Parathyroid Flashcards
What are the two cells of the parathyroid gland?
Chief cells- produce PTH
Oxyphil cells- packed with mitochondria (granular/pink on H and E)
What triggers the release of PTH from chief cells of the parathyroid?
Low serum (ionized) calcium levels
not under Hypothalamic-pituitary axis..
What is the effect of PTH?
Increase serum calcium
How does PTH increase serum calcium levels?
Increase renal tubular reabsorption
Increase vitamin D to its active form
Decrease serum phosphate by increasing urinary excretion
Increase GI calcium absorption
What are two causes of hypercalcemia with elevated PTH levels?
Primary Hyperparathyroidism
Familial hypocalciuric hypercalcemia
What are a few causes of hypercalcemia with low PTH levels?
Hypercalcemia of malignancy Vitamin D toxicity Immobilization Thiazide diuretics Granulomatous disease (like sarcoidosis)
How can malignancy cause hypercalcemia?
Tumors to the bones –> increased resorption
-or-
Paraneoplastic syndrome: release of parathyroid hormone-related peptide (PTH-RP)
What is far and away the most common lesion of the parathyroid gland?
Parathyroid adenoma
What is the gene involved in MEN1 syndrome?
MEN1- (parathyroid, pancreas and pituitary)
MEN1 is a tumor suppressor gene
What is the gene mutated in MEN2A syndrome?
Activating mutation of RET (tyrosine kinase)
What is the genetic mutation associated with familial hypocalciuric hypercalcemia
CASR- AD disorder
Ca2+ sensing receptor gene in the renal tubules
What is the half life of PTH? Why is this useful?
3 minutes-
You can remove an parathyroid gland suspected of causing primary hypercalcemia and check the PTH levels. If you got the right one, the levels will drop in half within a few minutes
What type of cells are missing from parathyroid adenomas?
Fat
Can occupy up to 30% of adult parathyroid glands
Define parathyroid hyperplasia
When the disease affects more than one gland.
Parathyroid adenomas are localized to a single gland
What are the clinical manifestations of hypercalcemia?
Painful bones, renal stones, abdominal groans and psychic moans
Osteofibrosis cystica, osteoporosis, nephrolithiasis, nephrocalcinosis, gallstones, PUD, acute pancreatitis, CNS depression, seizures…
What is the most common cause of secondary hyperparathyroidism?
Renal failure (often with diabetes)
What is secondary hyperparathyroidism?
Process of chronic depression or decrease in calcium that causes compensatory over activity of the parathyroid glands
What does renal insufficiency cause secondary hyperparathyroidism?
Renal insufficiency causes decreased phosphate excretion –> hyperphosphatemia –> decreased ionized serum calcium
What is tertiary hyperparathyroidism?
Autonomous hyperparathyroidism without symptomatic hypercalcemia- follows chronic hypercalcemia due to secondary hyperparathyroidism (again, often due to renal insufficiency)
Which is more common: hyper or hypoparathyroidism?
Hyperparathyroidism is way more common than hypoparathyroidism
What is the most important cause of hypoparathyroidism?
Surgically induced
With what syndrome can you have congenital absence of parathyroid?
DiGeorge’s Syndrome
What are the CNS manifestations of hypoparathyroidism?
Tetany: especially perioral numbness
Chvostek sign: tap along course of facial nerve
Trousseau sign: carpal spasms following occlusion of circulation of the forearm
Mental status change
How is the QT interval affected by hypoparathyroidism?
Prolonged QT (with low calcium)
