2.Nutrition Lecture 2.pdf

Lecture - 2 Nutrition in the Human Body: Nutrition as Chemistry: Digestion, Absorption and Transport.  OBJECTIVES After studying this chapter, you should be able to: Describe the processes of digestion, absorption, and metabolism Name the organs in the digestive...

Lecture - 2 Nutrition in the Human Body: Nutrition as Chemistry: Digestion, Absorption and Transport.  OBJECTIVES After studying this chapter, you should be able to: Describe the processes of digestion, absorption, and metabolism Name the organs in the digestive system and describe their functions Name the enzymes or digestive juices secreted by each organ and gland in the digestive system  What is Digestion? Digestion is the process of breaking large, insoluble food molecules into smaller molecules for absorption into the bloodstream. Loading… This process involves the use of many digestive fluids and enzymes such as saliva, mucus, bile and hydrochloric acid, among others. Four primary stages of food digestion : After the intake of food through the mouth, it makes its way through the stomach into the small intestine, where it is digested. The nutrients from the digested food get absorbed into the bloodstream through small pores in the small intestine. The remaining undigested food is sent to the large intestine, where any unprocessed water or nutrients are reabsorbed into the body.  Types of Digestion Digestion occurs through two types of action: Mechanical and chemical. During MECHANICAL DIGESTION, food is Loading… broken into smaller pieces by the teeth. It is then moved along the gastrointestinal tract through the esophagus, stomach, and intestines. This movement is caused by a rhythmic contraction of the muscular walls of the tract called peristalsis.  Mechanical digestion helps to prepare food for N = r · - -  Chemical Digestion During chemical digestion, the composition of carbohydrates, proteins, and fats is changed. Chemical changes occur through the addition of water and the resulting splitting, or breaking down, of the food molecules. This process is called hydrolysis. Food is broken down into nutrients that the tissues can absorb and use. Hydrolysis also involves digestive enzymes that act on food substances, causing them to break down into simple compounds.  An enzyme can also act as a catalyst, which  Carbohydrates are one of the essential nutrients in the human diet. There are two types of carbohydrates that can be digested by the human digestive system– sugar and starch. Sugar is broken down in the gastrointestinal tract by the small intestine and three enzymes present in the mouth, namely, Lactase, Sucrase, and Maltase. In the same way, starch is broken down with the help of the Amylase enzymes which are present in the mouth and the stomach. After digestion, carbohydrates are absorbed in the small intestine with the help of minute finger-shaped projections known as Villi.  The chemical digestion of carbohydrates begins in the mouth. The below flowchart explains in detail about the series of steps Loading… involved in breaking down the carbohydrates into their monomers.  The digestion of proteins takes place in the stomach with the help of protease and pepsin enzymes, which breaks down the proteins into amino acids. The process is facilitated by the hydrochloric acid present in the stomach. Amino acids are tiny elements which get absorbed into the blood system through the wall of the small intestine.  Digestion and Absorption of Lipids Lipids are organic compounds comprising fatty acids, which are insoluble in water. The insoluble property of lipids makes the digestion and absorption of fats a complicated process. Since they are hydrophobic, fats stick together as a large glob of insoluble mass after reaching the stomach. It is broken down with the help of bile juice, which contains bile salts. These broken molecules are then acted upon by pancreatic lipase, the major fat-absorbing enzymes in the body. Pancreatic lipase breaks down fats into tiny molecules of free fatty acids and monoglycerides, which are small enough for the small intestine to push through into the bloodstream.  What is Absorption? Absorption is the process of absorbing or assimilating substances into the cells or across the tissues and organs through the process of diffusion or osmosis. Absorption is the passage of nutrients into the blood or lymphatic system (the lymphatic vessels carry fat-soluble molecules that are too large to pass through the capillaries into the bloodstream).  Absorption in the Small Intestine The small intestine is approximately 22 feet long. Its inner surface has mucosal folds, villi, and microvilli to increase the surface area for maximum absorption. The fingerlike projections called villi have hundreds of microscopic, hairlike projections called microvilli. The microvilli are very sensitive to the nutrient needs of our bodies. Each villus contains numerous blood capillaries (tiny blood vessels) and lacteals (lymphatic vessels). The villi absorb nutrients  from the chyme by way of these blood Absorption in the Large Intestine When the chyme reaches the large intestine, most digestion and absorption have already occurred. The major tasks of the large intestine are to absorb water, to synthesize some B vitamins and vitamin K (essential for blood clotting), and to collect food residue. Food residue is the part of food that the body’s enzyme action cannot digest and consequently the body cannot absorb. Such residue is commonly called dietary fiber. Adequate fiber is important as it promotes the health of the large intestine by helping to produce softer stools and more frequent bowel movements. Undigested food is excreted as feces by way of the rectum. In  healthy people, 99% of carbohydrates, 95% of fat, and 92% of Metabolism After digestion and absorption, nutrients are carried by the blood to the cells of the body. Within the cells, nutrients are changed into energy through a complex process called metabolism. During aerobic metabolism, nutrients are combined with oxygen within each cell. This process is known as oxidation. Oxidation ultimately reduces carbohydrates to carbon dioxide and water; Proteins are reduced to carbon dioxide, water, and nitrogen.  As nutrients are oxidized, energy is released. When this released energy is used to build new substances from simpler ones, the process is called anabolism. An example of anabolism is the formation of new body tissues. When released energy is used to reduce substances to simpler ones, the process is called catabolism. This building up (anabolism) and breaking down (catabolism) of substances is a  Metabolism and the Thyroid Gland Metabolism is governed primarily by the hormones secreted by the thyroid gland. These secretions are triiodothyronine (T3) and thyroxine (T4). When the thyroid gland secretes too much of these hormones, a condition known as hyperthyroidism may result. In such a case, the body metabolizes its food too quickly, and weight is lost.  When too little T4 and T3 are secreted, the Refernces Ruth A. Roth, MS, RD (2011). Nutrition & Diet Therapy, 10th edition, Delmar, Cengage Learning, ISBN-13: 978-14354-8629-4, ISBN-10: 1-4354-8629-3 2. THANK YOU