Megaloblastic Anaemia Flashcards
what are megaloblastic anaemias?
A group of anaemias in which there is delayed maturation of the erythroblast nucleus in relation to the cytoplasm
what deficiencies usually cause megaloblastic anaemia?
vitamin b12 or folate
what is an erythroblast?
an immature erythrocyte, still containing a nucleus
what causes megaloblastic anaemias?
asynchronous maturation of the nucleus due to defective synthesis - seen in the bone marrow
how could megaloblastic anaemia also be caused if not deficiency?
abnormalities of vitamin b12 or folate metabolism
defects of DNS synthesis- rare
what are vitb12 and folate crucial in
DNA synthesis
what is the scientific name for vitb12
cobalamin
where is vit b12 synthesised
by micro-organisms animals must consume it through the diet
where is b12 found
food of animal origin - 50% of young vegans have subnormal levels of b12
what is the major storage site for vit b12?
the liver
how much b12 does the body store?
3-4 years worth - short term dietary deficiency not problematic
what is the process of b12 absorption?
b12 is consumed with dietary proteins
salivary glands secrete R-Protein
parietal cells in stomach secrete intrinsic factor
chief cells in stomach secrete pepsin
pepsin catabolises dietary proteins and separates the b12
R-protein (from the mouth) binds free b12
b12, R-protein and IF move into the duodenum
pancreas starts to secrete digestive enzymes (lipases, proteases etc)
pancreatic proteases catabolise R-protein and free up the b12
free b12 is now able to bind to IF
what must b12 be attached to for it to be absorbed?
IF
what do receptors on enterocytes recognise?
the B12-IF complex
What does IF protect the b12 from?
catabolism by intestinal bacteria
what % of b12 can be absorbed in the absence of IF?
1%
where are b12-IF complexes absorbed?
the terminal ileum
what happens to b12 once it has been absorbed?
it passes into the portal blood. it attaches to transcobalamin which delivers b12 to the bone marrow and other tissues. Megaloblastic anaemia can also result from transcobalamin deficiency but vitb12 in take is normal.
what happens tol b12-transcobalamin in the bone marrow/tissues
binds to a receptor and is endocytosed
properties of folate
humans are able to synthesise folate
require pre-formed folate in the diet-mostly in green leafy vegetables foliage