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CHAPTER 41ANIMAL NUTRITION

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You Must Know:The major compartments of the alimentary canal—oral cavity, pharynx, esophagus, stomach, small intestine, large intestine—and their contributions to animal nutritionThe major digestive glands—salivary glands, pancreas, liver, and gallbladder—and their contributions to animal nutritionThe general scheme of chemical digestion of carbohydrates, fats, proteins, and nucleic acids

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I. Concept 41.1A. Essential Nutrients

1. Are nutrients required by an animal 2. Include minerals and organic molecules that the animal

cannot produce themselves3. Four classes of essential nutrients:•Amino acids•Fatty acids (linoleic acid)•Vitamins•Minerals (Ex: Calcium and phosphorus)

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II. Concept 41.2A. Four main stages of food processing:

1. Ingesting—the act of taking in food2. Digestion—the breakdown of food into small molecules

capable of being absorbed by the cells of the body•Macromolecules are digested by enzymatic hydrolysis—the breaking of bonds with the addition of a water molecule

3. Absorption—the stage when the body’s cells take up small molecules such as amino acids and simple sugars from the digestive tract

4. Elimination—passing of undigested material from the digestive tract

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B. Intracellular Digestion•Occurs within a cell enclosed by a protective membrane•Ex: sponges

C. Extracellular Digestion•Carried out by most animals•Food is broken down outside cells•Allows animals to devour much larger sources of food than can be handled using only intracellular digestion

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D. Gastrovascular Cavity•Where digestion occurs in many simple animals•Animals have a single opening through which food enters and waste are released•Ex: cnidarians, flatworms

E. Complete Digestive Tract (Alimentary Canal)•Found in more complex animals•Are one-way digestive tubes with a mouth and an anus

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III. Concept 41.3A. Movement of food through digestive system is controlled by :

•peristalsis—the rhythmic waves of contraction by smooth muscles in the walls of the alimentary canal•sphincters—muscular, ringlike valves that regulate the passage of material between digestive compartments

B. When food is in the mouth (oral cavity), saliva is secreted into the mouth•Functions of saliva:

-lubricate the food to aid in swallowing-start digestion of starch and glycogen by saliva amylase

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C. The ball of chewed food is referred to as a bolus and enters the pharynx upon swallowing•The pharynx is common to the digestive and respiratory systems and leads to the esophagus and the trachea•The epiglottis is a cartilaginous flap that prevents food and liquid from entering the trachea when swallowing•The esophagus joins the pharynx to the stomach

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D. F(x) of stomach:•To store food•To secrete gastric juice

E. Two components of gastric juice that carry out digestion:•Hydrochloric acid (ph 2)which breaks down the extracellular matrix of meat and plant materials, kills most of the bacteria ingested with food, and activates pepsinogen•Pepsin—an enzyme which begins the digestion of proteins

-released in the inactive “pepsinogen” to protect the stomach from self-digestion-mucus produced by the stomach lining also

provides protection from digestion

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F. Acid chyme is the result of digestion in the stomach and enters the duodenum of the small intestine via the pyloric sphincter

G. Duodenum•First section of the small intestine•Major site of chemical digestion•Acid chyme mixes with secretions from the pancreas (bicarbonate fluid and pancreatic juices) and liver (bile) via the gallbladder •Bicarbonate fluid—neutralizes acidic contents of chyme•Pancreatic juices—contain enzymes to digest everything•Bile—stored in the gallbladder and functions to emulsify fats by breaking large fat droplets into smaller ones which are easier to digest

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H. Chemical Digestion in the Duodenum Summarized1. Carbohydrates•Breakdown of starch and glycogen begins in the mouth with saliva amylase and is continued in the small intestine by pancreatic amylase•Starch and glycogen are broken down into disaccharides (sucrose, maltose, and lactose)•Disaccharides are broken down into monomers (monsaccharides) as they are absorbed by the duodenal epithelium

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2. Proteins•Digestion of proteins begins in the stomach with pepsin•In the duodenum, trypsin and chymotrypsin (both from the pancreas) break polypeptides into small chains•Dipeptidases, carboxypeptidase, and aminopeptidase break apart polypeptides into amino acids

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3. Nucleic Acids•Are broken down into nucleotides by nucleases found in the pancreatic juice

4. Fats•Fat digestion starts in the small intestine•Bile salts (bile) emulsifying the fats then the enzyme pancreatic lipase hydrolyzes the small fat droplets into fatty acids and glycerol

I. The epithelial lining of the small intestine has folds called villi which bear projections called microvilli•Villi and microvilli increase the surface area for absorption

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J. Inside each villus are capillaries which absorb monosacchrides, amino acids, and nucleotides and a lacteal (part of lymphatic system) which absorbs small fatty acids•Absorption is carried out by passive-facilitated diffusion and active transport across intestinal membrane into blood capillaries

K. Capillaries and veins that take the nutrients away from the villi form the hepatic portal vessel which carries blood to the liver•The liver then regulates the distribution of nutrients to the body

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L. Hormones are chemical messengers that travel to target tissue through the blood. They help coordinate the digestive process as follows:1. Gastrin—produced in stomach and incrase the production

of gastric juices2. Enterogastrone—produced by duodoenum in the presence of fat•Slows down peristalsis to allow more time for fat digestion

3. Secretin and cholecystokinin (CCK)—secreted by walls of duodenum

•Increase the flow of digestive juices from the pancreas and gallbladder

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M. Large Intestine (colon)•Connected to the small intestine by a sphincter•Point of connection is the cecum which is a small pouch with the appendix attached•F(x): to compact waste and recover water•Contains mostly harmless bacteria—Escherichia coli

N. Rectum—end of colon where feces (solid waste) are stored until eliminated through the anus

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III. Concept 41.5A. Evolutionary Adaptation of Vertebrates

1. Dentition (teeth)—correlated with diet• Mammals have specialized teeth that best enables them to ingest their food

2. Herbivores have longer alimentary canals than carnivores because of the longer time it takes to digest vegetation•Much of their chemical energy comes from cellulose•Many vertebrates (as well as termites) house large populations of symbiotic bacteria and protists whose enzymes actually digest cellulose

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