Chapter 41 Animal Nutrition Dietary Categories of Animals пЃ® Herbivores eat mainly autotrophs (plants and algae) пЃ® Carnivores eat other animals пЃ® Omnivores regularly consume animals as well as plants or algal matter Basic Nutritional Needs пЃ® Regardless of what an animal eats, an adequate diet must satisfy three nutritional needs пЃ® пЃ® пЃ® Fuel for all cellular work The organic raw materials for biosynthesis Essential nutrients, substances such as vitamins that the animal cannot make for itself Feeding Mechanisms SUSPENSION FEEDERS SUBSTRATE FEEDERS Feces Baleen Caterpillar FLUID FEEDERS BULK FEEDERS Suspension feeders shift small particles from water Substrate feeders live in or on their food source Bulk feeders eat largish pieces of food Fluid feeders вЂ¦well that is pretty obvious Bioenergetics - basics пЃ® Energy Budget can be viewed as the flow of food energy into and out of the animal пЃ® ATP is the energy currency of life пЃ® Nearly all of an animalвЂ™s ATP generation пЃ® Is based on the oxidation of energy-rich molecules: carbohydrates, proteins, and fats Glucose Regulation as an Example of Homeostasis пЃ® Animals store excess calories as glycogen in the liver and muscles and as fat пЃ® When fewer calories are taken in than are expended вЂ¦ fuel is taken out of storage and oxidized пЃ® Glucose is a major fuel for cells пЃ® Its metabolism, regulated by hormone action, is an example of homeostasis Glucose Metabolism 1 When blood glucose level rises, a gland called the pancreas secretes insulin, a hormone, into the blood. 2 Insulin enhances the transport of glucose into body cells and stimulates the liver and muscle cells to store glucose as glycogen. As a result, blood glucose level drops. STIMULUS: Blood glucose level rises after eating. Homeostasis Glucose 90mg/dl 4 Glucagon promotes the breakdown of glycogen in the liver and the release of glucose into the blood, increasing blood glucose level. STIMULUS: Blood glucose level drops below set point. 3 When blood glucose level drops, the pancreas secretes the hormone glucagon, which opposes the effect of insulin. Caloric Imbalance пЃ® Undernourishment пЃ® Occurs in animals when their diets are chronically deficient in calories пЃ® Overnourishment пЃ® пЃ® пЃ® пЃ® Results from excessive food intake Leads to the storage of excess calories as fat Obesity contributes to a number of health problems, including diabetes, cardiovascular disease, and colon and breast cancer Some Stats on US Obesity пЃ® пЃ® пЃ® пЃ® пЃ® 58 Million Overweight; 40 Million Obese; 3 Million morbidly Obese Eight out of 10 over 25's Overweight 78% of American's not meeting basic activity level recommendations 25% completely Sedentary 76% increase in Type II diabetes in adults 30-40 yrs old since 1990 Regulation of Body Weight Hormones and appetite пЃ® Several hormones regulate both long-term and short-term appetite by affecting a вЂњsatiety centerвЂќ in the brain Secreted by the stomach wall, ghrelin is one of the signals that triggers feelings of hunger as mealtimes approach. In dieters who lose weight, ghrelin levels increase, which may be one reason itвЂ™s so hard to stay on a diet. Produced by adipose (fat) tissue, leptin suppresses appetite as its level increases. When body fat decreases, leptin levels fall, and appetite increases. Ghrelin The hormone PYY, secreted by the small intestine after meals, acts as an appetite suppressant that counters the appetite stimulant ghrelin. Insulin Leptin PYY A rise in blood sugar level after a meal stimulates the pancreas to secrete insulin In addition to its other functions, insulin suppresses appetite by acting on the brain. Role of Leptin пЃ® Mice that inherit a defect in the gene for leptin become very obese Obesity and Evolution пЃ® The problem of maintaining weight may partly stem from our evolutionary past when fat hoarding was a means of survival WhatвЂ™s in the Diet пЃ® An animalвЂ™s diet must supply пЃ® Fuel (energy) пЃ® Carbon skeletons пЃ® пЃ® Essential nutrients Supplied in preassembled form пЃ® An animal that is malnourished is missing one or more essential nutrients in its diet Malnutrition is much more common than undernutrition in human populations пЃ® пЃ® To build the complex molecules it needs to grow, maintain itself, and reproduce an animal must obtain organic precursors (carbon skeletons) from its food Mineral deficiencies пЃ® Herbivorous animals may suffer mineral deficiencies if they graze on plants in soil lacking key minerals Essential Amino Acids пЃ® Animals require 20 amino acids пЃ® пЃ® They can synthesize about half of them from the other molecules they obtain from their diet The remaining amino acids, the essential amino acids, must be obtained from food in preassembled form Protein Deficiency пЃ® A diet that provides insufficient amounts of one or more essential amino acids causes a form of malnutrition called protein deficiency Kwashiorkor- enough calories but protein is very deficient Essential Amino Acids пЃ® Complete proteins provide all essential AAs in their proper proportions пЃ® Incomplete proteins do not пЃ® пЃ® Most plant proteins are incomplete in amino acid makeup So individuals who must eat only plant proteins need to eat a variety to ensure that they get all the essential amino acids Essential amino acids for adults Beans Methionine and other legumes Valine Together corn and beans would provide all 8 of the essential amino acids for humans Threonine Phenylalanine Corn (maize) and other grains Leucine Isoleucine Tryptophan Lysine пЃ® Some animals have adaptations that help them through periods when their bodies demand extraordinary amounts of protein пЃ® Penguins use their muscle protein as an AA source for building new proteins when their replace feathers after molting Essential Fatty Acids пЃ® Animals can synthesize most of the fatty acids they need пЃ® The essential fatty acids are certain unsaturated fatty acids (linoleic acid in humans) пЃ® Deficiencies in fatty acids are rare Vitamins пЃ® Vitamins are organic molecules required in the diet in small amounts пЃ® 13 vitamins essential to humans have been identified пЃ® Vitamins are grouped into two categories пЃ® пЃ® Fat-soluble (A, D, E, and K) Water-soluble Minerals пЃ® Minerals are simple inorganic nutrients usually required in small amounts Food Processing пЃ® The main stages of food processing пЃ® Ingestion: Intake of food пЃ® Digestion: Process of breaking food down into molecules small enough to absorb пЃ® пЃ® пЃ® Involves enzymatic hydrolysis of polymers into their monomers Absorption: The uptake of nutrients by body cells Elimination: occurs as undigested material passes out of the digestive compartment Food Processing пЃ® The four stages Small of food processing molecules Pieces of food Mechanical digestion Chemical digestion (enzymatic hydrolysis) Nutrient molecules enter body cells Undigested material Food 1 INGESTION 2 DIGESTION 3 ABSORPTION 4 ELIMINATION Digestive Compartments пЃ® Most animals process food in specialized compartments пЃ® Intracellular digestion пЃ® Food particles are engulfed by endocytosis and digested within food vacuoles пЃ® Extracellular digestion пЃ® Is the breakdown of food particles outside cells Gastrovascular Cavity пЃ® Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients Tentacles Mouth Food Gastrovascular cavity Epidermis Mesenchyme Gastrodermis Nutritive muscular cells Flagella Gland cells Food vacuoles Hydra (a cnidarian) Mesenchyme Digestive Tube пЃ® Animals with a more complex body plan пЃ® Have a digestive tube with two openings, a mouth and an anus пЃ® This digestive tube is called a complete digestive tract or an alimentary canal Organization of Digestive Tube пЃ® The digestive tube can be organized into specialized regions that carry out digestion and nutrient absorption in a stepwise fashion Pharynx Earthworm. The digestive tract of an earthworm includes a muscular pharynx that sucks food in through the mouth. Food passes through the esophagus and is stored and moistened in the crop. The muscular gizzard, which contains small bits of sand and gravel, pulverizes the food. Digestion and absorption occur in the intestine, which has a dorsal fold, the typhlosole, that increases the surface area for nutrient absorption. Esophagus Crop Esophagus Intestine Crop Pharynx Anus Mouth Gizzard Intestine Typhlosole Lumen of intestine Foregut Grasshopper. A grasshopper has several digestive chambers grouped into three main regions: a foregut, with an esophagus and crop; a midgut; and a hindgut. Food is moistened and stored in the crop, but most digestion occurs in the midgut. Gastric ceca, pouches extending from the midgut, absorb nutrients. Gizzard Midgut Esophagus Hindgut Crop Esophagus Rectum Midgut Anus Hindgut Mouth Crop Gastric ceca Esophagus Bird. Many birds have three separate chambersвЂ” the crop, stomach, and gizzardвЂ”where food is pulverized and churned before passing into the intestine. A birdвЂ™s crop and gizzard function very much like those of an earthworm. In most birds, chemical digestion and absorption of nutrients occur in the intestine. Gizzard Mouth Intestine Crop Stomach Esophagus Crop Anus Stomach Gizzard Intestine Mammalian Digestive System A Tour of the Tube Overview of the System Tongue Salivary glands Salivary glands Cardiac orifice Oral cavity Parotid gland Sublingual gland Mouth Pharynx Submandibular gland Esophagus Esophagus Pyloric sphincter Liver Ascending portion of large intestine Stomach Gallbladder Gallbladder Liver Pancreas Stomach Small intestines Pancreas IIeum of small intestine Small intestine Duodenum of small intestine Large intestine Rectum Large intestines Rectum Anus A schematic diagram of the human digestive system Appendix Anus Cecum Food is pushed along the digestive tract by peristalsis вЂ¦ Rhythmic waves of contraction of smooth muscles in the wall of the canal The Oral Cavity, Pharynx, and Esophagus пЃ® Oral cavity пЃ® Food is lubricated and digestion begins пЃ® Teeth chew food into smaller particles that are exposed to salivary amylase, initiating the breakdown of starch пЃ® Tongue forms the food bolus and pushes it to the pharynx пЃ® Pharynx (throat) пЃ® The common passage way for air and ingesta пЃ® Esophagus пЃ® Conducts food from the pharynx down to the stomach by peristalsis From Mouth to Stomach 4 The esophageal sphincter relaxes, allowing the bolus to enter the esophagus. Epiglottis up Bolus of food Tongue Glottis down and open Epiglottis up Pharynx Esophageal Epiglottis sphincter down contracted Glottis Larynx Trachea Esophagus To lungs To stomach 1 When a person is not swallowing, the esophageal sphincter muscle is contracted, the epiglottis is up, and the glottis is open, allowing air to flow through the trachea to the lungs. Glottis up and closed 2 The swallowing reflex is triggered when a bolus of food reaches the pharynx. Esophageal sphincter relaxed 5 After the food Esophageal sphincter contracted has entered the esophagus, the larynx moves downward and opens the breathing passage. Relaxed muscles Contracted muscles 3 The larynx, the upper part of the 6 Waves of muscular respiratory tract, contraction moves upward and (peristalsis) tips the epiglottis move the bolus over the glottis, down the esophagus preventing food to the stomach. from entering the trachea. Relaxed muscles Stomach GERD пЃ® Gastroesophageal reflux disease (GERD) пЃ® Better known as heartburn The Stomach пЃ® Stomach пЃ® Stores food пЃ® Secretes gastric juice, which converts a meal to acid chyme пЃ® Gastric juice пЃ® Hydrochloric acid пЃ® Pepsin (enzyme) пЃ® Mucus (which coated the stomach lining and protects the cells from acidity Stomach structure Gastric gland пЃ® Goblet (mucus) cells Esophagus Cardiac orifice пЃ® Chief cells pepsinogen пЃ® Parietal cells пЃ® HCl Interior surface of stomach. The interior surface of the stomach wall is highly folded and dotted with pits leading into tubular gastric glands. Gastric gland. The gastric Stomach Pyloric sphincter 5 Вµm пЃ® Small intestine Folds of epithelial tissue Epithelium 3 Pepsinogen 2 HCl glands have three types of cells that secrete different components of the gastric juice: mucus cells, chief cells, and parietal cells. Pepsin (active enzyme) 1 Pepsinogen and HCI are secreted into the lumen of the stomach. 1 2 HCl converts pepsinogen to pepsin. Mucus cells secrete mucus, which lubricates and protects the cells lining the stomach. Chief cells secrete pepsinogen, an inactive form of the digestive enzyme pepsin. Parietal cell Parietal cells secrete hydrochloric acid (HCl). Chief cell 3 Pepsin then activates more pepsinogen, starting a chain reaction. Pepsin begins the chemical digestion of proteins. Gastric Ulcers пЃ® Caused mainly by the bacterium Helicobacter pylori Bacteria 1 Вµm Mucus layer of stomach The Small Intestine пЃ® Small intestine пЃ® пЃ® пЃ® Longest section of the alimentary canal (six meters in humans) The major organ of digestion and absorption Sections пЃ® пЃ® пЃ® Duodenum Jejunum Ileum Enzymatic Action in the Small Intestine пЃ® In the duodenum acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and intestine itself Pancreatic enzymes Liver Trypsin and Chymotrypsisn Bile Lipases Gallbladder Amylase Stomach Bile salts aid in the digestion and absorption of lipids via Emulsification Nucleases Acid chyme Intestinal juice Pancreatic juice Pancreas Duodenum of small intestine The intestinal brush border produces a variety of enzymes that contribute to digestion Enzymatic digestion Protein digestion Carbohydrate digestion Oral cavity, pharynx, esophagus Polysaccharides (starch, glycogen) Nucleic acid digestion Fat digestion Disaccharides (sucrose, lactose) Salivary amylase Smaller polysaccharides, maltose Stomach Proteins Pepsin Small polypeptides Lumen of small intestine Polysaccharides Pancreatic amylases Maltose and other disaccharides Polypeptides Pancreatic trypsin and chymotrypsin (These proteases cleave bonds adjacent to certain amino acids.) Smaller polypeptides DNA, RNA Pancreatic nucleases Nucleotides Pancreatic carboxypeptidase Small peptides Disaccharidases Monosaccharides Amino acids Fat droplets (A coating of bile salts prevents small droplets from coalescing into larger globules, increasing exposure to lipase.) Glycerol, fatty acids, glycerides Nucleotidases Nucleosides Dipeptidases, carboxypeptidase, and aminopeptidase (These proteases split off one amino acid at a time, working from opposite ends of a polypeptide.) Bile salts Pancreatic lipase Amino acids Epithelium of small intestine (brush border) Fat globules (Insoluble in water, fats aggregate as globules.) Nucleosidases and phosphatases Nitrogenous bases, sugars, phosphates Hormonal Regulation of Digestion пЃ® Hormones help coordinate the secretion of digestive juices into the alimentary canal Enterogastrone secreted by the duodenum inhibits peristalsis and acid secretion by the stomach, thereby slowing digestion when acid chyme rich in fats enters the duodenum. Liver Enterogastrone Gallbladder CCK Gastrin recirculates via the bloodstream back to the stomach, where it stimulates the production of gastric juices. Stomach Amino acids or fatty acids in the duodenum trigger the release of Gastrin from the stomach Pancreas cholecystokinin (CCK), which stimulates the release of digestive enzymes from the pancreas and bile from the gallbladder. Secretin Duodenum CCK Key Stimulation Inhibition Secreted by the duodenum, secretin stimulates the pancreas to release sodium bicarbonate, which neutralizes acid chyme from the stomach. Small IntestineвЂ¦Absorption of Nutrients пЃ® The small intestine has a huge surface area due to the presence of villi and microvilli Microvilli (brush border) Vein carrying blood to hepatic portal vessel Blood capillaries Epithelial cells Muscle layers Epithelial cells Large circular folds Villi Lacteal Key Nutrient absorption Intestinal wall Villi Lymph vessel The absorptive surface area of the small intestine is roughly 250 square meters - the size of a tennis court! Absorption of Nutrients пЃ® The core of each villus пЃ® Contains a network of blood vessels and a small vessel of the lymphatic system called a lacteal пЃ® Amino acids and sugars пЃ® Pass through the epithelium of the small intestine and enter the bloodstream пЃ® After glycerol and fatty acids are absorbed by epithelial cells пЃ® They are recombined into fats within these cells Fat absorption пЃ® These fats are then mixed with cholesterol and coated with proteins forming small molecules called chylomicrons, which are transported into lacteals Fat globule 1 Large fat globules are emulsified by bile salts in the duodenum. Bile salts Fat droplets coated with bile salts Micelles made up of fatty acids, monoglycerides, and bile salts Epithelial cells of small intestine Lacteal 2 Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides, which then form micelles. 3 Fatty acids and monoglycerides leave micelles and enter epithelial cells by diffusion. 4 Chylomicrons containing fatty substances are transported out of the epithelial cells and into lacteals, where they are carried away from the intestine by lymph. The Large Intestine пЃ® Functions пЃ® Recover water that has entered the alimentary canal пЃ® Form compact and propel the feces to the anus пЃ® The colon is home to a variety of bacteria including Escherichia coli Adaptations of the Mammalian Digestive System Variations in Dentition пЃ® Mammals have specialized dentition that best enables them to ingest their usual diet Pointed incisor and canines. Jagged premolars and molars Incisors Canines (a) Carnivore Molars Premolars Broad ridged surfaces for grinding Reduced/absent canines (b) Herbivore Chisel shaped incisors Generalized/unspecialized dentition (c) Omnivore Stomach and Intestinal Adaptations пЃ® Herbivores generally have longer alimentary canals than carnivores reflecting the longer time needed to digest vegetation Small intestine Small intestine Stomach Many large carnivores have large very expandable stomachs Cecum Colon (large intestine) Carnivore Snakes can вЂњunhingeвЂќ their jaws Herbivore Symbiotic Adaptations пЃ® Many herbivorous animals have fermentation chambers where symbiotic microorganisms digest cellulose. пЃ® пЃ® Horses, rabbits, and koalas have very large cecums housing symbionts Ruminants have large populations of symbiotic prokaryotes and protozoa in their rumens and reticulums Ruminant Digestion 1 Rumen . When the cow first chews and swallows a mouthful of grass, boluses (green arrows) enter the rumen. 2 Reticulum . Some boluses also enter the reticulum. In both the rumen and the reticulum, symbiotic prokaryotes and protists (mainly ciliates) go to work on the cellulose-rich meal. As by-products of their metabolism, the microorganisms secrete fatty acids. The cow periodically regurgitates and rechews the cud (red arrows), which further breaks down the fibers, making them more accessible to further microbial action. Intestine Esophagus 4 Abomasum . The cud, containing great numbers of microorganisms, finally passes to the abomasum for digestion by the cowвЂ�s own enzymes (black arrows). 3 Omasum . The cow then reswallows the cud (blue arrows), which moves to the omasum, where water is removed.