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MLSCI 230 > Vit B12 & Folate Metabolism > Flashcards

Vit B12 & Folate Metabolism Flashcards

1
Q

cobalamin

A

vit B 12

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2
Q

T or F. Vit B 12 is an essential nutrient and the body is unable to make so it must be obtained from dietary sources

A

T!

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3
Q

Role of Vitamine B12

A
  • DNA synthesis: tissue growth and regeneration
  • maintenance of myelin sheath (B12 only)
  • functions as a coenzyme: metabolism of homocysteine; methylmalonyl CoA metabolism
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4
Q

hydroxocobalamin

A

mechanism involves rapidly removing cyanide (fires) from tissue by forming cyanocobalamin, which is then excreted unchanged in the urine

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5
Q

dietary sources of B12

A
  • eggs
  • red meat and poultry
  • milk and milk products
  • some fortified cereals and meat substitutes
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6
Q

Proteins involved in Vit B12 absorption and metabolism

A
  • Haptocorrin (R protein or Transcobalamin I)
  • Intrinsic factor
  • Transcobalamin (II)
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7
Q

Haptocorrin

A
  • present in saliva

- delivers vit B12 to the duodenum

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8
Q

Intrinsic Factor

A
  • released from gastric parietal cells

- picks up vit B12 from duodenum for transport across the ileum

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9
Q

Transcobalamin II

A
  • from enterocytes

- main transporter of vit B12 to tissues

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10
Q

causes of vitamin B12 deficiency

A
  • inadequate intake (rare)
  • increased need (pregnancy, lactation, and growth)
  • impaired absorption
    > failure to separate from food proteins or haptocorrin
    > lack of IF
    > malabsorption
    > competition for vit B12
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11
Q

What causes failed separation of B12

A
  • hypochloridia in the stomach: increased pH results in inability to release B12
  • vit B12 remains complexed with food or with haptocorrin
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12
Q

Causes of lack of IF

A
  • gastrectomy: loss of parietal cells
  • H. pylori infection: colonizes gastric mucosa and progressively destroys parietal cells
  • hereditary IF deficiency: absence of non-functionality of IF
  • autoimmune disease: pernicious anemia
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13
Q

which cells produce IF?

A

parietal cells

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14
Q

autoimmune disorder characterized by impaired absorption of vit B12 due to the lack of IF

A

Pernicious Anemia

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15
Q

Progression of Pernicious Anemia

A
  • autoimmune destruction of parietal cells => decreased IF
    => chronic inflammation and gradual atrophic gastritis
    => decreased If and achlorhydria
    => detectable levels of Abs to intrinsic factor or parietal cells
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16
Q

Malabsorption of B12

A
  • tropical sprue
  • Celiac disease
  • surgery
  • inflammatory bowel disease
  • hereditary disorders
    > RARE; autosomal recessive mutations resulting in decreased endocytosis of IF-B12 complex or decreased transcobalamin
17
Q

Diphyllobothrium latum

A
  • fish tapeworm

- competes for B12 with IF

18
Q

overgrowth of bacteria that utilize vit B12 in stenotic loops of the intestine

A

Blind loop syndrome

19
Q

folic acid vs. folate

A
  • folate = general term for all forms

- folic acid = synthetic form found in supplements

20
Q

What is Folate used for?

A
  • DNA synthesis
  • many metabolic functions: homocysteine metabolism, not for methylmalonic acid metabolism; metabolism of some amino acids and nucleotides
  • neurological development of fetus
21
Q

dietary sources of folate

A
  • leafy green vegetables
  • legumes
  • liver and red meat
  • fortified cereals
  • oranges and some fruits
  • yeast
22
Q

cooking folate vs vit B12

A

Cooking folate can inactivate it, whereas B12 cooked is still gonna be there (eggs, meat, etc.)

23
Q

T or F. Folate is heat-stable

A

F! it is heat-labile

24
Q

Which has a higher rate of loss - Folate or Vitamin B12?

A

Folate! stores can be depleted in months!

25
Q

Process of Folate absorption and metabolism

A
  • absorbed in jejunum in the polyglutamic acid form (no binding protein needed)
  • hydrolyzed to monoglutamate, then reduced and methylated to methyl tetrahydrofolate (5-methyl THF)
  • transported to liver and tissues by proteins
26
Q

Causes of Folate deficiency

A
  • inadequate intake: poor diet, overcooked foods, alcoholism
  • increased need
  • impaired absorption
  • impaired use: drug-induced
  • excessive loss through hemodialysis
27
Q

T or F. Both Vitamin B12 and Folate are involved in the synthesis of methionine from homocysteine

A
  • Folate is the methyl group donor
  • vit B12 is the coenzyme for methyltransferase
  • further rxns take place which result in DNA synthesis
28
Q

T or F. Need folate in production of heme, not B12

A

F! need B12 for heme production

29
Q

Treatment for Vit B12 and folate deficiencies

A
  • correct deficiency (iron concurrently given); quick recovery!
  • treat CAUSE of deficiency
30
Q

Lab tests for Vit B12 deficiency

A
  • serum gastrin and gastric analysis
  • antibody assays: IF and parietal cells
  • stool analysis for parasites
31
Q

Symptoms of B12 and Folate deficiencies

A
  • anemia
  • GI symptoms
  • Glossitis
  • neurological symptoms (B12 ONLY)
32
Q

Results of B12 and Folate deficiencies

A
  • decreased THF => decreased dTTP so uridine is incorporated into DNA instead which leads them to break = non-functional DNA
  • increased homocysteine: hyperhomocysteinemia may be associated w atherosclerosis and blood clots
33
Q

Screening tests for vit B12 and folate deficiencies

A
  • CBC = decreased Hgb, pancytopenia w reticulocytopenia, high MCV, increased RDW
  • peripheral blood smear: macroovalocytes, hypersegmented neutrophils, tears, schistocytes, HJ bodies, basophilic stippling
34
Q

Confirmatory Testing for Folate and B12 defs

A
  • serum vit B12 and Folate (immunoassay)
  • bone marrow examination: megaloblastic changes, nuclear-cytoplasmic asynchrony, decreased M:E ratio
  • methylmalonic acid levels
  • homocysteine levels

MLSCI 230 (36 decks)

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