Essential amino acids from a vegetarian diet 8 Essential amino acids for adults Methionine Beans and other legumes Valine Threonine Phenylalanine Leucine Corn (maize) and other grains Figure 41.2 Essential amino acids from a vegetarian diet Isoleucine Tryptophan Lysine

Humpback whale, a suspension feeder Baleen Figure 41.6 Four main feeding mechanisms of animals Humpback whale, a suspension feeder

Substrate feeders are animals that live in or on their food source. Leaf miner caterpillar, a substrate feeder Figure 41.6 Four main feeding mechanisms of animals Caterpillar Feces

Fluid feeders suck nutrient-rich fluid from a living host. Figure 41.6 Four main feeding mechanisms of animals Mosquito, a fluid feeder

Bulk feeders eat relatively large pieces of food. Figure 41.6 Four main feeding mechanisms of animals Rock python, a bulk feeder

The four stages of food processing Small molecules Pieces of food Chemical digestion (enzymatic hydrolysis) Nutrient molecules enter body cells Mechanical digestion Food Undigested material Figure 41.7 The four stages of food processing 1 Ingestion 2 Digestion Mechanical & Chemical 3 Absorption 4 Elimination

Digestion in a hydra Gastrovascular cavity Tentacles Food Mouth Figure 41.8 Digestion in a hydra Epidermis Gastrodermis

Variation in alimentary canals Crop Gizzard Esophagus Intestine Pharynx Anus Mouth Typhlosole Lumen of intestine (a) Earthworm Foregut Midgut Hindgut Esophagus Rectum Anus Crop Mouth Gastric cecae Figure 41.9 Variation in alimentary canals (b) Grasshopper Stomach Gizzard Intestine Mouth Esophagus Crop Anus (c) Bird

human digestive system Tongue Sphincter Salivary glands Oral cavity Salivary glands Pharynx Mouth Esophagus Esophagus pyloric sphincter Liver Stomach Gall- bladder Ascending portion of large intestine Stomach Gall- bladder Duodenum of small intestine Pancreas Small intestine Liver Small intestine Small intestine Figure 41.10 The human digestive system Pancreas Large intestine Large intestine Rectum Rectum Anus Anus Appendix A schematic diagram of the human digestive system Cecum

From mouth to stomach: the swallowing reflex and peristalsis Food Epiglottis up Tongue Pharynx Esophageal sphincter contracted Epiglottis down Glottis Glottis down and open Esophageal sphincter contracted Larynx Trachea Esophagus Esophageal sphincter relaxed Glottis up and closed Relaxed muscles To lungs To stomach Contracted muscles Relaxed muscles Sphincter relaxed Figure 41.11 From mouth to stomach: the swallowing reflex and esophageal peristalsis Stomach

The stomach and its secretions Esophagus Sphincter Stomach Sphincter 5 µm Small intestine Folds of epithelial tissue Interior surface of stomach Epithelium 3 Pepsinogen and HCl are secreted. 1 Pepsinogen Pepsin 2 Gastric gland HCl 2 HCl converts pepsinogen to pepsin. 1 Figure 41.12 The stomach and its secretions Mucus cells H+ Cl– 3. 3 Pepsin activates more pepsinogen. Chief cells Chief cell Parietal cells Parietal cell

Enzymatic hydrolysis in the human digestive system Carbohydrate digestion Protein digestion Nucleic acid digestion Fat digestion Oral cavity, pharynx, esophagus Polysaccharides Disaccharides (starch, glycogen) (sucrose, lactose) Salivary amylase Smaller polysaccharides, maltose Proteins Stomach Pepsin Small polypeptides Lumen of small intestine Polysaccharides Polypeptides DNA, RNA Fat globules Pancreatic amylases Pancreatic trypsin and chymotrypsin Pancreatic nucleases Bile salts Maltose and other disaccharides Fat droplets Nucleotides Smaller polypeptides Pancreatic lipase Pancreatic carboxypeptidase Figure 41.13 Enzymatic hydrolysis in the human digestive system Glycerol, fatty acids, monoglycerides Amino acids Epithelium of small intestine (brush border) Small peptides Nucleotidases Nucleosides Disaccharidases Dipeptidases, carboxypeptidase, and aminopeptidase Nucleosidases and phosphatases Monosaccharides Amino acids Nitrogenous bases, sugars, phosphates

Hormonal control of digestion Liver Gallbladder Bile Stomach Secretin and CCK – Gastrin + CCK + Pancreas Hormonal control of digestion Figure 41.14 Hormonal control of digestion Duodenum of small intestine Secretin + Key CCK + Stimulation Inhibition + –

Structure of the small intestine Microvilli (brush border) at apical (lumenal) surface Vein carrying blood to hepatic portal vein Lumen Blood capillaries Epithelial cells Basal surface Muscle layers Large circular folds Epithelial cells Villi Lacteal Figure 41.15 The structure of the small intestine Key Lymph vessel Nutrient absorption Villi Intestinal wall

Digital image of a human colon Figure 41.17 Digital image of a human colon

Dentition and diet Incisors Molars Canines Premolars (a) Carnivore (b) Herbivore Figure 41.18 Dentition and diet (c) Omnivore

Alimentary canals of a carnivore (coyote) and herbivore (koala) Small intestine Stomach Small intestine Cecum Figure 41.19 The alimentary canals of a carnivore (coyote) and herbivore (koala) Colon (large intestine) Carnivore Herbivore

Ruminant digestion Rumen Reticulum Intestine Esophagus Abomasum Omasum 1 Rumen 2 Reticulum Intestine Esophagus Figure 41.20 Ruminant digestion 4 Abomasum 3 Omasum

Homeostatic regulation of cellular fuel Stimulus: Blood glucose level rises after eating. Homeostasis: 90 mg glucose/ 100 mL blood Stimulus: Blood glucose level drops below set point. Figure 41.21 Homeostatic regulation of cellular fuel Homeostatic regulation of cellular fuel

appetite-regulating hormones Ghrelin Figure 41.23 A few of the appetite-regulating hormones Insulin Leptin PYY

A plump petrel chick Figure 41.25 A plump petrel

Fat cells from the abdomen of a human Figure 41.22 Fat cells from the abdomen of a human

Review Bloodstream Veins to heart Lymphatic system Hepatic portal vein Liver Lipids Absorbed food (except lipids) Absorbed water Mouth Stomach Esophagus Small intestine Anus Secretions from the gastric glands of the stomach Large intestine Rectum Secretions from the pancreas and the liver

You should now be able to: Name the three nutritional needs that must be met by an animal’s diet. Describe the four classes of essential nutrients. Distinguish among undernourishment, overnourishment, and malnourishment. Describe the four main stages of food processing. Distinguish between a complete digestive tract and a gastrovascular cavity.

Follow a meal through the mammalian digestive system: List important enzymes and describe their roles Compare where and how the major types of macromolecules are digested and absorbed Relate variations in dentition with different diets. Explain where and in what form energy-rich molecules may be stored in the human body.