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Chapter 9- Water and Minerals Water Water acts as a solvent- it dissolves many body compounds such as sodium chloride (table salt) Water is the perfect medium for body processes because it enables chemical reactions to occur Forms the greatest component of the human body, making up 50% to 70% of the body’s weight (about 10 gallons) Lean muscle tissue contains about 73% water Adipose tissue is about 20% water An adult can survive for about 8 weeks without eating food but only a few days without drinking water WATER IN THE BODY-INTRACELLULAR AND EXTRACELLULAR FLUID Water inside cells forms part of the intracellular fluid (fluid within the cell) When water is outside cells or in the bloodstream, it is part of the extra cellular fluid (the outside cells) Water shifts freely in and out of cells If blood volume decreases, water can move from the areas inside and around cells to the bloodstream to increase blood volume Blood volume increases, water can shift out of the bloodstream into c3ells and the surrounding areas, leaving to edema The body controls the amount of water in the intracellular and extra cellular compartments mainly by controlling ion concentrations Ions are minerals that have electrical charges, and so are called electrolytes Water is attracted to sodium, potassium, chloride, phosphate, magnesium and calcium By controlling the movements of ions in and out of the cellular compartments The body maintains the appropriate amount of water in each compartment using a process called osmosis Overall, where ions go, water follows WATER CONTRIBUTES TO BODY TEMPERATURE REGULATION Water temperature changes slowly because it has a great ability to hold head When overheated, the body secretes fluids in the form of perspiration, which evaporates through skin pores To evaporate water, heat energy is required As perspiration evaporates, heat energy is taken from the skin, cooking it in the process About 60% of the chemical energy in food is turned directly into body heat the other 40% is converted to forms of energy cells can use, and almost all of that energy eventually leaves the body in the form of heat if this heat could not be dissipated, the body temperature would rise enough to prevent enzyme systems from functioning efficiently perspiration is the primary way to prevent this rise in body temperature too cool efficiently, perspiration must be allowed to evaporate evaporation of perspiration occurs quickly when humidity is low this is why humans can cool off and therefore tolerate hot, dry climates far better than they do not, humid climates WATER HELPS REMOVE WASTE PRODUCTS water is an important vehicle for transporting waste products from the body most unusable substances in the body can dissolve in water and exit the body through the urine urea is a major body waste product this by-product of protein metabolism contains nitrogen the more protein we eat the more nitrogen we excrete-in the form of urea-in the urine likewise the more sodium we consume, the more sodium we excrete in the urine the amount of urine a person needs to produce is determined primarily by excess protein and salt intake a typical urine volume is about 1 liter or more per day a somewhat greater urine output than that is fine, but less (especially less than 500 mL) forces the kidneys to form very concentrated urine the simplest way to determine if water intake is adequate is to observe the color of one’s urine whereas urine should be clear or pale yellow, concentrated urine is very dark yellow in color the heavy ion concentration in turn increases the risk of kidney stone formation in susceptible people kidney stones are formed from minerals and other substances that have precipitated out of the urine and accumulated in kidney tissues HOW MUCH WATER DO WE NEED PER DAY the adequate intake for total water intake is 2.7 liters for adult women and 3.7 liters for adult men coffee, tea, and soft drinks often contain caffeine, which increases urine output much of the water needed is used to produce urine thirst mechanism can lag behind actual water loss, however, during prolonged exercise and illness, as well as in one’s older years athletes especially should monitor fluid status once the body registers a shortage of available water, it increases fluid conservation 2 hormones that participate in this process are antidiuretic hormone and aldosterone Antidiuretic hormone to force the kidneys to conserve water Aldosterone, which signals the kidneys to retain more sodium and, in turn, more water By the time a person loses 1-2% of body weight in fluids, he or she will be thirsty At a 4% loss of body weight, muscles lose significant strength and endurance At a 20% reduction, coma and death may soon follow Too much water can also lead to ill health, such as low blood electrolyte concentrations Blurred vision is one resulting symptom Minerals- An Overview Some minerals work as cofactors, which enable enzymes to function. They also contribute too many body compounds (iron is a component of red blood cells). Sodium, potassium, and calcium aid in the transfer of nerve impulses throughout the body. Body growth and development also depend on certain minerals (calcium). Water balance requires sodium, potassium, calcium, and phosphorus. If we require greater than 100 milligrams of a mineral per day, it is considered a major mineral; otherwise, it is considered a trace mineral. Mineral Bioavailability The concept of absorbing variable amounts of a nutrient from food sources is called bioavailability. Overall, minerals from animal products are better absorbed than those from plants because binders and fiber are not present to hinder absorption. The mineral content of plants greatly depends on mineral concentrations of the soil in which they are grown. The more refined a plant food, like white flour, the lower its content of minerals. Oxalic acid (oxalate): an organic acid found in spinach, rhubarb, and other leafy green vegetables that can depress the absorption of certain minerals present in the food, such as calcium. Phylate: components of fiber that limits the absorption of some minerals by binding to them. Mineral toxicities An excessive mineral intake can have toxic results, especially with the trace minerals, such as iron and copper. Supplements pose the biggest threat for mineral toxicity because they exceed current standards for mineral needs, especially those that supply more than 100% of the daily values. Sodium: The body absorbs almost all the sodium that gets eaten. It is the major ion in extra cellular fluid and a key factor in retaining body water. Only when weight loss from sweat is over 2-3% of the total body weight (5 or 6 pounds) should sodium losses raise concern. Salting foods is sufficient in restoring body sodium for most people. The more processed and restaurant food one consumes, generally the higher the sodium intake. The daily value for sodium is 2300 milligrams. Potassium: it performs many of the same functions as sodium (fluid balance and nerve impulse transmission). The difference is it operates inside, rather than outside of the cells. Intracellular fluids contain 95 % of the potassium in the body. Low blood potassium is a life threatening problem, causing heart beat irregularity, decreasing the blood pumping capacity. Major contributors to the diet include: milk, potatoes, beef, coffee, tomatoes, and orange juice. Adequate intake is about 4700 milligrams. Taking diuretics can deplete the body’s potassium (caffeine in coffee). Chloride: a component of the acid produced in the stomach. They are used during immune responses as white blood cells attack foreign cells. We consume most chloride as salt added to foods. Calcium: More than 99% of the calcium in the body is used to strengthen bones and teeth. This calcium represents 40% of all the minerals present in the body. The calcium circulating in the bloodstream supplies the calcium needs of body cells. The amount of calcium in the body depends greatly on its absorption from the diet. It requires an acidic environment in the intestinal tract to be absorbed efficiently (it is absorbed in the upper level of the tract, where stomach acid lingers primarily). Adults absorb about 25% of the calcium in the foods eaten, but during time when the body needs extra calcium (infancy and pregnancy), absorption increases to as high as 60%. Factors enhancing calcium absorption: A. the blood levels of parathyroid hormone. B. the presence of glucose and lactose in the diet. C. the flow of digestive contents through the intestine. What limits calcium absorption? A. acid in fiber from grains. B. excess phosphorus in the diet. C. polyphenols in tea D. vitamin D deficiency E. diarrhea F. old age We have excellent hormonal systems to control blood calcium levels, so a normal value can be maintained despite an inadequate calcium intake, but the bones pay the price…they are the calcium bank that can be added or withdrawn. The bone loss caused from low calcium absorption from the bank proceeds slowly. By not meeting calcium needs, people (especially women) are setting the stage for future bone fractures. Functions of calcium: 1. blood clotting and muscle contraction: if blood calcium falls below a critical point, muscles cannot relax after contraction. The body stiffens and shows involuntary twitching. 2. Nerve transmission: calcium assists the flow of neurotransmitters to prevent nerve function failure. 3. Cellular metabolism regulation: enzyme and hormone activity helps to aid cellular metabolism. The lack of calcium to perform any of these is called TETANY. Calcium also reduces colon cancer risk and lowers LDL cholesterol. Calcium sources 75% of the calcium in North American diets is from dairy products. (The exception is cottage cheese: calcium is lost during production). If you don’t like dairy, use leafy greens, broccoli, sardines, salmon, fortified OJ and breakfast cereals. The most nutrient-dense source of calcium is nonfat milk. The adequate intake for calcium is 1000-1200 milligrams per day; while upper levels are 2500 milligrams (greater intake increases the risk for some forms of kidney stones People who do not like milk will take calcium supplements. Calcium carbonate is the most common supplement used (calcium based antacid tablets). There is some evidence that calcium supplementation may decrease zinc absorption. Food sources are the best choice for absorption. Yogurt is the highest food source of calcium. Osteoporosis- loss of bone calcium. High risks for this include a poor dietary intake of calcium. There are 1.5 million bone fractures per year in the U.S., usually in the hip, spine, or wrist. The slender inactive woman who smokes is most susceptible to osteoporosis. There are 2 primary bone structure types: A. cortical bone: dense, compact bone that comprises the outer surface and shafts of bone, also called compact bone. B. trabecular bone: spongy inner bone found in the spine, pelvis, and ends of bones, especially in heavily stressed areas, such as joints. Bone mass strength depends on bone mass and bone mineral density. The more bone there is, and the more densely packed bone crystals there are in the bone, the stronger the bone structure. The ultimate amount of bone built by a person is clearly dependent on gender, race, and family patterns. There is also a genetic pattern of the degree of calcium absorption. Men have higher bone mass than women, and blacks have heavier skeletons than whites Bone loss begins at age 30 and proceeds slowly to menopause (around 50), and then it speeds up. Osteoporosis prevention involves 3 main elements -meeting calcium needs -since the hormones of regular menstruation contribute to bone maintenance in young women, any sign of menstrual irregularities is reason to see a doctor. -an active lifestyle that includes weight bearing activity. 99% of calcium in the body is found in bones. Phosphorous The body absorbs phosphorus quite efficiently. About 85% of the body’s phosphorus is inside bone (provided by milk, cheese, meat, and bread). Vitamin D enhances phosphorus absorption (the same for calcium). Phosphorus is a component of enzymes, DNA (genetic material), and compounds of energy metabolism. Magnesium _important for nerve and heart function and aids many enzyme reactions. Rich sources for magnesium are plant products, such as whole grains. The refined grain products that dominate the diets of many North Americans are poor sources of this mineral. Milk, meat, coffee, broccoli, potatoes, squash, beans, nuts, and seeds are good sources of magnesium. Sulfur Sulfur helps in the balance of acids and bases in the body and is an important part of the liver’s drug detoxifying pathways. It is usually supplied by proteins Trace Minerals Trace minerals are also called micro minerals Although we need 100 milligrams or less of each trace mineral daily, they are just as essential to good health as are major minerals Evidence of trace minerals is still unfolding 1961 researchers linked dwarfism in middle eastern villagers to a zinc deficiency IRON (FE) iron deficiency is still one of the most common nutrient deficiencies worldwide iron is the only nutrient for which young women have a greater RDA than do adult men the body uses several mechanisms to regulate iron absorption controlling absorption is important because our bodies cannot easily eliminate excess iron once it is absorbed overall, iron absorption depends on its form in the food, the body’s need for it, and a variety of other factors the form of iron in foods especially influences how much is absorbed about 40% of the total iron in animal flesh is in the form of hemoglobin and myoglobin the heme iron is absorbed about two or three times more efficiently than the simple elemental iron, called nonheme iron consuming heme iron and nonheme iron together increases nonheme iron absorption overall, eating meat with vegetables and grain products enhances the absorption of all nonheme iron present vitamin C in amounts of about 75 milligrams can increase nonheme iron absorption so one should consider drinking a glass of orange juice when taking an iron supplement overall, the most important factor influencing nonheme iron absorption is the body’s need for it iron needs are increase during pregnancy and growth at high altitudes, the lower oxygen concentration of the air causes an increase in the hemoglobin concentration of blood and thus an increase in iron needs FUNCTIONS OF IRON iron is part of the hemoglobin in red blood cells and myoglobin in muscle cells if neither the diet nor body stores can supply the iron needed for hemoglobin synthesis, the number of red blood cells decreases in the bloodstream physicians use both the percentage of red blood cells (called hematocrit) and the hemoglobin concentration to asses iron status when hematocrit and hemoglobin fall, an iron deficiency is suspected in severe deficiency, hemoglobin and hematocrit fall so low that the amount of oxygen carried in the bloodstream is decreased such a person has anemia, defined as a decreased oxygen-carrying capacity of the blood while there are many types of anemia, iron-deficiency anemia is the major type worldwide women are also very vulnerable during childbearing years from blood loss during menstruation SOURCES animal sources contain some heme iron, the most bioavailable form the major iron sources in the adult diet are ready-to-eat breakfast cereals, animal products and bakery items, such as bread milk is a very poor source of iron a common cause of iron-deficiency anemia in children is an over reliance on milk, coupled with an insufficient meat intake total vegetarians (vegans) are particularly susceptible to iron-deficiency anemia because of their lack of dietary heme iron the higher RDA for young and middle-age women is primarily because of menstrual blood loss UPPER LEVEL FOR IRON the upper level for iron is 45 milligrams per day although iron overload is not as common as iron deficiency, it can be a serious result of misuse because it can easily build up in the body and lead to toxic symptoms Zinc Most people worldwide rely on cereal grains for their source of protein, and calories, but adequate zinc absorption becomes a problem. Up to 200 enzymes (including the one that aids in metabolizing alcohol), require zinc for optimal activity. Zinc aids in DNA synthesis, protein metabolism, immune function, development of sexual organs, storage, release, and function of insulin, cell membrane structure and function, and it aids in the production of an enzyme that keeps cells from damaging. Animal foods supply almost half of an individual’s zinc intake. Many companies are singing the praises of zinc as a cold remedy. Even though studies showed that cold symptoms went away in half the time, nausea was a side effect, and it showed that there is different bioavailability of zinc, and some zinc pills were more potent. Selenium Its best role is aiding the activity of the enzyme that participates in reducing the damage that free radicals do to cell membranes. Vitamin E works together with selenium by donating electrons to electron seeking compounds. Selenium deficiency symptoms include muscle pain and certain form of heart damage. Sources are fish, organ meats, eggs, and shellfish Chromium It aids in the action of the hormone insulin, and the maintenance of glucose uptake into cells (a major prevention of diabetes). A deficiency is characterized by impaired blood glucose control and elevated blood cholesterol and triglycerides. Egg yolks, whole grains, organ meats, mushrooms, nuts, and beer are good sources.
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