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Digestion of zinc
Eaten attached to amino acids. The stomach and small intestine with the help of proteases, nucleases and HCl take the zinc off the amino acid
in the proximal small intestine (jejunum). Is a carrier mediated process with Nramp2 (natural resistance associated macrophage 2) and DC/MT (divalent cation/mineral transporter).
Enhancers of zinc absorption
ligands: citric acid, amino acids (histimine, cysteine), tri-peptides (glutathione); pancreatic secretions
Inhibitors of zinc absorption
phytates: phytic acid, inosital hexaphosphate or inositol polyphosphate. Found in cereals and grains; oxalates: spinach, chard, berries, chocolate, tea; polyphenols: tea, fibers
zinc in the enterocyte
it is used within the cell. Stored in CRIPs (cysteine rich intestinal proteins) and metallothionein (zinc attached to thionine): binds both zinc and copper. First zinc binds to CRIPs
storage of zinc
metallothionein: the thioneine is a protein and storage for metals but becomes metallothionein when metal is attached. It has cysteine residues that bind metals Cu, Cd, Hg. It is found in most tissues (liver, pancreas, kidney, intestine, RBC). MT-1 through MT-4
zinc catalytic function
carbonic anhydrase: Erythrocytes and respiration, CO2 + H20 <-- carbonic anhydrase --> H+ + HCO3. Zinc speeds up this reaction.
zinc catalytic function
aminolevulinic acid dehydratase: heme synthesis, aminolevulinic synthase is B6 dependent
lead replaces zinc on dehydratase enzyme causing build-up of ALA because reaction can't occur
tissue growth: protein synthesis and nucleic acids (zinc regulated protein synthesis and tissue growth), bone formation and cell-mediated immunity
zinc deficiency = decreased insulin and the response = impaired glucose tolerance
It is rare. symptoms: growth retardation, skeletal abnormalities, poor wound healing, dermatitis, alopecia, hypogeusia, night blindness, delayed sexual maturation, impaired immune function, decreased taste acuity, depression, anorexia
225-450 mg. symptoms: metallic taste, nausea, vomiting, abdominal cramps, bloody diarrhea. can cause copper deficiency
at risk population for zinc: dietary deficiency
protein-energy malnutrition, poor food choices, vegan diets, IV w/o zinc
at risk population for zinc: increased requirements
burn patients, growth spurts, pregnancy and lactation, chronic infection
at risk population for zinc: malabsorption
celiac, chron's, cystic fibrosis, high-phytate diets, chronic iron supplementation
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