731
CHAPTER EIGHTEEN
Nutrition and Metabolism
d. Sulfur
(1) Sulfur is incorporated into two of the twenty
amino acids.
(2) It is also in thiamine, insulin, biotin, and
mucopolysaccharides.
e. Sodium
(1) Most sodium is in extracellular fl
uids or is
bound to the inorganic salts of bone.
(2) The kidneys, under the infl uence of aldosterone,
regulate the blood concentration of sodium.
(3) Sodium helps maintain solute concentration
and regulates water balance.
(4) It is essential for nerve impulse conduction
and moving substances through cell
membranes.
f. Chlorine
(1) Chlorine is closely associated with sodium as
chloride ions.
(2) It acts with sodium to help maintain osmotic
pressure, regulate pH, and maintain electrolyte
balance.
(3) Chlorine is essential for hydrochloric acid
formation and for carbon dioxide transport by
red blood cells.
g. Magnesium
(1) Magnesium is abundant in the bones as
phosphates and carbonates.
(2) It functions in ATP production and in the
breakdown of ATP to ADP.
(3) A reserve supply of magnesium is stored in the
bones; excesses are excreted in the urine.
3. Trace elements
a. Iron
(1) Iron is part of hemoglobin in red blood cells
and myoglobin in muscles.
(2) A reserve supply of iron is stored in the liver,
spleen, and bone marrow.
(3) It is required to catalyze vitamin A formation;
it is also incorporated into various enzymes
and the cytochrome molecules.
b. Manganese
(1) Most manganese is concentrated in the liver,
kidneys, and pancreas.
(2) It is necessary for normal growth and
development of skeletal structures and other
connective tissues; it is essential for the
synthesis of fatty acids, cholesterol, and urea.
c. Copper
(1) Most copper is concentrated in the liver, heart,
and brain.
(2) It is required for hemoglobin synthesis, bone
development, melanin production, and myelin
formation.
d. Iodine
(1) Iodine is most highly concentrated in the
thyroid gland.
(2) It is an essential component of thyroid
hormones.
(3) It is often added to foods as iodized table salt.
e. Cobalt
(1) Cobalt is widely distributed throughout the
body.
(2) It is an essential part of cyanocobalamin and is
required for the synthesis of several enzymes.
(7) Folacin (folic acid)
(a) Liver enzymes catalyze reactions that
convert folacin to physiologically active
folinic acid.
(b) It is a coenzyme needed for the
metabolism of certain amino acids, DNA
synthesis, and the normal production of
red blood cells.
(8) Biotin
(a) Biotin is a coenzyme required for the
metabolism of amino acids and fatty acids,
and for nucleic acid synthesis.
(b) It is stored in metabolically active organs,
including the brain, liver, and kidneys.
c. Ascorbic acid (vitamin C)
(1) Vitamin C is similar chemically to
monosaccharides.
(2) It is required for collagen production, the
metabolism of certain amino acids, and iron
absorption.
(3) It is not stored in large amounts; excess is
excreted in the urine.
18.7
MINERALS (PAGE 717)
1. Characteristics of minerals
a. Minerals account for about 4% of body weight.
b. About 75% by weight of the minerals are found in
bones and teeth as calcium and phosphorus.
c. Minerals are usually incorporated into organic
molecules, although some are in inorganic
compounds or are free ions.
d. They compose structural materials, function in
enzymes, and play vital roles in various metabolic
processes.
e. Homeostatic mechanisms regulate mineral
concentrations.
f. The physiologically active form of minerals is the
ionized form.
2. Major minerals
a. Calcium
(1) Calcium is essential for forming bones and
teeth, neurotransmitter release, contracting
muscle ±
bers, clotting blood, and activating
various enzymes.
(2) Existing calcium concentration, vitamin D,
protein intake, and motility of the digestive
tract affect calcium absorption.
b. Phosphorus
(1) Phosphorus is incorporated into the salts of
bones and teeth.
(2) It participates in nearly all metabolic reactions
as a constituent of nucleic acids, proteins, and
some vitamins.
(3) It also is in the phospholipids of cell
membranes, in ATP, and in phosphates of body
uids.
c. Potassium
(1) Potassium is concentrated inside cells.
(2) It maintains osmotic pressure, regulates pH,
and plays a role in nerve impulse conduction.
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