Midterm 3 (lecture 10) Flashcards
Iron intro
Homeostasis regulated primarily by absorption
- no regulatory mechanism for excretion
Makes a strong interest in iron deficiency
- most common nutritional deficiency worldwide
- 30% worldwide have iron deficiency
Iron key notes
Iron has two main ionic states
- oxidized: ferric iron: Fe3+ (lost 3 e-)
- reduced: ferrous iron: Fe++ (lost 2 e-)
Iron serves as a cofactor for oxidation- reduction reactions
- “can switch between states easily”
Iron absorption
Affected by three factors that all inter relate:
1. Amount of iron from diet
- iron food sources or supplements
2. Form of dietary iron
- heme vs nonheme
3. Iron absorption
- absorption enhancers and inhibitors “(influenced by many things)”
- iron status: decrease in iron equals better absorption
Iron content of diet : food sources
Red meats, fish, poultry = MFP factor
Eggs, legumes, dried fruits
Must consider heme iron or nonheme iron
Heme vs non heme iron
Heme iron
- animal foods only
- 10% daily intake
- 25-35% absorbed (consistent)
- rate of absorption is consistent, not susceptible to enhancers/inhibitors
Non heme iron
- both plant and animal foods
- 90% daily intake
- 2-20% absorbed (variable)
- rate of absorption is not consistent as it depends on enhancers and inhibitors
- from figure: non heme iron must be dissolved before uptake, bc if low absorption reactive free iron ions remain in the gut
Iron non heme absorption enhancers
MFP factor
- meat fish and poultry factor
- provided high absorbable heme iron AND promotes absorption of non heme iron from other foods eaten in the same meal
- facto is associated with the digestion process
Vitamin C
Gastric acid
Other organic acids such as lactic, malic, tartaric
How do the acids enhance iron absorption?
Ferrous iron (Fe++) is better absorbed
Acids can donate. Hydrogen to ferric iron (Fe3+) reducing it to ferrous iron (Fe++)
Thus the acids REDUCE the ferric iron and convert it to ferrous iron
- reduction = gain of hydrogens/electrons
- Fe3+ (ferric) reduced to Fe2+ (ferrous)
Iron non heme absorption inhibitors
Bind with dietary non heme iron (phytate)
- phytate is in high fiber foods (also helps increase non heme iron so it’s ironic)
Polyphenols (fruit, vegetables, coffee, wine)
- inihibtiroy effects reduced by presence of vitamin C (enhancer)
Oxalate (spinach, rhubarb)
- ironic again: good iron source but also inhibits
Iron and zinc : classic nutrient nutrient interaction
Zinc and iron compete for absorptive pathways due to chemical similarity
Zinc supplements can inhibit iron absorption
Iron biological function: iron proteins
Relates to its involvement in proteins
Certain proteins depend on iron for their synthesis and function
Metabolic function is classified by the type of iron structure contain
- Heme proteins (eg, hemoglobin)
- and non heme proteins - Iron sulfur cluster proteins
- Proteins with single iron atoms
- Proteins with oxygen bridged iron
Iron transport and storage
Efficient mechanisms for iron assimilation and storage because:
- iron is essential for oxygen requiring processes, electron transfer, DNA synthesis, etc
- iron can participate in free radical processes
Therefore, want to control iron exchange, transport and storage (don’t want deficiency or hemochromatosis)
Of course, these involve specific iron containing proteins
Iron transport proteins
TRANSFERRIN
- major plasma protein for iron transport
- high affinity for ferric iron (Fe3+)
- iron is part of the protein
- binding and release of iron result in conformational change of protein
- two domains that are:
—- OPEN without iron
—- CLOSED with iron
- trivial amount of iron carrying
Capacity related to transferrin
Ferritin
- major iron storage protein ( best way to assess iron status)
- can house large amount of iron in a soluble, non toxic, bioquailable form
- single best way to access iron stores
Hemosiderin
- increase in iron overload
- closely related to ferritin
Iron deficiency
- 30% of world population
- various biochemical indices
- physical symptoms largely due to anemia:
— decreased work capacity
— tiredness, fatigue: “ linked to metabolic role in hemoglobin delivery to cells - pica
- in children specifically:
—- adverse effects on cognitive function
—- increased risk of lead poisoning
Stage one of iron deficiency
Iron depletion
- depleted iron stores due to progressive reduction in amount of storage iron
- a decrease in serum ferritin (iron storage protein) making it a good early indicator of deficiency
- transport iron and hemoglobin are normal at this stage
Stage two of iron deficiency
Iron deficient erythropoietin
- complete exhaustion of iron stores
- decreased blood iron concentrations
- less iron delivered to erythropoietic cells resulting in: deceased iron transport, decreased percent transferrin saturation (“it’s always there therefore we look at its saturation”)
- increase in erythrocyte protoporphyrins (precursor to hemoglobin, accumulate in RBC when iron supply not adequate for heme synthesis)
- hemoglobin usually within normal range
