Calcium and Bone Flashcards
What is the entry, storage, exit and control site of Ca2+
- Entry: Intestines/gut
- Storage: bone
- Exit: kidney
- Control: PT gland
Describe the effects of 1,25(OH2)D3 (Vit. D) on Ca2+ and phosphate homeostasis?
- Stimulates intestinal absorption of Ca and P
- Promotes bone formation AND resorption by stimulating OB and OC
- Enhance reabsorption of C at kidney
- Enhance P retention at kidney
- Inhibit (so does Ca2+) PTH synthesis and release from parathyroid gland
- Induce RANKL in OBs–> role in bone mineralization
NET effect: increase Ca2+ and P
Describe the effects of PTH on Ca2+ and phosphate homeostasis?
- Promote bone formation and resorption by stimulating OB and OC
- Enhance reabsorption of Ca2+ at kidneys
- Renal excretion of P
- Renal production of active Vit. D synthesis stimulation
in pharmacologic concentrations, calcitonin can ____ by ___
reduce serum Ca2+ and P by inhibiting bone resorption
What stimulates and inhibits PTH
Stimulates: hypocalcemia
2. Vit. D and high Ca inhibit PTH
PTH increases the number and activity of OC via actions on OB to induce ___
RANKL (which acts on OC to increase their activity and increase bone remodeling)
Net effect of excess PTH is to ____ BUT low and intermittent doses of PTH _____
increase bone resorption
stimulate formation w/o first increasing bone resorption
Describe the metabolism of Vit. D
- 7-dehydrocholesterol converted to D3 via UV light and heat
- D3 (diet) is converted to 25(OH)D3 in liver
- 25(OH)D3 is converted to active D3 1,25(OH)2 D3 in kidney
Which of the following drugs is routinely added to calcium supplements and milk for the purpose of preventing rickets in children and osteomalacia in adults? A. Cholecalciferol B. Calcitriol C. Calcitonin D. Dihydrotachysterol E. Fluoride
A. Cholecalciferol
What is cholecalciferol and its use?
Vit. D3 supplement
*preferred over other metabolites due to modest cost
What is ergocalciferol and its use?
Vit. D2 (from plants)
-LESS efficient that D3
What is calcitriol and its use?
1,25(OH)2 D3 (ACTIVE D3)
Uses:
In those w/ decreased synthesis of calcitriol
1. CKD
2. Type 1 (vit. d dependent) rickets
Adverse reaction of calcitriol
- hypercalcemia
What is calcifediol and its use?
24(OH)2 D3
*use in liver dz bc does not require hepatic 25-hydroxylation
what is dihydrotachysterol use?
alternative for use in disorders that calcitriol is used
A 67-year-old man with chronic kidney disease was found to have an elevated serum PTH concentration and a low serum concentration of 25-hydroxy vitamin D. He was
successfully treated with ergocalciferol. Unfortunately, his kidney disease progressed so that he required dialysis and his serum PTH concentration became markedly elevated. Which of the following drugs is most likely to lower this patient’s serum PTH concentration?
A. Cholecalciferol
B. Alendronate
C. Teriparatide
D. Raloxifene
E. Calcitriol
E. Calcitriol
Side effects associated with the use of calcitriol in the treatment of hyperparathyroidism include: A. Erosive esophagitis B. Thromboembolic disorders C. Hypercalcemia D. Endometrial cancer E. Kidney stones
C. Hypercalcemia**
E. Kidney stones
The active metabolites of vitamin D act through a nuclear receptor to produce which of the following effects?
A. Decrease the absorption of calcium from bone
B. Decrease PTH formation
C. Increase renal production of erythropoietin
D. Increase the absorption of calcium from the GI tract
E. Lower the serum phosphate concentration
B. Decrease PTH formation
D. Increase the absorption of calcium from the GI tract
Which of the following statements concerning vitamin V3 and its metabolites is FALSE?
A. One of the gene products resulting from the action of vitamin D is a calcium binding protein.
B. Glucocorticoids can antagonize the actions of vitamin D on both intestine and bone.
C. The most potent and rapid acting vitamin D metabolite (calcitriol) is synthesized in the liver.
D. The conversion of 7-dehydrocholesterol to vitamin D3 occurs in the skin and requires UV radiation.
E. Vitamin D is necessary for both bone resorption and bone mineralization.
C. The most potent and rapid acting vitamin D metabolite (calcitriol) is synthesized in the liver.
What stimulates calcitonin release
Hypercalcemia
*it TONES DOWN Ca2+
What effect does calcitonin have on Ca2+ and P levels
- Increase OC bone resorption (decrease C and P)
- reduce reabsorption/increase excretion of Ca and P
NET: decrease Ca and P
What are estrogens actions on bone?
- Positive effect on bone mass–> agonist at ERalpha receptors on OBs and OCs
1. decrease OC number and activity
2. Increase OB production of OPG**–> binds RANKL–> decrease OC activity
3. Increase OC apoptosis
4. Anti-reasorptive agent* (use in osteoporosis)
What is OPG
produced by OBs and it is a decoy receptor that binds RANKL and prevents OC activation
What 4 things lead to increase bone fraction in postmenopause due to decrease in estrogen?
- Increased production of cytokines–> activate OCs
- Longer lifespan of OCs (decrease apoptosis)
- Shorter lifespan of OBs (increase apoptosis)
- Short lifespan of osteocytes (increase apoptosis)
How do GC affect bone denisty
decrease bone density
GCs action on bone
- lower serum Ca2+–> increase PTH–> stimulate OC activity
- Increase RANKL production by OBs and decrease OPG–> increase OC activation–>
- Increase bone resorption
- Suppressive effects on OBs
What thing increase OC (bone resportion)
- increased RANKL
- Decreased OPG
- high OC
What things increase OB (bone formation)
- high PTH
- High activated D3
- low sclerostin Ab
Osteoporosis is defined as bone mineral density:
A. 2.5 or more standard deviations below the mean value at the spine, femoral neck,, or total hip in young adults
B. 1 standard deviation below the mean value at the spine, femoral neck, or total hip in young adults
C. 1 standard deviation below the mean value at the spine, femoral neck, or total hip in adults of the same age
D. Lower than the mean value in adults of the same age
A. 2.5 or more standard deviations below the mean value at the spine, femoral neck,, or total hip in young adults
Pharmacologic treatment for postmenopausal osteoporosis should be considered for women with:
A. A hip or spine fracture
B. A T-score of -2.5 or below at the spine, femoral neck, or total hip
C. A T-score between -1.0and -2.5 and a 10-year FRAX risk of ≥ 3% for hip fracture or ≥ 20% for humerus, forearm, or clinical vertebral fracture
D. All of the above
D. All of the above
What is Denosumab?
RANKL Ab hat binds RANKL and prevent the RANK-RANKL interaction
**Anti-resorptive agent used in osteoporosis
What drugs decrease OC activity
- Bisphosphates
- Cacitonin
*inhibit bone resorption by OC
Examples of Bisphosphates
- Alendronate
- Risedronate
- ibandronate