5. The Thyroid Gland Flashcards
What is the primary secretory product of thyroid follicular cells?
T4
At what point would radio labeled iodine uptake peak if the patient had hyperthyroidism not related to Graves’ disease?
Roughly 18 hours.
Why might hypothyroidism contribute to type II diabetes?
Because thyroid hormone enhances insulin-dependent glucose uptake.
Hypothyroidism means more insulin is necessary to uptake the same amount of glucose, which can lead to glucose resistance.
How might hypothyroidism structurally damage the heart?
Thyroid hormone stimulates the construction of myosin.
Hypothyroidism results in deficits of myosin.
What amino acid is the backbone for all of the thyroid hormones?
Tyrosine.
What is the relationship between cholesterol/triglycerides and thyroid hormone?
They are inversely related. High thyroid hormone corresponds with low triglycerides/cholesterol.
What two precursor molecules come together to form tetraiodothyronine (T4)?
Diiodotyrosine + diiodotyrosine = tetraiodothyronine (T4).
Why would a thyroid binding resin test come back differently in a patient early on in pregnancy to a patient later on in pregnancy?
Early on, TBG levels increase, resulting in less free T3. Later on T3 and T4 synthesis increases, resulting in “clinically euthyroid” results.
What three clinical states are associated with reduced conversion of T4 to T3?
Fasting.
Medical and surgical stress.
Catabolic disease.
How might hypothyroidism damage the contractility of the heart?
Thyroid hormone stimulates the production of Ca2+ ATPase.
Hypothyroidism damages Ca2+ ATPase, which is necessary for proper cardiac contraction.
What would be the effect of hyperthyroidism on the intestines?
Diarrhea.
What should we suspect if we see a decreased T3 resin uptake?
Increased TBG.
Less T4 (hypothyroidism).
Pregnancy (early phases of high TBG, before T3 and T4 synthesis increases).
What would be the effect of excess thyroid hormone on bone?
Osteoporosis.
What are the effects of hypothyroidism on the skin?
Dry skin.
Myxedema.
What are the three functions of thyroid peroxidase?
Oxidizes I- (I- -> I2).
Binds I2 to thyroglobulin, forming MIT and DIT.
Uses MIT and DIT to make T3 and T4.
At what point would radio labeled iodine uptake into the thyroid gland peak if the patient was normal?
What percentage of the radio labeled iodine would be absorbed?
Roughly 12 hours.
25% of radio labeled iodine would be absorbed.
What are the symptoms of cretinism?
Feeding problems.
Respiratory difficulty.
Protruding tongue.
Curse facial features.
Growth and mental retardation.
Jaundice.
Dry skin.
Hypotonia.
On the most basic molecular level, what is responsible for the actions of thyroid hormone?
Thyroid hormone activates nuclear receptors and the cAMP second messenger system.
If a patient presents with an anti-thyroid antibody, what disease should you immediately be thinking?
Hashimoto’s thyroiditis.
What would the effects of hypothyroidism be in a fetus?
What would cause these issues?
Lack of proper bone formation due to a lack of thyroid hormone’s synergistic effects on growth hormone and somatomedin.
Abnormal synaptic development, decreased dendritic branching and myelination, and cretinism. This is due to thyroid hormone’s essential function in the development of the central nervous system.
What would a T3 binding resin test show if the patient had hepatic failure?
Increase in the level of free T3 and T4, followed by inhibition of synthesis of T3 and T4.
What would be the effect of hypothyroidism on the cardiovascular system?
Bradycardia.
Decreased contractility.
Decreased cardiac output.
Heart failure.
What are the possible causes of goiter discussed in class?
TSH excess - such as from a pituitary adenoma or Hashimoto’s
Iodine deficiency.
If the thyroid is not producing T4, what hormone would we expect to be increased?
Thyroid stimulating hormone.
T4 inhibits thyroid stimulating hormone, so its absence increases thyroid stimulating hormone.
Thyrotropin releasing hormone (TRH) does not appear to be elevated as a result of absent or reduced T4.
