calcium metabolism

Question 1

parathyroid glands originate from

Answer 1

3rd + 4th branchial pouches

Question 2

parathyroid gland innervated by

Answer 2

cervical sympathetic ganglia
don’t directly innervate it but
controls blood flow to parathyroid glands

Question 3

causes of hypercalcemia

Answer 3

90% cases:
*1° hyperparathyroidism (most common in outpatients): solitary parathryoid adenoma (95%), parathyroid hyperplasia
*malignancy (most common in inpatients):
squamous cell cancers (lung/head/neck via PTHrP)
renal cell carcinoma (via PTHrP)
breast mets to BONE (via PTHrP - stimulate osteoclasts locally)
multiple myeloma (local osteoLYTIC factors)
10% cases:
excess vitamin D ingestion
excess Ca ingestion: milk-alkali syndrome (ca-based antacids)
granulomatous disease: macrophages in granulomas produce 1,25 OH D3 due to sarcoid or TB
↑ bone turnover: hyperthyroidism, vit. A intoxication, immobilization
thiazide diuretics: ↓ renal excretion of Ca (loops lose Ca, thiazides retain Ca)

Question 4

causes of hypocalcemia

Answer 4

1) hypoparathyroidism:
parathyroidectomy (d/t thyroidectomy)
autoimmune destruction of parathyroids (rare)
pseudohypoparathyroidism (kidney unresponsive to PTH): ↓Ca (lose in urine)→↑ PTH
DiGeorge syndrome: no parathryoid (CV, hypoplastic thymus)
2) vitamin D deficiency:
nutritional deficiency and paucity of sunlight
chronic renal failure
3) acute pancreatitis: Ca can precipitate in abdomen and bind to fatty acids → soap (saponification)

Question 5

MEN’s associated with hyperparathyroidism

Answer 5

MEN 1: paraythroid adenoma

MEN 2A: parathyroid hyperplasia

Question 6

cause of 2° hyperparathyroidism

Answer 6

chronic hypocalcemia due to vitamin D deficiency:

1) chronic renal disease: can’t make calcitriol → no Ca absorption in gut → osteodystrophy
2) dietary vitamin D deficiency: rickets (similar to osteodystrophy)

Question 7

cause of 3° hyperparathyroidism

Answer 7

long-standing 2° hyperparathyroidism: chronic renal disease →↓ vit. D →↓ Ca → parathyroid hyperplasia →autonomously functioning parathyroids → able to ↑ Ca, but PTH stays ↑

Question 8

mutation in GNAS1 (codes G protein at PTH R in kidney) can cause

Answer 8

pseudohypoparathyroidism: renal tubules to be resistant to PTH

Question 9

AD
Albright's hereditary osteodystrophy:
short stature
obesity
underdevelopment of 4th/5th digits
severe: osteitis fibrosa cystica

Answer 9

type 1 A pseudohypoparathyroidism: ↓ Ca → ↑PTH