Regulation of Calcium

Question 1

What is Chovstek Sign?

Answer 1

Twitching of the facial nerve subsequent to ipsilateral tapping; indicates hypocalcemia

Question 2

What is Trousseau sign?

Answer 2

Carpopedal spasms when a blood pressure cuff is increased higher than the systolic value; indicates hypercalcemia

Question 3

What is the resulting change with ionized calcium, in regards to increased plasma protein concentration?

Answer 3

No change (it does increase total Ca2+ concentration)

Question 4

What can result from Alcoholism, in terms of PTH?

Answer 4

Alcoholism: Causes Mg2+ deficiency (hypomagnesemia) –> inhibition of PTH synthesis

Question 5

What are the general mechanisms via which PTH affects Ca2+ & K+ levels?

Answer 5

1) Stimluates Ca2+ reabsorption

2) Stimulates K+ Secretion

Question 6

What is the last step in the mechanism of action, regarding PTH action, on the kidney?

Answer 6

PTH: Inhibits Na+/Phosphate cotransport along the lumen side of proximal tubule cell & distal convoluted tubule; results in increase phosphate excretion

Question 7

What are the resulting actions of PTH on RANKL and OPG levels?

Answer 7

PTH= Increased RANKL and Decreased OPG

Question 8

What are the resulting actions of Vitamin D on RANKL levels?

Answer 8

They decreased RANKL levels

Question 9

What is RANKL?

Answer 9

1) RANKL = Produced via osteoblasts and dying osteoclasts –> primary mediator for osteoclast formation

Question 10

What is OPG?

Answer 10

OPG= Soluble protein, produced via osteoblasts that acts as a decoy for the RANKL receptor –> prevents RANKL/RANK interaction

Overall: Inhibits Osteoclast function

Question 11

What is M-CSF?

Answer 11

It induces stem cells to differentiate into osteoclast percursors

Question 12

What is Vitamin D’s effect in the small intestine?

Answer 12

It increases Ca2+ and Phosphate absorption via increased expression of Calbindin

Question 13

What are Vitamin D’s effects on bone?

Answer 13

1) Sensitizes Osteoblasts to PTH’

2) Regulates Osteoid production and Calcification

Question 14

What is the effect of Vit D on the Kidney?

Answer 14

It stimulates NPT2a expression; increasing phosphate reabsorption

Question 15

What are Vit D’s effects on the Parathyroid gland?

Answer 15

1) Directly inhibits PTH expression

2) Directly stimulates CaSR gene expression

Question 16

What are the three effects of PTH in the kidney?

Answer 16

1) Stimulates 1a-hydroxylase activity
2) Stimulates Ca2+ reabsorption along the TAL & Distal tubule
3) Inhibits Phosphate reabsorption via repressing NPT2a expression

Question 17

In regards to the thyroid role of release of Calcitonin and its affect on calcium levels.

A) What is its function?

B) What is the effect on Ca2+ metabolism with a thyroidectomy & thyroid tumor, respectively?

Answer 17

1) Calcitonin: Inhibits Ca2+ reabsorption

2) Calcitonin has no effect on Ca2+ metabolism; doesn’t play role in the immediate regulation

Question 18

What is the etiology of Albright Hereditary Osteodystrophy?

Also, what is the resulting pathology?

Answer 18

AKA: Pseudohypoparathyroidism type Ia

Etiology: Gs for PTH in bone and kidney is defective

Pathology: Hypocalcemia and hyperphosphatemia

Question 19

What is the etiology and pathology of Humoral Hypercalcemia of Malignancy?

Answer 19

Etiology: Increased PTHrP (Parathyroid related peptides); same action as PTH

Pathology: Same as PTH; except there is:
Decreased Vit D
Decreased PTH
Decreased bone formation

Question 20

What is the etiology and pathology of Familial Hypocalciuric Hypercalcemia?

Answer 20

Etiology: Mutations that inactive CaSR and Ca2+ receptors in the TAL of the kidney

Pathology: Decreased urinary Ca2+ excretion and increased serum Ca2+ concentration

Question 21

Vitamin D dependent Rickets Type I; characterized by?

Answer 21

Decreased activity of 1a- hydroxylase

Question 22

Vitamin D dependent Rickets type II; characterized by?

Answer 22

Decreased Vitamin D receptor