B12 + Folate deficiency Flashcards
Both B12 and folate deficiency lead to ? anaemia by a common
mechanism;
B12 acts as a co-enzyme for the conversion of folate (B9) to activated folate.
Activated folate is required for ? synthesis, and thus if there is a deficiency in either B12 or folate, ? synthesis malfunctions.
In this case, the ? fails to ‘?’ erythrocyte development, leading to very ? cells, which eventually are trapped and destroyed in the reticuloendothelial system. (give increased ?)
megaloblastic DNA DNA DNA stop large bilirubin
B12 deficiency;
Humans rely on ? sources of B12, e.g. meat, fish, eggs and milk.
The ? contains a very large store of B12, and it is excreted in ? but around 70% of this is normally reabsorbed.
Free vitamin B12 binds to R proteins in the ? GI tract, but these complexes are degraded by ? proteases.
animal liver bile upper pancreatic
B12 def
Intrinsic factor (IF) is secreted by the ? ? cells, and binds free B12 with far ? affinity than R proteins, but the IF-B12 complex is highly resistant to ? ?.
Receptors for the IF-B12 complex are present on the brush border of the
? ?, where B12 is absorbed.
gastric parietal
less
protease degradation
terminal ileum
B12 def
IF is generally necessary for B12 ingestion, but even in its complete absence around 2% of B12 can still be ingested, so ? dose ? supplementation can be enough to treat ?anaemia.
—> o Initially patients are often treated with ? B12 on ? days, before switching to ? B12 for ?.
Even in total malabsorption, body stores will last for 3 ?.
high PO pernicious IM alternate PO maintenance years
Causes of B12 deficiency;
o Chronic low dietary intake: ?.
o Impaired binding in the stomach: ? anaemia, ? absence of ?, ?-omy.
o Small bowel disease: resection, ?’s/ backwash ? in UC, ? overgrowth.
? , ? disease and ? can all cause mild impairment of B12 absorption, but not enough to cause significant B12 deficiency
vegans pernicious congenital IF gastrectomy Crohns ileitis bacterial pancreatitis coeliac metformin
Pernicious anaemia;
? disease resulting in severe B12 deficiency.
There are three autoantibodies that may contribute towards disease; o Autoantibodies against ? cells. o Blocking antibodies. • Prevent IF-B12 ?. • ? common abnormality. o Binding antibodies. • Prevent IF binding to ? receptors.
autoimmune parietal binding most ileal
Subacute combined degeneration of the cord;
Simultaneous ? column (LMN) and ? ? (UMN) loss due to B12 deficiency, and gives a combination of ? and ? signs.
Initial presentation is with ? neuropathy, and on examination there is a classical triad of extensor ?, brisk ? reflex but absent ? reflex.
o Tone and power are usually ?, gait may be ?.
posterior corticospinal tract umn lmn peripheral plantars knee ankle normal ataxic
Folate Deficiency;
Folate (folic acid monoglutamate) is not itself present in nature, but occurs as
polyglutamates dihydrofolate (?) or tetrahydrofolate (?).
These are found in ? vegetables and offal, however ? causes a loss of up to 90% of the folate.
DHF
THF
green
90%
Folate deficiency
DHF and THF are converted to folate in the ? GI tract, and folate is then
absorbed in the ?.
The body’s reserves of folate are ?, and on a deficient diet folate deficiency will develop in around ? ?.
upper
jejunum
low
3 months
Folate deficiency
Causes of folate deficiency;
o Poor nutritional intake: poor diet, ?excess (impairs utilisation), ?.
o Malabsorption: ? disease.
o Anti-folate drugs: trimethoprim, ?, anti-?.
o Excess physiological use: ?, ?, prematurity
o Excess pathological use: excess erythrocyte production (e.g. in ?), ?, ? diseases.
alcohol anorexia coeliac mtx convulsants preg lactation haemolysis malign inflam
Folate def
Treatment is with ? acid ?mg/day ? for ? months, always with combined ? unless the patient is known to have a ? B12 level;
o Folate can precipitate subacute combined degeneration of the ?.
folic 5 PO 4 B12 normal cord
