Flashcards in Endocrine Disorders Deck (200)
What is the pathway for thyroid regulation?
Hypothalamus - thyrotropin-releasing hormone (TRH) => anterior pituitary - thyroid stimulating hormone (TSH) => thyroid - T4 and T3 => plasma - T4 and free T4/T3 and free T4 => peripheral tissues - free T4/free T3/reverse T3
What is the condition with low TSH and low free T4?
What is the condition with normal TSH and low free T4?
What is the condition with high TSH and low free T4?
What is the condition with low TSH and normal free T4?
What is the condition with normal TSH and normal free T4?
What is the condition with high TSH and normal free T4?
What is the condition with low TSH and high free T4?
What is the condition with normal TSH and high free T4?
non-thyroid illness or patient on Eltroxin (levothyroxine)
What is the condition with high TSH and high free T4?
What is the normal range for TSH?
0.5 - 5.0 mU/L (upper limit soon to be revised to 2.5 mU/L)
What is the normal range for free T4?
0.7 - 2.1 ng/dL
What do the parathyroid glands do?
Chief cells synthesize and secrete parathyroid hormone - polypeptide hormone
What are the roles of parathyroid hormone?
plays a major role in bone remodeling, calcium homeostasis, regulation of calcium levels, and bone mass; participates in renal excretion of phosphate and activation of vitamin D
How is parathyroid hormone regulated?
by serum ionized calcium via calcium-sensing receptors on the surface of parathyroid cells => high serum calcium levels suppress PTH secretion while low levels stimulate PTH release
How is primary hyperparathyroidism diagnosed?
patients exhibit elevated levels of serum calcium (10-11 mg/dL) and parathyroid hormone - may occur when patients are taking lithium or thiazide diuretics
What is primary hyperparathyroidism?
abnormal regulation of PTH secretion => hyper secretion of PTH relative to the serum calcium concentration
What are the effects of increasing levels of PTH?
stimulates bone resorption, leading to an increase in serum calcium levels and increased activation of vitamin D
What is the negative feedback loop relating to the parathyroid glands?
when serum calcium levels increase, PTH decreases (and vice versa) => when serum calcium levels decrease, PTH increases (and vice versa)
What are the clinical manifestations of primary hyperparathyroidism?
elevated PTH levels, hypercalcemia, hypercalciuria (and possible increased formation of kidney stones/urolithiasis), decrease serum phosphate levels ("stones, bones, abdominal groans, psychic moans")
What is the normal range for parathyroid hormone?
10 - 60 pg/mL
What is the negative feedback loop in the thyroid gland?
As TSH increases, free T4 decreases => as TSH decreases, free T4 increases
What are some causes of hypercalcemia?
primary hyperparathyroidism, vitamin D intoxication, use of thiazide diuretics or lithium, hyperthyroidism, pheochromocytoma, adrenal insufficiency, immobilization
What are signs and symptoms of excess parathyroid hormone?
s/s of hypercalcemia (weakness and myalgia, confusion, lethary, parethesias), bone pain, osteoporosis, nephrolithiasis (kidney stones), hypophosphatemia, increased calcitriol, hyperuricemia, gout, anemia, HTN, abdominal pain, nausea, peptic ulcer, constipation, pancreatitis
What is the most common cause of secondary hyperparathyroidism?
chronic renal failure - normally, reduction in plasma vitamin D and moderate decreases in serum calcium lead to greater synthesis and secretion of PTH => in chronic renal disease, parathyroid expression of vitamin D and calcium receptors is reduced making the gland resistant to the usual negative feedback loop
What is a classic sign of hypoparathyroidism?
Chvostek sign - twitching or contraction of the facial muscles in response to tapping the facial nerve at a point anterior to the ear and above the zygomatic bone - due to hypocalcemic tetany
What is the mechanism of pseudohypoparathyroidism?
abnormal response to PTH due to a congenital defect in the G protein (NOT due to decreased PTH levels)
What are the classic features of pseudohypoparathyroidism type 1a?
generalized hormone (TSH, LH, FSH) resistance to PTH - abnormal physical features (round face), short stature, skeletal abnormalities (short metacarpals)
What are the classic features of pseudohypoparathyroidism type 1b?
renal resistance to PTH - low plasma calcium levels, high phosphate levels, elevated PTH levels with a normal appearance