MP322 - VITAMIN DEFICIENCIES

Question 1

vitamins

Answer 1

organic compounds that are required in small quantities for a variety of biochemical functions

Question 2

water-soluble vitamins

Answer 2

B12
B9
C (Ascorbic acid)

Question 3

fat-soluble vitamins

Answer 3

A (retinol)
D (cholecalciferol)
E (tocopherol)
K

Question 4

sources of vitamin B12 (cobalamin)

Answer 4

• synthesised solely by microorganisms
• source is food of animal origin
• strict vegetarians/vegans at risk of developing B12 deficincy

Question 5

Passive absorption of vitamin B12

Answer 5

through buccal, duodenal and ileal mucosa
rapid but inefficient

Question 6

active transport absorption of vitamin B12

Answer 6

• normal physiological mechanism
• occurs through ileum
• mediated by gastric intrinsic factor

Question 7

plasma transport of vit B12 and cellular uptake

Answer 7

• B12 is transported in the plasma bound to transcobalamin I, II or III
• internalisation occurs in complex with transcobalamin receptor (CD320) via endocytosis
• the transcobalamin is degraded
• excess vitamin B12 sent to liver for storage

Question 8

role of intrinsic factor in absorption

Answer 8

• produced in parietal cells and its secretion parallels that of acid
• in absence of intrinsic factor inadequate amounts of B12 are absorbed
• results in megaloblastic anaemia

when absence of intrinsic factor = pernicious anaemia

Question 9

pernicious anaemia

Answer 9

autoimmune atrophic gastritis
- destruction of gastric parietal cells and lack of intrinsic factor
- immune response directed against H+/K+ ATPase
- causes achlorhydria (production of gastric acid low/absent)
- can be caused by antibodies directed against intrinsic factor

Question 10

aetiology of B12 deficiency

Answer 10

• inadequate dietary intake
• loss of gastric parietal cells or intrinsic factor
• functionally abnormal intrinsic factor
• bacterial overgrowth in intestine
• disorders of ileal mucosa
• disorders of plasma transport
• dysfunctional uptake and use of B12 by cells

Question 11

treatment of B12 deficiency

Answer 11

oral - cyanocobalamin
parenteral - hydroxycobalamin

must be parenteral in pernicious anaemia or total gastrectomy
lifelong treatment

Question 12

sources of vitamin B9 (folate, folic acid)

Answer 12

• dark green veg and dried legumes
• fruit and fruit juices
• meat, seafood, poultry and eggs
• fortified cereals and bread

Question 13

folic acid daily requirements

Answer 13

200 MICROGRAMS/DAY
400 MICROGRAMS/DAY SUPPLEMENT IN PREGNANCY

Question 14

plasma transport of folate and cellular uptake

Answer 14

• most folate transported as mono-glutamyl derivative
• most folate circulates free in the blood (or bound to albumin)
• cellular uptake by 3 mechanisms (PCFT, RFC, and folate receptor)
• intracellular folates exist primarily as polyglutamate conjugates

Question 15

cellular requirements for folate

Answer 15

folate is crucial for the transfer of one-carbon units to amino acids, nucleotides, and other biomolecues

Question 16

aetiology of folate deficiency

Answer 16

• inadequate dietary intake
• congenital defects in the uptake system (e.g. PCFT)
• intestinal disease (e.g. coeliac, IBD)
• chronic alcohol use
• increased cellular requirement (pregnancy)

Question 17

symptoms of folate deficiency

Answer 17

• sore tongue (glossitis) and pain upon swelling
• GI symptoms (nausea, vomiting, abdominal pain, diarrhoea)
• neurological (cognitive impairment, dementia, depression)

Question 18

treatment of folate deficiency

Answer 18

oral folic acid for 1-4 months
treated until haematological recovery occurs