Topic 31 - 36 - Principle of Nutrition in Health PDF

1  SUB-TOPICS Nutrition in nursing Carbohydrate Proteins Lipids Sumathy Vitamins Water and minerals Energy balance Guideline for healthy eating Consumer issues Cultural and religious influences on food and nutri...

1  SUB-TOPICS Nutrition in nursing Carbohydrate Proteins Lipids Sumathy Vitamins Water and minerals Energy balance Guideline for healthy eating Consumer issues Cultural and religious influences on food and nutrition Healthy eating for healthy babies Nutrition for infants, children and adolescents Nutrition for older adults 2 3  INTRODUCTION Carbohydrates are composed of the elements carbon (C), hydrogen (H) and oxygen (O). These three elements occur in the ratio of 1:2:1 or CH2O. Carbohydrates are divided into three groups – monosaccharides, disaccharides and polysaccharides. They have roles as both biological fuels (to supply energy as ATP) and as structural units within cells. Their structure is described as a hydrocarbon chain with attached hydroxyl groups. 4  LEARNING OUTCOMES On successful completion of the lesson, the student will be able to: explain different classes of carbohydrates: monosaccharides, disaccharides and polysaccharides. 5  Monosaccharides Monosaccharides (mono, meaning ‘one’ and sakcharon meaning ‘sugar’) are sugars that in nature cannot be broken down any further. They are also called single or simple sugars. The three types of monosaccharide sugars are glucose, fructose and galactose. They are isomers of each other. (Isomers are compounds that have the same formula but different structures). 6 Monosaccharides (cont.) The formula for glucose, fructose and galactose is C6H12O6, but, as seen above, the structures are different. 7  Monosaccharides (cont.) Glucose Glucose (dextrose or grape sugar) is a very important sugar. It is the main source of energy in cells. Glucose is carried by the bloodstream to individual cells and is thus called ‘blood sugar.’ In the cell, glucose combines with oxygen in a chemical reaction called oxidation, which produces high-energy molecules of adenosine triphosphate (ATP). The ATP molecule provides the energy source for the cell or microbe and its many cellular or microbial activities. 8  Monosaccharides (cont.) Fructose Fructose is a sugar found in fruits and honey; it is the sweetest monosaccharide. It is an important isomer of glucose because, in the absence of glucose, fructose becomes involved in energy – releasing reactions. 9  Monosaccharides (cont.) Galactose Galactose can be synthesized in the human body from glucose. Galactose is not an essential nutrient, which means need not to get it from food to be healthy. Galactose can bind to glucose to make lactose (in breast milk), to lipids to make glycolipids (for example, molecules that constitute blood groups A, B and AB), or to proteins to make glycoproteins (for example, in cell membranes). The main dietary source of galactose is lactose from milk and yogurt, which is digested to galactose and glucose. 10  Disaccharides Sugars do not exist only as monosaccharides. The simplest is the linkage of two monosaccharides to form a disaccharide. The common disaccharides are: 11  Disaccharides (cont.) Sucrose It is made up of the monosaccharides glucose and fructose. In the form of sugar, sucrose is a very important component of the human diet as a sweetener. People with congenital sucrase-isomaltase deficiency (CSID) are sucrose intolerant and cannot digest it well because they are missing the enzyme sucrose-isomaltase. 12  Disaccharidess (cont.) Lactose Lactose or milk sugar, is made up of galactose and glucose. Milk is high in lactose and provides nutrients for infants. In humans, an enzyme known as lactase is responsible for breaking down lactose for digestion. This is particularly important in infants, who need lactase to digest breast milk. Lactose intolerance is a condition characterized by symptoms such as stomach pain, bloating, gas and diarrhea, which are caused by lactose malabsorption. 13  Disaccharides (cont.) Maltose Maltose, also known as malt sugar, is formed from two glucose molecules. Malt is formed when grains soften and grow in water and it is a component of beer, starchy foods like cereal, pasta and potatoes and many sweetened processed foods. In plants, maltose is formed when starch is broken down for food. It is used by germinating seeds in order to grow. 14  Polysaccharides A large number of carbohydrates found in or made by living organisms and microbes are polysaccharides. A polysaccharide is a large molecule made of many smaller monosaccharides bonded together in one long chainlike molecule. There are a vast number of different polysaccharides which occur with the three most abundant being: Starch ─ an energy source obtained from plants Cellulose ─ a structural polysaccharide in plants; when consumed, it acts as a dietary fiber Glycogen ─ a storage form of glucose in the human liver and muscles 15  Polysaccharides (cont.) A polysaccharide is also called a glycan. A polysaccharide can be a homopolysaccharide, in which all the monosaccharides are the same or a heteropolysaccharide in which the monosaccharides vary. A molecule with a straight chain of monosaccharides is called a linear polysaccharide, while a chain that has arms and turns is known as a branched polysaccharide. 16  Polysaccharides (cont.) Starch An energy source from glucose units that are widely obtained from plants. Many starches are cereal grains, bread, pasta, pastries, cookies, potatoes, tapioca, wheat, oats, rye, barely, rice and yams, etc. They are a polysaccharide energy source when digested in the body. 17 Polysaccharides (cont.) Cellulose A structural polysaccharide in plants that when consumed, it acts as a dietary fiber. Cellulose is the most abundant organic molecule on earth, since it is the main component of plant cell walls. It is one of the molecules which gives plant material rigidity and thus provides some of the useful properties of materials that are used by humans, such as wood and paper. Cellulose has a different bonding structure linking adjacent glucose molecules in the polymer as such it is indigestible by humans. The human gut lacks the enzymes necessary to digest cellulose. 18  Polysaccharides (cont.) Glycogen It acts more like a long-term storage option. Glycogen is mainly produced by the liver and muscles, but it can also be made during a process called glycogenesis, which occurs in both the brain and stomach. (refer to previous note) 19 SUMMARY 20  SUMMARY (cont.) Carbohydrates provides energy and regulation of blood glucose. Most of the carbohydrates in the foods are digested and broken down into glucose before entering the bloodstream. Carbohydrates also have other important functions in humans, animals and plants. 21 22  INTRODUCTION Proteins are organic compounds containing the elements carbon, hydrogen, oxygen and nitrogen and most times, phosphorus and sulfur. Proteins are among the most diverse and essential organic compounds found in all living organisms, including microbes. Proteins are found in every part of a living cell. They are found in the nucleus, the cellular organelles and in the cell membrane. 23 24  LEARNING OUTCOMES On successful completion of the lesson, the student will be able to: explain the categories of amino acids; identify the components of enzyme; explain the function of enzyme. 25  DESCRIPTION Proteins are large polymers of amino acids. There are twenty-two different amino acids that can be combined in any number and sequence to makeup the various kinds of proteins. Amino acids are categorized as essential or nonessential. 26  Amino Acids Essential amino acids They are those that cannot be manufactured in the body and must be supplied as part of the protein ingested in the diet. Nine essential amino acids are necessary for tissue growth and maintenance. 27  Amino Acids (cont.) Essential amino acids (cont.) Phenylalanine: It is a precursor for the neurotransmitters tyrosine, dopamine, epinephrine and norepinephrine. It plays an integral role in the structure and function of proteins and enzymes and the production of other amino acids. Valine: It is one of three branched-chain amino acids, meaning it has a chain branching off to one side of its molecular structure. Valine helps stimulate muscle growth and regeneration and is involved in energy production. 28  Amino Acids (cont.) Essential amino acids (cont.) Threonine: It is a principal part of structural proteins such as collagen and elastin, which are important components of the skin and connective tissue. It also plays a role in fat metabolism and immune function. Tryptophan: Though often associated with causing drowsiness, tryptophan has many other functions. It’s needed to maintain proper nitrogen balance and is a precursor to serotonin, a neurotransmitter that regulates your appetite, sleep and mood. 29  Amino Acids (cont.) Essential amino acids (cont.) Methionine: It plays an important role in metabolism and detoxification. It’s also necessary for tissue growth and the absorption of zinc and selenium, minerals that are vital to your health. Leucine: Like valine, leucine is a branched-chain amino acid that is critical for protein synthesis and muscle repair. It also helps regulate blood sugar levels, stimulates wound healing and produces growth hormones. Isoleucine: The last of the three branched-chain amino acids, isoleucine is involved in muscle metabolism and is heavily concentrated in muscle tissue. It is also important for immune function, hemoglobin production and energy regulation. 30  Amino Acids (cont.) Essential amino acids (cont.) Lysine: It plays major roles in protein synthesis, hormone and enzyme production and the absorption of calcium. It is also important for energy production, immune function and the production of collagen and elastin. Histidine: It is used to produce histamine, a neurotransmitter that is vital to immune response, digestion, sexual function and sleep-wake cycles. It is critical for maintaining the myelin sheath, a protective barrier that surrounds your nerve cells. 31  Amino Acids (cont.) Nonessential amino acids They are those that the body can manufactured. The body takes apart amino acids derived from the diet and reconstructs new ones from their basic elements (carbohydrates and nitrogen). 32  Amino Acids (cont.) Nonessential amino acids (cont.) Activity: Find out the function of Nonessential Amino Acids 33  Amino Acids (cont.) Large protein molecules are constructed from any number and sequence of these amino acids. The quantity of amino acids in any given protein molecule can number from 300 to several thousand. A series of amino acids linked together in fashion is called a polypeptide. Polypeptides with a biological function are commonly referred to as proteins. Proteins can have several structures. 34  Amino Acids (cont.) The primary protein structure is a sequence of amino acids in a single chain. Most polypeptides twist into a spiral shape called a helix. These proteins are known as secondary protein structures. Fibrous proteins such as hair and nails are secondary protein structures. When the long coil becomes folded and twisted, the characteristic three-dimensional tertiary protein structure is formed. Enzymes are typical tertiary structures. A fourth, quaternary structure exist when two or more polypeptide chains are bonded together. Hemoglobin is such a structure. 35 Amino Acids (cont.) 36  Enzymes Enzymes are specialized protein molecules that are found in all living cells and microbes. They help with the fine control of the various chemical reactions occurring in a cell and in a microbe, so each reaction occurs at just the right moment and at the right speed. Enzymes help provide energy for the cell, assist in the making of new cell parts and control almost every process in a cell or microbe. Because enzymes are capable of such activity, they are known as organic catalysts. An enzyme or organic catalyst affects the rate or speed of a chemical reaction without itself being changed. Enzymes can also be used repeatedly. An enzyme molecule is highly specific in its action. 37  Enzymes (cont.) Components of enzyme Enzyme molecules are very large and complex protein molecules. Enzymes are make up of either all protein or part protein attached to a non-protein part. The protein part of an enzyme molecule is known as an apoenzyme, and the non-protein component is called the coenzyme. Minerals such as calcium (Ca), iron (Fe), magnesium (Mg) and copper (Cu) and vitamins such as C and B-complex serve as coenzymes. 38  Enzymes (cont.) How enzymes function Enzyme molecules are much larger than the molecules with which they have to interact. When an enzyme molecule reacts with another molecule, the reaction occurs only at a highly specific place on the enzyme. This localized site on the enzyme molecule is called the active site. Each enzyme has its own pattern on its active site; therefore, no two enzymes are alike. An enzyme reacts with a reactant whose molecular pattern fits the enzyme’s molecular pattern. The molecule that the enzyme reacts with is called a substrate molecule. 39  Enzymes (cont.) How enzymes function (cont.) The function of an enzyme is explained by a theory called the ‘lock- and-key’ model. The relation between an enzyme molecule and its specific substrate molecule can be compared with the relation between a lock and the key that fits and turns that lock. Similarly; only a substrate molecule having a particular pattern can fit into the active site of its specific enzyme molecule. When this fit is ‘good’, the enzyme molecule alters the substrate molecule chemically. The temporary physical binding of the enzyme molecule and the substrate molecule is called an enzyme-substrate complex. Enzyme activity occurs while the enzyme-substrate complex is together. 40 Enzymes (cont.) 41 Enzymes (cont.) 42  Enzymes (cont.) Any Protein molecules The name of an enzyme usually ends in -ase. The -ase ending is added to the stem word taken from the substrate. 43  Enzymes (cont.) Example of bacteria enzyme action Many bacteria have an enzyme that needs a compound called para- aminobenzoic acid (PABA). PABA helps bacteria to synthesize a vitamin called folic acid, which the bacteria need for proper growth. Figure A shows the structural formulas of Figure A PABA and the antibiotic drug sulfanilamide. 44  Enzymes (cont.) Example of bacteria enzyme action (cont.) Upon close examination, both compounds structurally are much alike. When the antibiotic sulfanilamide is given to the bacteria, instead of PABA, the sulfanilamide molecules attach themselves to the active sites of the bacteria. Thus, the active sites on the bacteria cannot attract PABA molecules and folic acid cannot be made. When this happens, the bacteria cannot grow. When sulfanilamide is used to treat bacterial diseases, bacteria become weak, cannot grow, and are readily killed by white blood cells. 45  SUMMARY Proteins are a primary constituent of living things. Proteins provide most of the molecular machinery of cells. Many are enzymes or subunits of enzymes. Each protein is linear polymers built of amino acids. Proteins are also nutrient sources for organisms that do not produce their own energy from sunlight and/or are unable to fix nitrogen. Proteins can interact with one another and with others molecules to form complexes. 46 47  INTRODUCTION Lipids have the same elements (carbon, hydrogen and oxygen) as carbohydrates, but they contain a higher proportion of hydrogen but less oxygen. Fats are lipids that are solid at room temperature; oils are lipids that are liquids at room temperature. Lipids are found in many living organisms and they are categorized into three groups: simple lipids, compound lipids and derived lipids. 48 49  LEARNING OUTCOMES On successful completion of the lesson, the student will be able to: describe the three groups of lipids; identify the functions of lipids. 50  Simple lipids Simple lipids contain the elements carbon, hydrogen and oxygen. Examples are fats and oils such as butter and margarine and corn, olive, peanut, and sunflower oils. Simple lipids (fats and oils) contain one glycerol molecule and three fatty acid molecules. They may be saturated fats (when all bonds between carbon bonds are single because each carbon atom is saturated with hydrogen) or unsaturated fats (when two or more of the hydrogen bonds are replaced with double bonds between the carbon atoms (CC). The more double carbon bonds in a fat the more unsaturated the fat or oil will be. Of the two types of simple lipids, unsaturated fats are easier to digest and are better for us. 51 52  Compound lipids Compound lipids are composed of carbon, hydrogen, oxygen, nitrogen and phosphorus. They include the phospholipids, which are found in cell membranes, and the glycolipids in brain and nerve cells. Compound lipids are not fats, and their amounts remain constant in the organism. These are classified as (i) Phospholipids (ii) Glycolipids (ii) Lipoproteins. 53  Compound lipids (cont.) Phospholipids A phospholipid is made up of two fatty acid tails and a phosphate group head. As membrane components, phospholipids are semi-permeable - only certain molecules can pass through them to enter or exit the cell. Molecules that dissolve in fat can pass through easily, while molecules that dissolve in water cannot. Oxygen, carbon dioxide and urea are some molecules that can pass through the cell membrane easily. Large molecules like glucose or ions like sodium and potassium cannot pass through easily. This helps keep the contents of the cell working properly and separates the inside of the cell from the surrounding environment. 54  Compound lipids (cont.) Phospholipids (cont.) Phospholipids can be broken down in the cell and used for energy. They can also be split into smaller molecules called chemokines, which regulate a variety of activities in the cell such as production of certain proteins and migration of cells to different areas of the body. They are found in areas such as the lung and in joints, where they help lubricate cells. 55  Compound lipids (cont.) Glycolipids Glycolipids are components of cellular membranes comprised of a hydrophobic lipid tail and one or more hydrophilic sugar groups linked by a glycosidic bond. Glycolipids are found on the outer leaflet of cellular membranes where it plays not only a structural role to maintain membrane stability but also facilitates cell-cell communication acting as receptors, anchors for proteins and regulators of signal transduction Glycolipids are found widely distributed throughout all cells and primarily localized, but not exclusively, to the plasma membrane. 56  Compound lipids (cont.) Lipoproteins Lipoprotein is formed by combination of lipid with a prosthetic group protein. The primary purpose is to transport hydrophobic lipid (also known as fat) molecules in water, as in blood plasma or other extracellular fluid. They have a single-layer phospholipid and cholesterol outer shell, with the hydrophilic portions oriented outward toward the surrounding water and lipophilic portions of each molecule oriented inwards toward the lipids molecules within the particles. Thus, the complex serves to emulsify the fats in extracellular fluid. 57  Derived lipids Derived lipids containing only carbon, hydrogen and oxygen. They include the steroids found in the male and female sex hormones, vitamin D, cholesterol, and the fat-soluble vitamins A, E, and K. These substances are classed as lipids only because they are soluble in fat solvents. 58  FUNCTIONS OF LIPIDS As an energy source, lipids provide 9 kcal of energy per gram. Triglycerides provide energy storage in adipocytes. Phosphoglycerides, sphingolipids, and steroids are structural components of cell membranes. Steroid hormones are critical intercellular messengers. Lipids help in absorption of fat soluble vitamins (A, E, D, K). Dietary fat acts as a carrier of lipid-soluble vitamins into cells of small intestine. Provide shock absorption and insulation. 59  SUMMARY Lipids are molecules that contain hydrocarbons and make up the building blocks of the structure and function of living cells. Lipids are utilized directly or otherwise synthesized, from fats present in the diet. There are numerous biosynthetic pathways to both break down and synthesize lipids in the body. The main biological functions of lipids include storing energy, as lipids may be broken down to yield large amounts of energy. Lipids also form the structural components of cell membranes, and form various messengers and signaling molecules within the body. 60 61  SUB-TOPICS Nutrition in nursing Carbohydrate Proteins Lipids Sumathy Vitamins Water and minerals Energy balance Guideline for healthy eating Consumer issues Cultural and religious influences on food and nutrition Healthy eating for healthy babies Nutrition for infants, children and adolescents Nutrition for older adults 62 63  INTRODUCTION Vitamins are organic compounds that are needed in small quantities to sustain life. Most vitamins need to come from food. Each organism has different vitamin requirements. Different vitamins have different roles, and they are needed in different quantities. 64  LEARNING OUTCOMES On successful completion of the lesson, the student will be able to: describe the classification of vitamins; explain the types of vitamins. 65  DESCRIPTION Vitamins are essential to normal metabolism. If any kind of vitamin is not sufficient, it can cause certain medical conditions. A vitamin is an essential nutrient that body cannot produce enough of and which it needs to get from food. There are currently 13 recognized vitamins. 66  CLASSIFICATION Vitamins are either fat-soluble or water-soluble. Fat-soluble vitamins Fat-soluble vitamins are stored in the fatty tissues of the body and the liver. Vitamins A, D, E and K are fat-soluble. These are easier to store than water-soluble vitamins and they can stay in the body as reserves for days and sometimes months. Fat-soluble vitamins are absorbed through the intestinal tract with the help of fats or lipids. 67  CLASSIFICATION (cont.) Vitamins are either fat-soluble or water- soluble (cont.). Water-soluble vitamins Water-soluble vitamins do not stay in the body for long. The body cannot store them and they are soon excreted in urine. Because of this, water-soluble vitamins need to be replaced more often than fat- soluble vitamins. Vitamin C and all the B vitamins are water soluble. 68  TYPES Vitamin A (retinol) Chemical names: Retinol, retinal and four carotenoids, including beta carotene. It is fat soluble. Storage: In hepatic cells (Ito cells) within the perisinusoidal space (of Disse). 69 TYPES (cont.) 70  TYPES (cont.) Vitamin D (calciferol) Chemical names: Ergocalciferol, cholecalciferol. It is fat soluble. Storage: Mainly in adipose tissue as 25-hydroxycholecalciferol Synthesis: Liver: cholesterol → 7-dehydrocholesterol (provitamin D3) Enzyme: cholesterol dehydrogenase Skin: Storage of 7-dehydrocholesterol; Cleavage of 7- dehydrocholesterol via irradiation with UV light → cholecalciferol (in the stratum basale of the skin) Liver: hydroxylation of cholecalciferol to 25-hydroxyvitamin D (25-OH D3, calcidiol; activated vitamin D2) Kidneys: 1α-hydroxylase hydroxylates 25-hydroxyvitamin D → 1,25- dihydroxyvitamin D 71 Vitamin D synthesis 72 TYPES (cont.) 73  TYPES Vitamin E (tocopherol) Chemical names: Tocopherols, tocotrienols It is fat soluble. Storage: Adipose tissue, parenchymal cells of the liver. 74 TYPES (cont.) 75  TYPES (cont.) Vitamin K (phytomenadione) Chemical names: Phylloquinone, menaquinones. It is fat soluble. Storage: Liver. 76 TYPES (cont.) 77  TYPES (cont.) Vitamin K (phytomenadione) Chemical names: Phylloquinone, menaquinones. It is fat soluble. Sources: Leafy green vegetables (vitamin K1) Eggs, dairy, and meat (vitamin K2) Synthesized in small amounts by intestinal flora Storage: Liver. 78 79  TYPES (cont.) Find out the information for Water-soluble vitamins 80  SUMMARY Vitamins are a group of chemically diverse organic compounds that an organism requires for normal metabolism. Apart from a few exceptions (e.g., vitamin D), the human body cannot synthesize vitamins on its own in sufficient amounts and must, therefore, ensure a steady supply through the diet. Vitamins are micronutrients that do not provide energy (like macronutrients) but instead have very specific biochemical roles. Vitamins are classified into fat-soluble vitamins, which the body can store and water-soluble vitamins, which, with the exception of vitamins B9 (folate) and B12 (cobalamin), the body cannot store over significant periods of time and therefore, require continuous intake. A balanced diet typically supplies the body with all vitamins it requires. Deficiencies occur mainly due to malnutrition, malabsorption disorders, or restrictive diets (e.g., vitamin B12 deficiency in a vegan diet). 81 82  INTRODUCTION Water is the major constituent of human body. The average body water is 50-70% of the body weight. Females have little less water than males. Living beings have organic and inorganic types of chemical constituents. The organic constituents i.e. proteins, carbohydrates, fats, etc. are made up of C, H, O and N. The inorganic constituents described as ‘minerals’ comprise of the elements present in the body other than C, H, O and N. Although they constitute a relatively small amount of the total body tissues, they are essential for many vital processes. 83  LEARNING OUTCOMES On successful completion of the lesson, the student will be able to: explain water metabolism distribution of water in the body factors influencing the distribution of body water normal water balance physiological functions of water regulation of passage of water explain mineral metabolism macrominerals microminerals 84  WATER METABOLISM Distribution of water in the body The water content of intracellular fluid is 50% of total body weight. The water content of extracellular fluid is 20% of the body weight, which is distributed as follows: 85  WATER METABOLISM (cont.) Factors influencing the distribution of body water The distribution of water is continuously changing. Osmotic forces are the principal factors for controlling the amount of fluid in various compartments of the body. These are maintained by the solutes of the body. Solutes are of three types Organic molecules of small molecular size (glucose, urea, amino acids etc.): Since these diffuse freely across the cell membrane, they are not important in the distribution of water. If they are present in large quantities, they can help retaining water. 86  WATER METABOLISM (cont.) Factors influencing the distribution of body water (cont.) Solutes are of three types (cont.) Organic substances of large molecular size (proteins): These substances can throw effect in the transport of fluid from one compartment to the other. The inorganic electrolytes: These inorganic electrolytes are the most important both in the distribution and in the retention of body water. 87  WATER METABOLISM (cont.) Factors influencing the distribution of body water (cont.) Two important factors influence the distribution of water between intracellular and extracellular compartments are: 1. Osmolality or Osmolarity Osmolality effects this distribution of water through the generation of osmotic pressure. The osmotic pressure generated by a solution is proportional to the number of particles per unit volume of solvent, not to the type, valence or weight of the particles. For very dilute solutions, osmolarity and osmolality are numerically the same. The difference between osmolality and osmolarity is called osmolar gap (for investigation). 88 WATER METABOLISM (cont.) 89  WATER METABOLISM (cont.) Factors influencing the distribution of body water (cont.) Two important factors influence the distribution of water between intracellular and extracellular compartments are (cont.): 2. Colloidal osmotic pressure The osmotic pressure of a solution is directly proportional to the concentration of osmotically active particles in that solution. In a normal person, the osmotic pressure of extracellular fluid (ECF) (mainly due to Na+ ions) is equal to the osmotic pressure of intracellular fluid (ICF) (which is mainly due to K+ ions). Due to this osmotic equilibrium there is no net movement of water in or out of the cells. 90  WATER METABOLISM (cont.) Factors influencing the distribution of body water (cont.) Two important factors influence the distribution of water between intracellular and extracellular compartments are (cont.): 2. Colloidal osmotic pressure (cont.) A change in the concentration of osmotically active ions in either of the water compartments creates a difference of osmotic pressure and consequently movement of water between compartment occur. Water diffuses from a compartment of low osmolality to one of higher osmolality until the osmotic pressure are identical in both of them. 91 WATER METABOLISM (cont.) 92  WATER METABOLISM (cont.) Normal water balance An equilibrium persists between the intake and output of water in the body. In addition to other factors, certain hormones such as ADH, vasopressin, oxytocin and aldosterone influence the regulatory mechanism. There is a continuous excretion of water in the form of digestive juices from the body into the alimentary canal. This water (except 100 ml) is reabsorbed with the water of the food and drinks. The amount of this internal secretion is 7 to 10 liters/day. 93  WATER METABOLISM (cont.) Normal water balance (cont.) Water intake: Water is supplied to the body by the following processes: Water taken orally. Along with food. Oxidation of food stuffs i.e. fats, proteins and carbohydrates yield water after combustion. Oral water intake is regulated by a thirst center located in hypothalamus. Increase in the osmolality of plasma causes increased water intake by stimulating thirst center. 94  WATER METABOLISM (cont.) Normal water balance (cont.) 95  WATER METABOLISM (cont.) Normal water balance (cont.) Water output/loss: Water is lost from the body by 4 routes Evaporation from lungs. Kidneys eliminate water as urine (insensible water loss). The intestines excrete in the feces. Perspiration (sensible water loss). 96 97  WATER METABOLISM (cont.) Physiological functions of water Specific heat: Heat is required to raise the temperature of 1 gm. of water through one degree Celsius is more than for almost any other solid or liquid. The high specific heat of water helps in minimizing the rise in body temperature due to the heat emitted out of chemical reactions. Latent heat of evaporation: Water has the highest latent heat of evaporation than any other liquid. A certain amount of water can cause maximum cooling by evaporation, so that body temperature does not rise. 98  WATER METABOLISM (cont.) Physiological functions of water (cont.) Solvent power: Water forms true solutions as well as colloidal solutions. Even water insoluble substances are made water soluble by the hydrotropic action. Therefore, it is the most suitable solvent for cellular components; water thus brings various substances in contact for chemical reactions to proceed. Dielectric constant: Oppositely charge particles can coexist in water. Therefore, it is a good ionizing medium. This stimulates the chemical reactions. 99  WATER METABOLISM (cont.) Physiological functions of water (cont.) Catalytic action: A large number of chemical reactions in the body are accelerated by water due to its ionizing power. All chemical reactions in the body proceed in presence of water only. Lubricating action: Water acts as a lubricant in the body to prevent friction in joints, pleura, conjunctiva and peritoneum. 100  WATER METABOLISM (cont.) Regulation of passage of water If capillary pressure is increased, more water will flow into the tissues. A fall in blood pressure helps in passage of water form the tissues to the blood. If the plasma proteins are decreased, water will flow into the tissues. Dilution of blood by excessive ingestion of water can lower the osmotic pressure of the plasma proteins and thus may increase capillary pressure. 101 102 103  MINERAL METABOLISM Minerals are inorganic elements, required for a variety of functions. Macro elements: required to be present in the diet, more than 1 mg. Micro elements: utilized in trace quantities (in microgram or Nano- gram). Hence they are called trace elements. 104  MINERAL METABOLISM (cont.) Calcium (Ca) Source: Milk (0.2 gm./100 ml) and cheese are important dietary sources. Other sources-are egg yolk, lentils, nuts, cabbage, cauliflower and asparagus, etc. Requirement: Men and women after 18 years of age require 800 mg/day. During lactation and in pregnancy of 2nd and 3rd term 1.2 gm/day is required. Infants under 1 year require-360-540 mg/day. Children of 1-18 years need 800-1200 mg/day. 105  MINERAL METABOLISM (cont.) Calcium (Ca) (cont.) Absorption: Ca is taken in the diet as calcium phosphate, carbonate, tartarate and oxalate. Ca is absorbed actively in the upper small intestine. The active process is regulated by 1,25 dihyrocholecalciferol, a metabolite of vitamin D which is produced in the kidney in response to low plasma Ca++ concentrations. Absorption of Ca by the intestine is never complete. Ca is absorbed by an active transport process occurring mainly in the upper small intestine. 106  MINERAL METABOLISM (cont.) Calcium (Ca) (cont.) Calcium absorption is influenced by the following factors: Vitamin D promotes absorption of Ca. Acidic pH favors calcium absorption because Ca salts (phosphate and carbonates) are quite soluble in acid solution arid are relatively insoluble in alkaline solutions. Organic acids, lactose and basic amino acids in the diet favors calcium absorption. Higher levels of proteins in the diet help to increase the absorption of calcium. If calcium: phosphorus ratio is much high, Ca3(PO4)2 will be formed and absorption of calcium is reduced. 107  MINERAL METABOLISM (cont.) Calcium (Ca) (cont.) Calcium absorption is influenced by the following factors (cont.): When fat absorption is impaired much free fatty acids are formed due to hydrolysis. These fatty acids react with free calcium to form insoluble calcium soap and then Ca is lost in faeces. Absorption of calcium is inhibited by a number of dietary factors that cause formation of insoluble calcium salts, i.e. phytate (cereal grain), oxalate, phosphate and iron, etc. High concentration of Mg in the diet decreases absorption of Ca. Presence of excess fibre in the diet interferes with the absorption of Ca. Percentage of calcium absorption decreases as its intake increases. Parathyroid hormone increases the intestinal absorption of calcium. 108  MINERAL METABOLISM (cont.) Calcium (Ca) (cont.) Calcium absorption is influenced by the following factors (cont.): Adrenal glucocorticoids diminish intestinal transport of Ca. After the age of 55 to 60 there is gradual reduction of intestinal transport of calcium. Kidney threshold regulates the blood calcium level. In a normal adult any extra calcium absorbed from the intestine is readily excreted in the urine. Excess of iron also dis-favors absorption of calcium and phosphorus, as ferric phosphate is highly insoluble. Oxalate in certain foods precipitate calcium in the intestine as insoluble calcium oxalate. The phytic acids of food form insoluble salt with calcium and reduce calcium absorption. 109  MINERAL METABOLISM (cont.) Calcium (Ca) (cont.) Biological role: Constituent of bones and teeth. Neuromuscular functions. Blood coagulation. It controls the permeability of all membranes and is often bound by lecithine in the membrane. Selected enzymatic reactions. Regulation of secretion of certain peptide hormones. 110  MINERAL METABOLISM (cont.) Calcium (Ca) (cont.) Metabolism: The blood cells contain very little amount of calcium, most of the blood calcium is therefore, in the plasma, where it is present in 3 fractions: 1. Ionized about 2 mg/100 ml. 2. Non-diffusible (protein bound) above 3.5 mg/100 ml. 3. A small amount as calcium complex of citrate and phosphate. All these forms of calcium in the serum are in equilibrium with one another. A decrease in ionized calcium in the serum causes tetany. This may be due to an increase in the pH of blood or lack of calcium because of poor absorption from the intestine, decreased dietary intake, increased renal excretion as in nephritis or parathyroid deficiency. 111  MINERAL METABOLISM (cont.) Calcium (Ca) (cont.) Excretion: Calcium is excreted in the urine, bile and digestive secretion. About 75% of dietary calcium is absorbed and rest is excreted as fecal calcium. Nearly 10 g of Ca is filtered by the renal glomeruli in 24 hours. But only 200 mg appear in the urine, which is in the ionic state as well as in the complexes with citrate and other organic anions. A very small amount of Ca is excreted into the intestine after absorption. About 15 mg of Ca is excreted in the sweat. Vigorous physical exercise increases the loss of Ca by way of sweat. 112  MINERAL METABOLISM (cont.) Phosphorus (P) Source: Phosphorus is present in nearly all foods therefore a dietary deficiency is not known to occur in man. Dairy products, cereals, egg yolk, meat, beans and nuts are usually rich sources. The daily average intake is 800-1000 mg and is about twice that of calcium. Absorption: Like calcium, phosphorus is also absorbed by upper small intestine and factors influencing the absorption are also similar. The normal range for plasma inorganic phosphorus is 3.0-4.5 mg/dl. In children values are higher (5-6 mg/dl) and remain so up-till puberty. 113  MINERAL METABOLISM (cont.) Phosphorus (P) (cont.) Distribution: Phosphorus is distributed more widely than calcium. 15% is found in muscle and other soft tissues and 85% in the inorganic mineral phase of bone. It is an integral part of many macromolecules; e.g. phospholipids, phosphoproteins and nucleic acids. 114  MINERAL METABOLISM (cont.) Phosphorus (P) (cont.) Functions: Formation of bone and teeth. Formation of phospholipids essential to every cell. Formation of nucleic acids and derivatives; e.g. Adenylic acid and is thus significant in (RNA and DNA) protein synthesis and from genetics point of view. Formation of organic phosphates as intermediate in metabolic processes; e.g. In glycolysis, Glucose + ATP → G-6-P + ADP. Formation of energy rich phosphate compounds; e.g. ATP (energy currency of the cell). Both inorganic and organic phosphates can take part in buffering the cell; e.g. Sodium-potassium-phosphates. Formation of coenzymes; e.g. TPP, NADP. Formation of phosphoprotein; e.g. Casein. 115  MINERAL METABOLISM (cont.) Phosphorus (P) (cont.) Excretion: Urinary excretion is equivalent to dietary phosphate intake. It varies diurnally, more being excreted at night. The usual daily loss is 600-800 mg, tubular resorption being 85-95%. Renal loss of phosphate can be of significant magnitude to lower serum phosphorus values and enhance osteoid demineralization. 116  MINERAL METABOLISM (cont.) Phosphorus (P) (cont.) Homeostasis: There is a greater fluctuation observed in blood phosphate values due to easy shift between extracellular fluid and intracellular compartments. Thus it is quite dependent on dietary phosphorus. Inorganic phosphate affects the net movement of calcium into and out of bone. Raised phosphate will lead to depression of the solubility of the calcium of bone crystals and thus shift equilibrium towards bone. In this manner it opposes the effect of the parathyroids. 117  MINERAL METABOLISM (cont.) Phosphorus (P) (cont.) Homeostasis (cont.): Ingestion of heavy dose of phosphate can lower serum calcium and increase excretion of calcium in urine. Lowered phosphorus on the other hand will make parathyroid activity more apparent. Hormonal factors are not directly linked. However renal phosphate clearance is very vital in homeostasis and seems to be secondarily involved in certain endocrinopathies, e.g. involving parathormone, growth hormone and corticosteroids. 118  MINERAL METABOLISM (cont.) Sodium (Na), Potassium (K), Chloride (Cl) Substances whose solutions conduct an electric current are called ‘electrolytes’. They are about 11 in general. Na, K, Ca and Mg are cations whereas CI, HCO3, HPO4, SO4, organic acids and proteins are anions. Among these sodium, potassium and chloride are important in the distribution and the retention of body water, thus have close relationship among them. 119  MINERAL METABOLISM (cont.) Sodium (Na), Potassium (K), Chloride (Cl) (cont.) Source: The most important source of Na and CI in the diet is common table salt (NaCl). The good source of K are chicken, calf flesh, beef liver, dried apricot, dried peaches, bananas, the juice of orange and pineapple, potatoes, etc. Absorption: Normally Na, K and CI are completely absorbed from the gastro- intestinal tract. 120  MINERAL METABOLISM (cont.) Sodium (Na), Potassium (K), Chloride (Cl) (cont.) Distribution: In the tissues both Na and K occur in a relatively large amount as compared to chloride and other inorganic salts as well as protein and organic salts. Sodium is present in extra cellular fluid and in a very low concentration inside the cells whereas potassium is mainly found inside the cells and in a very low concentration in the extracellular fluid. 121  MINERAL METABOLISM (cont.) Sodium (Na), Potassium (K), Chloride (Cl) (cont.) Functions of sodium and potassium: They maintain the acid base balance in the body. They maintain normal water balance. Na also functions in the preservation of normal excitability of muscle and the permeability of the cells. K inhibits ‘muscular contraction’ in general. High intracellular potassium concentrations are essential for several important metabolic functions, including protein biosynthesis by ribosomes. Sodium and Potassium chlorides maintain the viscosity of blood. 122  MINERAL METABOLISM (cont.) Sodium (Na), Potassium (K), Chloride (Cl) (cont.) Functions of sodium and potassium (cont.): Na helps in the formation of the gastric juice. NaCl takes part in the series of reactions as a result of which HC1 is manufactured by the stomach. K of KHb in the red cells helps in carbon dioxide transport. K ions inhibit cardiac contraction and prolong relaxation. K ions exert important effect on the function of nervous system. 123  MINERAL METABOLISM (cont.) Sodium (Na), Potassium (K), Chloride (Cl) (cont.) Functions of chloride: It provides 2⁄3 of the anion of plasma and is the main factor for regulating body reactions. NaCl and KCl are important agents in regulation of osmotic pressure in the body. HCl of gastric juice is ultimately derived from the blood chlorides. Chloride ions are essential for the action of ptyalin and pancreatic amylase. It is essential in acid-base regulation. Chloride plays a role in the body by chloride shift mechanism. 124  MINERAL METABOLISM (cont.) Sodium (Na), Potassium (K), Chloride (Cl) (cont.) Metabolism: Mainly adrenocortical steroids and some of the sex hormones facilitate the retention of sodium and chloride in the body and excretion of potassium by kidneys in the urine. In adrenocortical deficiency, serum sodium decreases because excretion increases. When atmospheric temperature is high as in summer, large amounts of sodium and chloride are lost in perspiration (sweating) and this loss may be checked when temperature is low (in winter). In renal disease, with acidosis, Na and CI ion excretion in urine is increased due to poor tubular reabsorption of sodium whereas that of K ion is decreased leading to hyponatraemia and hypochloraemia but hyperkalaemia. 125  MINERAL METABOLISM (cont.) Sodium (Na), Potassium (K), Chloride (Cl) (cont.) Excretion: Na: Urine - 5-35 gm; Skin - 25-50 mg; Stool - 10-125 mg K: normally eliminated almost entirely in urine and a small amount in the feces. Aldosterone exerts an influence on potassium excretion. In normal kidney function; K is very promptly and efficiently removed from the blood. CI: chiefly eliminated in the urine, also in sweat. Its concentration in sweat is increased in hot climates and decreased by aldosterone. 126  MINERAL METABOLISM (cont.) Magnesium (Mg) Source: Magnesium is present in milk, egg, cabbage, cauliflower etc. Daily requirement: Infants: 100-150 mg; Children: 150-200 mg and Adults: 200-300 mg. Absorption: A greater part of the daily ingested Mg is not absorbed. A very high intake of fat, phosphate, calcium and alkali diminish its absorption. Parathyroid hormone increases its absorption. 127  MINERAL METABOLISM (cont.) Magnesium (Mg) (cont.) Distribution: Whole blood it is 2-4 mg/dl, CSF it is 3 mg/100 ml and muscle it is 2 mg/100 ml. Functions: 70% of the total magnesium content (21g) of the body is combined with calcium and phosphorus in the complex salts of bone. The remainder is in the soft tissues and body fluids. It is the principal cation of the soft tissue. Magnesium ions act as activators for many of the phosphate group transfer enzymes. It is found in certain enzymes, such as co-carboxylase. It functions as a cofactor for oxidative phosphorylation. 128  MINERAL METABOLISM (cont.) Sulphur (S) Sources: Sulphur is taken mainly as cysteine and methionine present in proteins. Other compounds in the diet contribute small amounts of sulphur. Absorption: Inorganic sulphate is absorbed as such from intestine into the portal circulation. Small amount of sulphide may be formed in the bowel by the action of bacteria, but if absorbed into the blood stream, it is rapidly oxidized to sulphate. 129  MINERAL METABOLISM (cont.) Sulphur (S) (cont.) Sulphur in blood (serum): Inorganic: 0.5-1.1 mg/100 ml Ethereal sulphate: 0.1-1.0 mg/100 ml Neutral Sulphur: 1.7-3.5 mg/100 ml Physiological functions: Sulphur is present primarily in the cell protein in the form of cysteine and methionine. Cysteine plays important part in the protein structure and enzyme activity. 130  MINERAL METABOLISM (cont.) Physiological functions (cont.): Methionine is the principal methyl group donor in the body. The ‘activated’ form of methionine, s-adenosyl methionine is the precursor in the synthesis of a large number of methylated compounds which are involved in intermediary metabolism and detoxification mechanism. Sulphur is a constituent of coenzyme A and lipoic acid which are utilized in the synthesis of acetyl-CoA, malonyl CoA, Acyl-CoA and S-acetyl lipoate (involved in fatty acid oxidation and synthesis). It is a component of a number of other organic compounds such as heparin, glutathione, thiamine, pantothenic acid, biotin, ergothionine, taurocholic acids, sulphocyamides, indoxyl sulphate, chondroitin sulphate, insulin, penicillin, anterior pituitary hormones and melanin. 131  MINERAL METABOLISM (cont.) Sulphur (S) (cont.) Excretion: Excreted in urine in 3 forms. Total sulphate excretion may be diminished in renal function impairment and is increased in condition accompanied by excessive tissue breakdown as in high fever and increased metabolism. 132 133  MINERAL METABOLISM (cont.) Iron (Fe) Iron is present in all organisms and in all the cells. It does not exist in the free state, instead is always present in organic combination, usually with proteins. It exists in two forms i.e. Fe2+ (ferrous) and Fe3+ (ferric). It serves as an oxygen and electron carrier and is incorporated into redox enzymes and substances which carry out the function of oxygen transport such as haemoglobin and cytochromes. Total iron content in normal adult is 4 to 5 grams. 60-70% is present in hemoglobin, 3% in myoglobin and 0.1% in plasma combined with β-globulin transport protein transferrin. Hemoprotein and flavoprotein make up to less than 1% of total iron. Rest is stored as ferritin. 134  MINERAL METABOLISM (cont.) Iron (Fe) (cont.) Source: Rich – Liver, heart, kidney, spleen. Good – Egg yolk, fish, nuts, dates, beans, spinach, molasses, apples, bananas, etc. Poor – Milk, wheat flour, polished rice, potatoes; etc. Daily requirement (Only about 10% of ingested iron is absorbed): Infants – 10-15 mg Children – 1-3 years 15 mg 4-10 years – 10 mg Older children and adults of 11 to 18 years – 18 mg 19 years and above – 10 mg Females between 11 and 50 years of age and during pregnancy or lactation – 18 mg After 51 years of age – 10 mg 135  MINERAL METABOLISM (cont.) Iron (Fe) (cont.) Absorption: Very little (less than 10%) of dietary iron is absorbed. Excretion in the urine is minimal. Infants and children absorb more iron as compared to adults. Iron deficiency in infants is due to dietary deficiency. Iron deficient children absorb approximately twice as much as normal children do. Absorption mainly occurs in the duodenum and the proximal jejunum. A diet high in phosphate, phytic acid and oxalic acid decreases iron absorption since these substances form the insoluble compounds with iron. Conversely, a diet very low in phosphate markedly increases iron absorption. 136  MINERAL METABOLISM (cont.) Iron (Fe) (cont.) Absorption (cont.): Iron absorption is enhanced by protein, possibly as a result of the formation of low molecular weight digestive products (peptides, amino acids) which can form soluble iron chelates. Impaired absorption takes place in patients who have total removal of stomach or a removal of considerable amount of the intestine. Achlorhydria, administration of alkali, copper deficiency decrease iron absorption. Alcohol ingestion favors iron absorption. 137  MINERAL METABOLISM (cont.) Iron (Fe) (cont.) Physiological functions: Iron functions mainly in the transport of oxygen to the tissues. Involved in the process of cellular respiration. Essential component of hemoglobin, myoglobin, cytochromes and the respiratory enzyme systems (cytochrome oxidase, catalase and peroxidase). Non-heme iron is completely protein-bound (storage and transport). Non-heme iron is utilized in the structure of xanthine dehydrogenase (xanthine oxidase) and succinate dehydrogenase and also in the iron sulphur proteins of the respiratory chain. 138  MINERAL METABOLISM (cont.) Iron (Fe) (cont.) Excretion: Physiological excretion of iron is minimal. The normal routes of excretion are urine, bile, faeces, cellular desquamation and sweat. Daily excretion in an adult male is estimated to be about 1 mg. In women of reproductive age, additional loss through menstruation averages to 1 mg per day. 139  MINERAL METABOLISM (cont.) Copper (cu) Source: Rich – Liver, kidney, other meats, shell fish, nuts and dried legumes. Poor – Milk and milk products. The concentration of copper in the fetal liver is 5-10 times higher than that in liver of an adult. Daily requirement: Infants and children – 0.05 mg/kg body weight Adults – 2.5 mg A nutritional deficiency of copper has never been demonstrated in man, although it has been suspected in case of nephrosis. 140  MINERAL METABOLISM (cont.) Copper (cu) (cont.) Absorption: About 30% of the normal daily diet of copper is absorbed in the duodenum. Blood copper: The normal concentration of copper in serum is 90 µg/100 ml. Both RBC and serum contain copper. The plasma copper levels increase in pregnancy because of their estrogen content. Oral contraceptives have a similar effect. 141  MINERAL METABOLISM (cont.) Copper (cu) (cont.) Physiological functions: It has important role in hemoglobin synthesis. It is required for melanin formation, phospholipids synthesis and collagen synthesis. It has a role in bone formation and in maintenance of the integrity of myelin sheath. It is a constituent of several enzymes such as tyrosinase, cytochrome oxidase, ascorbic acid oxidase, uricase, ferroxidase I (ceruloplasmin), ferroxidase II, superoxide dismutase, amino oxidase and dopamine hydroxylase. Three copper containing proteins namely cerebrocuperin, erythrocuperin and hepatocuperin are present in brain, RBC and liver respectively. 142  MINERAL METABOLISM (cont.) Copper (cu) (cont.) Excretion: Only 10 to 60 mg of copper is excreted in the urine. 0.5 to 1.3 mg is excreted through bile 0.1 to 0.3 mg is excreted by intestinal mucosa into the bowel lumen. 143  MINERAL METABOLISM (cont.) Iodine (I) Source: Rich sources are sea water, marine vegetation and vegetables as well as fruits grown on the sea board. Plants grown at high altitudes are deficient in iodine because of its low concentration in the water. In such regions, iodide is commonly added to the drinking water or table salt in concentrations of 1:5000 to 1:200000. Daily requirement (Only about 10% of ingested iron is absorbed): Adults – 100 to 150 μg In adolescence and in pregnancy – 200 μg 144  MINERAL METABOLISM (cont.) Iodine (I) (cont.) Distribution: Normal iodine content of body is 10 to 20 mg. 70 to 80% of this is present in thyroid gland. Muscles contain large amount of iodine. The concentration of iodine in the salivary glands, ovaries, pituitary gland, brain and bile is greater than that in muscle. Iodine in saliva is inorganic iodide, while most of the iodine present in tissue is in the organic form. 145  MINERAL METABOLISM (cont.) Iodine (I) (cont.) Blood Iodine: Practically all the iodine in the blood is in the plasma. The normal concentration in plasma or serum is 4 to 10 μg/100 ml.  0.06 to 0.08 μg/100 ml is in inorganic form, 4 to 8 μg/100 ml is in the organic form bound to protein, precipitated by protein precipitating agents. 90% of the organic form consists of thyroxine and the remainder tri and di-iodothyronine. About 0.05% of thyroxine is in the free state. RBC contains no organic iodine. 146  MINERAL METABOLISM (cont.) Iodine (I) (cont.) Absorption: Iodine and iodide are absorbed most readily from the small intestine. Organic iodide compounds (di-iodothyronine and thyroxine) are partly absorbed as such and a part is broken down in the stomach and intestines with the formation of iodides. Absorption also takes place from outer mucus membrane and skin. 147  MINERAL METABOLISM (cont.) Iodine (I) (cont.) Storage: 90% of the iodine of the thyroid gland is in organic combination and stored in the follicular colloid as ‘thyroglobulin’ a glycoprotein containing thyroxine, di-iodothyronine and smaller amounts of triiodothyronine. On demand these substances are mobilized and thyroxine as well as triiodothyronine is passed into the systemic circulation. They undergo metabolic degradation in the liver. 148  MINERAL METABOLISM (cont.) Iodine (I) (cont.) Physiological functions: Iodine is required for the formation of thyroxine and triiodothyronine hormones of the thyroid gland. These thyroid hormones are involved in cellular oxidation, growth, reproduction and the activity of the central and autonomic nervous systems. Triiodothyronine is more active than thyroxine in many respects. 149  MINERAL METABOLISM (cont.) Iodine (I) (cont.) Excretion: Inorganic iodine is mostly excreted by the kidney, liver, skin, lungs and intestine and in milk. About 10% of circulating organic iodine is excreted in feces. This is entirely unabsorbed food iodine. 40 to 80 % is usually excreted in the urine, 20 to 70 μg daily in adults, 20 to 35 μg in children. The urinary elimination is largest when the intake is lowest. Urinary iodine is increased by exercise and other metabolic factors. 150  MINERAL METABOLISM (cont.) Selenium (Se) Good dietary sources are kidney cortex, pancreas, pituitary and liver. It is rapidly absorbed mainly in duodenum. It is distributed in liver 0.44 μg/gm in skin 0.27 μg/gm and in muscle 0.37 μg/gm. In the cells it is present as selenocystine nad selenomethionine. Selenium along with Vitamin E plays an important role in tissue respiration. 151  MINERAL METABOLISM (cont.) Selenium (Se) (cont.) Selenium is involved in biosynthesis of coenzyme Q (ubiquinone), which is involved in respiratory chain. Selenium acts as an antioxidant providing protection against peroxidation in tissues and membrane. It is an essential component of glutathione peroxidase, an enzyme which catalyzes the conversion of reduced glutathione to its oxidized form. Selenium is excreted in faeces, urine and via exhalation. It causes toxic effect called selenosis. 152 153  SUMMARY The body water balance is maintained within the fairly constant limits by regulation between water intake (by drinking, from food and metabolic water) and output (through urine, skin, lungs and stool). Minerals are inorganic elements, having vital structural and functional roles in the human body. Minerals are classified into 2 groups: macrominerals (that are required in amounts greater than 100 mg/day) microminerals (that are required in amounts less than 100 mg/day) 154  SUB-TOPICS Nutrition in nursing Carbohydrate Proteins Lipids SUMATHY Vitamins Water and minerals Energy balance Guideline for healthy eating Consumer issues Cultural and religious influences on food and nutrition Healthy eating for healthy babies Nutrition for infants, children and adolescents Nutrition for older adults 155 156