Osteo/ Vitamin D

Question 1

Process of de novo vitamin D synthesis

Answer 1

cholesterol becomes reduced, converted in the skin by UV light producing previtamin D3, previtamin is processed by the liver to 25- hydroxyvitamin D3, further hydroxylation takes place in kidney to form 1-25 dihydroxy-vitamin D (calcitrol)- which is the active form of vitamin D.

Question 2

Role of Vitamin D

Answer 2

positive regulator of calcium homeostasis from phosphate metabolism is affected by vitamin D in a manner parallel to calcium

Question 3

How does Vitamin D maintain normal concentrations of calcium and phosphate?

Answer 3

1. facilitate absorption by the small intestine
2. interact w/ PTH to enhance their mobilization from bone
3. decrease excretion by kidneys

Question 4

MOA of calcitrol

Answer 4

same as steroid and thyroid hormones
Binds to cytosolic receptors within target cells, and the receptor-hormone complex interacts w/ DNA to modify gene transcription

Question 5

What happens in vitamin D deficiency?

Answer 5

inadequate absorption of calcium and phosphate
decrease in plasma calcium stimulates PTH secretion, which acts to restore plasma concentration
Phosphate decreases due to effect of PTH

Question 6

Ergocalciferol

Answer 6

pure vitamin D2

given PO, IM, IV

Question 7

Dihydrotachysterol

Answer 7

reduction product of vitamin D2

Given PO

Question 8

Calcitriol

Answer 8

given PO & IV, important in renal failure

Question 9

Hypervitaminosis

Answer 9

Toxicity results from excessive intake of Vitamin C or over treatment of hypoparathyroidism
Greatest risk is severe hypercalcemia

Question 10

Primary Osteoporosis

Answer 10

2 different condition:

1. type 1- loss of trabecular bone due to estrogen lack at menopause
2. type 2- loss of cortical and trabecular bone in men and women due to long term modeling inefficiency, dietary inadequacy, and activation of parathyroid axis w/ age

Question 11

Calcium Carbonate

Answer 11

inexpensive, more elemental calcium than other salt forms

can be constipating in doses upward of 2000 mg/day

Question 12

Vitamin D and analogs

Answer 12

directly suppress parathyroid function and reduce bone turnover - possible toxicity

Question 13

Estrogen

Answer 13

used for post menopausal women

conjugated equine estrogens with or without progestins

Question 14

Raloxifene

Answer 14

acts as estrogen agonist in liver and bone, inactive on the uterus, anti estrogen on breast tissue

Question 15

Calcitonin

Answer 15

inhibitor of osteoclastic bone resorption

Question 16

Bisphosphonates

Answer 16

Alendronate
Pamidronate
Ibandronate
MAY CAUSE ESOPHAGEAL IRRITATION AND ESOPHAGEAL ULCERS

Question 17

Bisphosphonate MOA

Answer 17

Suppress bone resorption through an increase in osteoclastic apoptosis
Action is mainly the result of inhibition of farnesyl pyrophosphate synthase (FPPS), an enzyme of mevalonate biosynthetic pathway

Question 18

Thiazide diuretics

Answer 18

reduces calcium excretion

Question 19

testosterone

Answer 19

useful in hypogonadal males

Question 20

Denosumab

Answer 20

a human monoclonal antibody that binds RANKL, blocks the binding of RANKL to RANK (receptor on osteoclasts & precursors), reducing the formation, function, and survival of osteoclasts.
Results in decreased bone resorption & increased bone density