Ch. 21. Nutrition and Digestion All animals must eat to provide energy and the building blocks used to assemble new molecules. Animals also need essential vitamins and minerals. © 2012 Pearson Education, Inc. 1

21.2 Overview: Food processing occurs in four stages Food is processed in four stages. Ingestion is the act of eating. Digestion is the breaking down of food into molecules small enough for the body to absorb. Absorption is the take-up of the products of digestion, usually by the cells lining the digestive tract. Elimination is the removal of undigested materials out of the digestive tract. © 2012 Pearson Education, Inc. 2

Chemical digestion (hydrolysis) Nutrient molecules enter body cells Figure 21.2A Pieces of food Small molecules Mechanical digestion Undigested material Figure 21.2A The four main stages of food processing Chemical digestion (hydrolysis) Nutrient molecules enter body cells 1 Ingestion 2 Digestion 3 Absorption 4 Elimination 3

Protein- digesting enzymes Figure 21.2B Food Molecules Components Protein- digesting enzymes Protein Amino acids Carbohydrate- digesting enzymes Polysaccharide Disaccharide Monosaccharides Nucleic-acid- digesting enzymes Figure 21.2B Chemical digestion: the breakdown of large organic molecules to their components Nucleic acid Nucleotides Fat-digesting enzymes Fat Glycerol Fatty acids 4

21.3 Digestion occurs in specialized compartments Sponges digest food in vacuoles. Most animals digest food in compartments. Cnidarians and flatworms have a gastrovascular cavity with a single opening, the mouth. Food enters the mouth. Enzymes break down the food. Food particles move into cells lining the compartment. Undigested materials are expelled back out the mouth. © 2012 Pearson Education, Inc. 5

21.3 Digestion occurs in specialized compartments Most animals have an alimentary canal with a mouth, an anus, and specialized regions associated with one-way flow of food. © 2012 Pearson Education, Inc. 6

21.3 Digestion occurs in specialized compartments The normal one-way flow moves food into the pharynx or throat, down the esophagus to a crop where food is softened and stored, gizzard, where food is ground and stored, and/or stomach where food is ground and stored, to the intestines, where chemical digestion and nutrient absorption occur, and finally undigested materials are expelled through the anus. © 2012 Pearson Education, Inc. 7

Digestive enzymes being released from a gland cell Tentacles Figure 21.3A 1 Digestive enzymes being released from a gland cell Tentacles Mouth 2 Food digested to small particles Food (a water flea) 3 A food particle being engulfed Gastrovascular cavity 4 A food particle digested in a food vacuole Figure 21.3A Digestion in the gastrovascular cavity of a hydra 8

Earthworm Mouth Pharynx Intestine Esophagus Anus Crop Gizzard Figure 21.3B Earthworm Mouth Pharynx Intestine Esophagus Anus Crop Gizzard Grasshopper Esophagus Midgut Anus Mouth Crop Hindgut Gastric pouches Figure 21.3B Three examples of alimentary canals Bird Stomach Mouth Gizzard Intestine Esophagus Crop Anus 9

THE HUMAN DIGESTIVE SYSTEM THE HUMAN DIGESTIVE SYSTEM © 2012 Pearson Education, Inc. 10

21.4 The human digestive system consists of an alimentary canal and accessory glands In humans, food is ingested and chewed in the mouth or oral cavity, pushed by the tongue into the pharynx, Saliva begins breakdown of di- and polysaccharides moved along by alternating waves of contraction and relaxation by smooth muscle in the walls of the canal in a process called peristalsis, and moved in and out of the stomach by muscular ring-like valves called sphincters. © 2012 Pearson Education, Inc. 11

21.4 The human digestive system consists of an alimentary canal and accessory glands Food is pushed by the pharynx into the esophagus, which connects to the stomach. In the stomach, enzymes begin digestion of proteins. Enzymes from the pancreas and bile (stored in gall bladder) from the liver are added to the small intestine where digestion is completed and nutrient absorption occurs. Undigested materials move through the large intestine, feces are stored in the rectum, and then expelled out the anus. © 2012 Pearson Education, Inc. 12

A schematic diagram of the human digestive system Figure 21.4 Nasal cavity Oral cavity (mouth) A schematic diagram of the human digestive system Tongue Pharynx Salivary glands Oral cavity Esophagus Salivary glands Esophagus Liver Gall- bladder Esophagus Stomach Sphincters Small intestine Liver Gall- bladder Stomach Pancreas Figure 21.4 The human digestive system Large intestine Pancreas Small intestine Small intestine Rectum Anus Large intestine Key Alimentary canal Rectum Accessory digestive glands Anus 13

a. g. b. h. c. i. d. e. j. k. f. l. Figure 21.UN02 Figure 21.UN02 Connecting the Concepts, question 1 j. k. f. l. 14