Overview 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 and algae Carnivores eat other animals Omnivores regularly consume animals as well as plants or algal matter Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Concept 41 1 An animal s diet must supply chemical energy organic molecules and essential nutrients An animal s diet provides chemical energy which is converted into ATP and powers processes in the body Animals need a source of organic carbon and organic nitrogen in order to construct organic molecules Essential nutrients are required by cells and must be obtained from dietary sources There are 4classes of essential nutrients 1 Essential amino acids 2 Essential fatty acids 3 Vitamins 4 Minerals Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Essential Amino Acids Animals require 20 amino acids and can synthesize about half from molecules in their diet The remaining amino acids the essential amino acids must be obtained from food in preassembled form A diet that provides insufficient essential amino acids causes malnutrition called protein deficiency Meat eggs and cheese provide all the essential amino acids and are thus complete proteins Individuals who eat only plant proteins need to eat specific plant combinations to get all essential amino acids Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 41 2 Essential amino acids for adults Methionine Valine Threonine Phenylalanine Leucine Corn maize and other grains Isoleucine Tryptophan Lysine Beans and other legumes Essential Fatty Acids Animals can synthesize most of the fatty acids they need The essential fatty acids are certain unsaturated fatty acids that must be obtained from the diet Deficiencies in fatty acids are rare Vitamins Vitamins are organic molecules required in the diet in small amounts 13 vitamins essential to humans have been identified Vitamins are grouped in 2 categories fat soluble water soluble Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Table 41 1 Minerals Minerals are simple inorganic nutrients usually required in small amounts Assessing Nutritional needs and Dietary Deficiencies Insights into human nutrition have come from epidemiology the study of human health and disease in populations Undernourishment is the result of a diet that consistently supplies less chemical energy than the body requires Malnourishment is the long term absence from the diet of one or more essential nutrients Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Undernourishment An undernourished individual will Use up stored fat and carbohydrates Break down its own proteins and lose muscle mass Suffer protein deficiency of the brain Die or suffer irreversible damage Malnourishment Malnourishment can cause deformities disease and death Malnourishment can be corrected by changes to a diet Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Concept 41 2 The main stages of food processing are ingestion digestion absorption and elimination 1 Ingestion is the act of eating 4 kinds a Suspension Feeders Many aquatic animals are suspension feeders which sift small food particles from the water E g Whale b Substrate Feeders These are animals that live in or on their food source E g Caterpillar c Fluid Feeders are those that suck nutrient rich fluid from a living host E g Mosquito d Bulk feeders eat relatively large pieces of food e g human Python Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings 2 Digestion is the process of breaking food down into molecules small enough to absorb In chemical digestion the process of enzymatic hydrolysis splits bonds in molecules with the addition of water 3 Absorption is uptake of nutrients by body cells 4 Elimination is the passage of undigested material out of the digestive compartment Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 41 7 Small molecules Pieces of food Mechanical digestion Chemical digestion Nutrient enzymatic hydrolysis molecules enter body cells Undigested material Food 1 Ingestion 2 Digestion 3 Absorption 4 Elimination Digestive Compartments Most animals process food in specialized compartments These compartments reduce the risk of an animal digesting its own cells and tissues a In Intracellular digestion food particles are engulfed by endocytosis and digested within food vacuoles b Extracellular digestion is the breakdown of food particles outside of cells It occurs in compartments that are continuous with the outside of the animal s body Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Two kinds of Extracellular digestion 1 Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients 2 More complex animals 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 It can have specialized regions that carry out digestion and absorption in a stepwise fashion Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 41 8 Tentacles Food Mouth Epidermis Gastrodermis Gastrovascular cavity Fig 41 9 Crop Esophagus Gizzard Intestine Pharynx Anus Mouth Typhlosole Lumen of intestine a Earthworm Foregut Midgut Esophagus Hindgut Rectum Anus Crop Mouth Gastric cecae b Grasshopper Stomach Gizzard Intestine Mouth Esophagus Crop Anus c Bird Concept 41 3 Organs specialized for sequential stages of food processing form the mammalian digestive system The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts Mammalian accessory glands are the salivary glands the pancreas the liver and the gallbladder Food is pushed along by peristalsis rhythmic contractions of muscles in the wall of the canal Valves called sphincters regulate the movement of material between compartments Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 41 10 Tongue Sphincter Salivary glands Oral cavity Salivary glands Mouth Pharynx Esophagus Esophagus Sphincter Liver Stomach Ascending portion of large intestine Gallbladder Duodenum of small intestine Pancreas Small intestine Small intestine Large