Major Minerals and Water in the Body PDF

C H A P T E R Water and the 12 Major Minerals CHAPTER OUTLIN...

C H A P T E R Water and the 12 Major Minerals CHAPTER OUTLINE Water and the Body Fluids Water Balance and Recommended Intakes Blood Volume and Blood Pressure Fluid and Electrolyte Balance Fluid and Elec- trolyte Imbalance Acid-Base Balance The Minerals—An Overview Water is an essential nutrient, more important to life than any of the oth- Sodium ers. The body needs more water each day than any other nutrient. Further- Chloride more, you can survive only a few days without water, whereas a deficiency Potassium of the other nutrients may take weeks, months, or even years to develop. Calcium Calcium Roles in the Body This chapter begins with a look at water and the body’s fluids. The body Calcium Recommendation and Sources maintains an appropriate balance and distribution of fluids with the help Calcium Deficiency of another class of nutrients—the minerals. In addition to introducing the Phosphorus minerals that help regulate body fluids, this chapter describes many of the Magnesium other important functions minerals perform in the body. Sulfate HIGHLIGHT 12 Osteoporosis Water and the Body Fluids and Calcium Water constitutes about 60 percent of an adult’s body weight and a higher percent- age of a child’s (see Figure 1–1, p. 6). Because water makes up about three-fourths of the weight of lean tissue and less than one-fourth of the weight of fat, a person’s body composition influences how much of the body’s weight is water. The propor- tion of water is generally smaller in females, obese people, and the elderly because of their smaller proportion of lean tissue. In the body, water is the fluid in which all life processes occur. The water in the body fluids: Carries nutrients and waste products throughout the body Maintains the structure of large molecules such as proteins and glycogen Participates in metabolic reactions Serves as the solvent for minerals, vitamins, amino acids, glucose, and many other small molecules so that they can participate in metabolic activities © Michael Pole/CORBIS Acts as a lubricant and cushion around joints and inside the eyes, the spinal cord, and, in pregnancy, the amniotic sac surrounding the fetus in the womb Aids in the regulation of normal body temperature (Evaporation of sweat from the skin removes excess heat from the body.) Maintains blood volume Water is the most indispensable nutrient. 397 398 CHAPTER 12 To support these and other vital functions, the body actively maintains an appropri- ◆ Water balance: intake = output ate water balance. ◆ Water Balance and Recommended Intakes Every cell contains fluid of the exact composition that is best for that cell (intracel- lular fluid) and is bathed externally in another such fluid (interstitial fluid). In- ◆ Fluids in the body: terstitial fluid is the largest component of extracellular fluid. ◆ Figure 12-1 Intracellular (inside cells) illustrates a cell and its associated fluids. These fluids continually lose and replace Extracellular (outside cells) their components, yet the composition in each compartment remains remarkably Interstitial (between cells) constant under normal conditions. Because imbalances can be devastating, the Intravascular (inside blood vessels) body quickly responds by adjusting both water intake and excretion as needed. Con- sequently, the entire system of cells and fluids remains in a delicate, but controlled, state of homeostasis. Water Intake Thirst and satiety influence water intake, apparently in response ◆ Reminder: The hypothalamus is a brain cen- to changes sensed by the mouth, hypothalamus, ◆ and nerves. When water intake ter that controls activities such as mainte- is inadequate, the blood becomes concentrated (having lost water but not the dis- nance of water balance, regulation of body solved substances within it), the mouth becomes dry, and the hypothalamus initi- temperature, and control of appetite. ates drinking behavior. When water intake is excessive, the stomach expands and stretch receptors send signals to stop drinking. Similar signals are sent from recep- tors in the heart as blood volume increases. Thirst drives a person to seek water, but it lags behind the body’s need. When too much water is lost from the body and not replaced, dehydration develops. A first sign of dehydration is thirst, the signal that the body has already lost some of its fluid. If a person is unable to obtain fluid or, as in many elderly people, fails to per- ceive the thirst message, the symptoms of dehydration may progress rapidly from thirst to weakness, exhaustion, and delirium—and end in death if not corrected (see Table 12-1). Dehydration may easily develop with either water deprivation or exces- sive water losses. Water intoxication, on the other hand, is rare but can occur with excessive water ingestion and kidney disorders that reduce urine production. The symptoms may include confusion, convulsions, and even death in extreme cases. Excessive water ingestion (10 to 20 liters) within a few hours contributes to the dangerous water balance: the balance between water condition known as hyponatremia, sometimes seen in endurance athletes. For this intake and output (losses). reason, guidelines suggest limiting fluid intake during times of heavy sweating to intracellular fluid: fluid within the cells, 1 to 1.5 liters per hour.1 usually high in potassium and phosphate. Intracellular fluid accounts for approximately Water Sources The obvious dietary sources of water are water itself and other two-thirds of the body’s water. beverages, but nearly all foods also contain water. Most fruits and vegetables con- intra = within tain up to 90 percent water, and many meats and cheeses contain at least 50 per- interstitial (IN-ter-STISH-al) fluid: fluid cent. (See Table 12-2 for selected foods and Appendix H for many more.) Also, water between the cells (intercellular), usually high is generated during metabolism. Recall from Chapter 7 that when the energy-yielding in sodium and chloride. Interstitial fluid is a large component of extracellular fluid. inter = in the midst, between extracellular fluid: fluid outside the cells. TABLE 12-1 Signs of Dehydration Extracellular fluid includes two main components—the interstitial fluid and Body Weight plasma. Extracellular fluid accounts for approximately one-third of the body’s water. Lost (%) Symptoms extra = outside 1–2 Thirst, fatigue, weakness, vague discomfort, loss of appetite thirst: a conscious desire to drink. 3–4 Impaired physical performance, dry mouth, reduction in urine, flushed skin, impatience, apathy dehydration: the condition in which body water output exceeds water input. 5–6 Difficulty concentrating, headache, irritability, sleepiness, impaired tem- Symptoms include thirst, dry skin and perature regulation, increased respiratory rate mucous membranes, rapid heartbeat, low 7–10 Dizziness, spastic muscles, loss of balance, delirium, exhaustion, collapse blood pressure, and weakness. NOTE: The onset and severity of symptoms at various percentages of body weight lost depend on the activity, fitness level, water intoxication: the rare condition in degree of acclimation, temperature, and humidity. If not corrected, dehydration can lead to death. which body water contents are too high in all body fluid compartments.  WATER AND THE MAJOR MINERALS 399 TABLE 12-2 Percentage of Water in Selected Foods FIGURE 12-1 One Cell and Its Associated Fluids 100% Water Fluids are found within the cells (intra- 90–99% Fat-free milk, strawberries, watermelon, lettuce, cabbage, celery, spinach, broccoli cellular) or outside the cells (extracellu- 80–89% Fruit juice, yogurt, apples, grapes, oranges, carrots lar). Extracellular fluids include plasma (the fluid portion of blood in the 70–79% Shrimp, bananas, corn, potatoes, avocados, cottage cheese, ricotta cheese intravascular spaces of blood vessels) 60–69% Pasta, legumes, salmon, ice cream, chicken breast and interstitial fluids (the tissue fluid 50–59% Ground beef, hot dogs, feta cheese that fills the intercellular spaces between the cells). 40–49% Pizza 30–39% Cheddar cheese, bagels, bread 20–29% Pepperoni sausage, cake, biscuits 10–19% Butter, margarine, raisins 1–9% Crackers, cereals, pretzels, taco shells, peanut butter, nuts Fluid between the Cell cells (intercellular membrane 0% Oils, sugars or interstitial) nutrients break down, their carbons and hydrogens combine with oxygen to yield carbon dioxide (CO2) and water (H2O). As Table 12-3 shows, the water derived daily Nucleus from these three sources averages about 21/2 liters (roughly 21/2 quarts or 101/2 cups). Water Losses The body must excrete a minimum of about 500 milliliters (about 2 Fluid within the cups) of water each day ◆ as urine—enough to carry away the waste products gener- cell (intracellular) ated by a day’s metabolic activities. Above this amount, excretion adjusts to balance intake. If a person drinks more water, the kidneys excrete more urine, and the urine becomes more dilute. In addition to urine, water is lost from the lungs as vapor and from the skin as sweat; some is also lost in feces.* The amount of fluid lost from each Fluid (plasma) within the blood source varies, depending on the environment (such as heat or humidity) and physi- vessels (intravascular) cal conditions (such as exercise or fever). On average, daily losses total about 21/2 liters. Table 12-3 shows how water excretion balances intake; maintaining this bal- Blood vessel ance requires healthy kidneys and an adequate intake of fluids. ◆ The amount of water the body has to Water Recommendations Because water needs vary depending on diet, activity, excrete each day to dispose of its wastes is environmental temperature, and humidity, a general water requirement is difficult to the obligatory (ah-BLIG-ah-TORE-ee) establish. Recommendations ◆ are sometimes expressed in proportion to the amount water excretion—about 500 mL (about 2 of energy expended under average environmental conditions.2 The recommended c, or a pint). water intake for a person who expends 2000 kcalories a day, for example, is 2 to 3 liters of water (about 8 to 12 cups). This recommendation is in line with the Adequate ◆ Water recommendation: Intake (AI) for total water set by the DRI Committee. ◆ Total water includes not only 1.0 to 1.5 mL/kcal expended (adults)† drinking water, but water in other beverages and in foods as well. 1.5 mL/kcal expended (infants and athletes) Conversion factors: 1 mL = 0.03 fluid ounce TABLE 12-3 Water Balance 125 mL  1/2 c Easy estimation: 1/2 c per 100 kcal Water Sources Amount (mL) Water Losses Amount (mL) expended Liquids 550 to 1500 Kidneys (urine) 500 to 1400 Foods 700 to 1000 Skin (sweat) 450 to 900 ◆ AI for total water: Metabolic water 200 to 300 Lungs (breath) 350 Men: 3.7 L/day Women: 2.7 L/day GI tract (feces) 150 Conversion factors: Total 1450 to 2800 Total 1450 to 2800 1 L  1 qt  32 oz  4 c NOTE: For perspective, 100 mL is a little less than 1/2 cup and 1000 mL is a little more than 1 quart (1 mL = 0.03 oz). *Water lost from the lungs and skin accounts for almost one-half of the daily losses even when a per- son is not visibly perspiring; these losses are commonly referred to as insensible water losses. †For those using kilojoules: 4.2 to 6.3 mL/kJ expended. 400 CHAPTER 12 Because a wide range of water intakes will prevent dehydration and its harmful consequences, the AI is based on average intakes. People who are physically active or who live in hot environments may need more.3 Which beverages are best? Any beverage can readily meet the body’s fluid needs, but those with few or no kcalories do so without contributing to weight gain. Given that obesity is a major health problem and that beverages currently represent over 20 percent of the total energy intake in the United States, most people would do well to select water as their preferred beverage. Other choices include tea, coffee, nonfat and low-fat milk and soymilk, artificially sweetened beverages, fruit and vegetable juices, sports drinks, and lastly, sweetened nutri- ent-poor beverages.4 Some research indicates that people who drink caffeinated beverages lose a lit- tle more fluid than when drinking water because caffeine acts as a diuretic. The DRI Committee considered such findings in their recommendations for water in- take and concluded: “Caffeinated beverages contribute to the daily total water in- take similar to that contributed by non-caffeinated beverages.”5 In other words, it doesn’t seem to matter whether people rely on caffeine-containing beverages or other beverages to meet their fluid needs. As Highlight 7 explained, alcohol acts as a diuretic, and it has many adverse effects on health and nutrition status. Alcohol should not be used to meet fluid needs. Health Effects of Water In addition to meeting the body’s fluid needs, drinking plenty of water may protect against urinary stones and constipation.6 Even mild de- hydration seems to interfere with daily tasks involving concentration, alertness, and short-term memory.7 The kind of water a person drinks may also make a difference to health. Water is usually either hard or soft. Hard water has high concentrations of calcium and magnesium; sodium or potassium is the principal mineral of soft water. (See the accompanying glossary for these and other common terms used to describe water.) In practical terms, soft water makes more bubbles with less soap; hard water leaves a ring on the tub, a crust of rocklike crystals in the teakettle, and a gray residue in the laundry. Soft water may seem more desirable around the house, and some homeowners purchase water softeners that replace magnesium and calcium with sodium. In the G LOSSARY OF WATER TERMS artesian water: water drawn filtered water: water treated by natural water: water obtained soft water: water with a high from a well that taps a confined filtration, usually through from a spring or well that is sodium or potassium content. aquifer in which the water is activated carbon filters that certified to be safe and sanitary. spring water: water originating under pressure. reduce the lead in tap water, The mineral content may not be from an underground spring or bottled water: drinking water or by reverse osmosis units that changed, but the water may be well. It may be bubbly (carbon- sold in bottles. force pressurized water across treated in other ways such as ated), or “flat” or “still,” mean- a membrane removing with ozone or by filtration. ing not carbonated. Brand carbonated water: water that lead, arsenic, and some public water: water from a names such as “Spring Pure” contains carbon dioxide gas, microorganisms from tap water. municipal or county water do not necessarily mean that either naturally occurring or added, that causes bubbles to hard water: water with a high system that has been treated the water comes from a spring. form in it; also called bubbling or calcium and magnesium content. and disinfected. well water: water drawn from sparkling water. Seltzer, soda, and mineral water: water from a purified water: water that has ground water by tapping into tonic waters are legally soft drinks spring or well that typically been treated by distillation or an aquifer. and are not regulated as water. contains 250 to 500 parts per other physical or chemical distilled water: water that has million (ppm) of minerals. processes that remove dissolved been vaporized and recon- Minerals give water a distinctive solids. Because purified water densed, leaving it free of dis- flavor. Many mineral waters are contains no minerals or solved minerals. high in sodium. contaminants, it is useful for medical and research purposes.  WATER AND THE MAJOR MINERALS 401 body, however, soft water with sodium may aggravate hypertension and heart dis- ease. In contrast, the minerals in hard water may benefit these conditions. Soft water also more easily dissolves certain contaminant minerals, such as cadmium and lead, from old plumbing pipes. As Chapter 13 explains, these con- taminant minerals harm the body by displacing the nutrient minerals from their normal sites of action. People who live in old buildings should run the cold water tap a minute to flush out harmful minerals whenever the water faucet has been off for more than six hours. Many people select bottled water, believing it to be safer than tap water and therefore worth its substantial cost. IN SUMMARY Water makes up about 60 percent of the adult body’s weight. It assists with the transport of nutrients and waste products throughout the body, participates in chemical reactions, acts as a solvent, serves as a shock absorber, and regulates body temperature. To maintain water balance, intake from liquids, foods, and metabolism must equal losses from the kidneys, skin, lungs, and GI tract. The amount and type of water a person drinks may have positive or negative health effects. Blood Volume and Blood Pressure Fluids maintain the blood volume, which in turn influences blood pressure. The kid- ◆ Reminder: Antidiuretic hormone (ADH) is a neys are central to the regulation of blood volume and blood pressure.8 All day, hormone produced by the pituitary gland every day, the kidneys reabsorb needed substances and water and excrete wastes in response to dehydration (or a high with some water in the urine (see Figure 12-2 on p. 402). The kidneys meticulously sodium concentration in the blood). It stim- adjust the volume and the concentration of the urine to accommodate changes in ulates the kidneys to reabsorb more water the body, including variations in the day’s food and beverage intakes. Instructions and therefore to excrete less. on whether to retain or release substances or water come from ADH, renin, an- giotensin, and aldosterone. ◆ Recall from Highlight 7 that alcohol depresses ADH activity, thus promoting ADH and Water Retention Whenever blood volume or blood pressure falls too fluid losses and dehydration. In addition to low, or whenever the extracellular fluid becomes too concentrated, the hypothala- its antidiuretic effect, ADH elevates blood mus signals the pituitary gland to release antidiuretic hormone (ADH). ◆ ADH is a pressure and so is also called vasopressin water-conserving hormone ◆ that stimulates the kidneys to reabsorb water. Conse- (VAS-oh-PRES-in). quently, the more water you need, the less your kidneys excrete. These events also vaso = vessel trigger thirst. Drinking water and retaining fluids raise the blood volume and dilute press = pressure the concentrated fluids, thus helping to restore homeostasis. Renin and Sodium Retention Cells in the kidneys respond to low blood pressure by renin (REN-in): an enzyme from the kidneys that activates angiotensin. releasing an enzyme called renin. Through a complex series of events, renin causes the kidneys to reabsorb sodium. Sodium reabsorption, in turn, is always accompa- angiotensin (AN-gee-oh-TEN-sin): a hormone involved in blood pressure nied by water retention, which helps to restore blood volume and blood pressure. regulation. Its precursor protein is called Angiotensin and Blood Vessel Constriction In addition to its role in sodium angiotensinogen; it is activated by renin, an enzyme from the kidneys. retention, renin converts the blood protein angiotensinogen to its active form— vasoconstrictor (VAS-oh-kon-STRIK-tor): a angiotensin. Angiotensin is a powerful vasoconstrictor that narrows the diam- substance that constricts or narrows the eters of blood vessels, thereby raising the blood pressure. blood vessels. Aldosterone and Sodium Retention In addition to acting as a vasoconstrictor, aldosterone (al-DOS-ter-own): a hormone angiotensin stimulates the release of the hormone aldosterone from the adrenal secreted by the adrenal glands that regulates blood pressure by increasing the glands. Aldosterone signals the kidneys to retain more sodium, and therefore water, reabsorption of sodium by the kidneys. because when sodium moves, fluids follow. Again, the effect is that when more water Aldosterone also regulates chloride and is needed, less is excreted. potassium concentrations. All of these actions are presented in Figure 12-3 (p. 403) and help to explain why adrenal glands: glands adjacent to, and just high-sodium diets aggravate conditions such as hypertension or edema. Too much above, each kidney. 402 CHAPTER 12 FIGURE 12-2 Animated! A Nephron, One of the Kidney’s Many Functioning Units To test your understanding of these concepts, log on to academic.cengage.com/login. A nephron (a working unit of the kidney). Each kidney contains over one million nephrons. Blood vessel Glomerulus 1 1 Blood flows into the glomerulus, and some of its fluid, with dissolved substances, is Capillaries Kidney absorbed into the tubule. of glomerulus Ureter Tubule Pelvis Bladder 2 2 Then the fluid and substances To the body needed by the body are returned to the blood in vessels alongside Renal artery the tubule. Renal vein 3 3 The tubule passes waste materials on to the bladder. To the bladder Kidney, sectioned The cleansing of blood in the nephron is roughly analogous to the way you to show location of might clean your car. First 1 you remove all your possessions and trash so that nephrons the car can be vacuumed. Then 2 you put back in the car what you want to keep and 3 throw away the trash. sodium causes water retention and an accompanying rise in blood pressure or swelling in the interstitial spaces. Chapter 27 discusses hypertension in detail. IN SUMMARY In response to low blood volume, low blood pressure, or highly concentrated body fluids, these actions combine to effectively restore homeostasis: ADH retains water. Renin retains sodium. Angiotensin constricts blood vessels. Aldosterone retains sodium. These actions can maintain water balance only if a person drinks enough water. ◆ The major minerals: Sodium Chloride Fluid and Electrolyte Balance Potassium Calcium Maintaining a balance of about two-thirds of the body fluids inside the cells and one- Phosphorus third outside is vital to the life of the cells. If too much water were to enter the cells, Magnesium they might rupture; if too much water were to leave, they would collapse. To control Sulfur the movement of water, the cells direct the movement of the major minerals. ◆  WATER AND THE MAJOR MINERALS 403 FIGURE 12-3 Animated! How the Body Regulates Blood Volume To test your understanding of these concepts, log on to academic.cengage.com/login. Kidneys Brain The hypothalamus responds The kidneys respond to to high salt concentrations in reduced blood flow by the blood by stimulating the releasing the enzyme renin. pituitary gland. Renin Renin initiates the activation The pituitary gland releases of the protein angiotensinogen antidiuretic hormone (ADH). to angiotensin. Angiotensin Angiotensin causes Angiotensin signals ADH the blood vessels the adrenal glands to to constrict, ◆ To remember the difference between cations secrete aldosterone. raising pressure. and anions, think of the “t” in cations as a “plus” (+) sign and the “n” in anions as Aldosterone “negative.” ◆ A neutral molecule, such as water, that has Aldosterone and ADH signal the kidneys to retain sodium and water, respectively, thus opposite charges spatially separated within increasing blood volume. the molecule is polar. See Appendix B for more details. salt: a compound composed of a positive ion other than H+ and a negative ion other than OH-. An example is sodium chloride (Na+ Cl-). Dissociation of Salt in Water When a mineral salt such as sodium chloride Na = sodium (NaCl) dissolves in water, it separates (dissociates) into ions—positively and neg- Cl = chloride atively charged particles (Na+ and Cl–). The positive ions are cations; the negative dissociates (dis-SO-see-aites): physically ones are anions. ◆ Unlike pure water, which conducts electricity poorly, ions dis- separates. solved in water carry electrical current. For this reason, salts that dissociate into ions ions (EYE-uns): atoms or molecules that have are called electrolytes, and fluids that contain them are electrolyte solutions. gained or lost electrons and therefore have In all electrolyte solutions, anion and cation concentrations are balanced (the electrical charges. Examples include the number of negative and positive charges are equal). If a fluid contains 1000 nega- positively charged sodium ion (Na+) and the tive charges, it must contain 1000 positive charges, too. If an anion enters the fluid, negatively charged chloride ion (Cl-). For a closer look at ions, see Appendix B. a cation must accompany it or another anion must leave so that electrical neutral- ity will be maintained. Thus, whenever sodium (Na+) ions leave a cell, potassium cations (CAT-eye-uns): positively charged ions. (K+) ions enter, for example. In fact, it’s a good bet that whenever Na+ and K+ ions anions (AN-eye-uns): negatively charged ions. are moving, they are going in opposite directions. Table 12-4 (p. 404) shows that, indeed, the positive and negative charges inside electrolytes: salts that dissolve in water and dissociate into charged particles called ions. and outside cells are perfectly balanced even though the numbers of each kind of electrolyte solutions: solutions that can ion differ over a wide range. Inside the cells, the positive charges total 202 and the conduct electricity. negative charges balance these perfectly. Outside the cells, the amounts and pro- milliequivalents (mEq): the concentration portions of the ions differ from those inside, but again the positive and negative of electrolytes in a volume of solution. charges balance. (Scientists count these charges in milliequivalents, mEq.) Milliequivalents are a useful measure when considering ions because the number of Electrolytes Attract Water Electrolytes attract water. Each water molecule has a net charges reveals characteristics about the charge of zero, ◆ but the oxygen side of the molecule has a slight negative charge, solution that are not evident when the and the hydrogens have a slight positive charge. Figure 12-4 (p. 404) shows the result concentration is expressed in terms of in an electrolyte solution: both positive and negative ions attract clusters of water weight. 404 CHAPTER 12 TABLE 12-4 Important Body Electrolytes Intracellular Extracellular (inside cells) (outside cells) Concentration Concentration Electrolytes (mEq/L) (mEq/L) Cations (positively charged ions) Sodium (Na) 10 142 Potassium (K) 150 5 Calcium (Ca) 2 5 Magnesium (Mg) 40 3 202 155 Anions (negatively charged ions) Chloride (Cl) 2 103 Bicarbonate (HCO3) 10 27 Phosphate (HPO4) 103 2 Sulfate (SO4) 20 1 Organic acids (lactate, pyruvate) 10 6 Proteins 57 16 202 155 NOTE: The numbers of positive and negative charges in a given fluid are the same. For example, in extracellular fluid, the cations and anions both equal 155 milliequivalents per liter (mEq/L). Of the cations, sodium ions make up 142 mEq/L; and potassium, calcium, and magnesium ions make up the remainder. Of the anions, chloride ions number 103 mEq/L; bicarbonate ions number 27; and the rest are provided by phosphate ions, sulfate ions, organic acids, and protein. molecules around them. This attraction dissolves salts in water and enables the body to move fluids into appropriate compartments. Water Follows Electrolytes As Figure 12-5 shows, some electrolytes reside pri- marily outside the cells (notably, sodium and chloride), whereas others reside pre- ◆ The word ending -ate denotes a salt of the dominantly inside the cells (notably, potassium, magnesium, phosphate, ◆ and mineral. Thus, phosphate is the salt form sulfate). Cell membranes are selectively permeable, meaning that they allow the pas- of the mineral phosphorus, and sulfate is the salt form of sulfur. FIGURE 12-4 Water Dissolves Salts and Follows Electrolytes The structural arrangement of the two hydrogen atoms and one oxygen atom enables water to dissolve salts. Water’s role as a solvent is one of its most valuable characteristics. Cl– Na+ + H + Na+ O H – – Cl– The negatively charged electrons that bond the hydrogens to the oxygen spend most of their time near In an electrolyte solution, water molecules are attracted the oxygen atom. As a result, to both anions and cations. Notice that the negative the oxygen is slightly negative, oxygen atoms of the water molecules are drawn to the and the hydrogens are slightly sodium cation (Na+), whereas the positive hydrogen atoms positive (see Appendix B). of the water molecules are drawn to the chloride ions (Cl–).  WATER AND THE MAJOR MINERALS 405 FIGURE 12-5 A Cell and Its Electrolytes All of these electrolytes are found both inside and outside the cells, but each can be found mostly on one side or the other of the cell membrane. Chemical symbols: K = potassium P = phosphorus Mg = magnesium © Craig M. Moore S = sulfate Outside the cells Cell Na = sodium membrane Cl = chloride When immersed in water, raisins become K plump because water moves toward the higher Mg concentration of sugar inside the raisins. S Na P Cl Within the cell Key: Cations © Craig M. Moore Anions Blood vessel When sprinkled with salt, vegetables “sweat” because water moves toward the higher con- sage of some molecules, but not others. Whenever electrolytes move across the centration of salt outside the eggplant. membrane, water follows. The movement of water across a membrane toward the more concentrated solutes is called osmosis. The amount of pressure needed to prevent the move- ment of water across a membrane is called the osmotic pressure. Figure 12-6 presents osmosis, and the photos of salted eggplant and rehydrated raisins provide familiar examples. Proteins Regulate Flow of Fluids and Ions Chapter 6 described how proteins attract water and help to regulate fluid movement. In addition, transport proteins in FIGURE 12-6 Osmosis Water flows in the direction of the more highly concentrated solution. A B A B A B 1 With equal numbers 2 Now additional solute 3 Water can flow both ways of solute particles on is added to side B. across the divider, but has a solutes (SOLL-yutes): the substances that are both sides of the Solute cannot flow greater tendency to move dissolved in a solution. The number of semipermeable across the divider (in from side A to side B, where molecules in a given volume of fluid is the membrane, the the case of a cell, its there is a greater solute concentration. concentrations are membrane). concentration of solute. The osmosis: the movement of water across a equal, and the tendency volume of water becomes membrane toward the side where the solutes of water to move in greater on side B, and the are more concentrated. either direction is about concentrations on side A and osmotic pressure: the amount of pressure the same. B become equal. needed to prevent the movement of water across a membrane. 406 CHAPTER 12 the cell membranes regulate the passage of positive ions and other substances from one side of the membrane to the other. Negative ions follow positive ions, and wa- ter flows toward the more concentrated solution. A protein that regulates the flow of fluids and ions in and out of cells is the sodium-potassium pump. The pump actively exchanges sodium for potassium across the cell membrane, using ATP as an energy source. Figure 6-10 on p. 192 il- lustrates this action. Regulation of Fluid and Electrolyte Balance The amounts of various miner- als in the body must remain nearly constant. Regulation occurs chiefly at two sites: the GI tract and the kidneys. The digestive juices of the GI tract contain minerals. These minerals and those from foods are reabsorbed in the large intestine as needed. Each day, 8 liters of flu- ids and associated minerals are recycled this way, providing ample opportunity for the regulation of electrolyte balance. The kidneys’ control of the body’s water content by way of the hormone ADH has © Norbert Schaefer/CORBIS already been described (see p. 401). To regulate the electrolyte contents, the kidneys depend on the adrenal glands, which send out messages by way of the hormone al- dosterone (also explained on p. 401). If the body’s sodium is low, aldosterone stim- ulates sodium reabsorption from the kidneys. As sodium is reabsorbed, potassium (another positive ion) is excreted in accordance with the rule that total positive Physically active people must remember to charges must remain in balance with total negative charges. replace their body fluids. Fluid and Electrolyte Imbalance Normally, the body defends itself successfully against fluid and electrolyte imbal- ances. Certain situations and some medications, however, may overwhelm the body’s ability to compensate. Severe, prolonged vomiting and diarrhea as well as heavy sweating, burns, and traumatic wounds may incur such great fluid and electrolyte losses as to precipitate a medical emergency. Different Solutes Lost by Different Routes Different solutes are lost depending on why fluid is lost. If fluid is lost by vomiting or diarrhea, sodium is lost indis- criminately. If the adrenal glands oversecrete aldosterone, as may occur when they develop a tumor, the kidneys may excrete too much potassium. Also, the per- son with uncontrolled diabetes may lose glucose, a solute not normally excreted, and large amounts of fluid with it. Each situation results in dehydration, but drinking water alone cannot restore electrolyte balance. Medical intervention is required. Replacing Lost Fluids and Electrolytes In many cases, people can replace the fluids and minerals lost in sweat or in a temporary bout of diarrhea by drinking plain cool water and eating regular foods. Some cases, however, demand rapid re- placement of fluids and electrolytes—for example, when diarrhea threatens the life of a malnourished child. Caregivers around the world have learned to use simple ◆ Health care workers use oral rehydration formulas ◆ to treat mild-to-moderate cases of diarrhea. These lifesaving formulas do therapy (ORT)—a simple solution of not require hospitalization and can be prepared from ingredients available locally. sugar, salt, and water, taken by mouth—to Caregivers need only learn to measure ingredients carefully and use sanitary water. treat dehydration caused by diarrhea. A Once rehydrated, a person can begin eating foods. simple ORT recipe (cool before giving): 1/2 L boiling water A small handful of sugar (4 tsp) 3 pinches of salt (1/2 tsp) Acid-Base Balance The body uses its ions not only to help maintain fluid and electrolyte balance, but also to regulate the acidity (pH) ◆ of its fluids. The pH scale introduced in ◆ Reminder: pH is the unit of measure Chapter 3 is repeated here, in Figure 12-7, with the normal and abnormal pH expressing a substance’s acidity or ranges of the blood added. As you can see, the body must maintain the pH alkalinity. within a narrow range to avoid life-threatening consequences. Slight deviations in either direction can denature proteins, causing metabolic mayhem. Enzymes  WATER AND THE MAJOR MINERALS 407 FIGURE 12-7 The pH Scale Normal and abnormal pH of common substances pH ranges of blood Basic 14 Concentrated lye Death 8.00 13 12 Alkalosis 11 Household ammonia 10 9 Baking soda 7.45 8 Pancreatic juice Blood Normal pH neutral 7 Water 7.35 Milk 6 Urine 5 Coffee Acidosis 4 Orange juice 3 Vinegar Lemon juice 2 6.8 Gastric juice Death 1 Acidic 0 Battery acid NOTE: Each step is ten times as concentrated in base (1⁄10 as much acid, or H) as the one below it. couldn’t catalyze reactions and hemoglobin couldn’t carry oxygen—to name just two examples. The acidity of the body’s fluids is determined by the concentration of hydrogen ions (H+). ◆ A high concentration of hydrogen ions is very acidic. Normal energy ◆ The lower the pH, the higher the H+ ion metabolism generates hydrogen ions, as well as many other acids, that must be concentration and the stronger the acid. A neutralized. Three systems defend the body against fluctuations in pH—buffers in pH above 7 is alkaline, or base (a solution the blood, respiration in the lungs, and excretion in the kidneys. in which OH– ions predominate). Regulation by the Buffers Bicarbonate ◆ (a base) and carbonic acid (an acid) ◆ Reminder: Bicarbonate is an alkaline com- in the body fluids (as well as some proteins) protect the body against changes in pound with the formula HCO3. It is pro- acidity by acting as buffers—substances that can neutralize acids or bases. Figure duced in all cell fluids from the dissociation 12-8 (p. 408) presents the chemical reactions of this buffer system, which is primar- of carbonic acid to help maintain the ily under the control of the lungs and kidneys. body’s acid-base balance. (Bicarbonate is Carbon dioxide, which is formed all the time during energy metabolism, dis- also secreted from the pancreas during solves in water to form carbonic acid in the blood. Carbonic acid, in turn, dissociates digestion as part of the pancreatic juice.) to form hydrogen ions and bicarbonate ions. The appropriate balance between car- bonic acid and bicarbonate is essential to maintaining optimal blood pH. Regulation in the Lungs The lungs control the concentration of carbonic acid by raising or slowing the respiration rate, depending on whether the pH needs to be in- creased or decreased. If too much carbonic acid builds up, the respiration rate speeds up; this hyperventilation increases the amount of carbon dioxide exhaled, thereby carbonic acid: a compound with the formula H2CO3 that results from the combination of lowering the carbonic acid concentration and restoring homeostasis. Conversely, if carbon dioxide (CO2) and water (H2O); of bicarbonate builds up, the respiration rate slows; carbon dioxide is retained and particular importance in maintaining the forms more carbonic acid. Again, homeostasis is restored. body’s acid-base balance. 408 CHAPTER 12 FIGURE 12-8 Bicarbonate-Carbonic Acid Buffer System The reversible reactions of the bicarbonate-carbonic acid buffer system help to reg- ulate the body’s pH. Recall from Chapter 7 that carbon dioxide and water are formed during energy metabolism. Carbon dioxide (CO2) is a volatile gas that quickly dissolves in water (H2O), forming carbonic acid (H2CO3): CO2 + H2O H2CO3 carbon dioxide + water carbonic acid Carbonic –acid readily dissociates to a hydrogen ion (H+) and a bicarbonate ion (HCO3): – H2CO3 H+ + HCO3 carbonic acid hydrogen ion + bicarbonate ion Regulation in the Kidneys The kidneys control the concentration of bicarbonate by either reabsorbing or excreting it, depending on whether the pH needs to be in- creased or decreased, respectively. Their work is complex, but the net effect is easy to sum up. The body’s total acid burden remains nearly constant; the acidity of the urine fluctuates to accommodate that balance. IN SUMMARY Electrolytes (charged minerals) in the fluids help distribute the fluids inside and outside the cells, thus ensuring the appropriate water balance and acid- base balance to support all life processes. Excessive losses of fluids and elec- trolytes upset these balances, and the kidneys play a key role in restoring homeostasis. The Minerals—An Overview Figure 12-9 (p. 409) shows the amounts of the major minerals found in the body and, for comparison, some of the trace minerals. The distinction between the major and trace minerals does not mean that one group is more important than the other—all minerals are vital. The major minerals are so named because they are present, and needed, in larger amounts in the body. They are shown at the top of the figure and are discussed in this chapter. The trace minerals (shown at the bottom) are discussed in Chapter 13. A few generalizations pertain to all of the minerals and distinguish them from the vitamins. Especially notable is their chemical nature. Inorganic Elements Unlike the organic vitamins, which are easily destroyed, ◆ Reminder: An inorganic substance does not minerals are inorganic elements ◆ that always retain their chemical identity. contain carbon. Once minerals enter the body proper, they remain there until excreted; they can- not be changed into anything else. Iron, for example, may temporarily combine with other charged elements in salts, but it is always iron. Neither can minerals be destroyed by heat, air, acid, or mixing. Consequently, little care is needed to pre- serve minerals during food preparation. In fact, the ash that remains when a food major minerals: essential mineral nutrients is burned contains all the minerals that were in the food originally. Minerals can found in the human body in amounts larger be lost from food only when they leach into cooking water that is then poured than 5 g; sometimes called macrominerals. down the drain.  WATER AND THE MAJOR MINERALS 409 FIGURE 12-9 Minerals in a 60-kilogram (132-pound) Human Body Not only are the major minerals present in the body in larger amounts than the trace minerals, but they are also needed by the body in larger amounts. Recommended intakes for the major minerals are stated in hundreds of milligrams or grams, whereas those for the trace minerals are listed in tens of milligrams or even micrograms. Calcium 1150 Phosphorus 600 Potassium 210 MAJOR MINERALS Sulfur 150 The major minerals are those present in amounts Sodium 90 larger than 5 g (a teaspoon). A pound is about Chloride 90 454 g; thus only calcium and phosphorus appear in amounts larger than a pound. Magnesium 30 Iron 2.4 Zinc 2.0 Copper 0.09 TRACE MINERALS There are more than a dozen trace minerals, Manganese 0.02 although only six are shown here. Iodine 0.02 Selenium 0.02 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 Amount (g) The Body’s Handling of Minerals The minerals also differ from the vitamins in the amounts the body can absorb and in the extent to which they must be specially handled. Some minerals, such as potassium, are easily absorbed into the blood, transported freely, and readily excreted by the kidneys, much like the water-soluble vitamins. Other minerals, such as calcium, are more like fat-solu- ble vitamins in that they must have carriers to be absorbed and transported. And, like some of the fat-soluble vitamins, minerals taken in excess can be toxic. Variable Bioavailability The bioavailability ◆ of minerals varies. Some foods ◆ Reminder: Bioavailability refers to the rate at contain binders that combine chemically with minerals, preventing their ab- and the extent to which a nutrient is sorption and carrying them out of the body with other wastes. Examples of absorbed and used. binders include phytates, which are found primarily in legumes and grains, and oxalates, which are present in rhubarb and spinach, among other foods. These foods contain more minerals than the body actually receives for use. Nutrient Interactions Chapter 10 described how the presence or absence of one vitamin can affect another’s absorption, metabolism, and excretion. The same is true of the minerals. The interactions between sodium and calcium, for example, cause both to be excreted when sodium intakes are high. Phosphorus binds with magnesium in the GI tract, so magnesium absorption is limited when phosphorus intakes are high. These are just two examples of the interac- tions involving minerals featured in this chapter. Discussions in both this chap- ter and the next point out additional problems that arise from such interactions. Notice how often they reflect an excess of one mineral creating an inadequacy of another and how supplements—not foods—are most often to ◆ Key fluid balance nutrients: blame. Sodium, potassium, chloride Varied Roles Although all the major minerals help to maintain the body’s fluid balance as described earlier, sodium, chloride, and potassium are most noted for binders: chemical compounds in foods that combine with nutrients (especially minerals) that role.◆ For this reason, these three minerals are discussed first here. Later sec- to form complexes the body cannot absorb. tions describe the minerals most noted for their roles in bone growth and Examples include phytates (FYE-tates) and health—calcium, phosphorus, and magnesium. oxalates (OCK-sa-lates). 410 CHAPTER 12 IN SUMMARY The major minerals are found in larger quantities in the body, whereas the trace minerals occur in smaller amounts. Minerals are inorganic elements that retain their chemical identities. They usually receive special handling and regulation in the body, and they may bind with other substances or inter- act with other minerals, thus limiting their absorption. Sodium People have held salt (sodium chloride) in high regard throughout recorded his- tory. We describe someone we admire as “the salt of the earth” and someone we consider worthless as “not worth their salt.” Even the word salary comes from the Latin word for salt. Cultures vary in their use of salt, but most people find its taste innately appeal- ing. Salt brings its own tangy taste and enhances other flavors, most likely by sup- pressing the bitter flavors. You can taste this effect for yourself: tonic water with its bitter quinine tastes sweeter with a little salt added. Sodium Roles in the Body Sodium is the principal cation of the extracellular fluid and the primary regulator of its volume. Sodium also helps maintain acid-base balance and is essential to nerve impulse transmission and muscle contraction.* Sodium is readily absorbed by the intestinal tract and travels freely in the blood un- til it reaches the kidneys, which filter all the sodium out of the blood. Then, with great precision, the kidneys return to the bloodstream the exact amount of sodium the body needs. Normally, the amount excreted is approximately equal to the amount ingested on a given day. When blood sodium rises, as when a person eats salted foods, thirst signals the person to drink until the appropriate sodium-to-water ratio is restored. Then the kidneys excrete both the excess water and the excess sodium together. Sodium Recommendations Diets rarely lack sodium, and even when intakes are low, the body adapts by reducing sodium losses in urine and sweat, thus making deficiencies unlikely. Sodium recommendations ◆ are set low enough to protect ◆ AI for sodium: against high blood pressure, but high enough to allow an adequate intake of other 1500 mg/day (19–50 yr) nutrients with a typical diet. Because high sodium intakes correlate with high blood 1300 mg/day (51–70 yr) pressure, the Upper Level for adults is set at 2300 milligrams per day, slightly lower 1200 mg/day (70 yr) than the Daily Value used on food labels (2400 milligrams). The average sodium in- take for adults in the United States exceeds the Upper Level—and most adults will develop hypertension at some point in their lives. Sodium and Hypertension For years, a high sodium intake was considered the primary factor responsible for high blood pressure. Then research pointed to salt (sodium chloride) as the dietary culprit. Salt has a greater effect on blood pressure than either sodium or chloride alone or in combination with other ions. For some individuals, blood pressure increases in response to excesses in salt intake. People most likely to have a salt sensitivity include those whose parents had high blood pressure, those with chronic kidney disease or diabetes, African Americans, and people over 50 years of age.† Overweight people also appear to be particularly sensi- tive to the effect of salt on blood pressure. For them, a high salt intake correlates strongly with heart disease, and salt restriction helps to lower their blood pressure. sodium: the principal cation in the In fact, a salt-restricted diet lowers blood pressure in people without hyperten- extracellular fluids of the body; critical to the sion as well. Because reducing salt intake causes no harm and diminishes the risk maintenance of fluid balance, nerve impulse transmissions, and muscle contractions. salt sensitivity: a characteristic of individuals who respond to a high salt intake with an * One of the ways the kidneys regulate acid-base balance is by excreting hydrogen ions (H+) in exchange increase in blood pressure or to a low salt for sodium ions (Na+). † Compared with others, salt-sensitive individuals have elevated concentrations of renin in their blood. intake with a decrease in blood pressure.  WATER AND THE MAJOR MINERALS 411 Dietary Guidelines for Americans 2005 ◆ Salt (sodium chloride) is about 40% Consume less than 2300 mg (approximately 1 tsp of salt) of sodium per sodium. day. 1 g salt contributes 400 mg sodium 5 g salt = 1 tsp 1 tsp salt contributes 2000 mg sodium of hypertension and heart disease, the 2005 Dietary Guidelines advise limiting daily salt intake to about 1 teaspoon ◆ (the equivalent of 2.3 grams or 2300 milligrams of sodium). Higher intakes seem to be well tolerated in most healthy people, how- ever. The accompanying “How to” offers strategies for cutting salt (and therefore sodium) intake. One diet plan, known as the DASH (Dietary Approaches to Stop Hypertension) diet, also lowers blood pressure. The DASH approach emphasizes fruits, vegetables, and low-fat milk products; includes whole grains, nuts, poultry, and fish; and calls for reduced intakes of red meat, butter, and other high-fat foods. The DASH diet in combination with a reduced sodium intake is even more effective in lowering blood pressure than either strategy alone. Chapter 27 offers a complete discussion of hy- pertension and the dietary recommendations for its prevention and treatment. Sodium and Bone Loss (Osteoporosis) A high salt intake is also associated with increased calcium excretion, but its influence on bone loss is less clear.9 In ad- dition, potassium may prevent the increase in calcium excretion caused by a high- salt diet.10 For these reasons, dietary advice to prevent bone loss parallel those suggested for hypertension—a DASH diet that is low in sodium and abundant in potassium-rich fruits and vegetables and calcium-rich low-fat milk products.11 Sodium in Foods In general, processed foods have the most sodium, whereas un- processed foods such as fresh fruits, vegetables, milk, and meats have the least. In fact, as much as 75 percent of the sodium in people’s diets comes from salt added to foods by manufacturers; about 15 percent comes from salt added during cooking and at the table; and only 10 percent comes from the natural content in foods. HOW TO Cut Salt (and Sodium) Intake Most people eat more salt (and therefore Select low-salt or salt-free products when sodium) than they need. Some people can available. lower their blood pressure by avoiding Use these foods sparingly: highly salted foods and removing the salt- shaker from the table. Foods eaten without Foods prepared in brine, such as pickles, salt may seem less tasty at first, but with olives, and sauerkraut repetition, people can learn to enjoy the Salty or smoked meats, such as bologna, natural flavors of many unsalted foods. corned or chipped beef, bacon, frank- Strategies to cut salt intake include: furters, ham, lunch meats, salt pork, sausage, and smoked tongue Select fresh, unprocessed foods. Cook with little or no added salt. Salty or smoked fish, such as anchovies, caviar, salted and dried cod, herring, Prepare foods with sodium-free spices sardines, and smoked salmon such as basil, bay leaves, curry, garlic, ginger, mint, oregano, pepper, rosemary, Snack items such as potato chips, pret- and thyme; lemon juice; vinegar; or zels, salted popcorn, salted nuts, and © BSIP Agency/Index Stock Imagery wine. crackers Add little or no salt at the table; taste Condiments such as bouillon cubes; foods before adding salt. seasoned salts; MSG; soy, teriyaki, Worcestershire, and barbeque sauces; Read labels with an eye open for sodium. prepared horseradish, catsup, and (See the glossary on p. 58 for terms used mustard to describe the sodium contents of foods on labels.) Cheeses, especially processed types Canned and instant soups Fresh herbs add flavor to a recipe without adding salt. 412 CHAPTER 12 Because processed foods may contain sodium without chloride, as in additives such as sodium bicarbonate or sodium saccharin, they do not always taste salty. Most people are surprised to learn that 1 ounce of cornflakes contains more sodium than 1 ounce of salted peanuts—and that 1/2 cup of instant chocolate pudding con- tains still more. (The peanuts taste saltier because the salt is all on the surface, where the tongue’s sensors immediately pick it up.) Figure 12-10 shows that processed foods not only contain more sodium than their less processed counterparts but also have less potassium. Low potassium may be as significant as high sodium when it comes to blood pressure regulation, so processed foods have two strikes against them. Dietary Guidelines for Americans 2005 Choose and prepare foods with little salt. At the same time, consume potassium-rich foods, such as fruits and vegetables. Sodium Deficiency If blood sodium drops, as may occur with vomiting, diarrhea, or heavy sweating, both sodium and water must be replenished. Under normal con- ditions of sweating due to physical activity, salt losses can easily be replaced later in the day with ordinary foods. Salt tablets are not recommended because too much salt, especially if taken with too little water, can induce dehydration. During intense activities, such as ultra-endurance events, athletes can lose so much sodium and drink so much water that they develop hyponatremia—the dangerous condition of having too little sodium in the blood. FIGURE 12-10 What Processing Does to the Sodium and Potassium Contents of Foods People who eat foods high in salt often happen to be eating fewer potassium-containing foods at the same time. Notice how potassium is lost and sodium is gained as foods become more processed, causing the potassium-to-sodium ratio to fall dramatically. Even when potassium isn’t lost, the addition of sodium still lowers the potassium-to-sodium ratio. Limiting sodium intake may help in two ways, then—by lowering blood pressure in salt-sensitive individuals and by indirectly raising potassium intakes in all individuals. Milks Meats Vegetables Fruits Grains Milk (whole) Roast beef Fresh corn Fresh Rolled oats peaches Unprocessed Processed Matthew Farrugio (all) Key: Potassium Sodium Instant chocolate Chipped beef Canned Peach pie Oat cereal pudding cream corn  WATER AND THE MAJOR MINERALS 413 Sodium Toxicity and Excessive Intakes The immediate symptoms of acute sodium toxicity are edema and hypertension, but such toxicity poses no problem as long as water needs are met. Prolonged excessive sodium intake ◆ may contribute ◆ UL for sodium: 2300 mg/day to hypertension in some people, as explained earlier. IN SUMMARY Sodium is the main cation outside cells and one of the primary electrolytes re- sponsible for maintaining fluid balance. Dietary deficiency is rare, and ex- cesses may aggravate hypertension in some people. For this reason, health professionals advise a diet moderate in salt and sodium. The accompanying table summarizes information about sodium. Sodium Adequate Intake (AI) Deficiency Symptoms Adults: 1500 mg/day (19–50 yr) Muscle cramps, mental apathy, loss of appetite 1300 mg/day (51–70 yr) 1200 mg/day (>70 yr) Toxicity Symptoms Upper Level Edema, acute hypertension Adults: 2300 mg/day Significant Sources Chief Functions in the Body Table salt, soy sauce; moderate amounts in meats, milks, breads, and vegetables; large Maintains normal fluid and electrolyte balance; amounts in processed foods assists in nerve impulse transmission and muscle contraction Chloride The element chlorine (Cl2) is a poisonous gas. When chlorine reacts with sodium or hydrogen, however, it forms the negative chloride ion (Cl–). Chloride, an essential nu- trient, is required in the diet. Chloride Roles in the Body Chloride is the major anion of the extracellular fluids (outside the cells), where it occurs mostly in association with sodium. Chloride moves passively across membranes through channels and so also associates with potassium inside cells. Like sodium and potassium, chloride maintains fluid and electrolyte balance. In the stomach, the chloride ion is part of hydrochloric acid, which maintains the strong acidity of the gastric juice. One of the most serious consequences of vomiting is the loss of this acid ◆ from the stomach, which upsets the acid-base balance.* Such ◆ Reminder: The loss of acid can lead to alka- losis, an above-normal alkalinity in the imbalances are commonly seen in bulimia nervosa, as described in Highlight 8. blood and body fluids. Chloride Recommendations and Intakes Chloride is abundant in foods (es- pecially processed foods) as part of sodium chloride and other salts. Because the pro- portion of chloride in salt is greater than sodium, ◆ chloride recommendations are ◆ Salt (sodium chloride) is about 60% slightly higher than, but still equivalent to, those of sodium. In other words, 3/4 tea- chloride. spoon of salt will deliver some sodium, more chloride, and still meet the AI for both. 1 g salt contributes 600 mg chloride 5 g salt = 1 tsp Chloride Deficiency and Toxicity Diets rarely lack chloride. Chloride losses may 1 tsp salt contributes 3000 mg chloride occur in conditions such as heavy sweating, chronic diarrhea, and vomiting. The only known cause of high blood chloride concentrations is dehydration due to chloride (KLO-ride): the major anion in the * Hydrochloric acid secretion into the stomach involves the addition of bicarbonate ions (base) to the extracellular fluids of the body. Chloride is plasma. These bicarbonate ions (HCO + 3 ) are neutralized by hydrogen ions (H ) from the gastric secretions that are reabsorbed into the plasma. When hydrochloric acid is lost during vomiting, these hydrogen ions the ionic form of chlorine, Cl. See Appendix are no longer available for reabsorption, and so, in effect, the concentrations of bicarbonate ions in the B for a description of the plasma are increased. In this way, excessive vomi