Week 30. Water Balance and Minerals

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Water Balance and Minerals

Week 30

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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

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Basic Principles

Body water compartments

Intracellular

Extracellular

Intravascular

Interstitial

Membranes separate water compartments

Particles in solution

Homeostasis

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Functions of Water in the Body

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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

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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

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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

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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

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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

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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

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Plasma Proteins

Albumin

Globulin

Large molecules

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Small Organic Compounds

Dissolved in water

Usually small concentrations

Do not ordinarily influence water movement in the body

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Membranes

• Capillary membranes

• Cell membranes

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Movement of Water in the Body

Osmosis

Diffusion

Facilitated diffusion

Filtration

Active transport

Pinocytosis

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Hormonal Control

Antidiuretic hormone

AKA vasopressin

Aldosterone

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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

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Mineral Metabolism

Digestion

Absorbed as ions

Do not require mechanical or chemical digestion

Absorption

Transport

Tissue Uptake

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Functions of Minerals

Structure

Fluid balance

Acid---base balance

Nerve cell transmission and muscle contraction

Vitamin, enzyme, and hormone activity

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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

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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

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Sodium

One of the most plentiful minerals in the body

Function

Maintain water balance

Muscle action

Nutrient absorption

Deficiency: rare

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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

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Sodium

National Academy of Science’s Institute of Medicine

Healthy Adult 1500-2400mg Less if >50 or have HTN

Average Adult Male: 3300mg/d

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Descriptors of Sodium Content

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

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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

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Calcium Deficiency and Toxicity

Rickets

Related to inadequate vitamin D

Tetany

Osteoporosis

Toxicity unlikely from food sources

Kidney stones

Decreased absorption of other minerals

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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

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Phosphorus

Functions

Bone and tooth formation

Energy Metabolism

Acid-base balance

Sources

Found in all plant and animal cells

Deficiency and toxicity: rare

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Potassium

Functions

Water balance

Metabolic reactions

Muscle action

Insulin release

Blood pressure

AI =4.7g/day for all adults

Deficiency and Toxicity

Sources

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Chloride

Major extracellular anion

One of the elements in HCl

Acid-base balance

Deficiency and toxicity

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Magnesium

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

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Sulfur

Essential part of protein structure: hair, skin and nails, necessary for collagen formation

Supplied by protein foods

Deficiency and toxicity unseen

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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

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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

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Fluoride

Binds with calcium

Strengthens tooth enamel

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Zinc

Functions

Enzyme constituent

Immune system

Prohormone

Deficiency and Toxicity

Food sources

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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

Figure

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