Animal Nutrition

Chapter 41 Animal Nutrition Jesse Couch Haley McKay

41.1 Homeostatic Mechanisms manage an animal’s energy budget

Herbivores=eat mainly autotrophs (cattle, hares, snails) • Carnivores= eat other animals (hawks, spiders, sharks) • Omnivores= eat animals as well as plants or algal matter (humans, raccoons, bears) • A diet must satisfy 3 nutritional needs: fuel for cell work, the organic raw materials used in biosynthesis, and essential nutrients such as vitamins.

Four Main Feeding Mechanisms of Animals • Suspension feeders: sift small food particles from the water (whales) • Substrate feeders: live in or one their food source (caterpillars) • Fluid feeders: suck nutrient rich fluid from a living host (ticks) • Bulk feeders: eat relatively large pieces of food (python)

Glucose Regulation • If an animal isn’t growing or reproducing the body stores surplus energy in depots (in the form of glycogen in humans) • Caloric intake> caloric expenditure= calories stored as fat. • Caloric intake< caloric expenditure= fuel taken out of deposits and oxidized.

Caloric Imbalance • Undernourishment=occurs if the diet of the animal is chronically deficient in calories. - The stores of glycogen are used up and the body starts to break down proteins, muscles decrease in size, brain become protein-deficient. - Can cause death or irreversible side-effects • Over nourishment=excessive food intake (obesity) - Body hoards fat instead of using it for energy expenditure

Obesity as a human health problem • 15% of children and adolescents in the U.S. are overweight • Being overweight contributes to: • Diabetes • cancer of colon and breast • cardiovascular diseases that can lead to heart attacks and strokes. • Obesity can be inherited through the coding of genes that produce weight-regulating hormones. • Leptin produced by adipose (fat) is one of the feedback mechanisms that keep most people from becoming obese in spite of excess food.

Hormone Action on Satiety Center • Hormones regulate long-term and short-term appetite by affecting a satiety “center” in the brain • Ghrelin: signal that triggers feelings of hunger as mealtimes approach • Insulin: secreted from pancreas when after meals when there is an increased blood sugar level • Hormone PYY: secreted by small intestine after meals, suppresses appetite • Leptin: produced by fat tissue, suppresses appetite as its level increases.

Obesity and evolution • Fat hoarding may have been an evolutionary advantage in the past • humans used to be hunter-gatherers and the humans who had functions that induced them to devour rich, fatty foods when they had the chance • Individuals with genes that promoted storage of high-energy molecules during feasts would have out-lived thinner friends during famine.

41.2 An animal’s diet must supply carbon skeletons and essential nutrients.

Essential nutrients • . essential nutrients: cannot be made in cells; come in preassembled forms • malnourished: missing essential nutrients • Essential Amino Acids • must be obtained from food to make full proteins and avoid protein deficiency • animal proteins are complete; plant proteins are deficient in some amino acids • Essential Fatty Acids • particular unsaturated fatty acids; rare deficiencies

Vitamins and Minerals • Vitamins (see Table 41.1) • 13 organic molecules required in much less quantity than amino and fatty acids • water-soluble: B complex; coenzymes in metabolic processes • fat-soluble: A, D, E, and K; variety of functions • excess vitamins are either excreted through urine or kept in body fat (toxic) • Minerals (see Table 41.2) • inorganic and required in small amounts

41.3 The main stages of food processing are ingestion, digestion, absorption, and elimination.

First two stages • Ingestion: eating; first stage • animals can’t use macromolecules in their food directly since 1) they are too large over membranes; 2) they are not identical to what make up animal bodies • Digestion: breaking down food into smaller molecules (monomers) • enzymatic hydrolysis: breaks monomers apart by addition of water

Third and fourth stages • Absorption: cells take up monomers from digestive compartment • Elimination: undigested material exits digestive compartment • intracellular digestion: within the cell after pino- or phagocytosis • extracellular digestion: within continuous compartments • simple animals have gastrovascular cavity: sac with one opening • alimentary canal (complete digestive tract): mouth to anus (Figure 41.14)

41.4 Each organ of the mammalian digestive system has specialized food-processing functions

Peristalsis= rhythmic waves of contraction by smooth muscles in the wall of the canal which pushes food along the tract. • Sphincter=the muscular layer of ring-like valves which close off the tube like drawstrings, regulating the passage of materials between chambers of the canal. • Pancreas, liver, gallbladder are salivary glands which store digestive juices.

The Oral Cavity, Pharynx, and Esophagus • Mouth chews food into smaller pieces and increases surface area • Presence of food in oral cavity triggers reflex to secrete saliva through ducts. • Salivary amylase= an enzyme that hydrolyzes starch and glycogen and produces smaller polysaccharides and the disaccharide maltose.

Bolus= food ball formed by tongue when chewing food, then it is pushed into the pharynx • Pharynx= a junction that opens to both the esophagus and windpipe • When swallow, windpipe’s opening, the glottis, is blocked by epiglottis so bolus does not go down the windpipe • Esophagus= a channel that conducts food from the pharynx down to the stomach by peristalsis

The Stomach • Stomach= an organ of the digestive system that stores food and preforms first steps of digestion • Secretes gastric juice=digestive fluid and mixes it with the food through a churning action of smooth muscles in stomach wall • Gastric juice has a pH of 2 which is used in stomach to kill bacteria, break up cells in meat and plant material, and hydrolyze proteins through use of pepsin • Pepsin doesn’t destroy stomach cells b/c it is secreted in inactive from (pepsinogen) which is activated by the secretion of hydrochloric acid by parietal cells in gastric pits

The Stomach Continued • Mucus also protects stomach from self-digestion • About every 20 seconds, stomach contents are mixed (hunger pangs=empty stomach turning) • creates a nutrient broth (acid chyme) from the recently swallowed meal. • Opening from esophagus to stomach (cardiac orifice) normally dilates only when bolus arrives • Pyloric sphincter= muscular ring that regulates passage of chyme from stomach to intestine

Small intestine • duodenum: first section; acid chyme from stomach mixes with juices from pancreas, bile from the liver and gall bladder and gland cells of intestinal wall • absorption of nutrients occurs mostly in small intestine • increased by microvillar surface on villi: penetrated by capillaries and lacteal: lymphatic vessel • nutrients cross only two layers of epithelial cells from lumen to bloodstream through active or passive transport • fats are mixed with cholesterol and coated with proteins to form chylomicrons that enter lacteals

Large intestine • Large Intestine (Colon): connected to small intestine at T-shaped junction w/ sphincter controlled movement • cecum: one arm of T with appendix • recovers water in alimentary canal • feces is moved along organ at different speeds; normal speed is slow • rectum: end of colon where waste is stored until elimination (contractions of colon)

V. 41.5 Evolutionary adaptations of vertebrate digestive systems are often associated with diet

Some dental adaptations • Different mammals have different teeth for processing certain foods (Figure 41.26 pg. 863) • Non-mammalian vertebrate (lizards) usually have less specialized dentition with poisonous snakes as the exception (have specialized fangs with poison)

Stomach and Intestinal Adaptations • Large expandable stomachs are common in carnivores • Herbivores and omnivores have longer alimentary canals (digestive tract) b/c vegetation is harder to digest b/c of cell walls

Symbiotic Adaptations • Animals do not produce enzymes that can digest cellulose but their stomach houses microorganisms that do have these enzymes • Ruminants= an animal (cow, sheep, deer) with an elaborate, multi-compartmentalized stomach specialized for a herbivorous diet. (figure 41.28 pg.864)

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Animal Nutrition