Lecture 16 Iron Metabolism Flashcards
1
Q
Iron Compartments
A
68% hemoglobin, 18% storage, 10% myoglobin
2
Q
Heme iron
A
- mainly from meat
- absorbed more efficiently
3
Q
Nonheme iron
A
- sources are nonmeat such as legumes and leafy vegetables
- accounts for 90% of dietary iron
- only 2-20% absorbed depending on iron status
- absorption enhanced by citrate and acidic foods
- substances that inhibit absorption are phosphates, phytates, oxalates, calcium, foods that form insoluble iron complexes
4
Q
Ferroportin
A
- transports iron across enterocyte into blood circulation
5
Q
Ferritin
A
storage form of ferric iron
- apoferritin with iron
- can store up to 4500 iron atoms
- primary iron storage, readily available
- found in blood, bone marrow, liver and spleen
- reflective of amount of storage iron in body
6
Q
Transferrin
A
- blood iron transporter
- ferric iron bound to transferrin to be transported from duodenum enterocytes to bone marrow and tissues
7
Q
Hepcidin
A
- antimicrobial peptide produced in the liver
- negative regulator of intestinal iron
- degrades ferroportin
8
Q
Transferrin receptors
A
- present in large numbers of RBC normoblasts and other rapidly dividing cells (placenta, liver)
- glycoproteins located on virtually all cells except mature RBCs
- binds transferrin and takes it in by endocytosis
- also plays role in release of iron from transferrin in cell
- synthesis induced by iron deficiency
- when fully saturated, deposited in liver for storage
9
Q
Excretion and Regulation of iron
A
- humans have no effective means to excrete iron and rely on controlling absorption to regulate iron levels
- iron absorbed inversely proportional to iron stores
10
Q
Iron loss
A
- mainly by feces
- perspiration, natural skin exfoliation, lactation, menstruation
11
Q
Iron-responsive protein (IRP) and Iron-responsive elements
A
- responsible for increasing Hgb production when intracellular iron low
1. IRPs bind IRE to increase RNA product’n -> synth of transferrin receptors and ALA synthase
2. More iron uptake -> greater Hgb production
3. More protoporphyrin IX product’n to accomodate increased iron uptake - steps above -> greater Hgb product’n
12
Q
Hemosiderin
A
- storage form of iron
- found primarily in macrophages, formed by partial degradation of ferritin
- when there are hi levels of cellular iron, ferritin processed to form hemosiderin
13
Q
Ferritin and Hemosiderin are stored:
A
- mostly in the liver
- bone marrow
- spleen
14
Q
Serum iron
A
- measure of ferric iron bound to transferrin (excludes iron bound to Hgb)
- decreased in iron deficiency, inflammatory disorders, acute infection, heart attack
15
Q
Unsaturated iron binding capacity (UIBC)
A
iron binding sites not carrying iron
