L8: Iron metabolism and microcytic anaemias Flashcards
What are microcytic anaemias?
Erythrocytes are smaller
Reduced rate of haemoglobin synthesis
Cells paler (hypochromic)
What causes microcytic anaemias?
Reduced haem synthesis
-Anaemia of chronic disease –> Hepcidin result in functional iron deficiency (plenty of it but cant be used)
-Iron deficiency–> required for haem synthesis
-Lead poisoning–> acquired defect
-Sideroblastic anaemia–> inherited defect in haem synthesis
Reduced globin chain synthesis
- Thalassaemia –> α and β
–> α –> deletion or loss of one or more of α globin genes
–> β –> mutation in β globin genes leading to reduction or absence of the β globin
Mnemonic –> TAILS
What is iron? Whats its function?
Element
Essential in all living cells
Free iron–> potentially toxic to cells
Complex regulatory system–> safe utilisation, absorption and transport
Required for:
- O2 carriers –> haemoglobin in red cells
–> myoglobin in myocytes
-Cofactor in many enzymes–> cytochromes (OP), Krebs cycle enzymes, cytochrome P450 enzymes (detoxification), catalase
Body has no mechanism for excreting iron
What is the difference between ferrous and ferric?
Ferrous Fe2+ –> reduced form–> absorbed from diet in this form
Ferric Fe3+ –> oxidised form
How is ferric reduced to ferrous and vice versa?
Ferric (Fe3+) + e- –> Ferrous (Fe2+) reduction low pH (acid)
Ferrous (Fe2+) –> Ferric (Fe3+) + e- oxidisation high pH (alkaline)
What is the difference between haem and non-haem iron?
Haem–> associate with globin–> haemoglobin
Come from animals–> liver, kidney, steak, beef burgers etc
Easily/readily absorbed
Non-haem –> Ferrous or ferric form–> fortified cereals, raisins, beans, figs, barely, oats, rice and potatoes
Converted to ferrous for absorption
How much iron is needed in the diet and where is it absorbed?
10-15 mg/day
Absorbed in the duodenum and upper jejunum
How is iron absorbed into the bloodstream?
- Chyme enter duodenum/ upper jejunum
- a) Haem–> readily absorbed by the enterocytes
- inside Fe2+ released by haem oxygenase
b) Non Haem–> Fe3+ –> Fe2+ via reductase enzymes in brush border
–> Requires Vit C as electron donor
–> Fe2+ –> enters enterocyte through DMT1 (divalent metal transporter 1)- H+ ion out - Fe2+ stored- storage protein ferritin in Fe3+ form
OR - Enters bloodstream through ferroportin
- Transported- Fe3+ form- converted by Hephaestin
- Fe3+ binds to transferrin—> transported around the blood
What inhibits the role of ferroportin?
Hepcidin
Peptide hormone
Produced by liver
Bind to ferroportin–> degradation
What factors affect the absorption of non-haem iron from food?
Negative influences–> Tannis (in tea), phytates (pulses), fibre and antacids (gavison)
- -> bind to non-heam iron in the intestine reduce absorption
- -> need acidic environment to convert Fe3+–> Fe2+
Positive influences–> Vit C and citrate–> prevent formation of insoluble iron compounds
VitC require for conversion of Fe3+–> Fe2+
What is the difference between functional and stored iron?
Functional iron–> available
- Heamoglobin (2000mg)
- Myoglobin (300mg)
- Enzymes- cytochromes (50mg)
- Transported iron (transferrin) (3mg)
Stored iron (1000mg)
How can iron be stored?
Ferritin–> soluble form
- -> stored in enterocyte
- -> globular protein complex with hollow core–> pores allow iron to enter and be released
Haemosiderin –> insoluble form
- -> Aggregates of clumped ferritin particles, denatured protein and lipid
- -> Accumulates in macrophages, particular in liver and spleen
How is iron taken up into cells?
1- Fe3+ bound trasferrin binds transferrin receptor and enters the cytosol receptor-mediated endocytosis
2- Fe3+ within the endosome released by acidic microenvironment and reduced to Fe2+
3- The Fe2+ transported to the cystol via DMT1
4- Once in cystol Fe2+ can be:
- stored in ferritin
-exported by ferroportin (FPN1) or
-taken up by mitochondria - cytochrome enzymes
What is meant by iron recycling?
Small intake in diet Most (>80%) - recycled from damaged or senescent RBC Phagocytosis by macrophages Splenic macrophages and kupffer cells - Liver Catabolise haem released from RBC AA reused and iron: - exported to blood - transferrin - stored - Ferritin - macrophages
How is iron absorption regulated?
Determined by: dietary factors, iron stores, erythropoiesis
Sensed by enterocytes
Controlled mechanisms
- Regulation of transporter- ferroportin
- Regulation of receptors- Transferrin receptor and HFE protein (homeostatic iron regulator)
- Hepcidin and cytokines
- Crosstalk between the epithelial cells and other cells like macrophages