15.8 Parathyroid Glands

Question 1

Which cells regulate serum free (ionized) calcium via PTH secretion?

Answer 1

Chief cells (in the parathyroid)

Question 2

What are the three effects of PTH secretion?

Answer 2

1. increases bone osteoclast activity, releasing calcium and phosphate
2. activates vitamin D –> increased small bowel absorption of calcium and phosphate
3. increases renal calcium reabsorption (DCT) and DECREASES phosphate reabsorption (PCT)

Question 3

What is primary hyperparathyroidism?

Answer 3

excess PTH due to a disorder of the parathyroid gland itself

Question 4

What is the most common cause of primary hyperparathyroidism?

Answer 4

Parathyroid adenoma (sporadic parathyroid hyperplasia and parathyroid carcinoma are less common)

Question 5

Parathyroid adenoma most often results in asymptomatic

Answer 5

hypercalcemia

Question 6

5 possible symptoms of parathyroid adenoma

Answer 6

1. Nephrolithiasis
2. Nephrocalcinosis (metastatic calcification of renal tubules)
3. CNS disturbances
4. constipation, peptic ulcer dz, acute pancreatitis
5. osteitis fibrosa cystica

Question 7

lab finding of primary hyperparathyroidism

Answer 7

Increased serum PTH, calcium, alkaline phosphatase, and urinary cAMP
Decreased serum phosphate

Question 8

How do you treat primary hyperparathyroidism?

Answer 8

surgical removal of the affected gland

Question 9

what is secondary hyperparathyroidism

Answer 9

excess production of PTH due to a disease process extrinsic to the parathyroid gland.

Question 10

What is the most common cause of secondary hyperparathyroidism?

Answer 10

chronic renal failure

Question 11

How does chronic renal failure lead to lead to secondary hyperparathyroidism?

Answer 11

renal insufficiency –> decreased phosphate excretion –> increased serum phosphate (binds free calcium) –> decreased free calcium –> increased PTH –> bone resorption –> renal osteodystrophy

Question 12

lab findings of secondary hyperparathyroidism secondary to chronic renal failure

Answer 12

Increased serum PTH, phosphate, and alkaline phosphatase

Decreased serum calcium

Question 13

Why is there increased serum alkaline phosphatase in secondary hyperparathryoidism?

Answer 13

reflects osteoBLAST activity (necessary to activate osteoclasts)

Question 14

what is hypoparathyroidism?

Answer 14

low PTH

Question 15

name three causes of hypoparathyroidism

Answer 15

1. AI damage to parathyroids
2. surgical excision (botched thyroidectomy)
3. DiGeorge syndrome

Question 16

two symptoms of hypoparathyroidism –> hypocalcemia

Answer 16

1. numbness and tingling (circumoral)

2. muscle spasms (tetany)

Question 17

what do you call tetany that can be elected with filling of a BP cuff?

Answer 17

Trousseau sign (hypocalcemia

Question 18

what do you call tetany that can be elicited with tapping on the facial nerve?

Answer 18

Chvostek sign

Question 19

Labs of hypoparathyroidism

Answer 19

decreased PTH and calcium

Question 20

What is pseudohypoparathyroidism?

Answer 20

end-organ resistance to PTH

Question 21

labs of pseudohypoparathyroidism?

Answer 21

Increased PTH and decreased calcium

Question 22

differentiate pseudo and regular hypoparathyroidism by labs

Answer 22

pseudo - increased PTH
normal - decreased PTH
(both have low calcium)

Question 23

what causes the autosomal dominant form of pseudohypoparathyroidism?

Answer 23

Gs mutation

Question 24

AD pseudohypoparathyroidism is associated with

Answer 24

short stature and short 4th and 5th digits