03a: Thyroid Flashcards
Thyroid hormones contain (X)% (iodide/iodine).
X = 60-65
Iodine
(X) enzyme (oxidizes/reduces) (iodide/iodine) and organifies the product by attaching (Y).
X = thyroid peroxidase (TPO) Oxidizes Iodide (into iodine) Y = thyroglobulin
Thyroid: (X) enzyme couples MIT and DIT to form (Y).
X = thyroid peroxidase (TPO) Y = T3 (DIT+MIT) or T4 (2DIT)
T/F: A small portion, about 10%, of T3 is made by peripheral conversion of T4 to T3.
False - 80% is made in this manner
(X) enzyme converts T4 to T3
X = D1 deiodinase (kidney and liver)
T/F: T3 is 20-100x more bioactive than T4.
True
T/F: rT3 is biologically inactive
True
T/F: MIT and DIT are biologically inactive.
True
(X)% of T4 is free; the rest is bound to (Y).
X = 0.04 Y = TBG, transthyreitin, or albumin
Thyroid hormone acts at the
(hypothalamus/pituitary) to inhibit
secretion (X).
Both
X = TRH and TSH
Pregnancy may change thyroid hormone requirements due to (increase/decrease) in thyroid binding proteins
Increase
Cirrhosis and nephrotic syndrome may change thyroid hormone requirements due to (increase/decrease) in thyroid binding proteins
Decrease
OCP may change thyroid hormone requirements due to (increase/decrease) in thyroid binding proteins
Increase
T/F: T3 acts via RTK similar to IGF1.
False - intranuclear receptor
(X) is the BEST test to determine thyroid function because for every 2-fold change in (Y), there is a 100-fold change in (X).
X = TSH Y = free T4
Autoimmune Hypothyroidism is associated with Ab against (X)
X = TPO
Most common cause of mental retardation worldwide
Hypothyroidism (due to iodine deficiency)
90% of neonatal hypothyroidism is due to which cause?
Dysgenesis/Agenesis of thyroid (missing or severely underdeveloped)
About 10% of neonatal hypothyroidism is due to (X). What would you see on imaging?
X = Dyshormonogenesis (defects in thyroid hormone production; abnormal TPO activity)
Normally placed thyroid gland that’s normal size or enlarged (goiter)
Sarcoidosis can cause hypothyroidism, most commonly (primary/secondary/tertiary). What are other etiologies?
Tertiary (level of hypothalamus)
Histiocytosis, tumors, radiation
Most common cause of goiter worldwide is:
Iodine deficiency (hypothyroid)
(X) receptor mutation is a rare cause of hypothyroidism due to thyroid hormone resistance
X = T3
Pt Sx include mental retardation, hearing loss, and short stature. TSH levels are high, T4 levels are high. What is the likely cause of the (hypo/hyper)-thyroidism?
Hypothyroidism
Resistance to thyroid hormone (T3-R defect; v rare)
T/F: HT is symptom of hypothyroidism
True
T/F: Total and LDL cholesterol levels are decreased in hypothyroidism.
False - elevated
List some GI issues associated with hypothyroidism
- Abd distension, constipation
2. Autoimmune atrophic gastritis (achlorhydria, pernicious anemia)
What’s cretinism?
severely stunted physical and mental growth owing to untreated congenital hypothyroidism
Standard Rx for hypothyroidism is:
Oral L-thyroxine (T4)
Hypothyroidism: once patient is on Rx and reaches steady state, how often should (X) levels be checked?
X = TSH
6-12 months (unless symptoms occur)
Hypothyroidism: the rate of T4 replacement depends on which factor(s)?
Age and risk of CAD (titrate slowly in elderly to prevent CV issues)
Hypothyroidism: T4 dose is determined once which list of factors has been considered?
- Age/wt of pt
- Previous I-131 Rx
- Meds/pregnancy (increase thyroid hormone proteins)
- Diet/GI status that may interfere with T4 absorption
Decompensated state of severe hypothyroidism can result in (X), with as high as 50% mortality.
X = Myxedema coma
T/F: Pt presenting with Myxedema Coma has very low core temp so should be treated with heat blanket asap.
False!!! Avoid external warmth (sudden vasodilation and vascular collapse)
Myxedema Coma: key first steps in treatment
- IV L-thyroxine
- IV fluids (w glucose)
- Assisted ventilation (warm, moist air)
(X) Ab are the most specific
marker for Hashimoto’s.
X = Antimicrosomal antibodies against TPO
Antithyroglobulin Ab less specific
