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BIOL 100C: Introductory Biology III The Digestive System Dr. P. Narguizian Fall 2012 Principles of Biology OBTAINING AND PROCESSING FOOD Copyright © 2009 Pearson Education, Inc. Animals ingest their food in a variety of ways Most animals have one of three kinds of diets – Herbivores, plant-eaters—cattle, snails, sea urchins – Carnivores, meat-eaters—lions, hawks, spiders – Omnivores, eating both plants and other animals— humans, roaches, raccoons, crows Copyright © 2009 Pearson Education, Inc. Animals ingest their food in a variety of ways Animals obtain and ingest their food in different ways – Suspension feeding – Substrate feeding – Fluid feeding – Bulk feeding Copyright © 2009 Pearson Education, Inc. Caterpillar Feces Overview: Food processing occurs in four stages Food is processed in four stages – Ingestion – Digestion – Absorption – Elimination Copyright © 2009 Pearson Education, Inc. Small molecules Pieces of food Chemical digestion Nutrient Mechanical (hydrolysis) molecules digestion enter body cells Undigested material Food 1 Ingestion 2 Digestion 3 Absorption 4 Elimination Overview: Food processing occurs in four stages Mechanical digestion breaks food down into smaller pieces – Smaller pieces are easier to swallow – Smaller pieces have more surface area exposed to digestive fluids Copyright © 2009 Pearson Education, Inc. Overview: Food processing occurs in four stages Chemical digestion breaks down large organic molecules into their components – Proteins split into amino acids – Polysaccharides and disaccharides into monosaccharides – Nucleic acids into nucleotides Copyright © 2009 Pearson Education, Inc. Macromolecule Components Proteindigesting enzymes Protein Polysaccharide Amino acids Carbohydratedigesting enzymes Disaccharide Monosaccharides Nucleic aciddigesting enzymes Nucleic acid Nucleotides Fat-digesting enzymes Fat Glycerol Fatty acids Digestion occurs in specialized compartments Sponges digest food in vacuoles Most animals digest food in compartments – Enzymes break down the food – Food particles move into cells lining the compartment – Undigested materials are expelled Copyright © 2009 Pearson Education, Inc. Digestion occurs in specialized compartments Cnidarians and flatworms have a gastrovascular cavity with a single opening, the mouth – Food enters the mouth – Undigested food is expelled back out the mouth Copyright © 2009 Pearson Education, Inc. Mouth Tentacle 1 Digestive enzymes released from a gland cell 2 Soft tissues digested 3 Food particle Food (Daphnia, a water flea) engulfed Gastrovascular cavity 4 Food particle digested in food vacuole Digestion occurs in specialized compartments Most animals have an alimentary canal with – Mouth – Anus – Specialized regions Copyright © 2009 Pearson Education, Inc. Mouth Pharynx Esophagus Crop Anus Gizzard Intestine Dorsal fold Interior of intestine Wall of intestine Earthworm Esophagus Midgut Anus Mouth Crop Grasshopper Gastric pouches Hindgut Stomach Gizzard Intestine Mouth Esophagus Crop Anus Bird HUMAN DIGESTIVE SYSTEM Copyright © 2009 Pearson Education, Inc. Digestive System I: The Upper Gastrointestinal Tract http://educationportal.com/academy/lesson/digestive-system-i-theupper-gastrointestinal-tract.html The human digestive system consists of an alimentary canal and accessory glands Alternating waves of contraction and relaxation by smooth muscle in the walls of the canal move food along in a process called peristalsis Sphincters control the movement of food into and out of digestive chambers Copyright © 2009 Pearson Education, Inc. The human digestive system consists of an alimentary canal and accessory glands The pyloric sphincter – Regulates the passage of food from the stomach to the small intestine – Limits the upward movement of acids into the esophagus Copyright © 2009 Pearson Education, Inc. Mouth Salivary glands Esophagus Gallbladder Liver Pancreas Stomach Small intestine Large intestine Rectum Anus A schematic diagram of the human digestive system Oral cavity Tongue Mouth Pharynx Salivary glands Esophagus Liver Esophagus Sphincter Stomach Sphincter Gallbladder Pancreas Small intestine Large intestine Rectum Anus Small intestine Digestion begins in the oral cavity Teeth break up food, saliva moistens it – Salivary enzymes begin the hydrolysis of starch – Buffers neutralize acids – Antibacterial agents kills some bacteria ingested with food The tongue tastes, shapes the bolus of food, and moves it toward the pharynx Copyright © 2009 Pearson Education, Inc. Teeth Incisors Canine Premolars Molars Tongue Salivary glands Opening of a salivary gland duct “Wisdom” tooth After swallowing, peristalsis moves food through the esophagus to the stomach The trachea conducts air to the lungs The esophagus conducts food from the pharynx to the stomach Copyright © 2009 Pearson Education, Inc. Bolus of food Tongue Pharynx Epiglottis up Larynx up Larynx Trachea Epiglottis down Epiglottis up Larynx down Esophageal sphincter Esophagus Sphincter contracted Esophagus Sphincter relaxed Sphincter contracted After swallowing, peristalsis moves food through the esophagus to the stomach The swallowing reflex – Food moves from the pharynx into the esophagus – The swallowing reflex prevents food from entering the trachea – A coughing reflex helps expel materials that accidentally enter the trachea Copyright © 2009 Pearson Education, Inc. Esophageal sphincter (contracted) Bolus of food Bolus of food Muscles contract, constricting passageway and pushing bolus down Muscles relax, allowing passageway to open Stomach The stomach stores food and breaks it down with acid and enzymes Acid – pH 2 – Parietal cells secrete hydrogen and chloride ions, which combine to make HCl – Acid kills bacteria and breaks apart cells in food Pepsinogen and HCl produce pepsin – Pepsin production activates more pepsinogen production—positive feedback – Pepsin begins the chemical digestion of proteins – Acidic gastric juices mix with food to produce acid chyme Copyright © 2009 Pearson Education, Inc. The stomach stores food and breaks it down with acid and enzymes What prevents the gastric juices from digesting the walls of the stomach? – Mucus helps protect against HCl and pepsin – New cells lining the stomach are produced about every 3 days Copyright © 2009 Pearson Education, Inc. Esophagus Sphincter Lumen (cavity) of stomach Sphincter Small intestine Interior surface of stomach Stomach Gastrin Interior surface of stomach Pits Release of gastric juice (mucus, HCl, and pepsinogen) Pepsinogen Epithelium Mucous cells Gastric gland 3 Pepsin 2 (active HCl enzyme) 1 H+ Cl– Chief cells Parietal cells The small intestine is the major organ of chemical digestion and nutrient absorption Small intestine is named for its smaller diameter—it is about 6 meters long Alkaline pancreatic juice neutralizes acid chyme and its enzymes digest food Bile, made in the liver and stored in the gall bladder, emulsifies fat for attack by pancreatic enzymes Copyright © 2009 Pearson Education, Inc. Liver Bile Gallbladder Stomach Acid chyme Intestinal enzymes Duodenum of small intestine Pancreatic juice Pancreas Digestive System II: The Lower Gastrointestinal Tract http://educationportal.com/academy/lesson/digestive-system-ii-thelower-gastrointestinal-tract.html The small intestine is the major organ of chemical digestion and nutrient absorption Enzymes from cells of the intestine continue digestion Copyright © 2009 Pearson Education, Inc. The small intestine is the major organ of chemical digestion and nutrient absorption Surface area for absorption is increased by – Folds of the intestinal lining – Fingerlike villi Copyright © 2009 Pearson Education, Inc. Vein with blood en route to the liver Muscle layers Lumen Large circular folds Villi Nutrient absorption Intestinal wall The small intestine is the major organ of chemical digestion and nutrient absorption Nutrients pass across the epithelium and into blood Blood flows to the liver where nutrients are processed and stored Copyright © 2009 Pearson Education, Inc. Lumen of intestine Lumen of intestine Nutrient absorption into epithelial cells Nutrient absorption Microvilli Epithelial cells Amino acids and sugars Fatty acids and glycerol Fats Blood capillaries Lymph vessel Blood Lymph Villi Epithelial cells lining villus One of the liver’s many functions is processing nutrient-laden blood from the intestines Blood from the digestive tract drains to the liver The liver performs many functions – Glucose in blood is converted to glycogen and stored in the liver – Liver synthesizes many proteins including blood clotting proteins and lipoproteins that transport fats and cholesterol – Liver changes toxins to less toxic forms – Liver produces bile Copyright © 2009 Pearson Education, Inc. Heart Kidneys Liver Intestines Hepatic portal vein The large intestine reclaims water and compacts the feces Diarrhea occurs when too little water is reclaimed Constipation occurs when too much water is reclaimed Feces are stored in the rectum Colon bacteria produce vitamins—biotin, vitamin K, B vitamins Copyright © 2009 Pearson Education, Inc. The large intestine reclaims water and compacts the feces Appendix – Located near the junction of the small intestine and colon – Makes a minor contribution to immunity Copyright © 2009 Pearson Education, Inc. Large intestine (colon) Small intestine Sphincter End of small intestine Appendix Cecum Rectum Anus Unabsorbed food material EVOLUTION CONNECTION: Evolutionary adaptations of vertebrate digestive systems often relate to diet The length of the digestive tract often correlates with diet – Herbivores and omnivores have relatively longer digestive tracts than carnivores Copyright © 2009 Pearson Education, Inc. Stomach Small intestine Cecum Colon (large intestine) Carnivore Herbivore EVOLUTION CONNECTION: Evolutionary adaptations of vertebrate digestive systems often relate to diet Many herbivores have specializations of the gut that promote the growth of cellulose-digesting microbes – Rumen – Reticulum – Omasum – Abomasum Copyright © 2009 Pearson Education, Inc. Intestine Omasum Rumen Esophagus Rumen Abomasum Reticulum a. b. g. h. i. c. d. e. j. k. l. f. m. You should now be able to 1. Describe the four stages of food processing 2. Describe the main components of the human digestive tract and their functions 3. Explain how teeth and saliva help us swallow 4. Explain why the stomach does not digest itself 5. Compare the structures and functions of the small and large intestines 6. Compare the digestive tracts of carnivores and herbivores Copyright © 2009 Pearson Education, Inc.
