Chapter 41: Animal Nutrition

1. Chapter 41: Animal Nutrition Sam Orkin & Jamie Dunleavy

2. Nutritional Requirements • Animals are heterotrophs that require food for fuel in order to produce ATP, carbon skeletons to make their own molecules, and essential nutrients • A nutritionally adequate diet is essential in order to maintain homeostasis.

3. Three Fundamental Nutritional Needs • The body must meet three nutritional requirements in order to be properly nourished: fuel for ATP production, carbon skeletons, and essential nutrients • Fuel for ATP production • ATP accounts for the largest fraction of an animal’s energy budget • ATP is derived from oxidation of organic fuel molecules in cellular respiration • Carbohydrates, proteins, fats • Carbon skeletons • The organic raw materials animals use in biosynthesis • In order to build the complex molecules it needs to grow, an animal must obtain organic precursors from food • Once an animal is provided with a source of organic carbon and organic nitrogen , it can construct a variety of molecules

4. Essential Nutrients • In addition to fuel and carbon skeletons, an animal’s diet must have a supply of essential nutrients • Some are essential to all animals, but others are needed only for a specific species • Four classes of essential nutrients • Essential amino acids • Essential fatty acids • Vitamins • Minerals

5. Essential Amino Acids • Animals require 20 amino acids to make proteins • Essential amino acids- remaining amino acids that animals cannot synthesize themselves • 8 amino acids are essential in adult humans and most animals • Most reliable source of essential amino acids- meat, eggs, cheeses and other animal products • Complete vs. Incomplete proteins • Complete: proteins from animal products • Incomplete: proteins from plant products • Some animals have special adaptations to get them through periods when their bodies demand extra amounts of protein

6. Essential Fatty Acids • Essential fatty acids- the fatty acids animals cannot synthesize on their own • Unsaturated fatty acids • Deficiencies are rare • Most diets furnish ample amounts of fatty acids

7. Vitamins and Minerals

8. Improper Nourishment • Overnourishment • The human body hoards fat; the body stores excess fat obtained from food instead of using it for fuel (opposed to carbohydrates) • Amount of fat directly affects weight gain • Historically- fat hoarding would have been an advantage to hunting/gathering ancestors • Genes promoting storage of high energy molecules like fats would have survived famine. • Undernourishment • Occurs when animal’s diet is deficient in calories • Stored glycogen and fat is used up and body begins breaking down protein and muscles for fuel energy • Historically- common during times of drought, war, and other serious crises.

9. Improper Nourishment • Malnourishment • When an animal’s diet is lacking one or more essential nutrients • Much more common than undernourishment in human populations • Protein deficiency • Most common form of malnutrition among humans • Results from a diet that provides insufficient amounts of one or more essential amino acids

10. Food Types and Feeding Mechanisms • Most animals are opportunistic feeders • Generally, animals fit into one of three dietary categories: • Herbivores- eat mainly autotrophs • Carnivores- eat other animals • Omnivores- regularly consume both animals and plants • All animals consume bacteria with other types of food

11. Diverse Feeding Adaptations • Mechanisms by which animals ingest food are highly varied into four main groups: • Suspension-feeders- sift small food particles from the water • Substrate-feeders- live in or on their food source, eating their way through their food • Deposit-feeders- eat their way through the dirt, salvaging partially decayed organic material consumed along with the soil • Fluid-feeders- suck nutrient-rich fluid from a living host • Bulk-feeders- eat relatively large pieces of food • Adaptations include utensils such as: tentacles, pincers, claws, fangs, jaws, and teeth

12. Food Processing • The four main stages of food processing are: • Ingestion • Digestion • Absorption • Elimination

13. Stage 1-Ingestion • Ingestion- the physical act of eating • All animals deal with food that is packaged in bulk form containing complex molecules • Large polymers, substances that are difficult to process, toxic • Organic material consists of proteins, fats, and carbohydrates in the forms of starch and other polysaccharides • Animals cannot use macromolecules directly* • All organisms use common monomers • Proteins are all assembled from the same 20 amino acids

14. Stage 2- Digestion • Digestion- the process of breaking down food into molecules small enough for the body to absorb • Cleaves macromolecules into monomers • Animals use these as fuel for ATP production • Carbohydrates, fats, proteins and nucleic acids are all broken down • Digestion breaks the bonds that link monomers together with the enzymatic addition of water known as enzymatic hydrolysis • Different hydrolytic enzymes catalyze the digestion of each class of macromolecule

15. Stages 3-4: Absorption & Elimination • Absorption- the uptake of small nutrient molecules by an organisms own body • The animals cells absorb small molecules like amino acids and simple sugars form the digestive compartment • Elimination- the passing of undigested material out of the digestive compartment • Last step in food processing

16. Intracellular Digestion • Food vacuoles are the simplest digestive compartments • Newly formed food vacuoles fuse with lysosomes • This fusion mixes the food with hydrolytic enzymes, therefore allowing digestion to occur safely within an enclosed membrane • This is called intracellular digestion

17. Extracellular Digestion • Extracellular digestion- the breakdown of food outside cells • Occurs within compartments that are continuous with the outside of the animal’s body • Extracellular cavity is advantageous • Some animals have digestive sacs called gastrovascular cavities • Most have complete digestive tracts or alimentary canals • Food moves in one direction • Crop, gizzard, or stomach • Intestines

19. Mammalian Digestive System • The mammalian digestive system consists of: • Alimentary canals and different accessory glands that secrete digestive juices into the canal through ducts • Peristalsis- pushes food along the tract • Sphincters- close off the tube, regulating passage of material between different canal chambers • Accessory glands • 3 pairs of salivary glands • Pancreas • Liver • Gallbladder

20. Human Digestive System

21. The Oral Cavity • Teeth- various shapes cut, smash and grind food • Presence of food in the oral cavity triggers a nervous reflex • Causes salivary gland to deliver saliva • Pharynx- junction that opens to both esophagus and trachea • Esophagus- conducts food from the pharynx down to the stomach by peristalsis • The muscles at the top are voluntary, but the involuntary muscles take over to provide waves of contraction

22. The Stomach • The stomach stores food and performs preliminary digestion • Can stretch to accommodate 2 liters of food and fluid • Secretes gastric juice and mixes it with the food by churning • pH about 2 • Multifunctional • Pepsin- hydrolysis of proteins • A coating of mucus helps protect stomach lining and prevents self-digestion • Pyloric sphincter- opening from the stomach into the large intestine • Helps regulate the passage chyme into the intestine

23. The Small Intestine • The small intestine is the major organ of digestion and absorption • Longest section of the alimentary canal • Most enzymatic hydrolysis of food macromolecules occurs here • Most absorption of nutrients into the blood occurs here • Duodenum • Chyme from stomach mixes with digestive juices from pancreas, liver, gallbladder, and gland cells of the intestinal wall • Liver • Production of bile • Bile salts aid in digestion and absorption of fats

24. Enzymatic Action in the Small Intestine • Carbohydrate Digestion • Pancreatic amylases hydrolyze starch, glycogen and other polysaccharides into disaccharides • Disaccharides are built into the membranes and ECM • Terminal steps in carbohydrate digestion occur where monomers are absorbed into blood • Protein Digestion • Completes process begun by pepsin in the stomach • Enzymes in the duodenum dismantle polypeptides into their amino acids • Trypsin and chymotrypsin break large polypeptides into shorter chains • Dipeptidases split small peptides • Carboxypeptidase splits off one amino acid at a time, beginning at end with a free carboxyl group • Aminopeptidase works in opposite direction

25. Enzymatic Action in the Small Intestine • Nucleic Acid Digestion • Nucleases hydrolyze DNA and RNA into their component nucleotides • Other hydrolytic enzymes further break them down into nitrogenous bases, sugars, and phosphates • Fat Digestion • Nearly all fat in a meal is completely undigested when it reaches the small intestine • Emulsification • Jejunum and ileum- function in absorption of nutrients and water

26. Enzymatic Digestion in Human Digestive System

27. Absorption of Nutrients • Most nutrient absorption occurs in the small intestine • Large surface area • Villi- finger-like projections on the large circular folds in the lining • Microvilli- microscopic appendages on each epithelial cell of a villus • Lacteal- small vessel of the lymphatic system • Hepatic portal vessel- leads directly to the liver

28. Hormones help regulate Digestion • Hormones released by the wall of the stomach and duodenum ensure that digestive secretions are present only when needed • Enterogastrones- hormones that are secreted by the wall of the duodenum • Cholecystokinin (CCK)- a hormone secreted in response to presence of amino or fatty acids • Triggers the release of pancreatic enzymes

29. The Large Intestine • Reclaiming water is a major function of the large intestine • Recovers water that has entered the alimentary canal as the solvent of various digestive juices • Wastes from the digestive tract are moved along the colon by peristalsis • Bacteria live in the large intestine • E. Coli • Intestinal bacteria feed off of unabsorbed organic material • Many colon bacteria generate gases • Feces • Contains masses of bacteria, cellulose, and other undigested materials • Stored in the rectum until it can be eliminated

30. Evolutionary Adaptations • Structural adaptations of digestive systems are often associated with diet • Dentition • Carnivores • Herbivores • Omnivores • (pg 867) • Length of digestive system • Herbivores and omnivores have longer alimentary canals relative to body size than carnivores

31. Digestive Tract of Carnivores vs. Herbivores

32. Symbiotic microorganisms help nourish many vertebrates • Animals do not produce enzymes that hydrolyze cellulose • Many vertebrates solve this issue by housing large populations of symbiotic bacteria • These microorganisms have the enzymes that can digest cellulose • Depending on the animal, the location of these symbiotic microbes varies