721
CHAPTER EIGHTEEN
Nutrition and Metabolism
Manganese
(Mn) is most concentrated in the liver, kid-
neys, and pancreas. It is necessary for normal growth and
development of skeletal structures and other connective tis-
sues. Manganese is part of enzymes essential for the synthe-
sis of fatty acids and cholesterol, for urea formation, and for
the normal functions of the nervous system.
The daily requirement for manganese is 2.5–5 mg. The
richest sources include nuts, legumes, and whole-grain cere-
als; leafy green vegetables and fruits are good sources.
PRACTICE
68
What is the primary function of iron?
69
Why does the usual diet provide only a narrow margin of safety in
supplying iron?
70
How is manganese used?
71
Which foods are good sources of manganese?
Copper
(Cu) is in all body tissues but is most highly
concentrated in the liver, heart, and brain. It is essential for
hemoglobin synthesis, bone development, melanin produc-
tion, and formation of myelin in the nervous system.
iron assists in vitamin A synthesis, is incorporated into a
number of enzymes, and is included in the cytochrome mol-
ecules that participate in ATP-generating reactions.
An adult male requires from 0.7 to 1 mg of iron daily,
and a female needs 1.2 to 2 mg. A typical diet supplies about
10 to 18 mg of iron each day, but only 2% to 10% of the iron
is absorbed. For some people, this may not be enough iron.
Eating foods rich in vitamin C along with iron-containing
foods can increase absorption of this important mineral.
Liver is the only rich source of dietary iron, and because
liver is not a popular food, iron is one of the more diffi-
cult nutrients to obtain from natural sources in adequate
amounts. Foods that contain some iron include lean meats;
dried apricots, raisins, and prunes; enriched whole-grain
cereals; legumes; and molasses.
Pregnant women require extra iron to support the formation of a
placenta and the growth and development of a fetus. Iron is required
for the synthesis of hemoglobin in a fetus as well as in a pregnant
woman, whose blood volume increases by a third.
TABLE
18.10
|
Major Minerals
Mineral
Distribution
Functions
Sources and
RDA* for Adults
Conditions Associated with
Excesses
De±
ciencies
Calcium
(Ca)
Mostly in the inorganic
salts of bones and
teeth
Structure of bones and teeth; essential for neurotransmitter
release, muscle F
ber contraction, and blood coagulation;
increases permeability of cell membranes; activates certain
enzymes
Milk, milk products,
leafy green
vegetables
800 mg
Kidney stones,
deposition of
calcium phosphate
in soft tissues
Stunted
growth,
misshapen
bones, fragile
bones, tetany
Phosphorus
(P)
Mostly in the inorganic
salts of bones and
teeth
Structure of bones and teeth; in nearly all metabolic
reactions; in nucleic acids, many proteins, some enzymes,
and some vitamins; in cell membrane, ATP, and phosphates
of body ±
uids
Meats, cheese, nuts,
whole-grain cereals,
milk, legumes
800 mg
None known
Stunted
growth
Potassium
(K)
Widely distributed;
tends to be
concentrated inside
cells
Helps maintain intracellular osmotic pressure and regulate
pH; required for nerve impulse conduction
Avocados, dried
apricots, meats, nuts,
potatoes, bananas
2,500 mg
Uncommon
Muscular
weakness,
cardiac
abnormalities,
edema
Sulfur
(S)
Widely distributed;
abundant in skin, hair,
and nails
Essential part of certain amino acids, thiamine, insulin,
biotin, and mucopolysaccharides
Meats, milk, eggs,
legumes
No RDA established
None known
None known
Sodium
(Na)
Widely distributed;
mostly in extracellular
±
uids and bound to
inorganic salts of bone
Helps maintain osmotic pressure of extracellular ±
uids;
regulates water movement; plays a role in nerve impulse
conduction; regulates
pH and
transport of substances
across cell membranes
Table salt, cured ham,
sauerkraut, cheese,
graham crackers
2,500 mg
Hypertension,
edema, body cells
shrink
Nausea,
cramps,
convulsions
Chlorine
(Cl)
Closely associated
with sodium; most
highly concentrated
in cerebrospinal ±
uid
and gastric juice
Helps maintain osmotic pressure of extracellular ±
uids,
regulates pH; maintains electrolyte balance; forms
hydrochloric acid; aids transport of carbon dioxide by red
blood cells
Same as for sodium
No RDA established
Vomiting
Cramps
Magnesium
(Mg)
Abundant in bones
Required in metabolic reactions in mitochondria that
produce ATP; plays a role in the breakdown of ATP to ADP
Milk, dairy products,
legumes, nuts, leafy
green vegetables
300–350 mg
Diarrhea
Neuromuscular
disturbances
*
RDA = recommended daily allowance.
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