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15 Cards in this Set

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B12 also goes by what name?
Cobalamin
Describe the vitamin Cobalamin
It's HUGE. It contains cobalt & it can have different ligands attached: methyl or adenosyl.
What are analogs of cobalamin?
Analogs are produced by bacteria. They replace the 5,6 dimethylbenzimidazol with other groups. only the "true" b12 is functional in us.
What is the first step in cobalamin absorption?
Cobalamin is digested from proteins in the gut and attaches to R-proteins (retarded proteins).
Describe the steps of Cobalamin absorption
Also - what is required for the last step to happen?
!! Three Phase !!
1. GASTRIC: Digestion from food protein/attachment to R protein
2. LUMINAL: Cbl released and attaches to IF; complex attaches to cubilin receptor in lower 1/3 (ileum).
3. MUCOSAL: Absorption. Required Ca2+ and pH>5.4
Where does IF come from?
The parietal cells in the gut make IF (they also make HCl)
What is the name of the receptor that absorbs Cbl?
Cubulin; it's in the ileum
What conditions are required for absorption of Cbl?
Well, bseides there being IF:
pH>5,4 and Ca2+ in ileum
In what form is Cbl found in blood?
It's bound to Transcobalamin II
How is excess Cbl excreted?
In bile.
Cbl is recirculated via enterhepatic circulation; we are able to conserve much by reabsorption.
What is pernicious anemia? What is it caused by?
Pernicious anemia is a diseased caused by a metabolic deficiency of B12. It happens when there is a failure to secret IF & complex with Cbl and then it cannot be absorbed.

Macrocytic anemia.
Why is pernicious anemia so dangerous in elderly?
Besides typical symptoms of anemia, it also causes (PERMANENT) neurological damage - it shows initially as poor memory, confusion, etc. So it can be easily blamed as "aging".
What are some causes of B12 deficiency?
1. Lack of dietary intake
2. Pancreatic disease: no bicarbonate to neutralize pH in ileum
3. Tapeworm :) eats all B12
4. General intestinal disease prevents absorption
Why would one not have IF?
Lack of secretion because of autoimmune disorder affecting parietal cells
Old Age
What is the one reaction we learned that B12 participates in? (in the big schematic)
REMEMBER THE FOLATE SCHEME:
B12: enzyme required to convert homocysteine into methionine

Important for PROTEIN synthesis.

Methyl Cobalamin is participant.