Metabolism 2 test- Zinc

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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

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