Chapter 50 Animal Nutrition Chapter 50 Animal Nutrition

Chapter 50: Animal Nutrition Chapter 50 Animal Nutrition

Chapter 50: Animal Nutrition Nutrient Requirements Adaptations for Feeding Digestion Structure and Function of the Vertebrate Gut

Chapter 50: Animal Nutrition Control and Regulation of Digestion Control and Regulation of Fuel Metabolism The Regulation of Food Intake Toxic Compounds in Food

Chapter 50: Animal Nutrition Nutrient Requirements • Animals are heterotrophs that derive their energy and structural building blocks from food, therefore ultimately from autotrophs. 4

Chapter 50: Animal Nutrition Nutrient Requirements • Carbohydrates, fats, and proteins supply animals with metabolic energy. • A measure of the energy content of food is the calorie. • Excess caloric intake is stored as glycogen and fat. Review Figure 50. 2 5

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Chapter 50: Animal Nutrition Nutrient Requirements • An animal with insufficient caloric intake is undernourished and must metabolize its stored glycogen, fat, and finally its own protein. • Overnutrition in humans can be a serious health hazard. Review Figure 50. 3 7

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Chapter 50: Animal Nutrition Nutrient Requirements • For many animals, food provides essential carbon skeletons they cannot synthesize themselves. Review Figure 50. 4 9

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Chapter 50: Animal Nutrition Nutrient Requirements • Humans require eight essential amino acids. • All are available in milk, eggs, or meat, but not in all vegetables. • Thus, vegetarians must eat a mix of foods. Review Figure 50. 5 11

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Chapter 50: Animal Nutrition Nutrient Requirements • Different animals need mineral elements in different amounts. • Macronutrients are needed in large amounts. • Micronutrients are needed in small amounts. Review Table 50. 1 13

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Chapter 50: Animal Nutrition Nutrient Requirements • Vitamins are organic molecules that must be obtained in food. Review Table 50. 2 16

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Chapter 50: Animal Nutrition Nutrient Requirements • Malnutrition results when any essential nutrient is lacking from the diet. • Lack of any essential nutrient causes a deficiency disease. Review Table 50. 2 19

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Chapter 50: Animal Nutrition Adaptations for Feeding • Animals can be characterized by how they acquire nutrition • Saprotrophs and detritivores depend on dead organic matter • Filter feeders strain the environment for food • Herbivores eat plants • Carnivores eat animals. 22

Chapter 50: Animal Nutrition Adaptations for Feeding • Behavioral and anatomical adaptations reflect feeding types. • In vertebrates, teeth have evolved to match diet. Review Figure 50. 9 23

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Chapter 50: Animal Nutrition Digestion • Digestion involves the breakdown of complex food molecules into monomers that can be absorbed and utilized by cells. • In most animals, digestion is extracellular, external to the body, occurring in a tubular gut with regions specialized for different digestive functions. Review Figure 50. 10

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Chapter 50: Animal Nutrition Digestion • Absorptive areas of the gut are characterized by a large surface area. Review Figure 50. 11 28

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Chapter 50: Animal Nutrition Digestion • Hydrolytic enzymes break down proteins, carbohydrates, and fats into their monomeric units. • To prevent the organism itself from being digested, these are released as inactive zymogens, only activated when secreted into the gut. 31

Chapter 50: Animal Nutrition Structure and Function of the Vertebrate Gut • Cells and tissues of the vertebrate gut are organized in the same way throughout its length. • The innermost tissue layer, the mucosa, is the secretory and digestive surface. • The submucosa contains secretory cells and glands, blood and lymph vessels, and nerves. • External to the submucosa are two smooth muscle layers that move food through the gut. • Between these is a nerve network that controls gut movements. Review Figure 50. 13 32

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Chapter 50: Animal Nutrition Structure and Function of the Vertebrate Gut • The swallowing reflex pushes food into the esophagus. • Waves of smooth muscle contraction and relaxation (peristalsis) move food from the beginning of the esophagus through the length of the gut. • Sphincters block the gut at certain locations, but relax as a wave of peristalsis approaches. Review Figure 50. 14 34

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Chapter 50: Animal Nutrition Structure and Function of the Vertebrate Gut • Enzymatic digestion begins in the mouth, where amylase is secreted with saliva. • Protein digestion begins in the stomach with pepsin and HCl secreted by the stomach mucosa. • The mucosa also secretes mucus, to protect gut tissues. Review Figure 50. 15 37

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Chapter 50: Animal Nutrition Structure and Function of the Vertebrate Gut • In the duodenum, pancreatic enzymes carry out most of digestion. • Bile from liver and gallbladder assists in digestion of fats, breaking them into micelles. • Bicarbonate ions from the pancreas neutralize the p. H of the chyme entering from the stomach to produce an environment conducive to pancreatic enzyme action. Review Figure 50. 16, Table 50. 3 40

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Chapter 50: Animal Nutrition Structure and Function of the Vertebrate Gut • Final enzymatic cleavage of peptides and disaccharides occurs on the cell surfaces of the intestinal mucosa. • Amino acids, monosaccharides, and many inorganic ions are absorbed by the microvilli of the mucosal cells. • Often specific carrier proteins in the membranes of these cells transport nutrients into the cells. • Sodium cotransport is a common mechanism for actively absorbing nutrient molecules and ions. 43

Chapter 50: Animal Nutrition Structure and Function of the Vertebrate Gut • Fats are absorbed mostly as monoglycerides and fatty acids, the product of lipase action on triglycerides in food. • These products pass through mucosal cell membranes and are resynthesized into triglycerides within the cells. • The triglycerides are combined with cholesterol and coated with protein to form chylomicrons, which pass out of mucosal cells into lymphatic vessels in the submucosa. Review Figure 50. 17 44

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Chapter 50: Animal Nutrition Structure and Function of the Vertebrate Gut • Water and ions are absorbed in the large intestine so that waste matter is consolidated into feces. 46

Chapter 50: Animal Nutrition Structure and Function of the Vertebrate Gut • In herbivores such as rabbits and ruminants, some compartments of the gut have populations of microorganisms that aid in digesting molecules otherwise indigestible. Review Figure 50. 18 47

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Chapter 50: Animal Nutrition Control and Regulation of Digestion • Digestion processes are coordinated and controlled by neural and hormonal mechanisms. • Salivation and swallowing are autonomic reflexes. • Stomach and small intestine actions are largely controlled by the hormones gastrin, secretin, and cholecystokinin. Review Figure 50. 19

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Chapter 50: Animal Nutrition Control and Regulation of Fuel Metabolism • The liver interconverts fuel molecules and plays a central role in directing their traffic. • When food is being absorbed from the gut, the liver takes up and stores fats and carbohydrates, converting monosaccharides to glycogen or fat. • The liver also takes up amino acids and uses them to produce blood plasma proteins. 51

Chapter 50: Animal Nutrition Control and Regulation of Fuel Metabolism • Fat and cholesterol are shipped out of the liver as low-density lipoproteins. • High-density lipoproteins act as acceptors of cholesterol and are believed to bring fat and cholesterol back to the liver. 52

Chapter 50: Animal Nutrition Control and Regulation of Fuel Metabolism • Fuel metabolism during the absorptive period is controlled largely by insulin, which promotes glucose uptake and utilization by most cells of the body, as well as fat synthesis in adipose tissue. • During the postabsorptive period, lack of insulin blocks the uptake and utilization of glucose by most body cells except neurons. • If blood glucose levels fall, glucagon is secreted, stimulating the liver to break down glycogen to release glucose. • Review Figures 50. 20, 50. 21 53

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Chapter 50: Animal Nutrition The Regulation of Food Intake • Food intake is governed by sensations of hunger and satiety determined by brain mechanisms. • When one hypothalamic region is damaged, rats eat more; when another region is damaged, they eat less. • A number of molecules provide feedback information to these brain areas. 57

Chapter 50: Animal Nutrition The Regulation of Food Intake • Leptin is a hormone produced by fat cells that inhibits food intake. 58

Chapter 50: Animal Nutrition Toxic Compounds in Food • Even natural plant and animal foods can contain toxic compounds. • Human activities such as pesticide use and pollution of environment have made the problem of toxins in food worse. 59

Chapter 50: Animal Nutrition Toxic Compounds in Food • An organism can accumulate toxic compounds in its body, especially if those compounds are lipid-soluble or take the structural place of a natural molecule. 60

Chapter 50: Animal Nutrition Toxic Compounds in Food • Toxins such as PCBs and DDT that accumulate in the bodies of prey are transferred to and further concentrated in the bodies of their predators. • This bioaccumulation produces high concentrations of toxins in animals high up the food chain. 61