47 terms

Metabolism 2 test- Zinc

Zinc RDA for males ages 19-30
8 mg/d
Zinc RDA for females ages 19-30
18 mg/d
Zinc food sources
seafood, meats, eggs and dairy products, whole grains, vegetables
Endogenous sources of zinc
carboxypeptidases (metal enzyme)
Forms of zinc
Zn 2+ (universally found in divalent state
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
Zinc absorption
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).
High intakes of zinc
passive diffusion
Enhancers of zinc absorption
ligands: citric acid, amino acids (histimine, cysteine), tri-peptides (glutathione); pancreatic secretions
zinc status-homeostatically regulated
low zinc status = carrier mediated mechanisms are enhanced
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
processes that reduce zinc bioavailability
heating, maillard reactions: toasting bread
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
As zinc increases
metallothionein concentrations increase
zinc transport to tissues
via albumin and transferrin
zinc uptake in tissues
uptake by amino acids and enzyme synthesis
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
alakaline phosphatase: phosphate digestion and absorption, has 4 zinc ions
zinc catalytic function
alcohol dehydrogenase: alcohols to aldehydes, has 4 zinc ions, uses NADH
zinc catalytic function
carboxypeptidase: protein digestion, zinc bound to this exopeptidase
zinc catalytic function
aminolevulinic acid dehydratase: heme synthesis, aminolevulinic synthase is B6 dependent
zinc catalytic function
superoxide dismutase: antioxidant, 2O2- + H2+ --> SOD --> H2O2 + O2
lead poisoning
lead replaces zinc on dehydratase enzyme causing build-up of ALA because reaction can't occur
zinc regulatory
tissue growth: protein synthesis and nucleic acids (zinc regulated protein synthesis and tissue growth), bone formation and cell-mediated immunity
structure of zinc
zinc fingers, cell membrane
zinc fingers
help regulate DNA binding proteins
cell membrane
zinc bound to tubulin proteins that make up microtubules
carbohydrate metabolism
zinc deficiency = decreased insulin and the response = impaired glucose tolerance
Basal metabolic rate
zinc deficiency = decreased BMR
taste acuity/appetite
zinc deficiency = symptoms of anorexia and anhedonia
transport proteins
albumin and transferrin
neurotransmitter receptors
zinc changes the shape of the receptor to allow the signal
Vitamin A
zinc interacts with retinol --> retinal
Copper in reference to zinc
has a higher affinity than zinc for metallothionein
calcium in reference to zinc
with low amounts, zinc supplements can inhibit the absorption
cadmium in reference to zinc
competes for binding sites, especially in zinc fingers
lead in reference to zinc
zinc interacts with ALA dehydratase
excretion of zinc
GI tract, kidney, skin
assessment of zinc
serum/plasma: plasma zinc, plasma metallothionine, urinary zinc
urinary zinc
is not the best test, only shows severe deficiency
zinc deficiency
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
zinc toxicity
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
at risk population for zinc: increased losses
sickle cell, diabetes, renal disease, burns and surgery, chronic diarhhea