Hormonal Control of Calcium and Phosphate

Question 1

Which Ca2+ is physiologically active? Bound or free

Answer 1

the free Ca2+ is physiolgically active

Question 2

Describe alkalosis and acidosis effects on calcium concentration in the body?

Answer 2

alkalosis lowers free Ca2+ by increasing protein binding, while acidosis raises free Ca2+ by decreasing protein-bindng

Question 3

What is OPG?

Answer 3

osteoprotegerin binds RANK-L, thereby preventing it from binding onto precursor or osteoclast cells

“acts as a decoy for RANK-L”

Question 4

What are the 2 mechanisms by which estrogen is known for conserving bone integrity?

Answer 4

• induces the synthesis of OPG
• reduces the secretion of cytokines by T-lymphocytes; these cytokines stimulate differentiation of precursor cells into active osteoclasts and they stimulate activity of mature osteocytes
• by inhibiting cytokines and increasing OPG, estrogen reduces the activity of osteoclasts.

Question 5

How can PTH be used as a treatment in treating osteoporosis?

Answer 5

it can actually stimulate osteoblastic activity resulting in bone deposition if given intermittent spikes in PTH

Question 6

What is calcitonin?

Answer 6

a peptide hormone secreted by the parafollicular cells (C cells) of the thyroid gland; released in response to elevated free calcium

Question 7

What is the MOA of calcitonin?

Answer 7

lowers plasma calcium be decreasing the activity of osteoclasts; thus decreasing bone resorption

Question 8

What are conditions calcitonin in used to treat?

Answer 8

Paget disease, severe hypercalcemia, and osteoporosis

Question 9

What is the other name for calcitriol?

Answer 9

Vitamin D

Question 10

What are the sources of Vit. D?

Answer 10

Vit D2 (diet) (ergocalciferol)
Vita D3 (skin) (cholecalciferol)

Question 11

What is the active form of vit. D?

Answer 11

1,25 di-OH vitamin D (calcitriol)

Question 12

What is the enzyme in renal tubules that converts 25 OH vitamin D to the active form?

Answer 12

1 a-hydroxylase in renal proximal tubule

Question 13

What stimulates 1 a-hydroxylase activity?

Answer 13

low phosphate and PTH

Question 14

What are the actions of calcitriol on the body?

Answer 14

raises plasma Ca2+ and phosphate by

increasing absorption of Ca2+ and phosphate in intestinal mucosa by increasing the production of Ca2+ binding protein calbindin

Question 15

Calcitriol enhances PTH action at what part of the kidney tubule?

Answer 15

renal distal tubule

Question 16

Which type of hyperparathyroidism, primary or other, is associated with elevated plasma calcium and PTH normal or elevated?

Answer 16

primary hyperparathyroidsm

Question 17

What is pseuodhypoparathyroidism? Signs and symptom?

Answer 17

rare familial disorder characterized by target tissue resistance to PTH

usually accompanied by developmental defects: mental retardation, short and stocky stature, one or more metacarpal or metatarsal bones missing

Question 18

In cases of hypocalcemia. When plasma calcium and phosphate levels are changing in opposite direction that cause is primary or secondary?

Answer 18

primary disorder

Question 19

Can hyperphosphatemia lead to hypocalcemia?

Answer 19

yes

Question 20

When plasma calcium and phosphate are changing in the same direction, the origin is usually primary or secondary?

Answer 20

secondary disorder

secondary hyperparathyroidism: both decrease
secondary hypoparathyroidism: both increase

Question 21

Bone mineral density range for osteoporosis?

Answer 21

2.5 standard deviations below the average

Question 22

Bone mineral density range for osteopenia?

Answer 22

1-2.5 standard deviations below the avg. the equals osteopenia

Question 23

Which is seen before plate closure? Rickets or osteomalacia?

Answer 23

rickets seen before plate closure

Question 24

MOA denosumab?

Answer 24

inhibitor of RANKL (RANKL is a TNF family of cytokines that activates osteoclasts; thus, denosumab inhibits osteoclasts)

Question 25

MOA teriparatide?

Answer 25

synthetic PTH (when used intermittently, teriparatide has stimulatory effect on osteoblastic bone formation)

Question 26

What is raloxifene MOA?

Answer 26

SERM