Physiology Pre Dentistry 2025 PDF

Principles Of Animal Physiology For Pre dentistry By Doctor Abdelbaset Mohamed Ahmed Abdelreheem Professor of physiology Zoology Department Faculty of Science Al-Azhar University Assuit Branch 2005/4701 ‫رقم اإلي...

Principles Of Animal Physiology For Pre dentistry By Doctor Abdelbaset Mohamed Ahmed Abdelreheem Professor of physiology Zoology Department Faculty of Science Al-Azhar University Assuit Branch 2005/4701 ‫رقم اإليداع‬ 2024-2025 1  Chapter One 1-Introduction Physiology: is one of the many basic divisions of biology. The term physiology is derived from two Greek words, nature and speech. Physiology is the oldest branch of biological sciences. The first attempt towards the study of physiology appears to have been made by the Ionian Greek philosophers about 2000 years ago. I. History of physiology. The foundations of physiology were first laid by: 1. By ancient civilizations of Egypt and India. 2. The study of human physiology as a medical field dates from 420 BC to the time of Hippocrates, also known as the “father of medicine”. 3. Aristotle and his emphasis on the relationship between structure and function marked the beginning of physiology in ancient Greece. 4. Claudius Galenus (130-200 AD) was the first to use experiments to assess the body's functions. He was also the founder of Experimental Physiology. 5. Jean Fernel (1497-1558), a French physician introduced the term “Physiology.” 6. Physician William Harvey in 1628 discovered blood circulation. He also introduced vivisection into scientific practice. 7. In 1661 the capillaries were discovered by Malpighi. 8. Hale was the first to measure the blood pressure in the arteries in 1732. 10. In The early part of the 18th century the laws of chemistry were applied, to physiological processes when the theory of irritability of tissues was discovered. 9. Borelli discovered the respiratory act. 10. Spallan Zoni discovered the properties of gastric juice. 11. Henri Milne-Edwards, in the 1820s was a French Physiologist who introduced the notion of physiological division. 12. Joseph Lister (1858) studied the cause of blood coagulation and inflammation that resulted from previous injuries and surgical wounds. 13. Johannes Muller and Marshall Hall proposed the reflex theory at the beginning of the 19th century, and in recent years several tremendous advances. Have been made in various fields of physiology. 14. Physiology in the 20th century became the parent of a few related disciplines, of which biochemistry, biophysics, general physiology, and molecular biology are the most vigorous examples. Physiology is the functional sciences that are closely related to the field of medicine. The solution of the major unsolved problems of physiology will require technical and expensive research by teams of specialized investigators. Unsolved problems 2 include the unraveling of the ultimate bases of the phenomena of life. Research in physiology also is aimed at the integration of the varied activities of cells, tissues, and organ levels of the organism. In many instances, the solution is of practical value in medicine or helps to improve the understanding of both human beings and other animals. II. Divisions of physiology divided into various division are: A) General physiology studies vital phenomena in living organisms as a whole. B) Special physiology: It is a narrower field where the functions of organs or tissue is studied intensively. C). Comparative physiology: study functions of a wide variety of organisms. D) Applied physiology: Under this are several subjects such as hygiene, dietetics, chemistry, pharmacology, agriculture, and many other aspects of practical physiology. 1. Neurophysiology. The functions of the nerve cells and nervous system. 2. Endocrinology: deals with the study of the different endocrine glands. 3. Enzymology: deals with the study of the structure, chemical composition, and functions of enzymes. 4. Cellular physiology: of the dynamic unit of the body, namely the cell. 5. Insect physiology: specialization in the functions of the different organs of the insects. This is of great help to the agricultural economy. 6. Mammalian physiology: of man and his domestic animals. The physicists, chemists, and engineers who have opened new vistas in the field of physiology in the 20th century have developed several techniques and apparatus. The most active fields of physiological research are concerned with the excitation processes; the nature of cell surfaces, the relationship that exists between the ultra-microscopic structures of life and the physiological functions; the actual chemistry of photosynthesis, importance of vitamins and hormones in animals. III. Organization of living things all fields overlap and contribute to each other: 1. Principles of matter/energy (Physics) 2. Atoms -> molecules (Chemistry) 3. Complex organic molecules (Biochemistry) 4. Organelles -> cells (Cellular Biology) 5. Tissues (Histology) 6. Organs (Physiology/Anatomy) 7. Organ/body systems (Physiology/Anatomy) 8. Organism (Physiology/Anatomy) IV. Basic Functions of Organisms: A. Maintenance of Boundaries -‫ حدود‬separation of organism from outside world 3  a. virus - protein coat around DNA/RNA interior. b. cell - cell membrane (semipermeable - selective). c. organism - skin B. Movement - Ability to move self and materials. a. cells - cilia and flagella (sperm). b. human muscle cells & bone. C. Responsiveness (Irritability)- respond to both internal and external changes. a. Nervous system quick response. b. endocrine system - longer changes. D. Digestion - breaking down foodstuffs into useable/absorbable forms. E. Metabolism - Reactions in cells & body regulated by endocrine hormones. a. Anabolism synthesizing molecules. b. catabolism - breaking molecules F. Cellular respiration-breaking bond molecules for ATP used in: a. digestive system - mainly carbohydrates & fats b. respiratory system - oxygen and carbon dioxide c. cardiovascular system - distribution of nutrients and gases G. Excretion -Removing all types of waste from the body: a. digestive system - unused foodstuffs b. urinary system - nitrogenous wastes and electrolyte (salt) balance c. respiratory system - carbon dioxide H. Reproduction - creating more organisms of the same species. a. viruses depend on cells for their machinery. b. cells process of division (mitosis). c. human - sexual (sperm and egg). d. regulated by hormones (especially female) I. Growth - increase in the size of a cell, organ, or organism, and the number of cells can increase (mitosis). V. Basic Biological Needs of Humans: A. Nutrients - molecules for structure and energy 1. carbohydrates - primary energy source. 2. Proteins - primarily structural: a. 20 amino acids are basic building blocks. b. Actin and myosin of muscle. c. Receptors for hormones/neurotransmitters. d. Neuropeptides of NS. 3. Fats (lipids) - insulation, energy, structure. a. major component of membranes (phospholipids) b. highest energy content by weight (calories) 4. Vitamins - act as cofactors for enzyme functioning 5. Minerals - Essential for signaling and structure (table inorganic). 6. Water - essential for cellular reactions and transport. B. Oxygen - essential for maximum energy gain from food. 1.Cellular respiration depends on oxygen. 2.Nervous system alone uses 25% of all oxygen in humans. C. Body Temperature - Essential for cellular reactions. D. Atmospheric Pressure - for proper absorption of oxygen. 4  Physiology describes mechanisms at the level of the cell, and then how the cells interact in tissues. It considers how tissues combine to form organs, and how organs function together as a system. Finally, it shows how several organ systems can be integrated to produce an efficiently functioning body. The cell is the fundamental building block of the body; many cells can function, at least briefly in an independent way, but others are so specialized that they can only function as part of a larger group. A typical cell is surrounded by a plasma membrane, which acts as a boundary and a barrier between that cell and its neighbors or the environment. It usually has a nucleus containing the genetic material, which programs the manufacture of proteins and other substances within the cell, and it is composed largely of cytoplasm, which is the non-nuclear part where most of the cell’s functions, are performed. Among the organelles found in the cytoplasm are the mitochondria, which provide energy for cellular reactions, endoplasmic reticulum where proteins are manufactured or substances like calcium are stored, Golgi apparatus where cellular products are packaged for export, and various vesicles and contractile mechanisms according to the function of the cell. Groups of cells are linked together to form tissue in the body. All the tissues of the body can be placed in one of those four categories: 1. Epithelia are tissues, which line cavities and surfaces of glands and consist of sheets or layers of contiguous cells that form an impermeable barrier. 2. Connective tissues consist of collections of cells together with non-cellular material, which they produce, such as fibers or bone; they act as structural, supporting or packing components of the body. 3. Muscular tissues: have cells, which can contract to move, the beating of the heart or control of fluid flow in internal organs. 4. Nervous tissues: contain cells with the specialized property of electrical impulses and transmitting information around the body. Organs: These are the functional units of the body such as the heart, brain, kidney, and spleen, and can be seen as separate entities when one looks inside the body or at the body surface. An organ may consist of one type of cell or tissue or may contain a very large variety of tissues; an organ has a single specialized function, such as the heart, or it may have very many functions, like the liver. While several organs are parts of more complex organs function together. Many of the organ systems are inter-connected and interdependent; for example, almost all the body’s organs receive branches of the circulatory and nervous system. Homeostasis, the correct function of the body requires the integration of function of the various organ systems. The body has several very delicately balanced control mechanisms, whose function is to ensure the constancy of the internal environment. The maintenance of a constant internal environment despite variations in external conditions is a prerequisite for independent existence. 5  Chapter Two NUTRITION Nutrition is the science of nourishing the body. Nutrient substances for this purpose are provided by food. Many of the nutrients have been isolated and identified and are now available as pure chemical compounds. Food is a material, which, after ingestion by animals, is capable of being digested, absorbed, assimilated, and egestion. The diet of farm animals consists of plants and plant products, although some foods of animal origin such as fishmeal and milk are used in limited amounts. Animals depend upon plants for their existence and consequently, a study of animal nutrition must necessarily begin with the plant itself. Plants can synthesis complex materials from simple substances such as carbon dioxide from the air, water, and inorganic elements from the soil, using photosynthesis using energy from sunlight. The greater part of the energy, however, is stored as chemical energy within the plant itself and it is this energy which is used by the animal for the maintenance of life and synthesis of its body tissues. Plants and animals contain similar types of chemical substances and are grouped according to constitution, properties, and function. Table 1. The main components of foods, plants, and animals are: Food 1.water 2. Dry matter 1. Organic 2. Inorganic Carbohydrates, lipids, proteins, and vitamins Minerals and water THE PHYSIOLOGICAL FUNCTION OF FOOD: The physiological function of food may be divided into three general categories: (1) The need for food nutrients to supply energy: Nutrients, which supply energy; include carbohydrates, fats, and proteins. (2) The need for food nutrients to build and maintain body tissue: The building and maintenance of the body use proteins, minerals, and water. (3) The need for food nutrients to regulate body processes: All the nutrients play a role in the regulation of the body processes. I- THE CARBOHYDRATES Carbohydrates serve a unique function in nature because they are the chief source of nutriment for the animal kingdom. Through the process of photosynthesis, which involves a series of complex chemical reactions, the chlorophyll of the plant can use the sun’s energy to synthesize carbohydrates from the carbon dioxide of the air and the water from the soil. Thus, it is through the medium of the plant that animals can have food. All carbohydrates contain carbon, hydrogen, and oxygen. Many carbohydrates have the general chemical formula Cn (H2O) n. The carbon (C) atoms are bonded to hydrogen atoms (-H), hydroxyl groups (-OH; and carbonyl groups (-C=O), whose combinations, order, and geometric arrangement lead to many isomers with the same chemical formula but different properties. 6 A – Monosaccharides: They are formed of only one sugar unit and cannot be hydrolyzed: Trioses as glyceraldehydes (C3H6O3). Tetrises as eryterose (C4H8O4) Pentose as ribose, xylose (C5H10O5). Glucose (C6H12O6): It is grape sugar, and is widely distributed in nature:  In the plant, glucose is found in fruits, vegetables, and sap. Found in corn sugar and corn syrup, honey, and molasses. o In animals, it is a product of starch, sucrose, maltose, and lactose.  Functions of glucose: o It is found in the blood of animals; it serves as a source of immediate energy for body cells and tissues. A man’s normal level of blood glucose is about 80 mg of glucose per 100ml of blood. o Blood glucose originates from dietary carbohydrates, glycogen stores, or carbohydrate synthesis. o Glycogen, starch, and cellulose are formed from glucose. o Glucose is entered in the form of sucrose, maltose, and lactose. Fructose and Galactose: These two monosaccharides have the same chemical formula as glucose but differ in the arrangement of chemical groups along the chemical chain. Fructose: It has the sweetest taste; it is fruit sugar. It is found in the nectar of flowers, fruits, and vegetables. It is in honey (40%) and (8 %) molasses. It is produced during the hydrolysis of sucrose in digestion. Galactose:  It does not occur free in nature but is produced in the body during digestion by the disaccharide, lactose, which occurs in milk.  The lack of an enzyme to convert galactose to glucose results in a disorder in infants known as galactosemia. (B). The disaccharides: Sucrose, maltose, and lactose in the diet. Sucrose:  Found: White and brown sugar, produced from sugar cane and sugar beets. Sucrose occurs in some fruits and vegetables but is found more frequently in sweetening agents. Maple syrup and molasses contain more than 50 percent sucrose whereas lesser amounts are found in sorghum syrup, golden syrup, and honey. Functions: The digestion of sucrose forms glucose and fructose. Maltose and Lactose: (i). Maltose or malt sugar:  Occurs in sprouting grains, malted cereals, and malted milk. It is found only in corn syrup (26%) and corn sugar (4%). It is an intermediate product of starch digestion.  Functions: Digestion maltose yields two molecules of glucose. (ii). Lactose or milk sugar: It is found only in the milk of mammals. Functions: The digestion of lactose forms glucose and galactose. 7 (C) The polysaccharides: The polysaccharides are complex carbohydrates that contain many 2000 simple carbohydrate units arranged in long chains in either a straight or a branched structure occur in plants either as reserve food or as structural materials. Starch:  Sources of Starch: The plant produces roots and seeds. Corn, millet, rice, and wheat, the cereal grains, contain as much as 70% of this starch, whereas the percentage of starch found in the dried seeds of leguminous plants (e.g., beans, peas) averages about 40 %.  Functions: The digestion of sucrose forms glucose in the body. Dextrin: Sources: As metabolic products in animals and plants, and in germinating seeds. Dextrin is found in corn syrup. Functions: 1. Dextrin is an intermediate product of the hydrolysis of starch and glycogen to maltose and finally glucose. 2. Dextrin gives a characteristic flavor to baking food. Glycogen:  This is a polysaccharide that is found in the liver and muscle of all animals.  Glycogen yields molecules of glucose on hydrolysis. Only about 350 gm of it is found in the body as a reserve.  Muscle glycogen, which is about two-thirds of the total reserve, and liver glycogen is available as a source of energy to the body cells.  Formation of glycogen takes place when blood glucose increases beyond its normal level and extra amounts of glucose in the bloodstream.  In contrast, the breakdown of glycogen takes place when glucose is not being absorbed from the intestinal tract, liver glycogen, must be utilized until the cells can begin to synthesize glucose from non- carbohydrate sources.  An average of about 100 gm of glycogen, or 400 Cal, of energy, is stored as liver glycogen. Cellulose: Found in cell walls of all plants, in fibers and dried fruits, whole-grain cereals, nuts, fresh fruits, and vegetables. Functions: 1. In human diet: a. It is fiber in the human diet, and is not important to most mammals as a direct source of food because they lack the enzymes necessary to hydrolyze it to glucose. b. It is important to aid normal peristaltic action of intestines and play roles, in the removal of waste products. c. It is provides of roughage to the intestinal tract to absorb moisture and provides bulk to stimulate evacuation of the large intestine. 8  d. Daily need for fiber, estimated to be 4 to 7mg, obtained. 2.In herbivorous animals have bacteria in their rumens or stomachs that activate the breakdown of cellulose to useable carbohydrate products. Agar agar: It is formed from galactose units. It is prepared from seaweed. It is used as a culture for bacteria and treatment of constipation. Mucopolysaccharides: These occur in animal tissues either combined with proteins or free. They are in the structure of most tissues and are not oxidized to give energy. (Heparin, Muoitin sulfate, chondroitin sulfate, Hyaluronic acid, blood group substances, and some hormones). (a) Heparin: It consists of glucuronic acid and galactose amine or glucose amine and five molecules of sulphuric acid. It is produced by most cells. Function: It is a blood anticoagulant i.e. It prevents blood clotting. (b) Blood group substances: (A, B, AB, and O) are formed from protein and mucopolysaccharide. They determine the blood group of the individual. (c)Hyaluronic acid contains acetyl-D-glucosamine, which is found in the skin, synovial fluid, and the umbilical cord. It is a viscous substance that lubricates the joints. (d) Chondroitin sulfate: component of cartilage, tendons, bones. Functions OF Carbohydrates: (A)-The main function is to supply energy for the body processes, yield energy, (4 Cal. per gm). Normal adults need about 500 carbohydrates calories per day either in the diet or derived from body stores of protein or glycogen. (B)-The role of carbohydrates in the utilization of body fats: 1. The expression “fat burns in a flame of carbohydrates” is often used, complete oxidation of fats to carbon dioxide and water depends on an organic acid, formed during the oxidation of carbohydrates. 2. When there are not enough carbohydrates available, the body produces higher-than-normal amounts of ketone bodies. This leads to increased acidity and decreased alkalinity in the blood, a condition known as ketosis. If the blood's alkalinity is significantly reduced, ketosis can lead to a coma. Ketosis can occur in diabetes when cells cannot use glucose, and in starvation when cells rely on the body's fat stores for energy. (C)- Carbohydrates exert a sparing effect on protein: 1. At tissue building and maintenance, more protein is used for energy when the fat and carbohydrate content of the diet is below the level then when it is sufficient. 2. The first physiological demand of the body, the energy need, must be satisfied before nutrients are used for other functions. 3. carbohydrates is to spare protein for its primary purpose, that is, the building and repairing body tissue. (D)-They play important roles in the function of the intestinal system: 1. They serve as a source of energy for the microorganisms that synthesize some of the vitamins B-complex in the intestinal tract. 2. Cellulose’s provide fiber and bulk that promote healthy intestinal hygiene. (E)-They add flavor to the diet baking, and breads furnish body with protein. 9  2 - THE LIPIDS General characterized:  The lipids are an important group of chemical compounds that are widespread.  They are characterized by their insolubility in water and their solubility in ether, chloroform, benzene, and other fat solvents.  Like carbohydrates, lipids contain carbon, hydrogen, and oxygen, and some also have phosphorus and nitrogen in their chemical structure.  The lipids are classified into three groups according to their chemical structure: the simple lipids, the compound lipids, and the derived lipids.  The fatty acids, fats and oils, phospholipids, and sterols are several of the groups of compounds in the study of nutrition.  THE FATTY ACIDS  Fatty acids are composed entirely of carbon, hydrogen, and oxygen.  They are found in all the simple and compound lipids.  The simplest fatty acid is acetic acid, which gives vinegar its sour taste.  The fatty acids are found in butyric, caproic, myristic, palmitic, stearic, oleic, and linoleic (Table 1).  There are short-chain (under 12 carbon atoms), are found in coconut oil, milk fat, and butterfat  Long-chain (16 to 18 carbon atoms), in the average diet most of them are long-chain varieties.  And extra long-chain fatty acids (more than 20 carbon atoms) occur in fish oils and peanut oil. Types of fatty acids According to their degree of saturation or unsaturation (Table 1): The three general types of fatty acids found in foods are classified. saturated fatty acids: stearic acid, contain much hydrogen atoms as the carbon chain can hold. 10  The saturated fatty acids comprise about 40 % of the average human diet. sources. Are concentrated in foods from animals sours. However, the plant products, chocolate and coconut, both contain appreciable amounts of saturated fatty acids.  The most common ones found in foods are stearic acid and the long-chain fatty acid, palmitic. Butter and cow’s milk contain about 12 per cent stearic acid; other animal products contain larger amounts. The palmitic acid content of most animal fats ranges from 20 to 30 per cent.. Monounsaturated fatty acids: There is only one “double bond” linkage (two hydrogen atoms missing) in the carbon chain.  The quantity of monounsaturated fatty acids in the average human diet matches that of the saturated ones; about 40 %. The best example of this type is the long-chain fatty acid, oleic, which is found in appreciable amounts in most foods.. Polyunsaturated fatty acids may have 2, 3, 4, or more “double- bond” linkages in the carbon chain with 4, 6, 8, or more hydrogen atoms missing. This group of fatty acids is sometimes further classified as dienoic, trienoic, tetraenoic, and so forth, to identify the number of “double bond” linkages. Linoleic acid is classified as a dienoic acid, lnolenic and arachidonic acids as trienoic and tetraenoic, respectively.  The polyunsaturated fatty acids comprise a family of compounds that include the essential fatty acids and the extra long-chain fatty acids. The quantity of these acids in the average human diet is much less than either the saturated or monounsaturated ones. Although corn oil and safflower oil are among the richest food sources of this fatty acid group, fats from nuts, peanuts, poultry, legumes, and leafy-green vegetables are also important sources. 11 Table (1): Some of the Fatty Acids in Fats Number of Length of Occurrence Name Carbon Carbon Type In Food Atoms Chain Acetic 2 Short Saturated Vinegar Butyric 4 Short Saturated Butter Caproic 6 Short Saturated Butter Caprylic 8 Short Saturated Coconut Nutmeg and Myristic 14 Long Saturated mace Lard and palm Palmitic 16 Long Saturated oil Steric 18 Long Saturated Beef tallow Oleic 18 Long Monounsaturated Olive oil Linoleic 18 Long Polyunsaturated Corn oil Chupandonic 22 Extra long Polyunsaturated Fish oils THE FATS AND OILS:  A fat molecule consists of two main components—glycerol and fatty acids. Glycerol is an organic compound (alcohol) with three carbons, five hydrogens, and three hydroxyl (OH) groups. Fatty acids have a long chain of hydrocarbons to which a carboxyl group is attached, hence the name “fatty acid.” The number of carbons in the fatty acid may range from 4 to 36. The most common are those containing 12–18 carbons. In a fat molecule, the fatty acids attach to each of the glycerol molecule's three carbons with an ester bond through an oxygen atom  The ratio of carbon and hydrogen to oxygen in the fat molecule, is much greater than in a carbohydrate. For example, a fat found in beef which is called tristearin has 110 atoms of hydrogen to 6 atoms of oxygen, ascompared to two-to-one ratio of the same elements in the carbohydrate glucose. 12  When fat is burned in the body additional oxygen must be supplied by the cells to combine with all the carbon and hydrogen atoms, thus producing more heat. For this reason, a gram of pure fat gives the body 9 Cal. of energy, whereas a gram of pure carbohydrate yields only 4 Cal.  The nature of fat depends on the kinds of fatty acids linked to the glycerol core, the length of the carbon chain of the fatty acids, and the degree of saturation or unsaturation of the fatty acids.  The fatty acid pattern of fat may be three identical acids, three different ones, or a combination of two alike and one different.  The three fatty acids found in the fat tristearin are identical, that is, the long- chain, saturated stearic acid. When all the fatty acids in a fat molecule are the same, the fat is called a simple glyceride. Mixed glyceride is the term used to identify a fat with different fatty acids in its chemical structure. Tristearin is designated as a simple glyceride. The form of a glyceride, whether it is liquid or solid, depends on the kind of fatty acids in its structure.  Glyceride that is liquid at room temperature, is called oil and contains, more of the unsaturated fatty acids, whereas a glyceride that is solid at room temperature contains more of the saturated fatty acids in its structure and is called a fat.  Oils are the predominant glycerides in plants; fats are the predominant glycerides in animals.  The fats of animals differ from species to species and even vary in composition in the different parts of the body of the same species. This difference is to be expected because the fat around the kidneys cushions these vital organs to protect them from injury. Generally, the fats in the more active parts of the animal organism have a lower melting point and are more unsaturated, which means they are more easily oxidized than those stored as fatty tissues. 13 FUNCTION OF FATS AND OILS: Fats and oils play an important role in human nutrition because they are sources of energy and the essential fatty acids in the diet. In addition, fat deposits in the body serve as insulation and protective cushions for the organs. 1- Source of Energy: Fats are the most concentrated form of energy in foods, Yielding more than twice as much energy as equal to either carbohydrates or proteins because fats contain more hydrogen and carbon and contain less oxygen in structure. 2- Sources of Essential Fatty Acids:  It is known that the body can synthesize fatty acids from excess carbohydrates. However, some fatty acids are essential for good health, which the body cannot produce on its own. These essential fatty acids include linoleic, linolenic, and arachidonic acids.  The importance of these factors in nutrition was first demonstrated when rats that were fed a ration devoid of fat developed a scaly condition of the skin and tail, failed to grow, and eventually died.  All the known fatty acids were added to the fat-free diet of the animals, but only linoleic, linlenic, and arachidonic acids were the lipids effective in preventing this disorder.  In the animal organism linoleic acid has been shown to play an: a- Essential role in reproduction and lactation. b- Serves as a protective agent against radiation effects and to c- Prevents the excessive loss of water from the body by the development of the permeability of the skin capillaries. 3-Protection of the Body in two ways: a- The deposits of fat under the skin act as nonconductors of heat, helping to insulate the body and prevent the rapid loss of heat. b- The viscera and certain organs of the body, such as the kidneys, are supported and cushioned by fat. 4-The phospholipids and sterols: 14  A-The phospholipids:  They are found in very living cells. They aid in the transport of fatty acids in body cells.  Types of phospholipids (lechithins, cephalins, and sphingomyelins) are formed from glycerol, fatty acids, phosphoric acid, and a nitrogenous base. Choline is one of the nitrogenous bases found in phospholipids. B- Sterols:  Ergo sterol, (a plant sterol), 7-dehydrocholesterol (an animal sterol), and cholesterol are three important compounds found in the group of derived lipids known as sterols and are two forms of vitamin D.  Cholesterol, the best known of sterols, has attracted attention because it is an association of elevated blood cholesterol levels with atherosclerosis and coronary heart disease.  Cholesterol, a constituent of animal tissues, in cells and body fluids. Some of it is combined with fatty acids to form bound cholesterol, but for the most part, it is found in the body as free cholesterol.  The sum of the free and bound forms is referred to as total cholesterol. The body’s supply of cholesterol is derived in two ways:  1-From the foods in the diet (exogenous cholesterol).  2-By synthesis in the tissues, in the liver (endogenous cholesterol).  Blood cholesterol values vary from species to species and vary with age in the same species. The average serum cholesterol value, expressed as milligrams per 100 ml, is about 80 for the rat, 120 for the monkey, 140 for the dog, and 220 for the man. In man the total cholesterol value (milligram per 100 ml) increases with advancing age: 65 in fetal cord blood, 190 among young adult men and women (18 to 35 years), and 45 among middle-aged men and women (45 to 65 years).  Eggs, butter, lard, and meats are examples of foods rich in cholesterol  foods from plant sources are devoid of sterol. 15  3-THE PROTEINS AND AMINO ACIDS General characterized:  The word protein, derived from the Greek language, means “to come first”.  The chemical elements found in each protein are carbon, hydrogen, oxygen, nitrogen, Sulfur, phosphorus, iron, iodine, and cobalt of the elements present in the protein.  Nitrogen is the distinguishing protein because it does not occur in fat and carbohydrates and is always present in protein.  Proteins are formed from amino acids by the amino group of one acid linking to the carboxyl group of another with the elimination of a molecule of water. This grouping which joins the amino acids together is called the peptide linkage. A dipeptide results when two amino acids are joined by the peptide bond; three amino acids joined by two peptide bonds result in a tripeptide, and many amino acids joined together are polypeptides.  Proteins are classified based on their solubility and other physical properties. PROTEINS AND THEIR CLASSIFICATION: (1) Simple proteins: protein substances that yield amino acids after complete hydrolysis. Examples are albumen of egg, zein of corn, keratin of hair, and globin of hemoglobin. (2) Compound or conjugated proteins: compounds of a protein with some other non-protein molecules or with a metal. Examples are hemoglobin (protein + heme) in blood, casein (protein + phosphoric acid) in milk, mucin (protein + carbohydrate) in saliva, and lipoprotein (protein + lipid) in blood plasma. (3) Derived proteins: products formed from the partial breakdown of proteins by the action of heat and other physical forces, or by hydrolytic agents. Examples are peptones, polypeptides, and peptides which are mixtures of amino acids with decreasing numbers of amino acids in the chain length. 16 THE AMINO ACIDS:  Proteins are made up of amino acids, often called “building stones” of protein. As the name suggests, an amino acid is a compound which contains an amino group (- NH2) and carboxyl or acid group (-COOH).  Most food proteins are comprised of 12 to 22 amino acids linked together in one large molecule; however, some proteins may have as many as 280 amino acids in a single molecule.  Listed below are 22 of the amino acids that occur commonly in foods and body proteins, and although there are many more amino acids, they are not of recognized importance in nutrition: Alanine Hydroxyproline Serine Arginine Isoleucine Threonine Aspartic acid Lucine Thyroxine Cystine Lysine Tryptophan Glutamic acid Methionine Tyrosine Glycine Norleucine Valine Histidine Phenylalanine Hydroxyglutamic. Proline FUNCTIONS OF PROTEIN: A- Bodybuilding and Maintenance Substance:  Protein is present in every cell in the body.  The nature and behavior of protein in cells of various tissues differ, each contributing certain distinguishing characteristics.  The protein in muscle allows for contractibility and the capacity of muscle for holding fluid which gives that tissue a certain firmness even though it is composed of at least 75 percent water. ;  The protein in epithelial tissue is hard and insoluble, providing a protective covering for the body.  The protein in the walls of the blood vessels contributes elasticity, essential for the maintenance of normal blood pressure. 17   The mineral matter of bones and teeth is embedded in a framework composed of protein.  The need for protein to build new tissue and to maintain and repair the old continues throughout life.  Proteins in the body tissues are not stable chemical combinations. They are in a state of dynamic equilibrium, which means that body proteins are continually being broken down and replaced by new proteins synthesized from amino acids from both dietary and tissue sources. More than one- half of the protein of the liver and intestinal mucosa may be broken down and resynthesized in ten days. B-Protein Synthesis :  The preparation of amino acids in which carbon or nitrogen is radioactive made possible the initial breakthrough in the phenomena of protein synthesis.  The amino acids released from the degraded proteins are replaced by new ones from the blood in a continuous interchange between tissue and blood. Also, for a particular protein to be synthesized, all the amino acids needed for its formation must be available simultaneously and in the required proportion.  If even one of the needed amino acids is missing in the diet or the amount provided is insufficient, growth failure occurs in the young.  In adults if the amino acid is not available when needed, body tissue is broken down to supply it.  The necessity of having available simultaneously all amino acids essential for the synthesis of tissue proteins has practical implications in the planning of diets.  All functions of the living cell, including protein synthesis, reside in the deoxyribonucleic acids (DNA) found in the chromosomes of the cell, which in turn are in the nucleus. DNA operates through an intermediate set of ribonucleic acids (RNA)known as messenger-RNA (M-RNA). 18  Imprinted or coded on M-RNA are the directions for making one kind of protein. There are at least as many kinds of M-RNAs as there are different proteins. Other RNAs, known as transfer RNAs, pick up and move specific amino acids to M-RNA. The M-RNA then lines up the amino acids for the synthesis of a specific protein in a manner dictated by the code it carries from DNA. C-Building Substance for Enzymes, Hormones, and Antibodies:  Some of the compounds essential in vital processes in the body are made from amino acids.  In this group of nitrogen-containing compounds are the body enzymes, as digestive enzymes, and oxidation enzymes in the tissue cells.  Some of the hormones are nitrogen-containing compounds.  Still another protein compound of particular significance is gamma globulin, a normal protein in the blood that has been identified as an antibody.  Animals subjected to prolonged protein undernutrition exhibit a pronounced loss of the ability to manufacture antibodies and consequently are less able to resist infection.  The antibody-producing capacity is quickly restored when adequate amounts of high-quality proteins are ingested. D-Body Regulating Substance: 1- Movement of fluid. Protein is one of the factors that contribute to the control of fluid movement in and out of cells and movement to and from the bloodstream. The large size of the protein molecule prevents its passage through membranes, whereas water and materials in solution pass readily. Fluids move from a medium of lesser concentration to one of greater concentration. The process (osmosis) is one of the means the body has of maintaining normal composition of the blood and other body fluids. 2- Maintenance of normal reaction in the tissues. There are several mechanisms for maintaining a normal balance between acidic and basic substances in the body. Blood proteins help to maintain normal, slightly alkaline reactions of 19  the blood by buffering the action of protein blood plasma and the action of hemoglobin in the red cells. Hemoglobin carries CO2 to the lungs to be eliminated as a gas. If CO2 was not eliminated it would dissolve in water and from carbonic acid. Thus, hemoglobin and the lungs work together in the regulation of the acid-base balance of the blood and extracellular fluid. E-Source of Energy  One gram of protein supplies approximately 4 Cal. The extent protein is used for energy depends on the amount of carbohydrates and fat in the diet as well as the total intake of protein. There are several pathways that this fraction may take; it may be oxidized directly; it may be converted to either carbohydrate or fat; or it may be changed back to the nonessential amino acids by adding an available amino group, a process by which amino acids can be synthesized in the body. As for the nitrogen removed from the protein, most of it is eliminated as waste by way of the kidney. THE NUTRITIONAL VALUE OF PROTEINS 1- Incomplete proteins neither maintain life nor support growth. Most vegetable proteins are incomplete; the glycinin of soybeans is an exception. The zein of corn and the animal protein gelatin are incomplete. 2- Complete proteins maintain life and provide for normal growth of the young. The proteins of animal sources are complete including those of meat, fish, fowl, eggs, and milk; gelatin is an exception. Some proteins in legumes, grains, and nuts are complete such as glycinin of soybeans, glutenin of wheat, glutelin of corn, and excelsin in Brazil nuts. 3- Partially complete or incomplete proteins maintain life but fail to support normal growth. Examples include gliadin of wheat, hordein of barley. Essential Amino Acids:  There were ten amino acids found to be needed in the food intake; the body was unable to synthesize them at a rate sufficiently rapid to provide for the needs of growth. They are called “essential” or “indispensable” amino acids.  The ten amino acids essential for growth of young rats are listed in Table 3. 20  Those amino acids not needed in the diet are the ones the body can synthesize at the rate needed. They are designated as “nonessential” or “dispensable.” Eight amino acids were found to be essential for maintenance in young men, as indicated in Table (2). Nonessential Amino Acids:  The term nonessential as applied to amino acids should not mislead us as to the importance of these amino acids in the body. It simply means that they do not have to be provided “ready-made” in the diet; the body can supply them as it needs them.  To demonstrate that they are important, it may be pointed out that they comprise 40 percent or more of the tissue protein.  When they are supplied in the food intake, as they always are in an ordinary diet, less of the essential acids are needed.  The nonessential amino acids can supply nitrogen for the synthesis of some body compounds for which essential amino acids would otherwise be used. Table (2). Amino Acids are Essential for growth in Young Rat, Growth in Children, and for Maintenance in Adult Men.  Amino Acids essential for growth in young rats are ten: Arginine, Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine.  Amino Acids Essential for growth Children are night: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan and Valine.  Amino Acids Essential for growth young men are eight: Isoleucine, Leucine,  Lysine, Methionine, Phenylalanine, Threonine, Tryptophan and Valine Effects of protein deficiency: 1- Anemia and muscle wasting. 2- Poor resistance to infection. 3- Hypoproteinaemia. 4-Poor healing of wounds. 5- Oedema due to a decrease in osmotic pressure of plasma proteins. 6-Decrease in all endocrine and exocrine secretions. 21  4-Vitamins Vitamins do not constitute a class of chemically related compounds, as proteins or carbohydrates do. Indeed, they have nothing in common chemically except that they are all organic substances. What then is a vitamin? Vitamins derived from vital amines were coined by Funk to describe these accessory food factors. It is a naturally organic constituent of the diet that cannot be manufactured by the body having the following characteristics: 1. They play in plants and their importance in the metabolism of all living organisms, these are indispensable for the life of normal tissue activities. 2. They act as co-enzymes directly facilitating metabolic processes. 3. Animals depend on vitamins from plants and microorganisms because these can prepare their vitamins, while animals are unable to do so. 4. They do not enter the structure of the tissues. 5. Vitamins are named after the letters of the alphabet. 6. Vitamins can be divided into two groups based on their solubility, that is: Fat-soluble and water-soluble. A-Fat-soluble vitamins: These are present in fats of natural food and are soluble in fat solvents, (Vitamins, A, D, E, and K.) 1-Vitamin A (Antixerophtalmic): Primary sources: A- Animals' sources: 1. Vitamin A: in the liver this organ is likely to be a reliable source of liver animals and fish liver oil (cod-liver, halibut-liver, and Shark-liver). 2. Egg yolk, butter, milk, kidney, and fat of muscles. B-Vegetables sources: Vitamin A does not exist as such in green, or yellow. vegetables and fruits (Carrots, tomato, lettuce, apricots,), present as provitamins in the form of certain carotenoids which can readily be converted by the animal into the vitamin. Conversion of carotene into vitamin A occurs. in the intestinal wall and in the liver. Table5. Some typical values for liver reserves of vitamin A (µg/g liver) in species: 22 Vitamin 90 45 75 30 180 180 270 600 3000 6000 (µg/g liver) Species Man Cow Rat Pig Sheep Horse Hen Codfish Halibut Bear Functions of vitamin A in the body: A-In the eye: 1. Vitamin A is oxidized to the aldehyde which is converted into the all-cis isomer. The latter then combines with the protein opsin to form rhodopsin (visual purple) which is the Photoreceptor for vision at low light intensities. 2. When light falls on the retina, rhodopsin breaks down into two parts, opsin and all-cis retinaldehyde. This conversion results in the transmission of an impulse up the optic nerve. The all-trans retinaldehyde is isomerizes in the dark back to all-cis retinaldehyde which recombines with opsin regenerating rhodopsin and thus renewing the light sensitivity of retina. B-In its second role vitamin A: 1. It prevents the drying of body membranes (cornea, nose, and throat). 2. It ensures proper growth of nerve tissues and enamel of teeth and bones. 3. It controls the stability of cell and sub-cellular membranes. 4. It may have a role in protein synthesis. Deficiency symptoms: 1. Night blindness. 2. Nervous disorders. 3. Mucopolysaccharides are inhibited. 4. An increase in cerebrospinal fluid (CSF) pressure. 5. Dryness and roughness of mucous membranes, especially the cornea. Hypervitaminosis A:  Administration of large doses of vitamin A to infants and small children proved toxic, due to this vitamin not easily excreted.  The principal symptoms are, periosteal thickening of long bones, painful joints loss of hair, irritability, loss of appetite and weight loss. Requirements: minimum daily about five thousand international units for adults. Storage of vitamin A: The vitamin A is stored in the liver and absorbed from gut. 2-Vitamin D. (Antirachetic) or [anti-ricketic vitamin]: 23 This is a group of fat-soluble vitamins, D1 to D5. The most important are D2 and D3. Both are produced by the action of ultra-violet rays and sterols under skin. Primary sources: A- Animals' sources: 1-The best sources are cod liver oil, halibut liver and shark liver oils. 2- Egg yolk and liver, while milk is poor in Vitamin D. B- Plants sources: green vegetables are poor in vitamin D except in sun- dried roughages and the dead leaves of growing plants. C. sun energy. Physiological functions: 1. Vitamin D stimulates calcium and phosphorus absorption from the small intestine. 2. Vitamin D stimulates calcium and phosphorus deposition in bone, and it decreases calcium excretion in urine. Deficiency of vitamin D: 1. In young animals causes rickets which is a disturbance in the formation of bones due to decrease in the Ca and P content in the cartilaginous ends of bones. Consequently, bones become soft, especially in young individuals. 2.3. Rickets and osteomalacia are not specific diseases necessarily caused by vitamin D deficiency but can be caused by lack of calcium or phosphorus or an imbalance between these two caused by lack of calcium or phosphorus or an imbalance between these two elements. Hypervitaminosis D Large doses of vitamin D to infants and children are harmful. Anorexia, nausea, vomiting, weakness, and polyuria occur. Abnormal calcification of the tissues including lungs and kidneys is also found. Human requirements: The requirements of normal infants and children depend on exposure to ultraviolet light. The daily requirement is 400 I.U. for infants daily. Double this amount is advised for pregnant and lactating women. 24 3-Vitamin E. (Tocopherol, antisterilitic: Primary sources: A) Plant: from, wheat germ oil, lettuce, peanuts, and embryos of many seeds. B) Animals: Milk, milk products, and egg yolk. Need bile salts to be absorbed. Physiological roles: 1. Vitamin E acts within the phospholipid’s membrane of the vital organelles in preventing the formation of peroxides which are formed before they can damage cell. 2. It is an antioxidant of the lipid configuration of cell membranes. 3. Tocopherols increase the resistance of erythrocytes to hemolysis. 4. Vitamin E roles in the development and function of the immune system. 5. Vitamin E is necessary for a honeybee to be a queen. Deficiency symptoms: The absence of this vitamin causes a reduction in fertility in experimental animals. In females, death of the fetus in pregnant female rats occurs, and in males degeneration of the germinal epithelium occurs. Requirement.:The need for vitamin E is related to the amount of polyunsaturated fatty acids in the diet, daily amounts for adults range from 25-30mg. 4-Vitamin K [alpha naphthoquinone, antihaemorrhagic]- Vitamin K was originally discovered in 1935 to be an essential factor in the Prevention of hemorrhagic symptoms produced in chicks. The discovery was made by a group of Danish scientists who gave the name (Coagulation factor) to the vitamin, which became shorted to the K factor and eventually to Vitamin K. Primary sources: fat-soluble vitamin K found in: A. Green vegetables such as spinach, cabbage, Soya bean, tomatoes, and in most green. B. Animal origin, such as egg yolk, fish, and liver. C. Vitamin K2 is synthesized by bacteria in the digestive tract. Function: 1. It is necessary for the formation of prothrombin in the liver cells. 2. It plays a vital role in oxidative phosphorylation in mitochondria. Deficiency symptoms: 25  1. Failure of blood-clotting mechanisms and (anaemia in chicks). 2. And bleeding occurs from a minor injury. 3. Symptoms of vitamin K deficiency have not been reported in ruminant animals under normal conditions, and it is generally considered that bacterial synthesis in the digestive tract supplies sufficient vitamins for the animals’ needs. Several microorganisms are known to synthesize vitamin K, including Escherichia coli. A disease of cattle called "sweet clover disease" is associated with vitamin K in that spoiled sweet clover contains a compound, dicoumarol, which lowers the prothrombin content of the blood. The disease can be overcome by administering vitamin K to the animals. For this reason, dicoumarol is sometimes referred to as an antivitamin. Hypoervitaminosis K: A large dose of vitamin K to infants causes an increase in the level of blood bilirubin and jaundice. B-Water-soluble vitamins: Vitamin B complex: The vitamin includes all having the property of being soluble in water, and most of them are components of coenzymes. 1-Vitamin B1 (Thiamine): The member of the B complex contains pyrimidine and thiazol, molecules. In ruminants, all the vitamins in this group can be synthesized by microbial action in the rumen and provide amounts for normal metabolism in the host and secretion of adequate quantities into milk. However, under certain conditions, deficiencies of thiamin and cobalamin can occur in ruminants. Sources: 1. Animal products: egg yolk, liver, kidney, and spleen. 2. Plant sources: Present in yeast, germ of cereal grain, and is present in the aleuronic layer, beans, peas, and green leafy crops in some fruits. Biochemical roles [physiological functions: 26 1. The main function of vitamin B1 is to produce various enzymes that break down sugar. Vitamin B1 roles in the formation of co-enzymes involved in Krebs cycle. 2. Carbohydrate metabolism in all cells of the body depends on the presence of coenzyme thiamine pyrophosphate (TPP) or co-carboxylase, which is essential in the oxidative decarboxylation of keto acids, including pyruvic and - ketoglutaric to acetyl coenzyme A. 3. Absence (TPP), oxidative metabolism of glucose would not be possible and about 90 % of the energy contained in this compound would be lost. Deficiency symptoms: Loss of appetite, emaciation, muscular weakness, and progressive dysfunction of the nervous system, (Nerve cells are dependent on utilization glucose and for this reason; a deficiency of the vitamin has serious effect on nervous tissue. This vitamin causes Beriberi in humans and Polyneuritis in birds. These diseases are caused by an accumulation of pyruvic acid and its reduction product, lactic acid, in the body cells and by interference in nervous conditions, thus causing muscle weakness, decreased digestive juices, weak peristaltic movement of the alimentary canal and loss of appetite. Since acetyl coenzyme A is an important metabolite in the synthesis of fatty acids, fat synthesis is reduced. This disease is prevalent among people who feed on polished rice. Distribution of vitamin B1: It is absorbed from gut and stored in liver, brain, kidney and heart. Requirement: The daily allowances depend on the diet. A diet rich in protein and fat decreases the requirements while a diet rich in carbohydrates increases it. Averages are 1.5mg/day for adults, 2mg/day for pregnant and lactating women. 2- Vitamin B2 (Riboflavin) (C17H20N4O6): Sources Riboflavin is present in all biological materials: 1. Rich sources are milk (especially whey), liver, eggs, and heart. 2. The vitamin can be synthesised by all yeast. 3. In green vegetables, fungi, most bacteria, some fruits as banana and oranges. 27 Function: 1. It is a cofactor in oxidative phosphorylation; it acts as a carrier of oxygen. 2. It is also essential for growth. 3. Riboflavin is an important constituent of flavoproteins. The prosthetic group of these compound proteins contains riboflavin in the form of the (flavin mononucleotide or FMN), which functions, in the animal body; they are all concerned with chemical reactions involving the transport of hydrogen. Their importance in carbohydrate and amino acid metabolism. Deficiency symptoms: Vitamin B2 deficiency causes dermatitis in the face, eyes, hands, and feet; redness of the tongue; and inflammation in the alimentary canal, detrimental effect on the reproductive system of young sows. Chicks reared on riboflavin– deficient diet grow slowly and develop curled toe paralysis a specific symptom, caused by peripheral nerve degeneration, in which the chicks walk on their hocks with the toes curled inwards. In breeding hens, a deficiency results in decreased hatchability. Requirements mg/day: Adult, 1.7, pregnancy 1.8, and lactation 2 mg /day. 3-Niacin (Nicotinic acid) Vitamin B3): Sources: Nicotinamide can be synthesised from tryptophan in the body tissues, and since animals can convert, the acid to the amide-containing coenzyme 60 mg of tryptophan gives 1mg of Nicotinamide. Rich sources of vitamins are liver, milk, and eggs. Also, found in groundnut, sunflower meals, and cereal grains. Metabolism (physiological functions): In the animal body is the active group of two important coenzymes, nicotinamide-adenine dinucleotide (NAD) and nicotinamide-adenine dinucleotide, phosphate (NADP). These coenzymes participate in the mechanism of hydrogen transfer in the living cells. Deficiency symptoms: A disease called pellagra: all functions of the body depressed; lesions of epithelia 28 and involvement of the nervous system may lead to dermatitis, diarrhea, and dementia. Glossitis and stomatitis: (Inflammation of the tongue and mouth). Maize is deficient in nicotinic acid. It is also poor in tryptophane and thus, in farmers who depend on maize as their main diet pellagra is common. Other deficiency symptoms cause: 1. Pernicious anemia, 2. malformed red blood cells, 3. And slows growth in young individuals. 4-Pantothenic acid: Pantothenic acid is an amide of pantoic acid and B-alanine. Sources: In liver, egg yolk, groundnuts, peas, yeast, molasses, and grains. The free acid is unstable and the synthetically prepared calcium pantothenate is the product used commercially. Metabolism (functions): Pantothenic acid is a constituent of coenzyme A (a cyltransfer). Have many important of this coenzyme A in metabolism: a. Co-acetylase combines with acetic acid to form active acetate. Active acetate may be oxidized to give energy or may enter in the synthesis of cholesterol, steroid hormones, acetylcholine, and biochemical compounds. b. Co-acetylase combines with succinic acid to give active succinate. Active succinate enters in the synthesis of hem. Deficiency symptoms: In animals: Anemia due to decreased heme synthesis. Dermatitis, graying, and fall of hair. Hemorrhages and atrophy of the suprarenal gland. Pantothenic acid can be synthesized by rumen Escherichia coli, is known to produce this vitamin. Deficiencies rare humans. 5-Vitamin B6 (pyridoxine): Pyridoxine and two other closely related compounds, pyridoxal and pyrisoxamine, are grouped as vitamin B6. Functions: 29 1. It is essential in the metabolism of fatty acids and the Conversion of protein to fat. 2. It is used in the transport of amino acids and metal ions across cell membranes. 3. Pyridoxal phosphate is a coenzyme role in the decarboxylation of amino acids. Deficiency: 1. It is lack causes nervous disorders and muscular weakness. 2. Anaemia, 3. Vomiting and 4. Diarrhoea (diarrhea). 6-VitaminB12: Vitamin B12 has the most complex structure of all the vitamins. B12 is heat resistant in acidic or neutral solutions but is rapidly destroyed by alkali. Sources: Vitamin B12is considered to be synthesized exclusively by microorganisms and its presence in foods is thought to be of microbial origin. The main natural sources of vitamins are foods of animal origin, liver, meats, milk, cheese, and eggs. Its limited occurrence in higher plants and its presence in trace amounts may result from contamination with bacteria or insect remains. Metabolism (functions): Before vitamin B12 can be absorbed from the intestine, it must be bound to a highly specific glycoprotein, termed the intrinsic factor, which is secreted by the gastric mucosa. In man, the intrinsic factor may be lacking which leads to poor absorption of the vitamin resulting in a condition known as pernicious anemia. The coenzymes form of vitamin B12 function in several important enzyme systems. These include isomerases, dehydrases and enzymes involved in the biosynthesis of methionine form homocysteine. Of special interest in ruminant nutrition is the role of vitamin B12 in the metabolism of propionic acid into succinic acid. In this pathway, the vitamin is necessary for the conversion of methylmalonyl coenzyme A into succinyl coenzyme A. Deficiency: 30 Adult animals are less affected by a vitamin B12 deficiency than are young growing animals, in which growth is severely retarded and mortality high. In poultry, growth is retarded, feathering is poor and kidney damage may occur. Hen's hatchability is adversely affected. Results most commonly from defective absorption of B12 as in: a. Destruction of the gastric mucosa by antibodies against the gastric mucosa. b. After gastrectomy. c. Malabsorption syndromes Microorganisms in the rumen synthesize Vitamin B12 and some biologically inactive vitamin B12 analogs and, despite poor absorption of the vitamin from the intestine; the ruminant normally obtains an adequate amount of the vitamin from this source. However, if levels of cobalt in the diet are low, a deficiency of the vitamin can arise and cause reduced appetite, emaciation, and anemia. If cobalt levels are adequate, then except with young ruminant animals, a dietary source of the vitamin is not essential. Requirements: Adult 5µg/day.; pregnant 8µg/day and Lactating women 6µg/day. Table 6. Some coenzymes and enzyme prosthetic groups in the vitamins B Vitamin Coenzyme or prosthetic group Enzymatic and other function Thiamin Thiamin diphosphate (TDP) Oxidative decarboxylation Riboflavin Flavin mononucleotide (FMN) Hydrogen carrier Riboflavin Flavin adenine dinucleotide (FAD) Hydrogen carrier Nicotinamide Nicotinamide adenine dinucleotide Hydrogen carrier (NAD) Nicotinamide Nicotinamide adenine dinucleotide Hydrogen carrier phosphate (NADP) Pyridoxal Pyridoxal phosphate Transaminases and decarboxylases Pantothenic Coenzyme A(COA) Acyl transfer Folic acid Tetrahydrofolic acid One carbon transfer Biotin Biotin Carbon dioxide transfer Cobalamin Adenylcobamide Group transfer 31 7-Ascorbic acid (vitamin C): Vitamin C is a derivative of a sugar acid known as L-ascorbic acid. Primary sources: a. This is water-soluble vitamin found in citrus fruits, tomato, and b. And some animal organs as the adrenal glands, liver, and kidneys. C. Synthetic ascorbic acid is available commercially. Function: 1. It plays a vital role in collagen and ground substances. 2. Most animals can synthesize vitamin C, except man and other few animals. 3. It plays a role in oxidation processes in the body. 4. It is also essential for the formation of new cells and antibodies. 5. It is plays roles in the transport of iron ions from transferring, found in the plasma, ferritin which store in the bone marrow liver, and spleen. 6. It is required in the diet of only a few vertebrates–men, other primates. 7. Some insects and other invertebrates require a dietary source of vitamin c. 8. Other species synthesise the vitamin from glucose, via glucuronic acid and gulonic acid lactone; the enzyme L-gulonolactone oxidase is required for the synthesis and species requiring vitamin C are genetically deficient in this enzyme. Deficiency: 1. Its deficiency results in scurvy (bleeding in various places especially under Skin and gums; teeth become loose and fragile). 2. And brittleness of the newly formed bones. 3. Retardation in development of fibrous tissues and intracellular material. 32  5- Inorganic substances Functions of inorganic ions in biological system are many: 1. The activation of enzyme systems. 2. The stabilization of proteins in solution. 3. The development of electrical excitability. 4. The regulation of permeability of membranes. 5. The maintenance of a dynamic state of isotonicity between cells and the extra cellular fluid. The table lists the roles and sources of the major mineral nutrients essential to mammals. Mineral Function Primary sources Calcium Component of bone and teeth; essential for Milk and other dairy products, normal blood clotting; needed for normal green leafy vegetables. muscle, nerve, and cell function. Chlorine Principal negative ion in interstitial fluid; Most food, table salt. important in fluid balance and in acid-base balance. Cobalt Component of vitamin B12; essential for red Meat, dairy products. blood cell production. Copper Component of many enzymes; essential for Liver, eggs, fish, whole-wheat flour, melanin and for hemoglobin synthesis. beans. Fluorine Component of bone and teeth. Some natural waters may be added to water supplies. Iodine Component of hormones that stimulate Seafood, iodized salts, vegetables metabolic rate grown in iodine-rich Iron Compound of hemoglobin, myoglobin, Meat (especially liver) nuts, egg cytochromes, and other enzymes essential yolk, legumes (mineral most likely for oxygen transport and cellular to be deficient in diet). respiration. Magnesium Component of many coenzymes; balance Many foods between magnesium and calcium ions needed for muscle and nerve function. Manganese Activates many enzymes; as arginase, an Whole-grain cereals, egg yolk green enzyme essential for urea formation. vegetables. Phosphorus As calcium phosphate, an important All foods structural component of bone, essential for energy transfer and storage (component of ATP) and for many other metabolic processes; component of DNA, RNA and many proteins. Potassium Principal positive ion within cells; influences Many foods muscle contraction and nerve excitability. Sodium Principal positive ion in interstitial fluid; Most foods, table salt. important in fluid balance, essential for conduction of nerve impulses. Sulfur Component of many proteins; essential for Meat, Fish, legumes, nuts. normal metabolic activity. Zinc Component of at least coenzymes, including Shellfish oysters) meats, livers. carbonic anhydrase; component of some peptidases and thus important in protein digestion; may be important in would healing and fertilization. 33  6-Water ‟Water is best a substrate for life”. It was assuredly not chance that led Thales to found philosophy and science with the assertion that water is the origin of all things. The amount of water in the body of any given individual is constant. Its concentration varies from one tissue to another, being least in the dentin of teeth (10%) and greatest in the gray matter of the brain (85%). The younger and the more active the protoplasm, the greater the amount of water it contains. The human embryo at 6 weeks contains 97% water. Of the approximately 49 liters of water in the body of a man weighing 70 Kg, 14 liters are extracellular (3.5 liters in the plasma and 10.5 liters in the tissue fluids); the balance of about 35 liters is found within the cells-intracellular. Although the extracellular fluid (ECF) volume is less than half that of the intracellular fluid (ICF) volume, it is of great significance, since all exchanges between the tissues and the environment must occur through this compartment. On several occasions, it has been stated that living material, Protoplasm, is an intimate mixture of crystalloids and colloids in which water forms the solvent for the first and the medium for the dispersion or suspension of the second. From this, it is evident that water plays an important part in the existence and activity of living beings. This view is substantiated by the fact that, although a fasting animal may survive a loss of all its fat and half its proteins, a loss of one- fifth of its water content is fatal. Functions of water: 1. Solvent: Water dissolves or holds the other materials in protoplasm. 2. Medium: Water furnishes a medium for digestion, absorption, metabolism, secretion, and excretion. 3. Moistens surfaces: Water moistens the surfaces of the lungs for gas diffusion. 4. Temperature regulation: Water plays a dominant part in equalizing the temperature throughout the body and in maintaining it at a constant value. In these functions three physical properties of water are concerned: 34 a-Thermal conductivity. b- Specific heat (it is the amount of heat in calories required to raise the temperature of 1 gm of the substance 1C. for water is one: for iron, 0.11. for silver 0.057. d -High latent heat of vaporization. The latent heat of evaporation is the amount of heat required to evaporate 1 of liquid into vapor at the same temperature. For water (at 100C). 5. Cushion: Cerebrospinal fluid serves as a cushion for the brain and spinal cord. 6. Transportation: of the nutrients, waste, hormones, gases, and so on. 7. Hydrolysis: Water takes part in hydrolytic cleavages, as during digestion. 8. Lubricant: Water serves as a lubricant for moving surfaces, such as joints, (Synovial fluid) the heart, and intestine. 9. Sense organs. Water plays an indispensable part in sense organs. Taste and smell are the result of stimulation by chemical compounds in solution. Sound is conducted through the inner ear by a liquid, which is chiefly water. The function of the semicircular canals as sense organs of equilibrium depends on the presence of water in these canals. The transparency of media of the eye to light is maintained by water. 10. Regulation of water balance: The regulation of the intake and output of water is related respectively to the deficit and the excess of the normal water level in the body. The normal volume and osmolarity of the (ECF) and (ICF) compartments are controlled. It should be noted that the body controls its water content by loss through the skin and kidneys. How efficiently this is accomplished is at tested by the fact that the consumption, in six hours of as much as 5.5 liters of water (a quantity more than the entire volume of the blood) causes only a temporary dilution of the blood in the hematocrit. Three possible results of this large intake of water: 1. The absorbed water reduces osmotic pressure of the blood. This favors passage of water from the blood into the tissue spaces (especially in the skin) and into the cells. 35 2. The extra blood volume finds room by distension of previously closed, or Partly closed, capillaries and by storage in the sinusoids of the liver, spleen, and other organs. 3. However, the ability of the body to store water is limited, and while the reservoirs are being filled; the kidneys excrete some water. The ingestion of isotonic saline increases only the volume of the ECF since the isotonic solution causes neither exit nor entry of water into the cellular compartment. 11. Drinking and thirst: There are two categories of situations in which drinking occurs. Primary drinking is a response to an absolute or relative (hypertonicity) lack of water in one, or both, of the major body fluid compartments. Secondary drinking occurs despite no apparent internal need. Dryness of the mouth (from smoking or mouth breathing) consistency of the diet, activity (thermogenic stimulation of intake), and climatic conditions induce secondary drinking. Certain areas of the limbic (hippocampus and amygdala) system of the brain that connect with the lateral hypothalamic nuclei appear to exert both stimulatory and inhibitory influences on secondary drinking. Primary drinking and true thirst are emergency mechanisms for a response to an actual need for fluid. Receptors, which detect the need and initiate thirst and drinking, are in both major fluid compartments, the intracellular and the extracellular. Diminution in the ICF volume through water deprivation or potassium depletion of the cells is detected by osmoreceptors in the preoptic and supraoptic regions of the hypothalamus. Extracellular receptors are in the capacitance vessels near the heart and in the atria. These detectors are stretch receptors that respond to volume changes (hypovolemia) brought about by water or sodium deprivation, hemorrhage, vomiting, severe exercise, or diarrhea. They are reflexes connected to the centers for the secretion of ADH and, in some way, to the rennin–angiotensin–aldosterone mechanism for volume regulation. The extracellular receptors are important because all exchanges between the cells and the environment must occur through the ECF and the circulating volume of the blood must be protected. 36  Body water balance is often disturbed by disease: a. Diabetes insipid us in which there has been damage to the hypothalamic – The hypophyseal area of the brain produces polyuria and polydipsia. b. Many renal diseases are associated with excess fluid loss and resultant thirst. c. Hypercalcemia due to an increased absorption of calcium (vitamin D toxicity), or of bone decalcification, induces water loss and thirst. d. Chronic dehydration can result from diabetes mellitus where glucosuria and metabolic acidosis produce water and electrolyte loss from both fluid compartments. In hyperthyroidism, there is an increased fluid loss due to the metabolic rate increase and, consequently, thirst develops. Table 8. Composition of some plant and animal products (g/Kg): water Carbohydrate Fat Protein Ash Turnips 910 71 2 10 7 Pasture grass Young leafy 800 100 10 32 24 Wheat grain 130 712 19 122 17 Groundnuts 60 201 449 268 22 Dairy cow 570 2 206 172 50 Blood 820 1 6 164 7 Liver 740 13 65 168 14 Muscle 720 6 43 214 15 Milk (cows) 876 47 36 33 8 37  Chapter three The digestive system Nutrition in animals involves the following steps: (Ingestion, Digestion, Absorption, Assimilation, and Ejection). 1. Ingestion: The method of ingestion, i.e., taking of food, varies from one animal to another. 2. Digestion: This is the process of breaking down complex components of food into simpler substances. The process of digestion is different inhuman, grass- eating animals, amoeba, etc. 3. Absorption: This is the process of passing digested food into blood vessels in the intestine. 4. Assimilation: The conversion of absorbed food into complex substances such as proteins and vitamins required by the body. In other words, assimilation is the conversion of absorbed food (nutrients) into living tissues. Through the process of assimilation, the cells are supplied with oxygen and nutrients. 5. Ejection: This is the removal of waste materials from the body. Removed feces through the anus from time to time. Since the waste of food left after digestion is called feces, the process of ejection is also known as defecation. The digestive system is a set of organs concerned with 6 functions: 1. Ingestion. 2. Secretion of water, acid, buffers, and enzymes into the lumen. 3. Mixing and propulsion (‫(دفع‬. 4. Digestion:  Mechanical digestion churns food  Chemical digestion – hydrolysis 5. Absorption – passing the products into blood or lymph for transport to other parts of the body where they are built up again into the complex chemicals which the body needs. 6. Defecation – elimination of feces. Anatomy of the digestive tract: I) The alimentary canal is a coiled tube extending the full length of the trunk. It is divided into five segments: mouth and pharynx, esophagus, stomach, small intestine, and large intestine. The mouth is concerned with chewing the food (mechanical breakdown) and secreting saliva, which lubricates the food and starts some of the digestive process. The food is swallowed down the esophagus a conduit- and enters the stomach, which has a hopper function, storing the food and allowing it to be passed to the other digestive organs in small regular quantities so that digestion can proceed at an even pace for some hours 38  after a meal. There is also some mixing and digestive function in the stomach, the small intestine is the main site of digestion (breakdown) and absorption; the large intestine is concerned with the absorption of water and salts and with storage of the waste products of digestion (faces) until their elimination at the anus. II) The structure of the wall of the alimentary canal: The structure of the digestive tract (alimentary canal) gut and gastrointestinal tract follows the same basic pattern from the lower esophagus to the rectum; there may be individual variations in detail in the various parts; but is usually composed of several layers. From the outside, the coats are arranged in the following order: 1.A serous or fibrous coat: composed of a thin layer of connective tissue and a layer of squamous epithelium which forms the lining of the peritoneal cavity. The blood vessels and nerves reach a segment of the gut through the mesentery, a reflection of the serosal layers to form a pellicle of attachment of the gut to the body wall. Esophagus lacks serosa – has adventitia 2. The muscular coat: a-Voluntary skeletal muscle found in the mouth, pharynx, upper 2/3 of esophagus, and anal sphincter. b-Involuntary smooth muscle elsewhere:  Arranged in inner circular fibers and outer longitudinal fibers.  Myenteric plexus between muscle layers. 3.The sub mucosa: * Made up of loose connective tissue binding mucosa to muscularis. *Contains many blood and lymphatic vessels and, * Contain submucosal plexus. 4.The muscularis mucosa: The thin layer of smooth muscle cells makes folds to increase surface area. 5.The mucosa or mucous membrane: Epithelium protection, secretion, and absorption. The inner lining in which the glands peculiar to the alimentary tract are located. Lines the luminal surface of the digestive tract. Is highly folded to increase surface area available for absorption. The mucosa divided into: A) Mucous membrane, which contain: * Epithelial cells: absorb digestive nutrients. 39  * Exocrine cells: secrete digestive juices. *Endocrine cells: secrete gastrointestinal hormones. B) Lamina propria:  In addition to connective tissue, the lamina propria contains many blood and lymphatic vessels that transport nutrients absorbed through the alimentary canal to other parts of the body.  The lamina propria also serves an immune function by housing clusters of lymphocytes, making up the mucosa-associated lymphoid tissue (MALT). These lymphocyte clusters are particularly substantial in the distal ileum where they are known as Peyer’s patches. When you consider that the alimentary canal is exposed to foodborne bacteria and other foreign matter, the immune system is defending against the pathogens encountered within it. III) Constrictors or sphincters: At certain points along the alimentary tract, the circular muscles are hypertrophied, forming areas of constriction, or sphincters. These are found in: 1. The upper (hypo pharyngeal sphincter) and 2. Lower (cardiac sphincter) esophagus, 3. At the antral end of the stomach (pyloric and pylorus), 4. The ileocecal sphincter lies between the small and large intestines, 5. And the internal and external anal sphincters. The latter three sphincters are normally closed and restrict further passage of material while the first three areas assist in movement of the digestive contents. D) The associated glands and organs that are a part of the digestive tract, the liver, and the pancreas. The chemistry of the digestion: Many of the organic components of food are in the form of large insoluble molecules, which must be broken down into simpler compounds before they can pass through the mucous membrane of the alimentary canal into blood and lymph. Between the time an animal eats food and excretes undigested wastes, its body must absorb nutrients. The chemical part of the digestion process is the breakdown of foods into small absorbable units by enzymes. Chemical digestion: Breaks the bonds linking monomers into large protein, Carbohydrate and lipid polymers. These reactions often involve hydrolysis, with enzymes working in tandem to break first one molecular bond and then another. Let us take the breakdown of starch (amylase and amylopectin) as an example of the chemical digestion process. Amylase in the saliva begins the hydrolysis of starch. Amylase secreted by the pancreas into the small intestine 40 continues that process, but at an alkaline pH, yielding enormous amounts of the disaccharide maltose. Much disaccharide passes into epithelial cells on the villi of the small intestine and is digested by eight disaccharide-splitting enzymes. In addition, the enzyme maltase, located in the luminal membrane of cells in the wall of the small intestine, cleaves maltose to produce two molecules of the monosaccharide glucose. This sugar is then absorbed through the intestinal wall via active transport with sodium ions+. Secretions of the digestive system: The main secretions of the gut are saliva, gastric juice, bile, pancreatic juice, and the secretion of the intestinal wall (succus entericus). A-salivary glands and functions: Saliva: is secreted by the salivary glands whose ducts open into the mouth and about 750 ml of saliva is secreted per day from three pairs of main salivary glands these are: a- The parotid: about 20 % total salivary secretion, while the largest pair of salivary glands produce mostly pure serous watery saliva. They show pure serous acini and prominent striated secretory ducts. b- Submandibular: about 70% total salivary secretion, while the largest pair of salivary glands produce mixed compound saliva. The acini are serous forming 90% of the acini, there are few mucous and mixed acini. c- Sublingual glands: about 5% total salivary secretion. They are mixed compounds. Contains mucous acini forming 60% of the total acini, with some serous acini. d– And many small groups of glands cells on the surface tongue and the palate about 5%. Controlled the salivary glands: The salivary glands are controlled by the autonomic nervous system; parasympathetic nervous tissues stimulate the flow of a water fluid rich in enzymes, while the sympathetic nerves cause the secretion of more viscous fluid rich in mucus. Both types of nerve cause an increase in blood flow through the glands, but this is an indirect effect rather than a specific influence of any neurotransmitter on the blood vessels. Secretory activity in the glands, under autonomic control, causes the release of kallikrein, an enzyme, which converts tissue alpha globulins into bradykinin, a peptide with strong vasodilator properties. Salivary secretion is initiated by several reflexes; the sight, smell, or even the thought of food can cause salivation, though only to a small extent, and the presence of food in the mouth, stimulation of taste receptors and the act of chewing are very powerful stimuli to secretion, one of the most powerful stimuli is chewing candle wax. Functions of saliva: 41  Saliva is a water fluid with electrolyte content like plasma and a slight alkaline pH. Its major enzyme is ptyalin an alpha amylase. It also contains lysozyme, a non-specific enzyme, which has a protective function, breaking down bacteria in the mouth. This enzyme is also found in tears, nasal secretion, and other body fluids. 1. Facilitation of swallowing: by moistening and lubricating food bolus. 2. Regulation of water balance: in case of dehydration when secretion is decreased the sensation of thirst while drinking. 3. Facilitation of speech: moistening the mouth cavity, tongue, and lips. 4. Cleaning and antibacterial action: saliva washes food remains, which act as a medium for bacteria. In addition, salivary lysozyme (enzyme) destroys bacteria. 5. Excretion: of certain elements, e.g., Pb (lead) Hg (mercury), and I2 (iodine). Urea is excreted in saliva in kidney diseases and glucose in severe diabetes mellitus. 6. Solvent action: Saliva dissolves many food materials so that taste buds in the the tongue can be stimulated. 7. Buffering action: Salivary buffers, e.g., H2CO3; and NaHCO3 help in neutralizing acid or alkaline entering the mouth, which is thus protected. Acidity dissolves the enamel and dentine of teeth. Alkalinity helps the precipitation of calcium salts around teeth forming a crust called “Tartar” which helps bacteria to flourish under it. 8. Dilution of irritating substances and excessively hot or cold food. 9. Regulation of body temperature: in panting animals by evaporation of saliva. 10. Digestion: Salivary amylase digests cooked starch into maltose. B. Gastric secretions and functions Functional anatomy of the gastric mucosa: * Gastric mucosa is covered by surface epithelial cells, which secrete a thick, alkaline mucus, forming a gel layer that covers the surface of the mucosa. * Gastric mucosa is divided into 2 areas: oxyntic mucosa and pyloric gland area. A) Oxyntic mucosa: Its lines fundus and body stomach. There are gastric pits and gastric glands, which contain: 1. Mucous neck cells, which secrete thin, watery mucus. 2. Parietal and oxyntic cells, which secrete HCL and intrinsic factor. 3. Chief cells which secrete pepsinogen. 4. Enterochromaffin like cells, secrete the paracrine histamine which stimulates parietal cells. 42 B) Pyloric glands area: It lines the antrum, which contain: 1. G cells: secrete the hormone gastrin into the blood which stimulates Parietal, chief and Enterochromaffin cells. 2. D cells: secrete paracrine somatostatin which inhibits parietal, G and Enterochromaffin cells. 6. Cells: secrete mucus and lesser amounts of pepsinogen. 7. Number Cells for acid secretion: Gastric Secretion: The stomach produces about three liters of juice per day. There are two main types of secretion from the glands present in the mucosa of the fundus and body regions of the stomach: 1. Hydrochloric acid from the parietal or oxyntic cells of the neck’s glands. 2. Pepsinogen: from the chief cells in the depth of the glands. Pepsinate is the inactive precursor of the enzyme pepsin, a protease that breaks down. proteins to short chains of amino acids (polypeptides). 3. from the Antrum region. These include: a-Mucus (from mucous cells) which helps to protect against digestion. b- Rennin: This curdles milk and is important in infants. c- Intrinsic factor, which is essential to the absorption of vitamins. d- Gastric lipase: This is a weak lipolytic enzyme of optimum pH 5-6 and like rennin, it acts in the stomach of young. It hydrolyses emulsified fats into glycerol and fatty acids. e- Gastrin hormone from the antrum, which has roles in the control of gastric secretion. Function of gastric juices: A. Function of gastric HCl: 1. It changes the inactive enzyme pepsinogen to active pepsin. It provides optimum pH (1.5-2) for action of pepsin. 2. It has antibacterial action. Gastric juice in normal adults is sterile. 3. It is important for the absorption of calcium, iron, and other minerals. HCl dissolves calcium and prevents its precipitation by alkaline juices present in the intestine. Iron in the presence of HCL and ascorbic acid is changed to the ferrous form which is the absorbable type of iron. 4.It causes partial hydrolysis of some food it changes proteins to meta proteins. 43  5. It causes the release of secretin hormone which necessary to stimulate the secretion of pancreatic juice and bile flow. 6. It regulates the evacuation of the stomach. 7. It causes curdling and precipitation of milk in the stomach. This helps in Keeping milk exposed for a long time to the action of pepsin of the stomach. B. Function of pepsin: 1. It is a proteolytic enzyme that digests proteins into proteoses and peptones but few or no amino acids are formed, and the pH of pepsin action is 1.5-2. 2. Pepsin is an endopeptidase; it hydrolyses the peptide linkage in the middle of protein molecules. 3. It is secreted as inactive “pepsinogen” which is activated by HCl. 4. Pepsin is also a milk-clotting enzyme in human infants. C. Function of rennin: 1. Rennin in gastric of young animals not found in men (infants or adults). 2. It is called a milk-clotting enzyme because it transforms milk caseinogen into soluble casein, which in the presence of Ca2+ is transformed into calcium. caseinate which is the milk clot or milk crud at PH (5-6). D. Function of gastric lipase: 1. It is a weak lipolytic enzyme which has an optimum pH of 4-5. 2. Gastric lipase acts in babies where the pH of the stomach is more suitable (pH 5-6). E. Function of other gastric enzymes: 1. Lysozyme: is antibacterial enzyme. 2. Urease: This hydrolyses urea into NH3 and CO2. F. function of Intrinsic factor: 1. It is secreted by parietal cells from gastric mucosa. 2. It helps the absorption of vitamin B12 from the intestine. 3. It does cause pernicious anemia. 4. It reacts with substances present in certain foods and forms the haematinic principle, essential for the proper formation of R.B.C. G. Function of neuropoietin: 1. A substance essential for central nervous system nutrition. 2. It is absence causes degeneration of spinal cord as in pernicious anemia. 44 H. Function of mucin: 1. It forms a protective covering on gastric mucosa to prevent its irritation by mechanical or chemical factors. 2. It protects gastric mucosa against digestion by pepsin. 3. Alkaline mucus, forms a gel layer that covers the surface of the mucosa. It buffers a large quantity of HCl and protects mucosa against it. Mucin , therefore, is used as a drug for the treatment of gastric ulcers. 4. It contains the intrinsic factor. 5. Lubricant. I. Functions of the stomach: 1. The stomach acts as a reservoir for food. Funds contain only gas, no food. Body muscle layers are thin causing week peristalsis. So, food is stored without being mixed. Antrum muscle layers are thicker causing strong peristalsis and food mixing. 2. The stomach mixes the ingested food into a homogenous liquid called chyme” which is evacuated gradually in lesser amounts to the delicate duodenum. 3. Absorption of some H2O, alcohol, and glucose. 4. Digestive functions are done by gastric juice. 5. Gastric juice helps the absorption of many substances e.g., Ca, Fe, and vitamin B12 from the small intestine. Pernicious anemia results from a lack of gastric intrinsic factor that helps B12 absorption. J. Factors preventing the stomach from digesting itself: Although the stomach is a protein in nature and contact with proteolytic enzymes and strong acid, it is not digested because: 1. Mucus forms a thick layer separating the gastric wall from HCl and enzymes (Mechanical barrier). Also, the protein content of mucus and its slight alkalinity tends to neutralize and absorb HCl (Chemical barrier). 2. Membranes of gastric mucosal cells are impermeable to H+. Therefore, HCl cannot penetrate the cells. 3. Antienzymes exist in gastric mucosal cells. 4. Cells of the mucosa are tightly joined together giving no passage for diffusion of materials from gastric lumen to mucosa. 5. Continuous removal and regeneration of mucosal epithelium every 1-3 days. 6. The alkaline pH of stomach cells is unsuitable for pepsin activity. 7. Enzymes and HCl are formed in secretory mucosal cells in isolated vacuoles or canaliculated and do not mix with cell protoplasm. 8. Gastric mucosal cells are not permeable to pepsin in stomach lumen. 9.Urease enzyme exists in copious amounts in gastric mucosa. It hydrolyses urea into NH3 and CO2. NH3 neutralizes any HCl, which may enter the gastric cells. 45 C-The small intestine juices and functions Properties Small intestine: 1.Most digestion of food and absorption of nutrients and water take place in the small intestine, and formed from 3 regions, duodenum, jejunum, and ileum. 2. A lengthy stretch of gut between the stomach and the large intestine. 3. A human's small intestine is only about 4cm in diameter, but it is 7-8m long. 4.This long length provides a large total surface area for absorbing nutrients, but a more significant enlargement comes from convolutions and minutes. projections of the inner gut surface. 5.On the ridges and folds of the inner intestinal wall, thousands of tiny, fingerlike villi project from each square centimeter of the mucosa, giving it the appearance of velvet to the unaided eye. 6. Both the folds and the villi are covered by epithelial cells, each bearing numerous microvilli. These minute projections are packed at a density of 2ooooo per square millimeter and extend the surface area of the intestinal folds. and villi by a factor of twenty. 7. The inner wall of the human small intestine thus has a total surface area of some 250 m2- the size of a tennis court, the result is that daily about 17 billion cells weighing about 250 g pass into the intestinal lumen. 8. The first 30 cm of the human small intestine make up the duodenum, a region devoted solely to digestion. 9. The next 3m segment of the human small intestine is the jejunum and the final 4m segment is the ileum, both conduct absorption of nutrients to ileocecal valve. 10. The duodenum contains many digestive enzymes, some of these enzymes are secreted by glands in the duodenal mucosa; others are secreted in the pancreas and liver and flow into the duodenum through hepato pancreatic duct. 12. In the jejunum and ileum, amino acids, sugars, fatty acids, nucleic acid bases, minerals, and water are absorbed across the surfaces of the epithelial villi. 13. Small intestine juices, this is a watery, slightly alkaline fluid. It contains the following enzymes, which work efficiently at an optimum (pH of about 8.3) due to NaHCO3 and contains enzymes: 1- Glucosidases: which split disaccharides into monosaccharides, these include: A) Maltase splits maltose (malt sugar) into two molecules of glucose. B) Sucrase acts on sucrose (cane sugar) converting it into glucose and fructose. C) Lactase converts lactose (milk sugar) into glucose and galactose. This enzyme synthesized, by baby mammals but not by most adults, since they usually cease drinking milk at the time of weaning. II -Esterase: intestinal lipase hydrolyses fats into glycerol and fatty acids. I