Endocrine Flashcards
What percentage of T3 is derived from conversion of T4?
80%
What is the major thyroid hormone binding protein?
Thyronine binding globulin (TBG)
What percentage of T4 and T3 are bound?
Greater than 99.5%
What is the major cause of decreased T3 concentration in patients with a critical illness?
Impaired peripheral conversion of T4 to T3 secondary to inhibition of the deiodination process.
What factors decrease TSH secretions?
Acute and chronic illness, adrenergic agonists, calorie restriction, dopamine and dopamine agonists, surgical stress, and thyroid hormone metabolites. Minor decreases occur with carbamazepine, clofibrate, opiates, phenytoin, and somatostatin.
A patient with a history of radiation exposure as a child was found to have an enlarged lymph node on physical exam. The lymph node is removed, and there is normal appearing thyroid tissue in the lymph node. What is the diagnosis?
Papillary thyroid cancer. Treatment is total thyroidectomy, ipsilateral modified radical neck dissection, and post-operative ablative i-131 therapy. Bilateral neck dissection is reserved for clinically apparent bilateral nodal disease.
Name some negative prognostic variables for papillary thyroid carcinoma.
Age greater than 70 years old, vascular / lymphatic tumor invasion, high-grade tumor, and extra thyroid capsular extension.
What is the embryological origin of the thyroid gland?
From median downgrowth of the first and second pharyngeal pouches in the area of the foramen cecum.
What is the embryological origin of the parafollicular cells?
From the ultimobranchial bodies of the 4th and 5th branchial pouches. Neuroendocrine cell lineage.
What is the effect of pressor doses of dopamine on TSH regulation?
It decreases TSH levels to normal in patients with pre-existing hypothyroidism.
