Download Water Balance and Minerals

Week 30
Water Balance and Minerals
Water: more vital to life than food
• involved in almost every body function
• is not stored--excreted daily
• largest single constituent of the human body,
averaging 60% of total body weight
• although most people can survive 6 weeks or longer
without food, death occurs in a matter of days
without water
• occupies essentially every space within and
between body cells and is involved in virtually every
body function
Basic Principles
• Body water compartments
• Intracellular
• Extracellular
• Intravascular
• Interstitial
• Membranes separate water compartments
• Particles in solution
• Homeostasis
Functions of Water in the Body
Water
• Under normal conditions, water intake equals water
output to maintain water balance
• In most healthy people, thirst is a reliable indicator of
need
• The body’s need for water is influenced by many
variables
• A general guideline is to consume 1.0 mL of fluid per calorie consumed,
with a minimum of 1500 mL/day to meet metabolic needs
Water: an essential nutrient
• Water is an essential nutrient because the body cannot
produce as much water as it needs
• On average, adults lose approximately 1450 to 2800 mL
of water daily
Insensible water loss--immeasurable
• Insensible water losses from the skin and expirations
account for approximately half of the total water lost
daily
• Extreme environmental temperatures (very hot or very
cold), high altitude, low humidity, and strenuous
exercise increase insensible losses
• Water evaporation from the skin is also increased by
prolonged exposure to heated or recirculated air such
as during long airplane flights
Sensible water loss--measurable
• Sensible water losses from urine and feces make up
the remaining water loss
• Because the body needs to excrete a minimum of
500 mL of urine daily to rid itself of metabolic wastes,
the minimum daily total fluid output is approximately
1500 mL
• To maintain water balance, intake should
approximate output
Sources and average amounts of daily
water loss
Source of Water
Average Amount Loss
Lost (mL/d)
• Perspiration
450 to 900
• Exhalations
350
• Urine
500 to 1400
• Feces
150
• Total
1450 to 2800
Electrolytes
• Small, inorganic substances
• When they dissociate they carry a charge
• Cation
• Na+, K+, Ca++, Mg++
• Anion
• Cl-, HCO3-, PO4-, so4—
• Balanced
• Measured in milliequivalents
Plasma Proteins
• Albumin
• Globulin
• Large molecules
Small Organic Compounds
• Dissolved in water
• Usually small concentrations
• Do not ordinarily influence water movement in the body
Membranes
• Capillary membranes
• Cell membranes
Movement of Water in the
Body
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Osmosis
Diffusion
Facilitated diffusion
Filtration
Active transport
Pinocytosis
Hormonal Control
• Antidiuretic hormone
• AKA vasopressin
• Aldosterone
Minerals
• Minerals are inorganic substances that cannot be
broken down and rearranged in the body
• 117 known elements
• 25 essential to life and perform a variety of metabolic
functions
• 7 major and 18 minor minerals
Mineral Metabolism
• Digestion
• Absorbed as ions
• Do not require mechanical or chemical digestion
• Absorption
• Transport
• Tissue Uptake
Functions of Minerals
• Structure
• Fluid balance
• Acid---base balance
• Nerve cell transmission and muscle contraction
• Vitamin, enzyme, and hormone activity
Mineral toxicities
• are not likely to occur from diet alone
• are most often related to
• excessive use of mineral supplements
• environmental exposure
• alterations in metabolism
Mineral balance
• Depending on the mineral involved, the body can
maintain mineral balance by
• altering the rate of absorption
• altering the rate of excretion
• releasing minerals from storage when needed
• The absorption of many minerals is influenced by
mineral-mineral interactions
• Too much of one mineral may promote a deficiency of
another mineral
Sodium
• One of the most plentiful minerals in the body
• Function
• Maintain water balance
• Muscle action
• Nutrient absorption
• Deficiency: rare
Sodium and the American diet
• As much as 75% of sodium consumed in the
average American diet is from processed food
• Americans are urged to reduce their intake of
sodium because of its potential role in the
development of hypertension
Sodium
National Academy of Science’s Institute of
Medicine
Healthy Adult 1500-2400mg
Less if >50 or have HTN
Average Adult Male: 3300mg/d
Descriptors of Sodium Content
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•
•
If the label says . . . 1 serving contains . . .
Sodium free
<5 mg
Very low sodium
<35 mg
Low sodium
<140 mg
Reduced or less sodium 25% less sodium
Light in sodium
50% less sodium
Salt free
<5 mg
Unsalted or no added saltNo salt added during
processing
Calcium
• Many American adults consume less than optimal
amounts of calcium, placing them at risk of
osteoporosis and possibly hypertension
• Milk and yogurt are the richest sources of calcium, and
their vitamin D and lactose content promote its
absorption
• The National Academy of Science recommends
American adults consume 1000-1200 mg of calcium
daily
Calcium Deficiency and
Toxicity
• Rickets
• Related to inadequate vitamin D
• Tetany
• Osteoporosis
• Toxicity unlikely from food sources
• Kidney stones
• Decreased absorption of other minerals
Calcium Supplements
• TUMS is made of calcium carbonate--it is 40% elemental
calcium and is generally the least inexpensive calcium
supplement
• Calcium carbonate supplements can cause constipation-encourage an adequate fluid intake and a high fiber diet as
needed
• Calcium citrate is less likely to cause constipation than calcium
carbonate
• Calcium from supplements is absorbed best in doses of 500
mg or less--tablets should be spread out over the day
Phosphorus
• Functions
• Bone and tooth formation
• Energy Metabolism
• Acid-base balance
• Sources
• Found in all plant and animal cells
• Deficiency and toxicity: rare
Potassium
• Functions
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Water balance
Metabolic reactions
Muscle action
Insulin release
Blood pressure
• AI =4.7g/day for all adults
• Deficiency and Toxicity
• Sources
Chloride
• Major extracellular anion
• One of the elements in HCl
• Acid-base balance
• Deficiency and toxicity
Magnesium
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•
•
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Mostly in bone
A cofactor for more than 300 enzymes
Magnesium intake is 80% of recommended
Large doses of supplemental magnesium may cause diarrhea,
nausea, cramping
• Food sources
Sulfur
• Essential part of protein structure: hair, skin and
nails, necessary for collagen formation
• Supplied by protein foods
• Deficiency and toxicity unseen
Iron
• Essential but toxic in excess
• 70% of body’s iron is in hemoglobin
• Necessary for glucose metabolism, antibody
production, drug detoxification, conversion of
beta carotene to vitamin A
• Deficiency and toxicity
• Food sources
Iodine
• Component of T4 (thyroxine)
• Deficiency
• Goiter
• Cretinism
Hypothyroidism
• Hyperthyroidism
• Toxicity
• Food sources
• Food sources dependent on iodine in the soil
• Major reliable source: iodized salt
Fluoride
• Binds with calcium
• Strengthens tooth enamel
Zinc
• Functions
• Enzyme constituent
• Immune system
• Prohormone
• Deficiency and Toxicity
• Food sources
Encourage healthy beverage choices:
• Replace soft drinks with calorie-free versions such as
diet soda or sparkling water
• Use bottled water, if the taste of tap water is
objectionable
• Refrigeration usually improves the taste of tap water
• Drink a glass of water before each meal, especially if
weight control is a concern
• Eat enough fruits and vegetables