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Chapter 41 Animal Nutrition
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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 and algae) Carnivores eat other animals Omnivores regularly consume animals as well as plants or algal matter
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Fig. 41-1 Figure 41.1 How does a lean fish help a bear make fat? For the Discovery Video Nutrition, go to Animation and Video Files.
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Video: Lobster Mouth Parts Video: Shark Eating a Seal
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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
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Essential Nutrients There are four classes of essential nutrients:
Essential amino acids Essential fatty acids Vitamins Minerals
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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
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Meat, eggs, and cheese provide all the essential amino acids and are thus “complete” proteins
Most plant proteins are incomplete in amino acid makeup Individuals who eat only plant proteins need to eat specific plant combinations to get all essential amino acids
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Essential amino acids for adults
Fig. 41-2 Essential amino acids for adults Methionine Beans and other legumes Valine Threonine Phenylalanine Leucine Corn (maize) and other grains Figure 41.2 Essential amino acids from a vegetarian diet Isoleucine Tryptophan Lysine
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Some animals have adaptations that help them through periods when their bodies demand extraordinary amounts of protein
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Fig. 41-3 Figure 41.3 Storing protein for growth
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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
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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 and water-soluble
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Table 41-1
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Table 41-1a
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Table 41-1b
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Minerals Minerals are simple inorganic nutrients, usually required in small amounts
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Table 41-2
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Table 41-2a
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Table 41-2b
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Dietary Deficiencies 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
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Undernourishment An undernourished individual will
Use up stored fat and carbohydrates Break down its own proteins Lose muscle mass Suffer protein deficiency of the brain Die or suffer irreversible damage
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Malnourishment Malnourishment can cause deformities, disease, and death Malnourishment can be corrected by changes to a diet
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Fig. 41-4 Figure 41.4 Obtaining essential nutrients by eating antlers
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Assessing Nutritional Needs
Insights into human nutrition have come from epidemiology, the study of human health and disease in populations Neural tube defects were found to be the result of a deficiency in folic acid in pregnant mothers
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Fig. 41-5 Figure 41.5 Can diet influence the frequency of birth defects?
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Concept 41.2: The main stages of food processing are ingestion, digestion, absorption, and elimination Ingestion is the act of eating
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Suspension Feeders Many aquatic animals are suspension feeders, which sift small food particles from the water
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Humpback whale, a suspension feeder
Fig. 41-6a Baleen Figure 41.6 Four main feeding mechanisms of animals Humpback whale, a suspension feeder
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Substrate Feeders Substrate feeders are animals that live in or on their food source
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Caterpillar Feces Leaf miner caterpillar, a substrate feeder
Fig. 41-6b Leaf miner caterpillar, a substrate feeder Figure 41.6 Four main feeding mechanisms of animals Caterpillar Feces
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Fluid Feeders Fluid feeders suck nutrient-rich fluid from a living host
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Mosquito, a fluid feeder
Fig. 41-6c Figure 41.6 Four main feeding mechanisms of animals Mosquito, a fluid feeder
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Bulk Feeders Bulk feeders eat relatively large pieces of food
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Rock python, a bulk feeder
Fig. 41-6d Figure 41.6 Four main feeding mechanisms of animals Rock python, a bulk feeder
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Absorption is uptake of nutrients by body cells
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 Absorption is uptake of nutrients by body cells Elimination is the passage of undigested material out of the digestive compartment
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Nutrient molecules enter body cells Mechanical digestion
Fig. 41-7 Small molecules Pieces of food Chemical digestion (enzymatic hydrolysis) Nutrient molecules enter body cells Mechanical digestion Food Undigested material Figure 41.7 The four stages of food processing 1 Ingestion 2 Digestion 3 Absorption 4 Elimination
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Digestive Compartments
Most animals process food in specialized compartments These compartments reduce the risk of an animal digesting its own cells and tissues
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Intracellular Digestion
In intracellular digestion, food particles are engulfed by endocytosis and digested within food vacuoles
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Extracellular Digestion
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
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Gastrovascular cavity
Fig. 41-8 Tentacles Food Gastrovascular cavity Mouth Figure 41.8 Digestion in a hydra Epidermis Gastrodermis
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Video: Hydra Eating Daphnia
Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients Video: Hydra Eating Daphnia
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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
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Figure 41.9 Variation in alimentary canals
Crop Gizzard Esophagus Intestine Pharynx Anus Mouth Typhlosole Lumen of intestine (a) Earthworm Foregut Midgut Hindgut Esophagus Rectum Anus Crop Mouth Gastric cecae Figure 41.9 Variation in alimentary canals (b) Grasshopper Stomach Gizzard Intestine Mouth Esophagus Crop Anus (c) Bird
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Crop Gizzard Esophagus Intestine Pharynx Anus Mouth Typhlosole
Fig. 41-9a Crop Gizzard Esophagus Intestine Pharynx Anus Mouth Figure 41.9a Variation in alimentary canals Typhlosole Lumen of intestine (a) Earthworm
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Foregut Midgut Hindgut Esophagus Rectum Anus Crop Mouth Gastric cecae
Fig. 41-9b Foregut Midgut Hindgut Esophagus Rectum Anus Figure 41.9b Variation in alimentary canals Crop Mouth Gastric cecae (b) Grasshopper
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Stomach Gizzard Intestine Mouth Esophagus Crop Anus (c) Bird
Fig. 41-9c Stomach Gizzard Intestine Mouth Esophagus Crop Anus Figure 41.9c Variation in alimentary canals (c) Bird
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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
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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
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Fig Tongue Sphincter Salivary glands Oral cavity Salivary glands Pharynx Mouth Esophagus Esophagus Liver Sphincter Stomach Gall- bladder Ascending portion of large intestine Stomach Gall- bladder Duodenum of small intestine Pancreas Small intestine Liver Small intestine Small intestine Figure The human digestive system Pancreas Large intestine Large intestine Rectum Rectum Anus Anus Appendix A schematic diagram of the human digestive system Cecum
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Duodenum of small intestine
Fig a Tongue Sphincter Oral cavity Salivary glands Pharynx Esophagus Sphincter Liver Stomach Ascending portion of large intestine Gall- bladder Duodenum of small intestine Pancreas Figure The human digestive system Small intestine Small intestine Large intestine Rectum Anus Appendix Cecum
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A schematic diagram of the human digestive system
Fig b Salivary glands Mouth Esophagus Gall- bladder Stomach Small intestine Liver Figure The human digestive system Pancreas Large intestine Rectum Anus A schematic diagram of the human digestive system
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The Oral Cavity, Pharynx, and Esophagus
The first stage of digestion is mechanical and takes place in the oral cavity Salivary glands deliver saliva to lubricate food Teeth chew food into smaller particles that are exposed to salivary amylase, initiating breakdown of glucose polymers
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The tongue shapes food into a bolus and provides help with swallowing
The region we call our throat is the pharynx, a junction that opens to both the esophagus and the trachea (windpipe) The trachea leads to the lungs
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The esophagus conducts food from the pharynx down to the stomach by peristalsis
Swallowing causes the epiglottis to block entry to the trachea, and the bolus is guided by the larynx, the upper part of the respiratory tract Coughing occurs when the swallowing reflex fails and food or liquids reach the windpipe
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Esophageal sphincter contracted Glottis Larynx Trachea Esophagus
Fig Food Epiglottis up Tongue Pharynx Esophageal sphincter contracted Glottis Larynx Trachea Esophagus To lungs To stomach Figure From mouth to stomach: the swallowing reflex and esophageal peristalsis
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Esophageal sphincter contracted Epiglottis down Glottis Larynx Trachea
Fig Food Epiglottis up Tongue Pharynx Esophageal sphincter contracted Epiglottis down Glottis Larynx Trachea Esophagus Esophageal sphincter relaxed Glottis up and closed To lungs To stomach Figure From mouth to stomach: the swallowing reflex and esophageal peristalsis
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Esophageal sphincter contracted Epiglottis down Glottis
Fig Food Epiglottis up Tongue Epiglottis up Pharynx Esophageal sphincter contracted Epiglottis down Glottis Glottis down and open Esophageal sphincter contracted Larynx Trachea Esophagus Esophageal sphincter relaxed Glottis up and closed Relaxed muscles To lungs To stomach Contracted muscles Relaxed muscles Sphincter relaxed Figure From mouth to stomach: the swallowing reflex and esophageal peristalsis Stomach
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