Flashcards in Osteoporosis Deck (73)
Calcium in the bone is
bone forming cells
bone resorption cells
Factors released by osteocytes that stimulates osteoblasts
prostaglandins, NO, dentin matrix protein-1
Factors released by osteocytes that stimulates osteoclasts
sclerostin; osteocalcin; MEPE (matrix extracellular phosphoglycoprotein)
What does parathyroid hormone (PTH) do?
1. increased calcium reabsorption from CT
2. increased calcium resorption from bone
3. increased PO4 loss in urine
4. increased 1,25(OH)2D3 production by kidney
PTH secretion is triggered by
low serum Ca2+ levels
First step of vitamin D synthesis
7-dehydrocholesterol -> (UV) -> cholecalciferol (D3)
Cholecalciferol can be obtained
in the diet or via exposure to sun light
Under which conditions is 25-hydyoxyvitamin D3 converted into 1,25 Dihydroxy vit D3 (calcitriol)?
low phosphorus and Ca2+
Under which conditions is 25-hydyoxyvitamin D3 converted into 24,25 Dihydroxy Vit D3 (secalciferol)?
normal phosphorus and calcium
What reaction does 1-alpha-hydroxylase catalyze?
25-hydyoxyvitamin D3 -> 1,25 Dihydroxy vit D3 (calcitriol)
What reaction does 24-hydroxylase catalyze?
25-hydyoxyvitamin D3 -> 24,25 Dihydroxy Vit D3 (secalciferol)
Actions of vitamin D
1. increased calcium and PO4 absorption from small intestine
2. increased calcium and PO4 reabsorption
3. indirect (slow) effects on cells
4. feedback inhibition of PTH (1,25(OH)2D
What is upregulated by Vitamin D3?
Which cells secrete calcitonin?
cells in the thyroid gland
What does calcitonin do?
negative regulator of serum calcium;
1. inhibits osteoclastic bone resorption
2. increases calcium and PO4 loss in the urine
What is calcitonin stimulated by?
high serum calcium levels
Describe postmenopausal osteoporosis.
decrease in estrogen levels causes a decrease in bone mass; shift in bone remodeling balance toward resorption; spontaneous or minimal trauma fractures
Describe osteoporosis related to aging.
caused by age-related decrease in osteoblast activity in both men and women
Vertebral complications of osteoporosis
fragility fractures; pain; height loss; kyphosis; activity limitations; restrictive lung disease; psychological symptoms
Risk factors for osteoporosis
Physical inactivity; age; low calcium intake in early years; long-term glucocorticoid therapy
increased bone resorption and decreased calcium excretion
Hypercalcemia caused by malignant tumors
some tumors produce a peptide with PTH activity
CNS complications from hypercalcemia
depression and coma
Hypocalcemia can be caused by
hypoparathyroidism or vit. D deficiencies
Symptoms of hypocalcemia
causes neuromuscular disturbances, parasthesias, tetany, and muscle cramps
Vitamin D deficieny; weight bearing bone deformities in children
Vitamin D preparations
Cholecalciferol Vit D3 (OTC)
Calcifediol 25(OH)Vit D3 (Calderol)
Calcitriol 1,25(OH)2VitD3 (Rocaltrol)