© 2011 Pearson Education, Inc. 9 Nutrients Involved in Fluid and Electrolyte Balance

© 2011 Pearson Education, Inc. Body Fluids Body fluid is the liquid portion of cells and tissues Characterized by its ability to move freely and changeably, adapting to the shape of the container that holds it About 50−70% of healthy adult body weight

© 2011 Pearson Education, Inc. Body Fluids Intracelluar fluid: within the cell 2/3 of body fluid Extracellular fluid: outside the cell 1/3 of body fluid Interstitial fluid flows between cells that make up a particular tissue or organ (muscle, liver) Intravascular fluid is the water in the blood and lymph Plasma transports blood cells within arteries, veins, and capillaries Intracellular and Extracellular Fluid

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Body Fluids Fluid composition of tissue varies by: Tissue type: lean tissues have higher fluid content than fat tissues Gender: males have more lean tissue and therefore more body fluid than females Age: decrease in body water results partly from loss of lean tissue as people age

© 2011 Pearson Education, Inc. Electrolytes Dissolved substances that disassociate in solution into electrically charged particles called ions Positive charge: sodium, potassium Negative charge: chloride, phosphorus Predominant electrolytes Extracellular fluid: potassium, phosphorus Intracellular fluid: sodium, chloride Role of Electrolytes in Water Balance

© 2011 Pearson Education, Inc. Functions of Body Fluids Fluids dissolve and transport substances Water is an excellent solvent because it dissolves a variety of substances Water-soluble substances are readily transported in the bloodstream: amino acids, glucose, vitamins, minerals, medications Fatty substances must be attached to or surrounded by water-soluble proteins

© 2011 Pearson Education, Inc. Functions of Body Fluids Fluids account for blood volume Appropriate body fluid levels are essential for maintaining healthful blood volume Blood pressure increases when blood volume rises High blood pressure (hypertension) is a risk factor for heart disease and stroke Low blood pressure can cause people to feel tired, confused, or dizzy Kidneys help to regulate blood volume and blood pressure

© 2011 Pearson Education, Inc. Functions of Body Fluids Fluids account for blood volume Antidiuretic hormone (ADH) stimulates the kidneys to reabsorb water, reducing urine Renin responds to decreased blood pressure Angiotensin II (vasoconstrictor) increases blood pressure Aldosterone signals the kidneys to retain sodium and chloride, thereby retaining water, increasing blood pressure, and decreasing urine output

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Functions of Body Fluids Fluids help maintain body temperature Body temperature must be within a safe range Water has a high capacity for heat, which means that only sustained high heat can increase body temperature Sweating releases heat as the evaporation of water from the skin cools the skin and blood

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Functions of Body Fluids Protect and lubricate tissues Cerebrospinal fluid protects the brain and spinal cord Amniotic fluid protects the fetus Synovial fluid lubricates joints Tears cleanse and lubricate eyes Saliva moistens food for swallowing

© 2011 Pearson Education, Inc. Functions of Electrolytes Electrolytes help regulate fluid balance Cell membranes are permeable to water, but not freely permeable to electrolytes Water moves by osmosis to areas where the concentration of solute is high This action provides a means to control movement of water into and out of the cells Osmotic pressure keeps electrolytes in solution from drawing liquid toward them across a semipermeable membrane

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Functions of Electrolytes Electrolytes enable nerves to respond to stimuli Nerve impulses are initiated at nerve cell membranes in response to a change in electrical charge across the membrane Depolarization—Action Potential— Repolarization Sodium and potassium ensure that nerve impulses are generated, transmitted, and completed

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Functions of Electrolytes Electrolytes signal muscles to contract Muscles are stimulated to contract in response to stimulation of nerve cells Influx of calcium into the muscle from the extracellular space stimulates contraction Muscles can relax after contraction once the electrical signal is complete and calcium is pumped out of the muscle cell

© 2011 Pearson Education, Inc. Fluid Balance Thirst mechanism (hypothalamus) prompts us to drink when it is stimulated by Increased concentration of salt and other dissolved substances in the blood A reduction in blood volume and blood pressure, such as during profuse sweating, vomiting, diarrhea, or low fluid intake Dry mouth and throat from reduced saliva ADH signals the kidneys to retain water

© 2011 Pearson Education, Inc. Fluid Balance Body gains fluids Water enters the body through beverages Some foods have very high water content Water from metabolic reactions contributes 10−14% of daily water need

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Fluid Balance Sensible water loss Kidneys excrete water as urine Sweat during exercise or in hot environment Insensible water loss Skin (not sweating) or lungs during exhalation Significant loss Illness, injury, exercise, high altitude, pregnancy, breastfeeding, diuretics

© 2011 Pearson Education, Inc. Water Essential for life Amount needed varies with gender, age, body size, health status, physical activity level, environment Sources of drinking water: carbonated, mineral, distilled, purified, tap, bottled ABC Video Bottled Water

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Water What happens if we drink too much water? Becoming overhydrated is rare Dilution of blood sodium concentration What happens if we don’t drink enough water? Dehydration Leading cause of death around the world Water Balance

© 2011 Pearson Education, Inc. Sodium Major positively charged electrolyte in the extracellular fluid Blood pressure and acid−base balance Nerve impulse transmission Muscle contraction and relaxation Assists in glucose absorption from the small intestine

© 2011 Pearson Education, Inc. Sodium AI: 1,500 mg, most recommend < 2,300 mg/day Processed foods are high in sodium High blood pressure more common from high- sodium diets Excessive intake may increase urinary calcium excretion in some people, which in turn may increase the risk for bone loss

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Sodium What if you consume too much sodium? Hypernatremia is an abnormally high blood sodium concentration Patients with congestive heart failure or kidney disease cannot effectively excrete sodium Causes high blood volume, edema (swelling), and high blood pressure

© 2011 Pearson Education, Inc. Sodium What if you don’t consume enough sodium? Hyponatremia is an abnormally low blood sodium level From prolonged sweating, vomiting, diarrhea Symptoms: headaches, dizziness, fatigue, nausea, vomiting, and muscle cramps If untreated: seizures, coma, and death

© 2011 Pearson Education, Inc. Potassium Major positively charged electrolyte in the intracellular fluid Together with sodium, maintains fluid balance and regulates the contraction of muscles and transmission of nerve impulses High potassium intake helps maintain a lower blood pressure

© 2011 Pearson Education, Inc. Potassium Recommended intake 4,700 mg/day Sources of potassium Good sources: fresh fruits, vegetables, legumes, and whole grains Processing foods increases sodium and decreases potassium content

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Potassium What happens if you consume too much potassium? Hyperkalemia: high blood potassium levels Can alter normal heart rhythm, resulting in heart attack and death People with kidney disease are unable to regulate their blood potassium levels and should avoid consuming potassium-containing salt substitutes

© 2011 Pearson Education, Inc. Potassium What happens if you don’t consume enough potassium? Hypokalemia: low blood potassium levels Seen in people with kidney disease or diabetic ketoacidosis Can occur when taking certain diuretics and with extreme dehydration, vomiting, diarrhea, alcohol abuse, long-term consumption of natural licorice (glycyrrhizic acid or GZA), or eating disorder (abnormal heart rhythms)

© 2011 Pearson Education, Inc. Chloride Functions of chloride In extracellular fluid Aids digestion: hydrochloric acid (HCl) in the stomach Assists the immune system and in the transmission of nerve impulses Recommended intake AI: 2,300 mg/day

© 2011 Pearson Education, Inc. Chloride What happens if you consume too much chloride? Primary dietary source: table salt Hypertension in salt-sensitive individuals What happens if you don’t consume enough chloride? This is rare but can occur in people with severe dehydration, frequent vomiting, and eating disorders

© 2011 Pearson Education, Inc. Phosphorus Functions of phosphorus: Major intracellular negatively charged electrolyte Required for fluid balance Critical role in bone formation Regulates biochemical reactions by activating or deactivating enzymes (phosphorylation) Found in ATP, DNA, RNA, cell membranes (phospholipids), and lipoproteins

© 2011 Pearson Education, Inc. Phosphorus Recommended intake RDA for phosphorus is 700 mg/day Sources of phosphorus Widespread in many foods High in protein foods (meat, milk, eggs) More readily absorbed from animal sources Phytic acid: plant storage form Soft drinks

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Phosphorus What happens if you consume too much phosphorus? High blood phosphorus can occur among people with kidney disease or when taking too many vitamin D supplements Causes muscle spasms, convulsions What if you don’t consume enough phosphorus? Deficiencies of phosphorus are rare

© 2011 Pearson Education, Inc. Medical Disorders Disorders related to fluid and electrolyte imbalance include: Dehydration Heatstroke Water intoxication Hypertension Neuromuscular disorders Obesity

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Dehydration Dehydration occurs when fluid loss exceeds fluid intake Commonly due to heavy exercise or high environmental temperatures Elderly and infants are at increased risk

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Heatstroke Heatstroke occurs from failure in the body’s heat-regulating mechanisms Hot, humid environments Symptoms: rapid pulse, hot and dry skin, high body temperature, loss of consciousness Fatal during exercise in extreme heat Stop exercising when feeling dizzy, light-headed, disoriented, or nauseated

© 2011 Pearson Education, Inc. Water Intoxication Overhydration can occur but it is rare Kidneys retain too much water, causing overhydration and hyponatremia Documented cases of deaths among college students (hazing rituals)

© 2011 Pearson Education, Inc. Hypertension Hypertension: major chronic disease characterized by high blood pressure Often without symptoms Increases a person’s risk of heart disease, stroke, kidney disease Can reduce brain function, impair physical mobility, and cause death Systolic pressure over 140 mm Hg Diastolic pressure over 90 mm Hg

© 2011 Pearson Education, Inc. Hypertension What causes hypertension? Primary (or essential) hypertension: unknown cause for 90−95% of cases 5−10% are caused by kidney disease, sleep apnea, and chronic alcohol abuse Salt sensitivity: >50% adults with hypertension

© 2011 Pearson Education, Inc. Hypertension Recommendations for reducing hypertension: Losing weight Increasing physical activity Reducing alcohol intake Reducing sodium intake Eating more whole grains, fruits, vegetables, and low-fat dairy foods DASH diet

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Hypertension Medications Help in normalizing blood pressure Should also continue to practice healthful lifestyle changes Hypertension: “the silent killer” Often no obvious symptoms of this disease Importance of regular blood pressure check

© 2011 Pearson Education, Inc. Neuromuscular Disorders Electrolyte imbalances can alter nervous system and muscle function Seizures: uncontrollable muscle spasms Muscle cramps: involuntary, spasmodic, and painful muscle contractions

© 2011 Pearson Education, Inc. Obesity Popularity of sweetened beverages (U.S.) 21% of calories from beverages: sweetened soft drinks, fruit juices, sweetened bottled waters, bottled teas, specialty coffee Appetite not curbed: extra calories from drinks are not compensated for by eating less Displace more nutritious beverages such as milk (source of protein, calcium, vitamin D, and other nutrients important for bone health)

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