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Chapter 41

Chapter 41. Animal Nutrition. Dietary Categories of Animals. Herbivores eat mainly autotrophs (plants and algae) Carnivores eat other animals Omnivores regularly consume animals as well as plants or algal matter. Basic Nutritional Needs.

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Chapter 41

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  1. Chapter 41 Animal Nutrition

  2. Dietary Categories of Animals • Herbivores eat mainly autotrophs (plants and algae) • Carnivores eat other animals • Omnivores regularly consume animals as well as plants or algal matter

  3. Basic Nutritional Needs • Regardless of what an animal eats, an adequate diet must satisfy three nutritional needs • Fuel for all cellular work • The organic raw materials for biosynthesis • Essential nutrients, substances such as vitamins that the animal cannot make for itself

  4. Feces SUSPENSION FEEDERS SUBSTRATE FEEDERS Caterpillar Baleen FLUID FEEDERS BULK FEEDERS Feeding Mechanisms 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 …well that is pretty obvious

  5. Bioenergetics - basics • Energy Budget can be viewed as the flow of food energy into and out of the animal • ATP is the energy currency of life • Nearly all of an animal’s ATP generation • Is based on the oxidation of energy-rich molecules: carbohydrates, proteins, and fats

  6. Glucose Regulation as an Example of Homeostasis • Animals store excess calories as glycogen in the liver and muscles and as fat • When fewer calories are taken in than are expended … fuel is taken out of storage and oxidized • Glucose is a major fuel for cells • Its metabolism, regulated by hormone action, is an example of homeostasis

  7. When blood glucose level rises, a gland called the pancreas secretes insulin, a hormone, into the blood. 1 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. 2 Glucagon promotesthe breakdown ofglycogen in theliver and the release of glucose into the blood, increasing bloodglucose level. 4 When blood glucose level drops, the pancreas secretes the hormone glucagon, which opposes the effect of insulin. 3 Glucose Metabolism STIMULUS: Blood glucose level rises after eating. Homeostasis Glucose 90mg/dl STIMULUS: Blood glucose level drops below set point.

  8. Caloric Imbalance • Undernourishment • Occurs in animals when their diets are chronically deficient in calories • Overnourishment • 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 • 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

  9. Regulation of Body Weight

  10. 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 it’s so hard to stay on a diet. Produced by adipose (fat) tissue, leptinsuppressesappetite as its level increases. When body fat decreases, leptin levels fall, and appetite increases. Ghrelin Insulin Leptin The hormone PYY,secreted by the small intestine after meals, acts as an appetite suppressant that counters the appetite stimulant ghrelin. A rise in blood sugar level after a meal stimulates the pancreas to secrete insulinIn addition to its other functions, insulin suppressesappetite by acting on the brain. PYY Hormones and appetite • Several hormones regulate both long-term and short-term appetite by affecting a “satiety center” in the brain

  11. Role of Leptin • Mice that inherit a defect in the gene for leptin become very obese

  12. Obesity and Evolution • The problem of maintaining weight may partly stem from our evolutionary past when fat hoarding was a means of survival

  13. What’s in the Diet • An animal’s diet must supply • Fuel (energy) • Carbon skeletons • To build the complex molecules it needs to grow, maintain itself, and reproduce an animal must obtain organic precursors (carbon skeletons) from its food • Essential nutrients • Supplied in preassembled form • 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

  14. Mineral deficiencies • Herbivorous animals may suffer mineral deficiencies if they graze on plants in soil lacking key minerals

  15. Essential Amino Acids • Animals require 20 amino acids • 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

  16. Protein Deficiency • 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

  17. Essential amino acids for adults Beansand other legumes Methionine Valine Threonine Phenylalanine Leucine Corn (maize)and other grains Isoleucine Tryptophan Lysine Essential Amino Acids • Complete proteins provide all essential AAs in their proper proportions • Incomplete proteins do not • 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 Together corn and beans would provide all 8 of the essential amino acids for humans

  18. Some animals have adaptations that help them through periods when their bodies demand extraordinary amounts of protein • Penguins use their muscle protein as an AA source for building new proteins when their replace feathers after molting

  19. Essential Fatty Acids • Animals can synthesize most of the fatty acids they need • The essential fatty acids are certain unsaturated fatty acids (linoleic acid in humans) • Deficiencies in fatty acids are rare

  20. Vitamins • Vitamins are organic molecules required in the diet in small amounts • 13 vitamins essential to humans have been identified • Vitamins are grouped into two categories • Fat-soluble (A, D, E, and K) • Water-soluble

  21. Minerals • Minerals are simple inorganic nutrients usually required in small amounts

  22. Food Processing • The main stages of food processing • Ingestion: Intake of food • Digestion: Process of breaking food down into molecules small enough to absorb • 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

  23. ELIMINATION 4 ABSORPTION 2 DIGESTION 1 3 Food Processing • The four stages of food processing Smallmolecules Piecesof food Chemical digestion(enzymatic hydrolysis) Nutrient moleculesenter body cells Mechanicaldigestion Undigested material Food INGESTION

  24. Digestive Compartments • Most animals process food in specialized compartments • Intracellular digestion • Food particles are engulfed by endocytosis and digested within food vacuoles • Extracellular digestion • Is the breakdown of food particles outside cells

  25. Tentacles Mouth Food Gastrovascularcavity Epidermis Mesenchyme Gastrodermis Nutritivemuscularcells Flagella Gland cells Food vacuoles Mesenchyme Gastrovascular Cavity • Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients Hydra (a cnidarian)

  26. Digestive Tube • Animals with a more complex body plan • Have a digestive tube with two openings, a mouth and an anus • This digestive tube is called a complete digestive tract or an alimentary canal

  27. Anus Anus Gastric ceca Crop Organization of Digestive Tube • The digestive tube can be organized into specialized regions that carry out digestion and nutrient absorption in a stepwise fashion Pharynx Esophagus Crop Gizzard Intestine Earthworm. The digestive tract ofan earthworm includes a muscular pharynx that sucks food in through themouth. Food passes through the esophagus and is stored and moistened in the crop. The muscular gizzard, whichcontains 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 Gizzard Intestine Pharynx Mouth Typhlosole Lumen of intestine Esophagus Crop Midgut Hindgut 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. Midgut Hindgut Foregut Esophagus Rectum Mouth Crop Esophagus Bird. Many birds have three separate chambers—the crop, stomach, and gizzard—where food is pulverized and churned before passing into the intestine. A bird’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 Esophagus Crop Stomach Gizzard Intestine Stomach Anus

  28. Mammalian Digestive System A Tour of the Tube

  29. Salivaryglands Cardiacorifice Tongue Oral cavity Mouth Salivaryglands Pharynx Parotid gland Sublingual gland Esophagus Esophagus Submandibular gland Pyloricsphincter Liver Gall-bladder Stomach Stomach Gall-bladder Ascendingportion of large intestine Small intestines Liver Pancreas Pancreas IIeumof small intestine Large intestines Small intestine Duodenum of small intestine Rectum Anus Large intestine Rectum A schematic diagram of the human digestive system Appendix Anus Cecum Overview of the System Food is pushed along the digestive tract by peristalsis … Rhythmic waves of contraction of smooth muscles in the wall of the canal

  30. The Oral Cavity, Pharynx, and Esophagus • Oral cavity • Food is lubricated and digestion begins • Teeth chew food into smaller particles that are exposed to salivary amylase, initiating the breakdown of starch • Tongue forms the food bolus and pushes it to the pharynx • Pharynx (throat) • The common passage way for air and ingesta • Esophagus • Conducts food from the pharynx down to the stomach by peristalsis

  31. The esophageal sphincter relaxes, allowing the bolus to enter the esophagus. Epiglottisup Bolus of food Tongue Glottisdown and open Epiglottisup Esophageal sphincterrelaxed Pharynx Epiglottis down Esophageal sphinctercontracted Esophageal sphinctercontracted Glottis After the food has entered the esophagus, the larynx moves downward and opens the breathing passage. Larynx Esophagus Trachea To lungs To stomach Glottis upand closed Contractedmuscles Relaxedmuscles Relaxedmuscles The larynx, the upper part of the respiratory tract, moves upward and tips the epiglottis over the glottis, preventing food from entering the trachea. 2 1 6 4 5 3 Waves of muscular contraction (peristalsis) move the bolus down the esophagus to the stomach. 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. The swallowing reflex is triggered when a bolus of food reaches the pharynx. Stomach From Mouth to Stomach

  32. GERD • Gastroesophageal reflux disease (GERD) • Better known as heartburn

  33. The Stomach • Stomach • Stores food • Secretes gastric juice, which converts a meal to acid chyme • Gastric juice • Hydrochloric acid • Pepsin (enzyme) • Mucus (which coated the stomach lining and protects the cells from acidity

  34. Stomach Esophagus Cardiac orifice Folds of epithelial tissue Pyloric sphincter 5 µm Small intestine 2 3 1 1 3 2 Interior surface of stomach. The interior surface of the stomach wall is highly folded and dotted with pits leading into tubular gastric glands. Pepsinogen and HCI are secreted into the lumen of the stomach. Epithelium HCl converts pepsinogen to pepsin. Pepsinogen Pepsin (active enzyme) Gastric gland. The gastric glands have three types of cells that secrete different components of the gastric juice: mucus cells, chief cells, and parietal cells. HCl Pepsin then activates more pepsinogen, starting a chain reaction. Pepsin begins the chemical digestion of proteins. Mucus cells secrete mucus, which lubricates and protects the cells lining the stomach. Chief cells secrete pepsino- gen, an inactive form of the digestive enzyme pepsin. Parietal cell Chief cell Parietal cells secrete hydrochloric acid (HCl). Stomach structure Gastric gland • Goblet (mucus) cells • Chief cells • pepsinogen • Parietal cells • HCl

  35. Bacteria Mucuslayer of stomach 1 µm Gastric Ulcers • Caused mainly by the bacterium Helicobacter pylori

  36. The Small Intestine • Small intestine • Longest section of the alimentary canal (six meters in humans) • The major organ of digestion and absorption • Sections • Duodenum • Jejunum • Ileum

  37. Liver Stomach Bile Gall-bladder Acid chyme Intestinaljuice Pancreas Pancreatic juice Duodenum of small intestine Enzymatic Action in the Small Intestine • In the duodenum acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and intestine itself • Pancreatic enzymes • Trypsin and Chymotrypsisn • Lipases • Amylase • Nucleases Bile salts aid in the digestion and absorption of lipids via Emulsification The intestinal brush border produces a variety of enzymes that contribute to digestion

  38. Protein digestion Fat digestion Nucleic acid digestion Carbohydrate digestion Oral cavity, pharynx, esophagus Polysaccharides (starch, glycogen) Disaccharides (sucrose, lactose) Salivary amylase Smaller polysaccharides, maltose Stomach Proteins Pepsin Small polypeptides Polypeptides Lumen of small intes- tine Fat globules (Insoluble in water, fats aggregate as globules.) Polysaccharides DNA, RNA Pancreatic amylases Pancreatic nucleases Pancreatic trypsin and chymotrypsin (These proteases cleave bonds adjacent to certain amino acids.) Bile salts Maltose and other disaccharides Fat droplets (A coating of bile salts prevents small drop- lets from coalescing into larger globules, increasing exposure to lipase.) Nucleotides Smaller polypeptides Pancreatic carboxypeptidase Pancreatic lipase Amino acids Glycerol, fatty acids, glycerides Small peptides Nucleotidases Epithelium of small intestine (brush border) Nucleosides Disaccharidases Dipeptidases, carboxypeptidase, and aminopeptidase (These proteases split off one amino acid at a time, working from opposite ends of a polypeptide.) Nucleosidases and phosphatases Monosaccharides Nitrogenous bases, sugars, phosphates Amino acids Enzymatic digestion

  39. 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 Entero- gastrone Gall- bladder Gastrin from the stomach recirculates via the bloodstream back to the stomach, where it stimulates the production of gastric juices. Gastrin CCK Stomach Amino acids or fatty acids in the duodenum trigger the release of cholecystokinin (CCK), which stimulates the release of digestive enzymes from the pancreas and bile from the gallbladder. Pancreas Secretin Duodenum Secreted by the duodenum, secretin stimulates the pancreas to release sodium bicarbonate, which neutralizes acid chyme from the stomach. CCK Key Stimulation Inhibition Hormonal Regulation of Digestion • Hormones help coordinate the secretion of digestive juices into the alimentary canal

  40. Microvilli(brush border) Vein carrying blood to hepatic portal vessel Bloodcapillaries Muscle layers Epithelialcells Epithelial cells Largecircularfolds Lacteal Villi Key Lymph vessel Villi Nutrientabsorption Intestinal wall Small Intestine…Absorption of Nutrients • The small intestine has a huge surface area due to the presence of villi and microvilli The absorptive surface area of the small intestine is roughly 250 square meters - the size of a tennis court!

  41. Absorption of Nutrients • The core of each villus • Contains a network of blood vessels and a small vessel of the lymphatic system called a lacteal • Amino acids and sugars • Pass through the epithelium of the small intestine and enter the bloodstream • After glycerol and fatty acids are absorbed by epithelial cells • They are recombined into fats within these cells

  42. Fat globule Large fat globules are emulsified by bile salts in the duodenum. 1 Bile salts Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides, which then form micelles. 2 Fat droplets coated with bile salts Micelles made up of fatty acids, monoglycerides, and bile salts Fatty acids and mono-glycerides leave micelles and enter epithelial cells by diffusion. 3 Chylomicrons containing fattysubstances are transported out of the epithelial cells and into lacteals, where they are carried away from the intestine by lymph. 4 Epithelial cells of small intestine Lacteal Fat absorption • These fats are then mixed with cholesterol and coated with proteins forming small molecules called chylomicrons, which are transported into lacteals

  43. The Large Intestine • Functions • Recover water that has entered the alimentary canal • Form compact and propel the feces to the anus • The colon is home to a variety of bacteria including Escherichia coli

  44. Adaptations of the Mammalian Digestive System

  45. Incisors Canines Molars (a) Carnivore Premolars (b) Herbivore (c) Omnivore Variations in Dentition • Mammals have specialized dentition that best enables them to ingest their usual diet Pointed incisor and canines. Jagged premolars and molars Broad ridged surfaces for grinding Reduced/absent canines Chisel shaped incisors Generalized/unspecialized dentition

  46. Small intestine Stomach Small intestine Cecum Colon(large intestine) Stomach and Intestinal Adaptations • Herbivores generally have longer alimentary canals than carnivores reflecting the longer time needed to digest vegetation Snakes can “unhinge” their jaws Many large carnivores have large very expandable stomachs Carnivore Herbivore

  47. Symbiotic Adaptations • Many herbivorous animals have fermentation chambers where symbiotic microorganisms digest cellulose. • Horses, rabbits, and koalas have very large cecums housing symbionts • Ruminants have large populations of symbiotic prokaryotes and protozoa in their rumens and reticulums

  48. Rumen. When the cow first chews and swallows a mouthful of grass, boluses (green arrows) enter the rumen. Intestine 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. 4 2 1 3 Esophagus Abomasum. The cud, containing great numbers of microorganisms, finally passes to the abomasum for digestion by the cow‘s own enzymes (black arrows). Omasum. The cow then reswallows the cud (blue arrows), which moves to the omasum, where water is removed. Ruminant Digestion

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