Minerals Flashcards
Iron lifecycle
In adults red blood cells (RBC) are formed chiefly in the bone marrow, heme is synthesised from glycine and iron in the presence of pyridoxine and combined with the globin. RBC are non-nucleated and they live only as long as the enzymes remain functional, approximately 120 days. RBCs are removed from the circulation by the cells of the reticuloendothelium. The iron is released from the porphyrin, taken up by transferrin and either returned to the bone marrow for the production of new cells or to the liver or spleen for storage. Without this effective conservation it would be impossible to provide the iron needed from dietary sources.
Deficencies that accelerate rate of descturction of RBC
Deficiencies of vitamin C, vitamin E, folic acid, and vitamin B12
The major proteins for the transport and storage of iron within the body are ?
-describe each one AND the transferrin/transferrin receptor complex
transferrin and ferritin.
Transferrin is an abundant plasma protein which carries iron from the site of absorption (the proximal small intestine), and the sites of storage (e.g. the liver), to the cells and tissues where it will be utilised.
The transferrin/transferrin receptor complex is internalised by the cells and iron is released into the cytoplasm so that it may be used for various cellular functions. Cells with particularly high iron requirements, such as immature erythroid cells which need large amounts of iron for haemoglobin synthesis, invariably express high concentrations of transferrin receptors on their surface.
Once inside the cell iron which is not required combines with apoferritin to form ferritin. The storage of excess iron is important, since both ferric and ferrous iron are able to participate in reactions which generate potentially toxic oxygen radical
Iron overload vs iron def in terms of iron uptake
iron deficiency
- cells increase their uptake of iron to ensure that sufficient is available for the synthesis of iron-containing proteins. To do this they increase the expression of cell surface transferrin receptors, but repress their synthesis of intracellular ferritin since there is negligible excess iron in the cytoplasm.
The opposite expression is seen in states of iron overload.
Forms of dietary iron
- Heme iron in the form of haemoglobin and myoglobin (meat, fish, eggs)
- Non-heme iron (vegetable, pulses and inorganic iron added to cereals, dietary
supplements, etc.).
Absorption of heme iron
Heme iron is absorbed into the mucosal cell vua heme protein transporter 1 as the intact porphyrin complex and is
little effected by the composition of the meal and gastrointestinal secretions, but is effected by iron deficiency.
Absorption of non-heme iron:
- Iron must be present in the duodenum and upper jejunum in a soluble form.
- In the stomach non-heme iron is ionised by gastric juice as the chyme passes from the stomach to the duodenum, the pH increases to 7. Unless chelated, most ferric iron is precipitated. At the cell membrane of the brush border of the epithelial cell ferric iron is bound to a receptor protein called membrane iron binding protein which
then transfers iron into the cell - Non-heme iron absorption is affected by the composition of the meal, as well as other
factors
Transfer from mucosal cells to the body is slower than uptake and is affected by:
- size of the body stores;
- the quantity of iron in the diet.
DIETARY FACTORS WHICH ENHANCE OR DECREASE or INHIBIT ABSORPTION
Factors enhancing iron absorption
Ascorbic acid
MFP factor (meat, fat, protein)
Citric acid frm foods
Lactic acid from foods
Meat and Fish
Certain organic acids
Factors inhibiting iron absorption
Phytates (with 4 or more phosphate groups) Iron-binding polyphenols
Dietary Fibre
Tannins
Calcium
Factors decreasing absorption
Intestinal motility Steatorrhoea
Biochemical Measures of Iron Status for Each Stage of iron Deficiency
Stage 1
Depletion of iron stores
Low serum ferritin (<15mcg/l)
-less iron to make new RBC
Stage 2
Deficient
Low serum iron, high serum total iron-binding capacity, reduced serum transferrin saturation index (<16%), high free erythrocyte protophyrin
-not enough iron to make new RBC
Stage 3
Iron defiency anaemia
Low haemoglobin (<120g/l), hypochromic, microcytic anaemia, reduced mean blood corpuscular volume.
iodine:
Function
Food sources
Iodine is primarily utilised by the thyroid gland to produce thyroid hormones, which are essential for regulating metabolism, growth, and development.
Dietary sources of iodine include iodized salt, seafood (such as fish and seaweed), dairy products (milk, yogurt, cheese), eggs, and some fruits and vegetables.
Major Iron-containing and Iron-binding proteins and their functions
Haemoglobin
Myoglobin
Cytochrome oxidase
Cytochrome P450
Ribonucleotide reductase Procollagen propyl hydroxylase Phenylalanine hydroxylase
Haemoglobin - oxygen transport
Myoglobin - Oxygen supply to muscles
Cytochrome oxidase - Electron transport
Cytochrome P450- Metabolism of fatty acids, steroids, prostaglandins, leukotrienes
Ribonucleotide reductase - DNA Synthesis
Procollagen propyl hydroxylase - Collagen Synthesis
Phenylalanine hydroxylase - conversion of phenylalanine to tyrosine
Iron recycling/homeostasis diagram
LEctre Slide
Iron Absorption diagram
LEcture SLide
Process of Non heme and Heme in Duodenum & proximal Jejunum
No heme iron converst from Fe3+ to Heme (Fe2+) via DRA.
Fe2+ goes through DMT1(divalent metal transport protein 1) into cell. It can go either through ferroportin as Fe2+ and then to Fe3+ to bind to transferrin OR into ferritin
HEME:
Goes thorugh HCP1 and via heme oxygenase dismantles heme to be stored as Fe2+ as ferritin.
Hepcidin
- role
- mutations?
iron regulatory hormone
- Inactivates ferroportin stops iron getting out of cell
-leads to decreased gut iron absorption
Haemachromatosis:
Increases iron from enterocytes into body - very little control of iron intake, increase in amount stored in liver leading to cirrhosis and cancer.
Iron-deficiency anaemia under microscope vs B12/folate def
Microcytic
B12 &
folate deficiency =
macrocytic
