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Flashcards in Vitamins and Minerals Deck (15)
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describe vitamin A

  • collectively called retinoids
  • retinol: transport and storage
  • 11-cis retinal:is required for vision
    • retinol and retinal can be easily interconverted
  • retinoic acid: epithelial growth and differentiation
    • has steroid hormone like effects
    • can't be converted back to other forms 


describe the absorption and transport of vit. A


name the sources and functions of vit. A

  • sources:
    • liver, kidney, butter and cream products; egg yolk
    • yellow vegetables 
  • functions:
    • vision: 11-cis retinal is a component of rhodopsin 
    • maintenance of specialized epithelia, especially mucus secreting cells (retinoic acid)
    • growth (retinoic acid)
    • reproduction (retinol)


describe the mechanism of action of retinoic acid in epithelial cells

  • retinol enters the target cell and is oxidized to retinoic acid in the cytosol
  • from the cytosol, the retinoic acid moves into the nucleus with the help of cellular retinoid binding proteins
  • retinoic acid binds to nuclear receptors and activates transcription of specific genes (keratin)


describe cause and signs of deficiency of vitamin A 

  • dietary deficiency is the commenest cause; fat free diets
  • malabsorption of fats can lead to deficiency
  • signs and symptoms:
    • night blindness -- earliest symptom
      • regeneration of rhodopsin is delayed
    • xerophthalmia: dryness of the conjuctiva and cornea
    • keratomalacia: corneal erosion and ulceration
    • immune deficiency: weakened innate immunity


describe clinical uses of vitamin A and what happens in hypervitaminosis A

  • retinol or B-carotene: treatment of dietary deficiency
  • retinoic acid used in treatment of acne


  • hypervitaminosis A: raised intracranial pressure (headahces) 
    • enlarged liver
    • pregnancy: spontaneous abortions and congenital malformations in the fetus


describe the formation of calcitriol (1, 25 dihydroxy cholecalciferol) which is the active form of vit. D


describe the actions of vitamin D on serum calcium

  • intestine: stimulates intestinal absorption of calcium and phosphate by increased synthesis of calbindin
  • bone: stimulates the mobilization of calcium and phosphate from the bone in the presence of PTH (when serum calcium is low)
  • kidneys: inhibits calcium excretion by stimulating parathyroid dependent calcium reabsorption


describe the actions of vitamin D on serum phosphate

  • vitamin D increases serum phosphate by increasing its absorption from the intestine
  • in the presence of vit. D, serum Ca and phosphate are elevated
    • increases the tendency to form bone mineral 
  • in vit. D deficiency, reduced absorption of Ca reduces serum Ca level--stimulates secretion of PTH which in turn causes demineralization of bone


describe causes of vit. D deficiency

  • nutritional deficiency: decreased intake, fat malabsorption, exclusively breast fed infants
  • inadequate exposure to sunlight (common during winter)
  • chronic renal disease, chronic liver disease


describe effects of vit. D deficienccy

  • decreased calcium absorption from diet -> decreased serum calcium -> increased PTH release -> demineralization of bone
    • soft pliable bones
    • bow-leg deformity
    • overgrowth at costochondral junction: rachitic rosary
    • pigeon chest deformity
    • frontal bossing


what lab findings are seen in nutritional rickets?

increased serum alkaline phosphatase (ALP)


describe mutations in the calcitriol receptor

  • inheritied condition where calcitriol is unable to bind to its receptor in the intestinal mucosal cells 
  • as a result, these children have high levels of calcitriol (loss of negative feedback)
  • serum calcium and phosphate levels are low and 1,25-hydroxyvitamin D levels are high
  • compare to vit. D deficient rickets which has low serum calcium and phosphate and low levels of 25-hydroxyvitamin D


describe osteomalacia

  • vitamin D deficiency in an adult
  • bones are demineralized and are susceptible to fracture
  • osteomalacia can be secondary to dietary deficiency, renal disease or liver disease
  • lab findings = high ALP


describe hypervitaminosis D

  • characterized by high serum calcium and high serum phosphate
    • this results in an increased tendency for ectopic (soft tissues) mineralization