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Flashcards in Biochem: Vitamins Deck (105)
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91

Vitamin D3

- D3 = cholecalciferol
- consumed in milk
- formed in sun-exposed skin (stratum basale).
- 25-OH D3 = storage form.
- 1,25-(OH)2 D3 (calcitriol) = active form

92

Function of Vitamin D

- increased intestinal absorption of calcium and phosphate
- increased bone mineralization at low levels
- increased bone resorption at higher levels

93

Vitamin D Deficiency

- Rickets in Children (bone pain and deformity)
- osteomalacia in adults (bone pain and muscle weakness)
- hypocalcemic tetany
- Breastfed infants should receive oral vitamin D.
- Deficiency is exacerbated by low sun exposure, pigmented skin, prematurity

94

Excess of Vitamin D

- Hypercalcemia
- hypercalciuria
- loss of appetite
- stupor.
- Seen in granulomatous disease (activation of vitamin D by epithelioid macrophages)

95

Vitamin E (tocopherol/tocotrienol) Function

- Antioxidant (protects RBCs and membranes from free radical damage)
- Can enhance anticoagulant effects of warfarin

96

Vitamin E (tocopherol/tocotrienol) Deficiency

- Hemolytic anemia
- acanthocytosis
- muscle weakness
- posterior column and spinocerebellar tract demyelination.
- Neurologic presentation may appear similar to vitamin B12 deficiency, but WITHOUT
- megaloblastic anemia
- hypersegmented neutrophils, or
- increased serum methylmalonic acid levels

97

Vitamin K (phytomenadione, phylloquinone, phytonadione) Function

- "K is for Koagulation"
- Cofactor for the γ-carboxylation of glutamic acid residues on various proteins required for blood clotting
- Synthesized by intestinal flora
- Necessary for the maturation of clotting factors II, VII, IX, X, and proteins C and S.
- Warfarin = vitamin K antagonist

98

Vitamin K (phytomenadione, phylloquinone, phytonadione) Deficiency

- Neonatal hemorrhage with increased PT and increased aPTT but normal bleeding time (neonates have sterile intestines and are unable to synthesize vitamin K)
- Can also occur after prolonged use of broad-spectrum antibiotics.
- Not in breast milk; neonates are given vitamin K injection at birth to prevent hemorrhagic disease of the newborn

99

Vitamin C (ascorbic acid) Function

- Found in fruits and vegetables
- Antioxidant
- facilitates iron absorption by reducing it to Fe2+ state.
- (Pronounce “ABSORBic” acid.)
- Necessary
for hydroxylation of proline and lysine in collagen synthesis.
- Necessary for dopamine β-hydroxylase, which converts dopamine to NE.
- Ancillary treatment for methemoglobinemia by
reducing Fe3+ to Fe2+

100

Vitamin C (ascorbic acid) Deficiency

- "Vitamin C deficiency causes sCurvy due to a Collagen synthesis defect"
- Scurvy: swollen gums, bruising, petechiae, hemarthrosis, anemia, poor wound healing, perifollicular and subperiosteal hemorrhages, “corkscrew” hair.
- Weakened immune response

101

Vitamin C (ascorbic acid) Excess

- Nausea, vomiting, diarrhea, fatigue
- calcium oxalate nephrolithiasis.
- Can increase risk of
iron toxicity in predisposed individuals
(eg, those with transfusions, hereditary hemochromatosis)

102

Vitamin B12 (cobalamin)
- Function
- Where is it found?
- Storage?

- Cofactor for methionine synthase (transfers CH3 groups as methylcobalamin)
- and methylmalonyl-CoA mutase.
- Found in animal products
- Synthesized only by microorganisms.
- Very large
reserve pool (several years) stored primarily in the liver

103

1. Causes of Vitamin B12 (cobalamin) Deficiency
2. Diagnosis

1. Deficiency caused by: - malabsorption (eg, sprue, enteritis, Diphyllobothrium latum)
- lack of intrinsic factor (pernicious anemia, gastric bypass surgery)
- absence of terminal ileum (surgical resection, eg, for Crohn disease)
- or insufficient intake (eg, veganism).

2. Anti-intrinsic factor antibodies diagnostic for pernicious anemia

104

Scurvy Symptoms

- swollen gums
- bruising
- petechiae
- hemarthrosis
- anemia
- poor wound healing
- perifollicular and subperiosteal hemorrhages
- “corkscrew” hair

105

Signs/Symptoms of Vitamin B12 (cobalamin) Deficiency

- Macrocytic, megaloblastic anemia
- hypersegmented PMNs
- paresthesias
and subacute combined degeneration (degeneration of dorsal columns, lateral corticospinal tracts, and spinocerebellar tracts)
- due to abnormal myelin.
- Associated with increased serum homocysteine and methylmalonic acid levels.
- Prolonged deficiency can lead to irreversible nerve damage