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Flashcards in Vitamin B12 Deck (16):

What is another name for vitamin b12?



What are some of the main functions of vitamin b12?

- important for healthy nerve cells
- important for production of DNA and RNA
- works with vitamin B9 (folate) to help make red blood cells and helps iron work better in the body


What do the 8 B group vitamins do?

All B vitamins help the body convert food (carbohydrates) into fuel (glucose), which is used to produce energy.


How do B12 and folate work synergistically in the body? (how does B12 help activate folate)

In the cells folate is trapped in an inactive form and it requires B12 to bind to and remove a methyl.
Once the methyl group is removed there is a B12 coenzyme and a folate coenzyme and these are then used for DNA synthesis.


How is B12 made and what are the best sources?

B12 is a vitamin made by bacteria in the GI tract of animals. We as humans cannot made it in our bodies and so we must consume it.

The only natural sources are by eating animal products (fish, shellfish, beef, eggs, dairy etc). Otherwise it can also be obtained through an oral vitamin or by eating foods fortified with the vitamin eg foritified grains and cereals.


Who is at most risk to having a deficiency in B12?

Others at risk for B12 deficiency include:

Vegans and vegetarians who do not eat dairy or eggs, since vitamin B12 is found only in animal products

People with problems absorbing nutrients due to Crohn disease, pancreatic disease, weight loss surgery, or medications

People who are infected with Helicobacter pylori, an organism in the intestines that can cause an ulcer. H. pylori damages stomach cells that make intrinsic factor, a substance the body needs to absorb B12

People with an eating disorder

People with HIV

People with diabetes

The elderly


What is the resulting condition of a deficiency in B12 due to lack of intrinsic factor?

The specific condition is called pernicious anaemia. This is a type of megaloblastic anaemia (it can also be caused by a deficiency in folate) in which the red blood cells fail to form properly as B12 is needed for DNA synthesis.

This results in abnorally large RBC's which means they may not be able to exit the bone marrow to enter the bloodstream and deliver oxygen.


What is the cause for developing pernicous anaemia?

Most of the time people are ingesting enough B12 but it is due to a lack of intrinsic factor in the stomach which is needed to absorb B12.


Why is tiredness a common symptom?

The red blood cells are not formed/functioning properly so cant carry oxygen around the tissues effectively and therefore causes tiredness. For this reason people are also often out of breath.


What is the treatment for deficiency in B12?

For vegans - supplments/vitamins in their diet
For people with malabsorption syndromes (eg lack of intrinsic factor) - they require intramuscular injections


What are the steps of B12 absorption? (right from when we ingest the food)

1. Eat protein rich food containing B12

2. Once in stomach the B12 must be seperated from the protein by pepsin and HCL

3.Once seperated it must bind to haptoconin (produced by parietal cells) to travel to the duodenum

4. Once in the duodenum the pancreatic proteases seperate the B12 from hepatoconin

5. Intrinsic factor then binds to the B12 and travels to the terminal ileum where it can be absorbed into the enterocyte by binding to the brush border. Once in the enterocyte the IF is removed.

6. B12 then passes into the blood where 80% will join with haptoconin to be stored in the liver whilst 20% will join to holotrans to form holotranscobalamin which is taken up by DNA cells for synthesis.


What will be the cause of a deficiency in B12 if there is a problem with the stomach?

It is likely due to a lack of intrinsic factor. This is due to an autoimmune disorder (autoimmune gastritis) called pernicious anaemia where the body produces antibodies against intrinsic factor and parietal cells. If there is not enough IF to bind to B12 it cannot be absorbed.


NAME two ways you can test to see if it is the intrinsic factor that is causing the deficiency.

Take a blood test to see if there are anitbodies to intrinsic factor present.

Do a schillings test and obserb the IF in the urine.


Describe what happens in a schillings test

1. Give the patient an oral dose of radioisotopic B12 as well as an oral dose of a non radioactive B12 which will saturate all of the B12 binding sites in the body

2. Test the urine - if there is radioactive B12 in the urine then the IF is present and is working to allow B12 to be absorbed into the blood and then the urine from the gut. If the IF is lacking then the radioactive B12 will just continue through the gut and be excreted in the faeces.

3. The to confirm this you perform the test again but also give oral IF and if there is radioactive B12 in the urine you know that the problem was definetly lack of IF and if there isnt any radioactive B12 you need to think again.


What are likely causes if the B12 deficiency is caused by a problem with the small intestine?

Possibly due to surgery to remove the terminal ileum or crohns disease which causes inflammation of the terminal ileum.


Why would a partial gastroctomy cause pernicous anaemia? (eg pylorus region removed and antrum and proximal duodenum connected)

No antrum/pyloric region means no/little G cells.
No gastrin leads to:
- reduced gastric acid secretion (less hcl so B12 is harder to be detached from protein in food)
- less stimulation of pancreatic juices so less pancreatic protease so B12 cant be cleaved from haptoconin

No pylorus also leads to more bile reflux:
- causes degeneration of the body of the stomach (atrophic gastritis)
- this destroys the parietal cells so less IF produced