Principles of Biology BIOL 100C: Introductory Biology III The Digestive System Dr. P. Narguizian Fall 2012

Copyright © 2009 Pearson Education, Inc. 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 obtain and ingest their food in different ways –Suspension feeding –Substrate feeding –Fluid feeding –Bulk feeding Animals ingest their food in a variety of ways

Caterpillar Feces

Copyright © 2009 Pearson Education, Inc. Overview: Food processing occurs in four stages  Food is processed in four stages –Ingestion –Digestion –Absorption –Elimination

Mechanical digestion Pieces of food Food Chemical digestion (hydrolysis) Nutrient molecules enter body cells Small molecules Undigested material Digestion Ingestion 2 1 Absorption 3 Elimination 4

Copyright © 2009 Pearson Education, Inc.  Mechanical digestion breaks food down into smaller pieces –Smaller pieces are easier to swallow –Smaller pieces have more surface area exposed to digestive fluids Overview: Food processing occurs in four stages

Copyright © 2009 Pearson Education, Inc.  Chemical digestion breaks down large organic molecules into their components –Proteins split into amino acids –Polysaccharides and disaccharides into monosaccharides –Nucleic acids into nucleotides Overview: Food processing occurs in four stages

Protein- digesting enzymes Polysaccharide Macromolecule Protein Carbohydrate- digesting enzymes Components Amino acids Monosaccharides Disaccharide Nucleic acid- digesting enzymes NucleotidesNucleic acid Fat-digesting enzymes Fat Glycerol Fatty acids

Copyright © 2009 Pearson Education, Inc. 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.  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 Digestion occurs in specialized compartments

Food (Daphnia, a water flea) Gastrovascular cavity Food particle engulfed Soft tissues digested Tentacle Mouth Digestive enzymes released from a gland cell Food particle digested in food vacuole

Copyright © 2009 Pearson Education, Inc.  Most animals have an alimentary canal with –Mouth –Anus –Specialized regions Digestion occurs in specialized compartments

Mouth Pharynx Esophagus Crop Gizzard Anus Intestine Earthworm Dorsal fold Interior of intestine Wall of intestine

Esophagus Midgut Mouth Crop Grasshopper Anus Hindgut Gastric pouches

Mouth Esophagus Crop Gizzard Anus Intestine Bird Stomach

Copyright © 2009 Pearson Education, Inc. HUMAN DIGESTIVE SYSTEM

Digestive System I: The Upper Gastrointestinal Tract  portal.com/academy/lesson/digestive-system-i-the- upper-gastrointestinal-tract.html portal.com/academy/lesson/digestive-system-i-the- upper-gastrointestinal-tract.html

Copyright © 2009 Pearson Education, Inc. 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 pyloric sphincter –Regulates the passage of food from the stomach to the small intestine –Limits the upward movement of acids into the esophagus The human digestive system consists of an alimentary canal and accessory glands

Mouth Salivary glands Esophagus Gall- bladder Liver Pancreas Small intestine Stomach Rectum Anus Large intestine A schematic diagram of the human digestive system

Pharynx Esophagus Oral cavity Tongue Mouth Salivary glands Gall- bladder Liver Pancreas Small intestine Rectum Anus Large intestine Esophagus Stomach Small intestine Sphincter

Copyright © 2009 Pearson Education, Inc. 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

Opening of a salivary gland duct Salivary glands Tongue Incisors Premolars Molars “Wisdom” tooth Teeth Canine

Copyright © 2009 Pearson Education, Inc. 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

Epiglottis up Pharynx Esophageal sphincter Bolus of food Tongue Esophagus Larynx Trachea Sphincter contracted Epiglottis down Esophagus Larynx up Sphincter relaxed Epiglottis up Sphincter contracted Larynx down

Copyright © 2009 Pearson Education, Inc.  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 After swallowing, peristalsis moves food through the esophagus to the stomach

Esophageal sphincter (contracted) Bolus of food Muscles contract, constricting passageway and pushing bolus down Stomach Bolus of food Muscles relax, allowing passageway to open

Copyright © 2009 Pearson Education, Inc. 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.  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 The stomach stores food and breaks it down with acid and enzymes

Interior surface of stomach Lumen (cavity) of stomach Stomach Gastrin Esophagus Sphincter Small intestine

Interior surface of stomach Pits Release of gastric juice (mucus, HCl, and pepsinogen) Epithelium Gastric gland Mucous cells Chief cells Parietal cells Pepsin (active enzyme) Pepsinogen H+H+ Cl – HCl 2 3 1

Copyright © 2009 Pearson Education, Inc. 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

Gall- bladder Pancreatic juice Liver Bile Acid chyme Pancreas Stomach Intestinal enzymes Duodenum of small intestine

Digestive System II: The Lower Gastrointestinal Tract  portal.com/academy/lesson/digestive-system-ii-the- lower-gastrointestinal-tract.html portal.com/academy/lesson/digestive-system-ii-the- lower-gastrointestinal-tract.html

Copyright © 2009 Pearson Education, Inc.  Enzymes from cells of the intestine continue digestion The small intestine is the major organ of chemical digestion and nutrient absorption

Copyright © 2009 Pearson Education, Inc.  Surface area for absorption is increased by –Folds of the intestinal lining –Fingerlike villi The small intestine is the major organ of chemical digestion and nutrient absorption

Muscle layers Large circular folds Villi Lumen Nutrient absorption Intestinal wall Vein with blood en route to the liver

Copyright © 2009 Pearson Education, Inc.  Nutrients pass across the epithelium and into blood  Blood flows to the liver where nutrients are processed and stored The small intestine is the major organ of chemical digestion and nutrient absorption

Lymph vessel Blood capillaries Villi Nutrient absorption Epithelial cells Lumen of intestine Nutrient absorption into epithelial cells Microvilli Amino acids and sugars Fats Blood Fatty acids and glycerol Epithelial cells lining villus Lymph

Copyright © 2009 Pearson Education, Inc. 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

Heart Hepatic portal vein Kidneys Liver Intestines

Copyright © 2009 Pearson Education, Inc. 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.  Appendix –Located near the junction of the small intestine and colon –Makes a minor contribution to immunity The large intestine reclaims water and compacts the feces

Large intestine (colon) End of small intestine Appendix Cecum Sphincter Unabsorbed food material Anus Rectum Small intestine

Copyright © 2009 Pearson Education, Inc. 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

Small intestine Cecum Stomach Colon (large intestine) CarnivoreHerbivore

Copyright © 2009 Pearson Education, Inc.  Many herbivores have specializations of the gut that promote the growth of cellulose-digesting microbes –Rumen –Reticulum –Omasum –Abomasum EVOLUTION CONNECTION: Evolutionary adaptations of vertebrate digestive systems often relate to diet

Intestine OmasumRumen Esophagus Reticulum Abomasum Rumen

a. g. h. i. j. k. l. m. b. c. d. e. f.

Copyright © 2009 Pearson Education, Inc. 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