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Chapter 41 Animal Nutrition Pages 884-890 PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 41-1 Concept 41.3: Organs specialized for sequential stages of food processing form the mammalian digestive system • The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts • Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Food is pushed along by peristalsis, rhythmic contractions of muscles in the wall of the canal • Valves called sphincters regulate the movement of material between compartments Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 41-10a Tongue Sphincter Oral cavity Salivary glands Pharynx Esophagus Sphincter Liver Stomach Ascending portion of large intestine Gallbladder Duodenum of small intestine Pancreas Small intestine Small intestine Large intestine Rectum Anus Appendix Cecum Fig. 41-10b Salivary glands Mouth Esophagus Gallbladder Liver Pancreas Stomach Small intestine Large intestine Rectum Anus A schematic diagram of the human digestive system The Oral Cavity, Pharynx, and Esophagus • The first stage of digestion is mechanical and takes place in the oral cavity • Salivary glands deliver saliva to lubricate food • Teeth chew food into smaller particles that are exposed to salivary amylase, initiating breakdown of glucose polymers Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings • The tongue shapes food into a bolus and provides help with swallowing • The region we call our throat is the pharynx, a junction that opens to both the esophagus and the trachea (windpipe) • The trachea leads to the lungs Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings • The esophagus conducts food from the pharynx down to the stomach by peristalsis • Swallowing causes the epiglottis to block entry to the trachea, and the bolus is guided by the larynx, the upper part of the respiratory tract • Coughing occurs when the swallowing reflex fails and food or liquids reach the windpipe Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 41-11-1 Food Epiglottis up Tongue Pharynx Esophageal sphincter contracted Glottis Larynx Trachea Esophagus To To lungs stomach Fig. 41-11-2 Food Epiglottis up Tongue Pharynx Esophageal sphincter contracted Glottis Larynx Trachea Epiglottis down Esophagus To To lungs stomach Glottis up and closed Esophageal sphincter relaxed Fig. 41-11-3 Food Epiglottis up Tongue Epiglottis up Pharynx Esophageal sphincter contracted Glottis Larynx Trachea Epiglottis down Esophagus To To lungs stomach Glottis up and closed Esophageal sphincter relaxed Glottis down and open Esophageal sphincter contracted Relaxed muscles Relaxed muscles Contracted muscles Sphincter relaxed Stomach Digestion in the Stomach • The stomach stores food and secretes gastric juice, which converts a meal to acid chyme (ingested food and digestive juice) Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Chemical Digestion in the Stomach • Gastric juice is made up of hydrochloric acid and the enzyme pepsin ( a protease: an enzyme that digest proteins) • pH of gastric juice is highly acidic (~2) • The ingredients of gastric juice are kept inactive until released into the lumen (cavity of the stomach) • Parietal cells secrete hydrogen and chloride ions separately • Chief cells secrete inactive pepsinogen, which is activated to pepsin when mixed with hydrochloric acid in the stomach (by clipping off a small portion and exposing its active site) • Mucus: a viscous and slippery mixture of glycoproteins, cells, salts and water. • Mucus protects the stomach lining from gastric juice as well as to acid-tolerant pathogens in food Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 41-12a Esophagus Sphincter Stomach 5 µm Sphincter Interior surface of stomach Small intestine Folds of epithelial tissue Fig. 41-12b Interior surface of stomach Epithelium 3 Pepsinogen 2 1 Pepsinogen and HCl are secreted. HCl Gastric gland 1 Mucus cells Pepsin H+ – Cl 2 HCl converts pepsinogen to pepsin. 3 Pepsin activates more pepsinogen. Chief cells Chief cell Parietal cells Parietal cell • Barry Marshall and Robin Warren, 1982 • Gastric ulcers, lesions in the stomach lining, are caused mainly by the bacterium Helicobacter pylori • Nobel prize in 2005 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Stomach Dynamics • Coordinated contraction and relaxation of stomach muscle churn the stomach’s contents • Sphincters prevent chyme from entering the esophagus and regulate its entry into the small intestine • Acid reflux: a backflow of chyme from the stomach to lower end of esophagus. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Digestion in the Small Intestine • Most enzymatic hydrolysis of macromolecules from food occurs in the small intestine • The small intestine is the longest section of the alimentary canal (> 6 m) • It is the major organ of digestion and absorption Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 41-13 Carbohydrate digestion Oral cavity, pharynx, esophagus Protein digestion Nucleic acid digestion Fat digestion Polysaccharides Disaccharides (starch, glycogen) (sucrose, lactose) Salivary amylase Smaller polysaccharides, maltose Stomach Proteins Pepsin Small polypeptides Lumen of small intestine Polysaccharides Pancreatic amylases Polypeptides Pancreatic trypsin and chymotrypsin DNA, RNA Fat globules Pancreatic nucleases Bile salts Maltose and other disaccharides Nucleotides Fat droplets Smaller polypeptides Pancreatic lipase Pancreatic carboxypeptidase Glycerol, fatty acids, monoglycerides Amino acids Epithelium of small intestine (brush border) Small peptides Disaccharidases Monosaccharides Nucleotidases Nucleosides Dipeptidases, carboxypeptidase, and aminopeptidase Amino acids Nucleosidases and phosphatases Nitrogenous bases, sugars, phosphates Fig. 41-13a Carbohydrate digestion Oral cavity, pharynx, esophagus Polysaccharides Disaccharides (starch, glycogen) (sucrose, lactose) Salivary amylase Smaller polysaccharides, maltose Stomach Polysaccharides Lumen of small intestine Epithelium of small intestine (brush border) Pancreatic amylases Maltose and other disaccharides Disaccharidases Monosaccharides Fig. 41-13b Protein digestion Stomach Proteins Pepsin Small polypeptides Polypeptides Pancreatic trypsin and chymotrypsin Lumen of small intestine Smaller polypeptides Pancreatic carboxypeptidase Amino acids Small peptides Epithelium of small intestine (brush border) Dipeptidases, carboxypeptidase, and aminopeptidase Monosaccharides Amino acids Fig. 41-13c Nucleic acid digestion DNA, RNA Lumen of small intestine Pancreatic nucleases Nucleotides Nucleotidases Epithelium of small intestine (brush border) Nucleosides Nucleosidases and phosphatases Nitrogenous bases, sugars, phosphates Fig. 41-13d Fat digestion Fat globules Bile salts Lumen of small intestine Fat droplets Pancreatic lipase Glycerol, fatty acids, monoglycerides • The first portion of the small intestine is the duodenum, where acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the small intestine itself Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 41-14 Liver Gallbladder Bile When chyme rich in fats enters the Duodenum , secretin and CCK inhibit peristalsis and acid secretion thereby slowing digestion Stomach Circulates back to the stomach and stimulates production of gastric juices Secretin and CCK – Gastrin + CCK + Pancreas Duodenum of small intestine Amino acids or fatty acids trigger the release of cholecytokinin (CCK) which stimulates the release of enzymes from the pancreas and of bile from the gallbladder Secretin stimulates the pancreas to release sodium bicarbonate which neutralizes chyme, act as a buffer Secretin + Key CCK + + – Stimulation Inhibition Pancreatic Secretions • The pancreas produces proteases trypsin and chymotrypsin, protein-digesting enzymes that are activated after entering the duodenum • Its solution is alkaline (rich in bicarbonate) and neutralizes the acidic chyme Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Bile Production by the Liver • Bile is contains bile salts which act as detergents that aid in digestion and absorption of lipids in small intestine. • Bile is made in the liver and stored and concentrated in the gallbladder • Liver breaks down toxins and helps balance nutrient utilization • Bile is important in the liver in destruction of red blood cells that are no longer functional Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Secretions of the Small Intestine • The epithelial lining of the duodenum, called the brush border, produces several digestive enzymes • Enzymatic digestion is completed as peristalsis moves the chyme and digestive juices along the small intestine • Most digestion occurs in the duodenum; the jejunum and ileum function mainly in absorption of nutrients and water Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Absorption in the Small Intestine • The small intestine has a huge surface area, due to villi (finger-like projections) and microvilli that are exposed to the intestinal lumen • The enormous microvillar surface greatly increases the rate of nutrient absorption • Surface area ~ 300 m2. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 41-15a Vein carrying blood to hepatic portal vein Muscle layers Large circular folds Villi Key Nutrient absorption Intestinal wall Fig. 41-15b Microvilli (brush border) at apical (lumenal) surface Lumen Blood capillaries Epithelial cells Basal surface Epithelial cells Lacteal Villi Key Nutrient absorption Lymph vessel • Each villus contains a network of blood vessels and a small lymphatic vessel called a lacteal • After glycerol and fatty acids are absorbed by epithelial cells, they are recombined into fats within these cells • These fats are mixed with cholesterol and coated with protein, forming molecules called chylomicrons, which are transported into lacteals Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 41-16 Lumen of small intestine Triglycerides Fatty acids Monoglycerides 1. In the lumen, bile salts keep fat droplets from coalescing. Within the droplets, fats are broken down by the enzyme lipase Epithelial cell 2. After diffusing into epithelial cells, monoglycerides and fatty acids are reformed into fats Triglycerides Phospholipids, cholesterol, and proteins Chylomicron Lacteal 3. Triglycerides are incorporated into water-soluble globules called chylomicrons 4. Chylomicrons leave epithelial cells by exocytosis and enter lacteals, where they are carried away by the lymph and later pass into large veins • Amino acids and sugars pass through the epithelium of the small intestine and enter the bloodstream (by active transport) • Capillaries and veins from the lacteals converge in the hepatic portal vein and deliver blood to the liver and then on to the heart Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Absorption in the Large Intestine • The colon of the large intestine is connected to the small intestine • The cecum aids in the fermentation of plant material and connects where the small and large intestines meet • The human cecum has an extension called the appendix, which plays a very minor role in immunity Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 41-17 • A major function of the colon is to recover water that has entered the alimentary canal • Wastes of the digestive tract, the feces, become more solid as they move through the colon • Feces pass through the rectum and exit via the anus Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings • The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins • Feces are stored in the rectum until they can be eliminated • Two sphincters between the rectum and anus control bowel movements Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings The END Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings