Iron Flashcards
Which forms of iron exist in the body? which form is needed for oxygen transport? why is iron held in a prophyrin ring?
Fe2+ - ferrous = binds oxygen and is more easily absorbed
Fe3+ - ferric
Held in a porphyrin ring because it is toxic and generates free radicals
How is iron stored?
it is stored in RBCs within haemoglobin
it is stored in the liver (mainly) and in macrophages carried by ferritin
How is circulating iron carried?
it is bound to transferrin (protein with 2 binding sites for iron atoms) which transfers it from donor tissues (macrophages/intestinal cells/hepatocytes) to the bone marrow macrophages (and tissues expressing transferrin receptors) which ‘feeds’ it to RBC precursors
What tests are used to assess:
- functional iron
- transported iron
- storage iron
Functional iron - Hb
Transported iron - serum iron, transferrin, transferrin saturation (% saturation of transferrin measures iron supply)
Storage iron:
- ferritin (if this is too high = iron storage disorder, if this is too low = iron deficiency) = good test for iron deficiency
- Tissue biopsy (bone marrow for iron deficiency and liver for iron overload in hepatocytes)
what could cause transferrin % saturation to be low? what could cause it to be high? why does this mean it is a bad measure for iron deficiency?
Low - anaemia of chronic disease/iron deficiency
high - genetic haemochromotosis
What combination of test results confirms an iron deficiency?
- microcytic, hypochromic anaemia
- low ferritin
What are the three general reasons for iron deficiency?
Malabsorption
Low intake
Increased loss
What two causes are there for malabsorption of iron?
- coeliac as need large S/A to absorb iron
- Achlordia as need acid to absorb iron
What is the difference between relative and absolute low intake of iron?
Relative - pregnancy/women/children
Absolute - e.g. vegetarians
What 5 ways could a patient be losing iron?
- Haemorrhage
- Haematuria
- Menorrhagia
- GI (could be occult): tumours/ulcers/NSAIDs/parasitic infection
What is occult GI blood loss?
loss of 5-10ml per day, this is 4-5g of iron and max. iron absorption is 4-5mg.
Describe iron absorption from the gut
- iron enters body
- DMT-1 transports Fe2+ from duodenum to duodenal cell (Fe3+ is converted to Fe2+ by enzymes on duodenal cell surface)
- Ferroportin then transports Fe2+ from duodenal cell to blood. (this is downreg. By hepcidin)
What are the three factors that regulate iron absorption?
Systemic factors - hepcidin:
-produced in the liver in response to load and inflammation
=iron can not get out of duodenal enterocytes or macrophages
Intraluminal factors:
- solubility of inorganic iron: reduction of ferric to ferrous
Mucosal factors:
- ferroportin
- DMT1
What are the four disorders of iron metabolism?
1 - iron deficiency
2 - iron malutilisation (inflammation/chronic disease hepcidin is released from liver)
3 - primary iron overload causing iron deposition in organs/tissues (hereditary haemochromotosis)
4 - secondary iron overload:
Sources - repeated red blood cell transfusions, excessive iron absorption
Disorders - massive ineffective erythropoeisis (thalassaemia/sideroblastic anaemias), refractory hypoplastic anaemias (red cell aplasia/myelodisplasia)
Hereditary haemochromatosis:
- when does it present?
- clinical features 6
- presentation at middle age or later
- cardiomyopathy
- diabetes
- cirrhosis
- arthritis/joint pain
- weakness/fatigue
- impotence
