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ANIMAL ANATOMY UNIT 3 LESSON PLAN 4 DIGESTION SYSTEM Part A THE STRUCTURES AND FUNCTIONS OF THE HUMAN DIGESTIVE SYSTEM The main function of the human digestive system is to breakdown large food molecules into smaller molecules that can be absorbed by the body. Terms: Alimentary Canal or Gastrointestinal(GI) Tract Is a one way "tube system with specialization Performs "extracellular" digestion (digestion that takes place outside the cell) Major Sites of Digestion Mouth, stomach small intestine, large intestine Accessory Digestive Organs Liver, pancreas, gall bladder, salivary glands Assist by adding secretions to the digestive tract through ducts (small tubes that connect these organs to the digestive system Digestion Involves the conversion of food from its original form in the external environment into nutrient molecules small enough to enter body cells and participate in cell functions Ingestion Intake of food via the mouth Propulsion Movement of food along digestive tract Physical Digestion The breaking of large food pieces into smaller ones Chemical Digestion Chemically changing large complex food molecules (lipids, carbohydrates, proteins) into smaller simpler ones (fatty acids, glycerol, sugars, amino acids) by enzymes or acid (HCl) 1 Absorption The transport of nutrient molecules from the GI tract thru the walls, into the blood stream for distribution to cells Egestion Elimination of undigested food/waste in the form of feces (defecation) 2 HUMAN DIGESTIVE TRACT STRUCTURE Mouth Teeth Salivary Glands FUNCTION entrance to the digestive tract ingestion of food (digestive process starts) aids in the physical breakdown of food (mechanical digestion) teeth structure: incisors -- cuts food into smaller pieces canines & bicuspids -- pierce and tears food molars -- crush and grinds food secrete saliva (water & mucus) and amylase (enzyme) breaks down starch (carbohydrates) into maltose Tongue a muscular organ that moves the food around for chewing and mixing with saliva until it forms a bolus which is then pushed back into the pharynx Pharynx is a passage at the back of the mouth that receives both food and air Epiglottis a flap of tissue that prevents food from entering the trachea Esophagus is a muscular tube that connects the mouth to the stomach its main function is to push the bolus into the stomach by peristalsis Structure two muscle layers i) circular muscle fibres ii) longitudinal muscle fibres the contractions and relaxation of these muscles causes the food to be pushed down into the stomach Cardiac Sphincter is a ring-like muscle that controls the entry of food into the stomach 3 Stomach is a muscular organ that has three types of muscle layers i) circular ii) longitudinal iii) oblique the rhythmic contraction and relaxation of these muscles layers churns the partially digested food and mixes it with gastric juices gastric juice: is a mixture of i) hydrochloric acid (HCl): activates digestive enzymes breaks down fibrous tissue kills germs ii) pepsin(enzyme): breaks down proteins into long chains of amino acids called polypeptides (ie. peptones and protease) iii) mucus layer: protects the stomach from pepsin and HCl (without this layer the stomach would be digested resulting in a gastric ulcers pylorus: i) lower region of the stomach ii) contains partially digested food now called chyme chyme: is a mixture of food, water, and gastric juice Pyloric Sphincter controls the passage of chyme (food) from the stomach to the intestine Small Intestine aprox. 6.2 m in length 2.5 cm in diameter two muscle layers (circular & longitudinal) movement of food is by peristalsis is divided into three main sections: a) duodenum (25 cm long): i) ii) high digestive activity connected to the liver and pancreas by the bile duct and the pancreatic duct which releases their 4 digestive juices in this location iii) the acidic chyme is neutralized by bicarbonates released b the pancreas b) jejunum: i) has an increase number of folds compared to the duodenum ii) secretes enzymes that breakdown any remaining proteins (peptidase) into amino acids and carbohydrates (maltase, sucrase, lactase) into glucose iii) has a number of finger-like structures called villi which absorbs the nutrients and transfers them to the circulatory system c) ileum (3.5 m): i) ii) iii) iv) similar to the jejunum smaller and fewer villi produces few enzymes main function is absorption and to push any undigested material into the large intestine ACCESSORY ORGANS Liver largest gland of the body (1.5 kg) produces bile bile: i) is an emulsifying agent needed for the physical digestion of fat large fat globules + bile small fat globules (small surface (large surface area/volume ratio) area/volume ratio) ii) it exposes a large number of fat molecules for 5 digestion iii) is secreted continuously and is stored in the gall bladder Pancreas produces several digestive enzymes i) bicarbonates: neutralizes stomach acids which allow the intestinal enzymes to continue the process of chemical digestion of food ii) trypsin & chymotrypsin: the breakdown of proteins into dipeptides an amino acids iii) carboxypeptidase: cleaves peptides iv) pancreatic amylase: cleaves starch, glycogen v) lipase: cleaves lipids into glycogen and fatty acids vi) nucleases: cleaves nucleic acids these juices are carried to the duodenum by the pancreatic duct 6 Large Intestine aprox. 1.5 m long 5 -7 cm in diameter reabsorbs water, ions, vitamins production of vitamin K and some B vitamins are produced by bacteria (E. coli) the liquid waste becomes firmer and is called feces feces: consists of living and dead bacteria, cellulose and water as the feces is formed it pushed through the large intestine by peristalsis into the rectum Rectum expels waste weak sphincter muscle at its entrance prevents fecal matter from entering until it is ready for elimination Anus contains two sphincter muscles ( an internal and an external) that controls the final elimination of feces when the rectum is full the internal sphincter relaxes and sends a message to the brain the external sphincter remains contracted until it relaxes voluntarily for elimination 7 The Movement of Food The movement of food is accomplished by a series of wavelike muscular contractions and relaxations known as peristalsis. Peristalsis involves the circular and longitudinal muscles that surround the various parts of the digestive tract. To move food, the circular muscles over a food mass relax while the longitudinal muscles immediately in front of it contract. the circular muscles immediately behind the food mass then contract while the longitudinal muscles over the food mass relax. As succeeding muscular regions relax and contract, the food is pushed along 8 ANIMAL ANATOMY UNIT 3 LESSON PLAN 4 DIGESTION SYSTEM Part B Chemical Digestion and Enzymes The major nutrients taken in by the body through eating are carbohydrates, proteins, fats and nucleic acids. These large macromolecules need to be broken down by the digestive system into their simpler building blocks. In order to breakdown these nutrient they under go a chemical reaction called HYDROLYSIS. Hydrolysis is the use of water to break the bonds between the monomers (building blocks) of the macromolecules. Hydrolysis is a slow reaction and needs to be sped up. The body solves this problem by making a biological catalyst called enzymes. Enzymes are special proteins produced by the cell. Enzymes break the bonds between monomers at very specific locations (linkages). Enzymes often require special conditions in order to act i) ii) iii) iv) some work best in an acidic environment (i.e. pepsin in the stomach) other work in a neutral or alkaline (basic) environment (i.e.. the digestive enzymes in the small intestine) enzymes are affected by temperature changes (i.e. higher temperatures will denature the enzyme so that it is no longer functional) in order for the enzyme to function properly it may require the presence of metallic ions (i.e. cobalt and magnesium), vitamins, or coenzymes in order to function properly. There are three groupings of enzymes that are formed by secretory cells and then secreted into the digestive tract. Macromolecule carbohydrates proteins fats Enzyme Carbohydrases Proteases Lipases Monomers monosaccharides (glucose, galactose, fructose) amino acids glycerol + 3 fatty acids 9 Digestive Enzymes Most of the digestive enzyme names start with the name of the substrate they react on and have the ending "ase" added. Example: maltose is broken down by an enzyme called maltase. Some enzymes still use their older names such as pepsin. A Summary of Chemical Digestion In humans and other mammals, chemical digestion begins in mouth Salivary glands release the enzyme called salivary amylase, Amylase breaks down starch into smaller disaccharide sugar molecules gastric juice secreted by the stomach contains hydrochloric acid and the enzyme, pepsin. Pepsin begins the breakdown of protein in the stomach Pepsin functions well within a pH range of 1 to 2. stomach duodenu m is 25 cm long secretes enzymes from its lining, the pancreas and liver both empty their enzymes into the duodenum to complete the process of digestion. Pancreatic juice is alkaline and thus neutralizes the acidity of partially digested food coming from the stomach, stopping any further action of pepsin produces no enzymes water is absorbed from indigestible material through its walls anaerobic bacteria living there, digest some of this material, and some of it is absorbed for use by the body synthesize some B vitamins and Vitamin K which is then used by the body. The total digestion of a large meal takes about 24-33 h pancreas Large intestine 10 The Regulation of Digestive Secretions The secretion of digestive enzymes is regulated by both nerves and hormones. A hormone is a chemical regulator that is secreted in one part of the body and transported by the bloodstream to another part, where it causes a response. Examples a) Secretion of Gastric Juices Nerve impulse stimulates the lower part of the stomach to produce the hormone gastrin Gasterin enters the circulatory system and is carried back to the upper part of the stomach Gasterin then stimulates the digestive glands lining the walls of the upper part of the stomach to secrete mucin pepsin, hydrochloric acid, lipases. b) Neutralization of Chyme Chyme entering the duodenum stimulates the glands of the duodenum to secrete the hormone secretin into the bloodstream Secretin stimulates the duct cells of the pancreas to release an alkaline fluid containing sodium carbonate and sodium bicarbonate into the duodenum which changes the pH from 2 to 8 c) The hormone secretin and cholecystokinin (CCK) are secreted by the duodenum and stimulates the pancreas to release its digestive enzymes into the duodenum. These enzymes also stimulate the gall bladder to secrete bile salt. 11 Enzymes of the Human Digestive System Place where enzyme acts Substrate Enzyme mouth starch, glycogen salivary amylase stomach protein fats fats peptides peptides peptides starch small intestine ribonucleic acid deoxyribonucleic acid peptides tripeptides maltose sucrose lactose pepsin Products Origin of Enzyme maltose salivary glands peptides lipase glycerol + 3 fatty acids pancreatic lipase glycerol + 3 fatty acids trypsin chymotrypsin carboxypeptidase pancreatic amylase ribonuclease deoxyribonuclease aminopeptidase tripeptidase maltase sucrase lactase stomach glands simpler peptides simpler peptides simpler peptides pancreas maltose ribonucleotides deoxyribonucleotides simpler peptides dipeptide + amino acid glands in the walls of the small intestine glucose + glucose glucose + fructose intestinal glands glucose + galactose 12 The Roles of Related Organs Three other organs associated with the digestive tract are the liver, gall bladder, and pancreas. These organs play vital roles in the digestive process. The Liver The liver is the largest organ in the body and has been identified as having over 500 different functions that are essential to the body's general good health. produces bile salts from cholesterol which is released into the small intestine to emulsify fat globules (break up ) to allow lipase to chemical break the fat up into glycerol and fatty acids breaks down old red blood corpuscles, and hemoglobin the decomposed hemoglobin molecules are used to make bile salts. the liver collects from the bloodstream chemicals that are in excess of the amount needed by the body at any given time. The liver converts and stores all monosaccharides (except glucose), into glycogen The liver will convert the stored glycogen back into glucose when the glucose level in the bloodstream become low The liver also stores fat-soluble vitamins A, D, E, and K the liver works to detoxify various poisons ingested with food and drink in addition to those produced in the intestines. The liver is highly evolved organ that performs a wide range of important, specialized functions for the body. The Gall Bladder The gall bladder serves as the storage warehouse for bile produced in the liver. bile contains a number of chemicals that include cholesterol bile salts are used in fat digestion bile salts are reabsorbed by the small intestine and is carried back to the liver to be recycled back into bile 13 The Pancreas The pancreas is the source of several enzymes that act on carbohydrates, fats, and peptides (smaller segments of proteins) produces and releases a basic solution that changes the pH of chyme (from a strongly acid mixture to a weakly basic one) after it enters the duodenum. 14