Ca Balance

Question 1

3 things that raise PTH

Answer 1

Low Ca / Vit D, high phosphate

Question 2

Effects of PTH on Ca, Vit D, and phosphate

Answer 2

Raises Ca / Vit D, lowers phosphate

Question 3

What does Vit D do to PTH?

Answer 3

Inhibits secretion

Question 4

PTH action at the kidney (3)

Answer 4

Resorbs Ca at distal nephron, inhibits phosphate resorption by reducing # of proximal tubule Na-Phos contransporters, activates Vit D via increased transcription of 1-alpha-hydroxylase

Question 5

3 things that up regulate 1-alpha-hydroxylase

Answer 5

High PTH, low Ca, and low phosphate

Question 6

2 things that inhibit 1-alpha-hydroxylase

Answer 6

Ca and FGF-23

Question 7

What 2 things inhibit parathyroid proliferation?

Answer 7

Ca and Vit D

Question 8

Vit D action on bone (3)

Answer 8

• Stimulates FGF-23
• Stimulates differentiation of precursor cells into osteoclasts and
• Upregulates of RANKL on osteoblasts.

Question 9

2 actions of FGF-23

Answer 9

Inhibits 1-alpha-hydroxylase (leads to less phosphate absorption) and causes phosphate wasting in kidney.

Question 10

3 things that stimulate FGF23

Answer 10

High Vit D, Ca, and phosphate

Question 11

3 effects of excess FGF23

Answer 11

Low phosphate, poor bone mineralization, and low Vit D

Question 12

Sxs of primary hyperparathyroidism

Answer 12

“Bones, stones, abdominal groans, psychic moans”.
•Bone: bone resorption, “brown tumors” (of osteoclasts), and fractures.
•Renal: nephrolithiasis and nephrocalcinosis due to hypercalciuria.
•GI: nausea, vomiting, constipation.
•Psych: confusion, memory difficulties, difficulty concentrating.

Question 13

Familial Hypocalciuric Hypercalcemia
Cause
Inheritance
Presentation
Treatment

Answer 13

• Loss of function mutation in CaSR. Higher Ca levels are required before PTH is inhibited and before calciuria is induced (pee out Ca).
• Autosomal dominant.
• Presentation – mildly high serum Ca, mildly high / normal PTH, low urinary Ca.
• This condition is BENIGN. Do NOT treat.

Question 14

2 drugs that cause hypercalcemia

Answer 14

• Lithium increases setpoint for suppression of PTH → mildly elevated Ca / PTH
• Hydrochlorothiazide also causes mildly elevated Ca and PTH

Question 15

How does sarcoid / granulomatous disease cause hypercalcemia?

Answer 15

Upregulates 1a-hydroxylase

Question 16

How does hyperthyroidism cause hypercalcemia?

Answer 16

Excess TH –> bone breakdown

Question 17

3 causes of absence / destruction of parathyroid glands –> primary hypoparathyroidism

Answer 17

DiGeorge Syndrome, surgery, autoimmune

Question 18

Cause of pseudohypoparathyroidism

Answer 18

Resistance to PTH at kidney due to mutation in Gs-alpha component of PTH receptor.

Question 19

Type 1 pseudohypoparathyroidism

Answer 19

Renal resistance to PTH + AHO due to inheriting maternal defected Gs-alpha

Question 20

Albright’s Hereditary Osteodystrophy

4 characteristics

Answer 20

Short stature, round face, obese, short 4th metacarpal / metatarsal

Question 21

Pseudo-pseudohypoparathyroidism

Answer 21

AHO but normal PTH activity due to inheriting dad’s defected Gs-alpha

Question 22

2 common causes of secondary hyperparathyroidism

5 other causes

Answer 22

• Low Vit D – causes poor Ca absorption from gut.
• CKD - causes impaired phosphate clearance and impaired 1a-hydroxylase activity
• Others - critical illness, acute pancreatitis, massive blood transfusions, osteoblastic metastases, hungry bone syndrome