Iron absorption and deficiency Flashcards
why is iron essential in all living cells?
- required for oxygen carriers : HB in red cells, myoglobin in myocytes.
- co-factor in many enzymes : krebs, cytochromes, P450.
why must iron be closely regulated?
- free iron potentially very toxic to cells so must be ensured safe absorption, transportation, utilisation.
- No mechanism in body for excreting iron.
differentiate between ferrous and ferritin.
- ferrous Fe2+ is the reduced form and ferric Fe3+ oxidised form.
- dietary iron consists haem iron Fe2+ and non-haem mix of Fe2+ and Fe3+.
- Ferric iron must be reduced to ferrous to be absorbed, requires acidic conditions.
whats the difference between haem vs non-haem iron?
- Haem iron ( Fe2+ ) is the best source and found in animal base origins.
eg : liver, kidney, chicken, steak. - Non-Haem (Fe3+ and Fe 2+ ) iron is found in plant based food and not absorbed as well by body.
eg : raisin, beans, barley, rice.
*absorption at duodenum & upper jejunum.
briefly describe the dietary absorption of iron.
- DMT1 in enterocytes facilitates uptake of Fe2+.
- Ferric iron reduced to ferrous in intestinal lumen by DcytB before uptake by DMT1.
- stored as ferritin or transported around blood via ferroportin.
- most transported to BM or taken up by macrophages as storage pool in reticuloendothelial system.
how is absorption of iron regulated?
*regulated by hepicidin by liver, binds on ferroportin causing degradation so prevents iron leaving cell and down-regulates iron uptake by inhibiting transcription of DMT1 gene.
what factors may affect absorption of non-haem iron from food?
- negative and *positive.
- tannins in tea, phytates like pulses may bind to the non-haem iron in intestine reducing absorption.
- fibres negatively.
- antacids make environment alkaline affects reduction.
*vitamin C and citrate prevents formation of insoluble iron compounds and helps reduction of ferric to ferrous.
Iron is stored as Ferritin or Haemosiderin. what are these?
- Ferritin : globular protein with hollow core allowing iron to enter and be released. SOLUBLE
- Haemosiderin : aggregates of ferritin, denatured protein and lipid accumulated in macrophages in liver, spleen and marrow. INSOLUBLE
how is Iron taken up by cell?
- Fe3+ bound to transferrin enters cytosol via receptor mediated endocytosis.
- reduced by acidic environment to ferrous.
- transported via DMT1.
- then ferrous stored as ferritin, exported by ferroportin or taken up by mitochondria for cytochromes.
how is iron recycled?
- recycling of damaged or senescent RBC engulfed by macrophages in spleen or liver by Kupffer cells.
- macrophages catabolise haem released from RBC, aa reused and iron transported to blood (transferrin) or returned to storage pool as ferritin in macrophage.
*regulated by hepcidin, cytokines or crosstalk between epithelia cells.
why is Hepcidin a key player in all things iron?
- Hepcidin synthesis increased in iron overload and decreased when high EPO.
- INDUCES INTERNALISATION AND DEGRADATION OF FERROPORTIN.
- affects iron transport in blood.
what is iron deficiency and what are its causes?
- sign not a diagnosis, so must work to determine underlying cause.
- could be dietary, physiological (pregnancy) or pathological (bleeding).
*insufficient iron intake, malabsorption, bleeding, increased requirement in pregnancy or puberty, anaemia of chronic disease.
what groups are generally at risk from iron deficiency?
- infants.
- children.
- women of child bearing age.
- geriatric.
what are the signs and symptoms of iron deficiency?
- tiredness, dizziness, headache.
- pallor.
- reduced exercise tolerance as reduced O2 capacity.
- cardiac : angina, palpiations.
- Tachypnea : increased RR.
- Pica (unusual cravings ).
- Cold hands and feet.
- epithelial changes as rapid mitosis affected.
what are the features that can be seen in FBC and peripheral blood smear that can be associated with iron deficiency anaemia.
- FBC : low mean corpuscular volume, low HB, thrombocytosis, normal or elevated WBC, low serum ferritin, iron, low reticulocyte.
- Blood smear : Microcytic and hypochromic changes, anisopoikilocytosis (change in shape and size), pencil cells and target cells.
