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53 Cards in this Set
- Front
- Back
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What does 1,25-dihydroxyvitamin D do?
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increases absorption of calcium from the intestine and mobilizes calcium and phosphorus from bone
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What is the current RDA of vitamin D?
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200 IU/d
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How much vitamin D is in 1L of infant formula?
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400 IU vitamin D
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What are the 3 type of rickets caused by vitamin D abnormalities?
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Vitamin D Deficiency rickets, Vitamin D-resistant rickets, Vitamin D-dependent rickets
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What does PTH do?
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PTH increases the activity of enzyme 25-hydroxyvitamin D 1-alpha-hydroxylase
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clinical presentation of vitamin D deficiency rickets: skeletal findings
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craniotabes, enlargement of the costochondral junctions, scoliosis and kyphosis, enlargement at the wrists and ankles, coxa vara, and weak muscle tone; frontal bossing and rachitic rosaries (knobs along the anterior costochondral ridge)
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clinical presentation of vitamin D deficiency rickets: non skeletal findings
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Respiratory infections and pulmonary atelectasis that are related to severe chest deformities frequently are associated with rickets; convulsions, developmental delay, multiple fractures, decreased linear growth and bowing of the legs, short stature and poor weight gain
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Vit D2
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Ergocalciferol
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Vit D3
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Cholecalciferol
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Which form of vitamin D is used to fortify dairy products?
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Ergocalciferol (Vit D2)
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How does cholecalciferol (vit D3) become vitamin D?
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UV radiation causes cholecalciferol in skin to become vitamin D
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Which position is hydroxylated first in Vitamin D?
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25, then 1
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Where is Vitamin D hydroxylated first?
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in liver
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Where does 25-hydroxyvitamin D become hydroxylated into 1,25-dihydroxyvitamin D?
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in the kidney
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What happens to PTH when 25-hydroxyvitamin D decreases?
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As 25-hydroxyvitamin D levels decrease, parathyroid hormone (PTH) levels increase
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At what point in the disease do rachitic changes become florid?
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eventually both serum calcium and phosphorus concentrations decline as mineral absorption becomes inadequate to support normal serum calcium despite elevated PTH concentrations
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What happens to PTH and phosphorus when serum calcium falls?
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As serum calcium levels decrease, PTH increases. PTH restores calcium level in serum but leads to phosphaturia and decreased serum phosphate
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How do you screen for vitamin D deficiency?
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alkaline phosphatase and hemoglobin (level of 25-OH vitamin D is most sensitive but expensive)
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Work up for suspected vitamin D deficiency rickets
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Serum calcium, phosphorus, PTH, alkaline phosphatase, renal function tests, hydroxyvitamin D and dihydroxyvitamin D levels
+/- radiographs of long bones (ulna, radius, femur) |
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What causes congenital rickets?
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low maternal intake of vitamin D and calcium
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How do infants with congenital rickets present?
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Affected newborns have very low calcium levels and may present with seizures or tetany in early infancy
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Osteogenesis imperfecta is caused by what?
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a defect in type II collagen which results in the formation of brittle bones that are fractured easily
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How is diagnosis of OI made?
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fibroblast biopsy
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What is renal osteodystrophy?
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Renal calcium loss causes increased PTH and may result in renal osteodystrophy
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How does Renal tubular acidosis lead to bone disease?
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hypophosphatemia and phosphaturia
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What is Hyperphosphatasia?
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excessively elevated serum levels of the bone isozyme of alkaline phosphatase.
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How does hyperphosphatasia present?
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Significant growth failure, bowing and thickening of the diaphysis and osteopenia
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How does Primary chondrodystrophy present?
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bowing of the legs, short stature, and a waddling gait in the absence of abnormalities in serum calcium, phosphorus, alkaline phosphatase, or vitamin D
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What are the most sensitive/specific tests for vitamin D deficiency?
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assays for 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D may be most sensitive and specific in diagnosing vitamin D deficiency
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hypophosphatemic rickets
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vitamin D-resistant rickets
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What causes vitamin-D resistant rickets?
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Defect in tubular reabsorption of phosphate
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What causes Vitamin D-dependent rickets?
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Reduced activity of 25(OH) 1-alpha-hydroxylase
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What are the levels of 25-OH vitamin D in Vitamin D deficiency?
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decreased
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What are the levels of 25-OH vitamin D in Vitamin D resistant rickets?
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normal
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What are the levels of 25-OH vitamin D in Vitamin D dependent rickets?
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normal
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What are the levels of 1,25 (OH)2 vitamin D in Vitamin D deficiency?
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Normal or increased
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What are the levels of 1,25 (OH)2 vitamin D in Vitamin D resistant rickets?
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Normal or decreased
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What are the levels of 1,25 (OH)2 vitamin D in Vitamin D dependent rickets?
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decreased
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Treatment of vitamin D deficiency rickets:
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supplemental calcium and initiate vitamin D therapy after diagnosis of vitamin D deficiency is confirmed
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How much calcium?
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1,000 mg supplemental calcium daily; also, increased dietary calcium
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How much Vitamin D?
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800 to 1,000 IU/d
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How much calcium in 1 cup of milk?
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300 mg
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How much calcium in calcium fortified OJ?
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160 mg
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How much calcium in 1 cup yogurt?
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300 mg
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What is the level of calcium in Vitamin D deficiency rickets?
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Decreased
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What is the level of calcium in Vitamin D-resistant rickets?
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Normal
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What is the level of calcium in Vitamin D-dependent rickets?
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Normal or decreased
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What is the level of phosphorus in Vitamin D deficiency rickets?
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Decreased
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What is the level of phosphorus in Vitamin D-resistant rickets?
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Decreased
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What is the level of phosphorus in Vitamin D-dependent rickets?
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Decreased
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What is the level of PTH in Vitamin D deficiency rickets?
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Increased
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What is the level of PTH in Vitamin D-resistant rickets?
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Normal or Increased
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What is the level of PTH in Vitamin D-dependent rickets?
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Normal or Increased
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