Chapter 21 Nutrition and Digestion PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko Figure 21.0_2 Introduction 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. THE HUMAN DIGESTIVE SYSTEM © 2012 Pearson Education, Inc. Food processing occurs in four stages Food is processed in four stages. 1. Ingestion is the act of eating. 2. Digestion is the breaking down of food into molecules small enough for the body to absorb. • Remember: biomolecule subunits by hydrolysis 3. Absorption is the take-up of the products of digestion, usually by the cells lining the digestive tract. 4. Elimination is the removal of undigested materials out of the digestive tract. © 2012 Pearson Education, Inc. Mechanical digestion = mechanical breakdown of large small food particles •Just a physical change in material!! •Increases surface area of food particles for chemical digestion Pieces of food Small molecules Mechanical digestion 1 Ingestion 2 Digestion Undigested material Nutrient molecules enter body cells Chemical digestion (hydrolysis) 3 Absorption 4 Elimination Components Food Molecules Proteindigesting enzymes Chemical digestion •Hydrolysis of covalent bonds within molecules •Requires enzyme to catalyze these events Amino acids Protein Polysaccharide Carbohydratedigesting enzymes Disaccharide Monosaccharides Nucleic-aciddigesting enzymes Nucleotides Nucleic acid Fat-digesting enzymes Fat Glycerol Fatty acids Figure 21.4 Nasal cavity A schematic diagram of the human digestive system Oral cavity (mouth) Tongue Oral cavity Salivary glands Salivary glands Pharynx Esophagus Esophagus Liver Gallbladder Liver Pancreas Esophagus Stomach Small intestine Sphincters Gallbladder Large intestine Pancreas Rectum Anus Small intestine Large intestine Key Alimentary canal Accessory digestive glands Rectum Anus Stomach Small intestine Mouth pH = 7 Mechanical digestion – Chewing cuts, smashes, and grinds food, making it easier to swallow. Chemical digestion – Saliva releases salivary amylase – Polysaccharides + H2O mono and disaccharides © 2012 Pearson Education, Inc. Esophageal sphincter (contracted) Bolus of food Bolus of food Muscles contract, squeezing the bolus through the esophagus. Muscles relax, allowing the passageway to open. Stomach © 2012 Pearson Education, Inc. Peristalsis: Smooth muscle contractions that move food through digestive tract Stomach pH = 2 Mechanical digestion – Churning of stomach – Low pH denatures proteins Chemical digestion – Pepsin – Proteins + H2O amino acids Secretes gastric juice, made up of – Mucus (protects stomach lining from HCl) – Pepsinogen (inactive form of pepsin) – – Gastric juice secreted by gastric glands in response to GASTRIN hormone. Pepsinogen (inactive) pepsin (active) in presence of acid HCl – kills ingested bacteria, – breaks apart cells in food, and – denatures proteins. © 2012 Pearson Education, Inc. Figure 21.8 Esophagus Sphincter Lumen (cavity) of stomach Stomach Gastrin Release of gastric juice (mucus, HCl, and pepsinogen) Pits Sphincter Epithelium Small intestine Interior surface of the stomach Gastric juice secreted by gastric glands in response to GASTRIN hormone. 3 Pepsinogen 2 Mucous cells HCl 1 H Gastric gland Cl Chief cells Parietal cells Pepsin (active enzyme) Pancreas Produces and secretes: Pancreatic juice to small intenstine Liver Trypsinogen (inactive form of trypsin) Lipase Pancreatic juice released to small instestine in response to SECRETIN hormone Insulin and glucagon (regulate blood sugar) © 2012 Pearson Education, Inc. Stomach Gallbladder Na-bicarbonate (neutralize pH of incoming stomach secretions) Pancreatic amylase Bile Chyme Intestinal enzymes Duodenum of small intestine Pancreatic juice Pancreas Liver Produces bile converts glucose in blood to glycogen, stores glycogen and releases sugars back into the blood as needed, Detoxifies substances absorbed from digestive tract Processes amino acids and produces urea Liver Bile Stomach Gallbladder Chyme Intestinal enzymes Duodenum of small intestine © 2012 Pearson Education, Inc. Pancreatic juice Pancreas Gallbladder Stores bile produced by liver – Bile released to small intestine in response to hormone SECRETIN Bile – Synthesized from cholesterol, aids in physical digestion of lipids Liver Bile – Emulsify – disperse oil Stomach Gallbladder into water – Increases efficiency of chemical digestion of lipids by lipase © 2012 Pearson Education, Inc. Chyme Intestinal enzymes Duodenum of small intestine Pancreatic juice Pancreas Small Intestine Major organ of chemical digestion and nutrient absorption pH = 8 due to Na-bicarb released by pancreas Releases the hormone SECRETIN in response to food entering small intestine Final chemical digestion of macromolecules: – Pancreatic amylase – Poly and disaccrharides + H2O monosaccharides – Trypsinogen trypsin (active) at basic pH – Proteins + H2O amino acids – Chymotrypsinogen chymotrypsin (active) at basic pH – Proteins + H2O amino acids – Lipase (with assistance of bile) – Triglycerides + H2O glycerol + fatty acids © 2012 Pearson Education, Inc. Small intestine is site of absorption!! Villi and Microvilli increase surface area for absorption Lumen of intestine Nutrient absorption Vein carrying blood to the liver Microvilli Amino acids and sugars Epithelial cells Muscle layers Lumen Fats Blood capillaries Large circular folds Blood Lymph vessel VILLI Lymph Nutrient absorption VILLI Intestinal wall © 2012 Pearson Education, Inc. Fatty acids and glycerol Epithelial cells of a villus • Nutrients pass into epithelial cells by facilitated or active transport Small intestine is site of absorption!! Lumen of intestine Nutrient absorption Microvilli Amino acids and sugars Epithelial cells Fatty acids and glycerol Fats Blood capillaries Amino acids and sugars pass • out of the intestinal into blood Blood Lymph vessel Lymph Epithelial cells of a villus VILLI Fatty acids and glycerol are • • • © 2012 Pearson Education, Inc. recombined into fats, coated with proteins, and transported into lymph vessels. Blood from the digestive tract drains – into the hepatic portal vein Heart – to the LIVER. Liver Hepatic portal vein Intestines Large Intestine Excretes solid wastes Reabsorption of water Synthesis of several Large vitamins, like Vitamin intestine (colon) K, with help of End of bacteria small intestine Unabsorbed food material Appendix Cecum Small intestine Rectum Anus Figure 21.UN02 a. g. b. h. c. d. e. i. j. f. k. l.