SE of antithyroid meds)
fatigue, depression, sensitivity to cold, weight gain, goiter, muscle weakness, corsening of skin, dry or brittle hair, constipation, muscle cramps, increased risk of miscarriage
What are the antibodies against in Hashimoto’s thyroiditis?
- can be against thyroid peroxidase, sodium-iodide symporter, thyroglobulin, or TSH receptor
What is the preferred drug for treatment of hypothyroidism? How does it work?
- DOC: levothyroxine sodium, a synthetic version of T4
- longer half life than T3, takes 3-4 wks to see peak effect
- when giving to peds patients: infants and children need a higher dose due to their higher metabolic rate
- if the patient has hx of angina, start with low and slow doses!
What is the name of the synthetic version of T3? What special cases can this be used for?
- Liothyronine sodium
- IV formulation can be given in an acute emergency (myxedema coma)
- more rapidly effective and reaches peak levels in 2-4 hrs
- can sometimes convert into T2 or reverse T3, so effects and potency can be unpredictable
What is the most common preventable cause of mental handicap in the world?
- iodine deficiency
What common symptoms should clue you in to hyperthyroidism? (These can be from disease or from SE of thyroid replacement meds)
rapid heart rate, weight loss, nervousness, alertness, heat intolerance, fatigue, increased frequency of bowel movements, diarrhea, loss of sleep, tremors, excessive sweating, exophthalmus
What are potential causes of hyperthyroidism?
A) Grave’s disease: autoimmune disease caused by thyroid stimulating antibodies to the thyrotropin receptor
B) Nodular goiter: benign growths
C) Thyroiditis: inflammation of thyroid gland leading to the release of excess amounts of thyroid hormone
D) Thyroid cancer
What are 4 treatment strategies for correcting hyperthyroid conditions?
1) subtotal thyroidectomy + T4 replacement
2) irradiate thyroid + T4 replacement
3) inhibit thyroid peroxidase
4) interfere with symptoms by blocking sympathetic activity
The antithyroid drugs are _________ , ________ , and _______ . They work by _____ . Side effects include___________.
- propylthiouracil, methimazole, and carbimazole
- inhibit thyroid peroxidase activity (PTU can also reduce the deiodination of T4 to T3)
- SE: agranulocytosis (PTU more than meth), hepatitis, lupus-like syndrome
- PTU is less likely to transfer to the fetus, so this is the DOC for pregnant patients (too much or too little thyroid hormone is strongly associated with birth defects, so control this carefully!)
If a child has a hyperthyroid condition, what is the treatment of choice?
- antithyroid drugs
- don’t use radioiodine!
What is the beta blocker of choice when treating hyperthyroid conditions (usually used with moderate or severe symptoms while waiting for antithyroid meds to take effect)?
propanolol
