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Haematology > B vitamins & Folate > Flashcards

B vitamins & Folate Flashcards

1
Q

How is vitamin B12 (Cobalamin) made and where can you find it?

A

Synthesised exclusively by microorganisms. Found in liver and kidneys.

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2
Q

Why do we need vitamin B12?

A
  • Maintain the normal function of the brain and nervous system.
  • Involved in the formation of RBCs
  • Involved in metabolism of all cells
  • Key role in DNA synthesis and regulation.
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3
Q

What does vit B12 use for absorption and transport and where is it made?

A

Intrinsic factors. Made in gastric parietal cells.

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4
Q

Absorption process of vit B12 to the circulation.

A
  • B12 binds to IF
  • The B12/IF complex moves to the ileum
  • They bind to a receptor called cubilin on the enterocyte
  • B12 is absorbed and released into circulation.
  • IF is destroyed
  • Once inside, B12 binds to TC2 which acts as a plasma transporter.
  • The complex is bound to a receptor and is endocytosed.
  • One inside TC2 is degraded in the lysosome and vit B12 is released.
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5
Q

What is the biochemical function of Vitamin B9?

A

It is a co-factor for the conversion of succinyl coA and glycine into ALA by ALA synthase.

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6
Q

How is vit B9 absorbed?

A

Passive absorption in the jejunum and ileum.

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7
Q

What is the RDA of vit B9?

A

1.5-2.0mg

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8
Q

What is the metabolic function of vit B12?

A
  • Co-factor in the conversion of methylmalonyl-coA to Succinyl-coA.
  • Co-factor for the conversion of homocysteine to methionine.
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9
Q

How much vit B12 do we need to absorb daily?

A

To maintain body stores: 1-3ug

To maintain health: 0.5ug

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10
Q

Where is vit B12 stored and how is it lost?

A

Stored in the liver.

Lost via urine and faeces.

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11
Q

Sources of folate.

A
  • Leafy green vegetables
  • Liver and liver products
  • Fortified breakfast cereals
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12
Q

Why do we need folate?

A
  • Synthesis of purine/pyrimidine precursors of DNA.
  • Important during periods of rapid division and growth: pregnancy/infancy.
  • Production of healthy RBCs.
  • Needed for development of the neural tube.
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13
Q

How is Folic acid activated, absorbed and transported?

A
  • Folic acid needs to be reduced to tetrahydrofolate (THF).
  • Absorption takes place in duodenum and jejunum.
  • Absorbed folates are converted into 5-MTHF monoglutamate before entering the portal blood system.
  • Plasma folate circulates bound or unbound to plasma proteins.
  • Vit B12 is needed to convert methyl THF to THF
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14
Q

What are the causes of Vit B12 deficiency?

A
  • Pernicious anaemia: impairs absorption of vit B12 as a consequence of a reduction in IF.
  • Veganism: no vit B12 in plants.
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15
Q

What are the causes of folate deficiency?

A
  • Poor dietary habits: alcoholics
  • Impaired absorption, metabolism or increased demand for the vitamin.
  • Anticonvulsants and oral contraceptives.
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16
Q

Consequences of folate and vit B12 deficiency.

A
  • Closure of the neural tube around the 28th day of pregnancy.
  • Neural tube defects: Anencephaly
  • Neurological complications
17
Q

What are the clinical features of folate and vit B12 deficiency?

A
  • Mild jaundice
  • Neuropathy
  • Tingling in feet and difficulty in gait
  • Glossitis
18
Q

Haematological disorders due to folate and vit B12 deficiency?

A

Folate: megaloblastic anaemia

Vit B12: Pernicious anaemia (form of megaloblastic anaemia)

19
Q

What is megaboblastic anaemia and why does it occur?

A
  • Inhibition of DNA production during erythropoiesis
  • Erythroblasts in the bone marrow show maturation of the nucleus being delayed relative to the cytoplasm.
  • So, we have Megablasts in the bone marrow and large RBCs in the blood because DNA synthesis and division is delayed.
20
Q

Haematological features of Megaloblastic anaemia.

A
  • Macrocytosis
  • Increased MCV >90fl
  • Oval macrocytes
  • Increased lobe number (>5) in neutrophils
  • Low reticulocyte count
  • WBC and platelet count reduced.
  • Serum folate <3ug/L
21
Q

What is pernicious anaemia?

A

Megaloblastic anaemia caused by lack of IF.

22
Q

What happens in pernicious anaemia?

A
  • Autoimmune attack on the gastric mucosa so the stomach wall becomes thin and secretion of acid and IF are reduced.
  • Antibodies against gastric parietal cells are found in 85% of patients.
  • Serum gastrin levels are raised.
23
Q

What are the tests and treatment for pernicious anaemia?

A
  • Test for methylmalonyl coA
  • Intramuscular injection of vit B12
  • Vit B12 <200pg/mL
24
Q

How do you treat megaloblastic anaemia caused by folate deficiency?

A
  • Oral dose of folic acid

- Vit B12 deficiency must be ruled out before treating with folate.

Haematology (7 decks)

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