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1 Lecture 10 Outline (Ch. 41) I. Animal Nutrition Overview II. Essential Parts of Animal Diet III. Food Intake IV. Digestive Compartments V. Adaptations VI. Obesity VII. Preparation for next lecture 2 Overview: The Need to Feed • Food is taken in, taken apart, and taken up in the process of animal nutrition • In general, animals fall into three categories: – Herbivores eat mainly autotrophs (plants, algae) – Carnivores eat other animals – Omnivores regularly consume animals as well as plants or algal matter 3 Essential Parts of Diet • Chemical energy (converted to ATP) • Organic carbon and nitrogen • Essential nutrients must be obtained from dietary sources –Essential amino acids –Essential fatty acids –Vitamins –Minerals 4 Essential Parts of Diet • Meat, eggs, cheese - provide all nine essential amino acids ( “complete” proteins) • Individuals eating only plant proteins need specific plant combinations for all essential amino acids Essential amino acids for adults Methionine Valine Beans and other legumes Threonine Phenylalanine Leucine Corn (maize) and other grains Isoleucine Tryptophan Lysine 5 Essential Parts of Diet • Animals can synthesize most fatty acids they need • The essential fatty acids are certain unsaturated fatty acids that must be obtained from the diet • Vitamins: organic molecules needed in small amounts • 13 essential vitamins for humans • Fat-soluble & water-soluble Vitamin A B-complex Vitamin D Biotin/B7 Vitamin E Vitamin C (ascorbic acid) Vitamin K 6 Minerals • Minerals: inorganic nutrients, small amounts needed Calcium Phosphorus Potassium Sulfur Chlorine Sodium Magnesium Iron A diet missing a certain essential part or not enough calories overall leads to malnourishment or undernourishment 7 If a person is following a vegan diet, why is it recommended to eat a variety of plant sources? 1. 2. 3. 4. 5. Plants are not complete proteins They are likely missing specific vitamins Certain fatty acids may be missing They may lack particular minerals They do not contain chemical energy Food Intake Ingestion: the act of eating • Suspension feeders - many aquatic animals, which sift small food particles from the water • Substrate feeders are animals that live in or on their food source • Fluid feeders suck nutrient-rich fluid from a living host • Bulk feeders eat relatively large pieces of food 9 Leaf miner caterpillar, substrate feeder Baleen Humpback whale, a suspension feeder Caterpillar Mosquito, a fluid feeder Feces 10 Rock python, a bulk feeder Food Intake Digestion: process of breaking food down into molecules small enough to absorb. In chemical digestion, enzymatic hydrolysis splits bonds in molecules Small molecules Pieces of food Mechanical digestion Chemical digestion Nutrient (enzymatic hydrolysis) molecules enter body cells Undigested material Food 1 Ingestion 2 Digestion Absorption is uptake of nutrients by body cells 3 Absorption 4 Elimination Elimination is the passage of undigested material out of the digestive compartment Digestive Compartments • Most animals process food (i.e. hydrolysis) in specialized compartments • Reduces risk animal digesting its own cells/ Tentacles tissues Food Gastrovascular Cavity: Mouth Gastrovascular cavity For both digestion and distribution of nutrients Cells secrete digestive enzymes Epidermis 12 Gastrodermis Digestive Compartments Crop Gizzard Intestine Esophagus Pharynx Anus Mouth • More complex animals: digestive tube with two openings (mouth, anus) • Tube called a complete digestive tract or an alimentary canal • Can have specialized regions, carry out digestion and absorption stepwise Typhlosole Lumen of intestine (a) Earthworm Foregut Midgut Hindgut Rectum Anus Esophagus Crop Mouth Gastric cecae (b) Grasshopper Stomach Gizzard Intestine Mouth Esophagus Crop Anus 13 (c) Bird Digestive Compartments Food moves by peristalsis Tongue Sphincter Salivary glands Oral cavity Salivary glands Mouth Pharynx Esophagus Esophagus Sphincter Liver Stomach Ascending portion of large intestine Gallbladder Gallbladder Duodenum of small intestine Pancreas Liver Small intestine Small intestine Pancreas Large intestine Anus Cecum Small intestine Large intestine Rectum Anus Rectum Appendix Stomach A schematic diagram of the human digestive system • Mammalian alimentary canal and accessory glands that secrete digestive juices through ducts 14 Oral Cavity, Pharynx, Esophagus Food Epiglottis up Tongue Epiglottis up Pharynx Esophageal sphincter contracted Glottis Larynx Trachea Epiglottis down Esophagus To To lungs stomach Glottis up and closed Glottis down and open Esophageal sphincter relaxed • Food shaped into a • The esophagus bolus, lubricated by conducts food from the saliva, digestion begins pharynx down to the with amylase and mucus stomach by peristalsis • Pharynx, a junction that • Epiglottis blocks opens to both the entry to the trachea, esophagus and the and larynx. trachea (windpipe) Esophageal sphincter contracted Relaxed muscles Relaxed muscles Contracted muscles Sphincter relaxed Stomach 15 Digestion in the Stomach • The stomach stores food and secretes gastric juice, which converts a meal to acid chyme Sphincter Stomach 5 µm • Highly folded • Gastric juice hydrochloric acid (parietal cells) and the enzyme pepsin (chief cells) • Pepsin initially secreted as pepsinogen • Mucus protects the stomach lining from gastric juice Esophagus Interior surface of stomach Sphincter Small intestine Folds of epithelial tissue Epithelium 3 Pepsinogen Gastric gland 2 HCl Pepsin 1 Mucus cells Cl– H+ Chief cells Chief cell Parietal cells Parietal cell 16 Digestion in the Small Intestine • The small intestine: longest section of alimentary canal • Major organ of enzymatic digestion and absorption • First is the duodenum acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the small intestine itself. 17 Digestion in the Small Intestine liver/gallbladder pancreas bile aids digestion and absorption of fats proteases trypsin & chymotrypsin amylase & lipase bicarbonate neutralizes the acidic chyme small intestine lining of duodenum (brush border) produces several digestive enzymes jejunum and ileum mainly absorb18 water & nutrients Where are most fats broken and absorbed? 1. 2. 3. 4. 5. In the mouth In the stomach In the liver In the gall bladder In the small intestine Carbohydrate digestion Oral cavity, pharynx, esophagus Polysaccharides Disaccharides (starch, glycogen) (sucrose, lactose) Protein digestion Nucleic acid digestion Fat digestion 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 20 Absorption in the Small Intestine • small intestine has huge surface area, from villi and microvilli exposed to the intestinal lumen • enormous microvillar surface greatly increases rate of nutrient absorption Microvilli (brush border) at apical (lumenal) surface Lumen Vein carrying blood to hepatic portal vein Blood capillaries Muscle layers Epithelial cells Basal surface Large circular folds Villi Epithelial cells Lacteal Key Nutrient absorption Intestinal wall Villi Lymph vessel 21 Absorption in the Large Intestine • The colon of the large intestine is connected to the small intestine • The cecum aids in fermentation of plant material, - connects where the small and large intestines meet • Human cecum extension (appendix), -minor role in immunity Feces stored in rectum until eliminated 22 Absorption in the Large Intestine • The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins • Two sphincters between the rectum and anus control bowel movements – Internal smooth muscle sphincter (involuntary) – External striated muscle sphincter (voluntary) 23 Mutualistic Adaptations • Many herbivores have symbiotic microorganisms that digest cellulose • The most elaborate adaptations in ruminants 1 Rumen 2 Reticulum Intestine Esophagus 24 4 Abomasum 3 Omasum Adaptations • Herbivores generally have longer alimentary canals than carnivores, reflecting the longer time needed to digest vegetation • Coprophagy – method to recover more nutrients by ingesting feces Small intestine Stomach Small intestine Cecum Enzymes for digesting plant matter Colon (large intestine) 25 Carnivore Herbivore Where is most water absorbed? 1. 2. 3. 4. 5. In the stomach In the small intestine In the cecum In the large intestine In the bladder Energy Sources and Stores • Animals store excess calories as glycogen in the liver and muscles • Energy secondarily stored as adipose, or fat, cells • When fewer calories are taken in than are expended, fuel is taken from storage and oxidized • Obesity is due to excessive intake of food energy, excess stored as fat • Obesity contributes to diabetes (type 2), cancer of the colon and breasts, heart attacks, and strokes 100 µm Fat cells 27 Energy Sources and Stores Pancreas releases insulin – cells uptake sugars Stimulus: Blood glucose level rises after eating. Homeostasis: 90 mg glucose/ 100 mL blood Pancreas releases glucagon – liver releases sugars Stimulus: Blood glucose level drops below set point. If you eat a meal high in sugar, what happens? 1. 2. 3. 4. 5. Glucagon is released Glycogen is broken down Insulin is released Fats are broken down Starch is stored Energy Sources and Stores • The complexity of weight control in humans is wellstudied • Mice that inherit a defect in the gene for leptin become very obese Ghrelin – secreted by stomach, stimulates appetite Insulin – secreted by pancreas, suppresses appetite Leptin – released by fat cells, suppresses appetite PYY – secreted by Sm. Intestine, suppresses appetite hypothalamus Ghrelin Insulin Leptin PYY 30 Obese mouse with mutant ob gene (left) – mutant for leptin production – next to wild-type sibling mouse. 31 The gene db codes for the leptin receptor. If mice are mutant for the db gene what happens? 1. 2. 3. 4. They fail to make leptin – increased appetite They fail to detect leptin – decreased appetite They fail to detect leptin – increased appetite They fail to make leptin – decreased appetite Things To Do After Lecture 10… Reading and Preparation: 1. Re-read today’s lecture, highlight all vocabulary you do not understand, and look up terms. 2. Ch. 41 Self-Quiz: #2, 3, 4, 5, 6 (correct answers in back of book) 3. Read chapter 41, focus on material covered in lecture (terms, concepts, and figures!) 4. Skim next lecture. “HOMEWORK” (NOT COLLECTED – but things to think about for studying): 1. Describe the pathway that food molecules take from ingestion through elimination – where appropriate, indicate which digestive enzymes are secreted and what biomolecules are broken down. 2. Define, and then list: necessary vitamins and minerals. 3. Explain the difference between a substrate feeder and a bulk feeder. 4. Compare the function of leptin and ghrelin – where and when are each secreted/released?