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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 • • • • • • 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 • • • • • • • • 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 • • • • • 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 • • • • 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