Animal Nutrition. Nutritional Requirements Nutritional diet fulfills 3 needs: 1 Fuel – energy for work. 2 Raw materials – for biosynthesis. 3 Essential.

Animal Nutrition

Nutritional Requirements

• Nutritional diet fulfills 3 needs:• 1Fuel – energy for work.• 2Raw materials – for

biosynthesis.• 3Essential nutrients – body can’t

make.• Flow of energy in/out – budget.

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• ATP comes from oxidation of organic molecules.

• Take in more calories than needed – rest for biosynthesis.

• Liver stores excess as glycogen; above and beyond stores, stores as fat.

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• Regulation of blood glucose: glucose levels rise – pancreas secretes insulin – stimulates liver to store excess – decreases levels.

• Glucose drops – pancreas secretes glucagon – breakdown of glycogen – increases levels.

• Fewer calories than needed – fuel taken out of storage (liver 1st, muscles 2nd)

• Most people have enough stores to last weeks.

• Undernourishment – uses muscles for energy, eventually brain.

• Even if survives, permanent damage occurs.

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• Overnourishment – excessive food intake – results in obesity.

• Advantage during hunting/gathering days.

• Human body has set weight – sets limits on weight loss/gain.

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• Leptin (hormone) – produced by adipose cells – decreases hunger (when levels high).

• Decrease causes increase in appetite.

• Obesity beneficial in some species (travel long distances)

• Animal’s diet must supply materials for biosynthesis.

• Also supply essential nutrients (i.e. vitamin C)

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• Missing nutrients – malnourished.• More common than

undernourishment.• 20 amino acids needed to make

proteins – eight are essential (needed from diet).

• Protein deficiency most common malnourishment – causes mental retardation in children.

• Animal proteins – complete (have all essential amino acids)

• Plant proteins – incomplete.• Combination in plants fulfill all

essentials.• Can’t be stored – need to be

eaten daily.

• Animals adapt to needs – penguins use muscle proteins for energy for molting.

• Essential fatty acids needed as well.

• Vitamins – organic molecules needed in small quantities.

• 13 essential vitamins.

• Minerals – inorganic nutrients needed in small amounts.

• Excess of sodium (salt) dangerous – high blood pressure; excess iron – liver damage.

Food Types

• 3 categories of eating habits – 1herbivores (plant eaters), 2carnivores (meat eaters), 3omnivores (both)

• Most animals opportunistic – will eat outside category if needed.

• 4 ways to ingest food.

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• 1Suspenion-feeders – sift small particles from water (baleen whales)

• 2Deposit-feeders – eat through sediment; extract decaying organic material (earthworms)

• 3Substrate-feeders – live on food source (maggots)

• 4Fluid-feeders – suck fluids from host (mosquitoes, leeches)

• Most animals bulk-feeders – eat large pieces of food.

• Use fangs, teeth, claws, etc. to eat food.

Overview of food processing

• 1Ingestion - food taken into system. (Eating)

• Polymers broken down into monomers so body can digest them.

• 2Digestion - breaking food down into molecules small enough for body to absorb.

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• Digestion reverses process that cell uses to link together monomers to form macromolecules.

• Mechanical digestion - physical breaking down of food; chemical digestion - act of enzymes on broken down food.

• 3Absorption - animal’s cells take up small molecules (i.e. amino acids, simple sugars) from digestive compartment.

• 4Elimination - undigested material passes out of digestive compartment.

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• To avoid digesting own self, most digestion compartmentalized.

• In cell - food vacuoles - hydrolytic enzymes break down food without digesting cell’s own cytoplasm (intracellular digestion).

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• Protists - take in food by phagocytosis or pinocytosis.

• Food digested in food vacuole, then fuses with lysosomes to break food down further.

• Vacuole fuses with anal pore that eliminates it from body.

• Extracellular digestion - food broken down outside cell.

• Cnidaria have digestive sacs with single openings (gastrovascular cavities).

• Food taken in, eliminated through same opening.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 41.11

• Organisms have complete digestive tracts (alimentary canals) with mouth, digestive tube, anus - specialized to carry out digestion.

• Food ingested through mouth, pharynx passes through esophagus to crop, gizzard, or stomach, depending on species.

http://khoomei.com/pics/pharynx.jpg

• Crop (or stomach) - food storage.• Gizzard - breaks down food.• Allows organisms to ingest

additional food before earlier meals completely digested.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 41.12

Mammalian Digestive System

• Consists of alimentary canal, various accessory glands that secrete digestive juices into canal through ducts.

• Peristalsis, rhythmic waves of contraction by smooth muscles in walls of canal, push food along.

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• Sphincters, muscular ring-like valves, regulate passage of material between specialized chambers of canal.

• Accessory glands - salivary glands, pancreas, liver, gallbladder.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 41.13

• Physical, chemical digestion of food begins in mouth.

• Presence of food in oral cavity triggers nervous reflex - causes salivary glands to deliver saliva through ducts to oral cavity.

• Salivation may occur in anticipation -learned associations between eating, time of day, cooking odors, etc.

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• Saliva contains mucin - helps food slide down esophagus easier.

• Chemical digestion of carbohydrates main source of chemical energy, begins in oral cavity - done by salivary amylase.

• Food made into ball - bolus.

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• Pharynx (throat) - junction that opens to esophagus and trachea (windpipe).

• Swallow - top of windpipe moves up - opening, glottis, blocked by cartilaginous flap, (epiglottis) - helps to prevent us from choking.

• Not swallowing - esophageal sphincter muscles contracted - epiglottis up, glottis open, allowing airflow to lungs.

• When food bolus reaches pharynx, larynx moves upward and epiglottis tips over glottis, closing off trachea.

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• Esophageal sphincter relaxes, bolus enters esophagus.

• Larynx moves downward, trachea opened, peristalsis moves bolus down esophagus to stomach.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 41.14

• Esophagus conducts food from pharynx down to stomach by peristalsis.

• Stomach located in upper abdominal cavity, below diaphragm.

• Stomach secretes digestive fluid (gastric juice), mixes secretion with food by churning action of smooth muscles in stomach wall.

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• Gastric juice secreted by epithelium lining numerous deep pits in stomach wall.

• Contains hydrochloric acid (acidic enough to dissolve iron nails) and pepsin, enzyme that begins hydrolysis of proteins.

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• Pepsin secreted in inactive form, pepsinogen, by specialized chief cells in gastric pits.

• Parietal cells, also in pits, secrete hydrochloric acid - converts pepsinogen to active pepsin only when both reach lumen of stomach, minimizing self-digestion.

• Stomach’s 2nd line of defense against self-digestion is coating of mucus, secreted by epithelial cells, protects stomach lining.

• Ulcers occur when stomach lining eaten through.

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• Stomach churns food, produces chyme.

• Sometimes chyme backs up into esophagus (heartburn).

• Pyloric sphincter (at opening of small intestine) prevents material from moving into small intestine too quickly.

http://trc.ucdavis.edu/biosci10v/bis10v/week10/chyme.gif

• Small intestine longest section of alimentary canal.

• Most absorption takes place here.• Duodenum - chyme from stomach

mixes with digestive juices from pancreas, liver, gall bladder, gland cells of intestinal wall.

• Liver performs wide variety of important functions in body, including production of bile.

• Bile stored in gall bladder until ready to use.

• Bile used to breakdown fats.• Each enzyme has specific role in

digestion.

• Starch, glycogen continue to be broken down in small intestine.

• Pancreatic amylase aids in process.

• Digestion of proteins in small intestine completes process begun by pepsin.

• Done by several enzymes.

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• Trypsin, chymotrypsin attack peptide bonds adjacent to specific amino acids, breaking larger polypeptides into shorter chains.

• Dipeptidases, attached to intestinal lining, split smaller chains.

• Carboxypeptidase, aminopeptidase split off 1 amino acid from carboxyl or amino end of peptide, respectively.

• Nucleic acids digested in small intestines by an enzyme (nuclease).

• All fat in meal reaches small intestine undigested.

• Emulsification allows fat droplets to be coated by bile so they can pass through system.

• Lipase - enzyme that breaks fats down.

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• Most digestion occurs in duodenum.

• Other 2 sections of small intestine, jejunum and ileum, function mainly in absorption of nutrients and water.

• Nutrients in lumen must pass lining of digestive tract.

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• Surface area of small increased by microvilli - appendages off of villi.

• Help increase amount of absorption.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 41.19

• Transport of nutrients across epithelial cells can be passive.

• Active mechanisms of digestion, including peristalsis, enzyme secretion, active transport, may require animal to expend amount of energy = 3% - 30% of chemical energy contained in meal.

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• Hormones released by wall of stomach and duodenum ensure digestive secretions present only when needed.

• Can be released when we see or smell food.

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• Certain substances in food stimulate stomach wall to release hormone gastrin into circulatory system.

• As recirculates, gastrin stimulates further secretion of gastric juice.

• If pH of stomach contents become too low, acid will inhibit release of gastrin.

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• Other hormones, (enterogastrones), are secreted by walls of duodenum.

• Cholecystokinin (CCK), secreted in response to presence of amino acids or fatty acids, causes gallbladder to contract, release bile into small intestine; triggers release of pancreatic enzymes.

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• Large intestine (colon) connected to small intestine where sphincter controls movement of materials.

• Small cecum (1st part of colon) of humans has appendix - makes minor contribution to body defense.

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• Major function of colon - to recover water that has entered alimentary canal as solvent to digestive juices.

• Digestive wastes, feces, become more solid as move along colon by peristalsis.

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• In large intestine - rich flora of mostly harmless bacteria.

• Feces contain masses of bacteria and undigested materials including cellulose.

• Terminal portion of colon - rectum, feces stored until eliminated.

• 2 sphincters, 1 involuntary, 1 voluntary, control movement of feces out of rectum.

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Evolutionary Adaptations

• Vertebrate digestive systems alike, have some differences based on diets.

• Dentition (animal’s assortment of teeth) example of structural variation reflecting diet.

• Nonmammalian vertebrates - less specialized dentition (exceptions)

• Snakes - ability to swallow food whole.

• Unhinge jaw to get entire organism in.

• Large, expandable stomachs common in carnivores - may go for long time between meals; must eat as much as they can when they catch prey.

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• Length of vertebrate digestive system correlated with diet.

• More plants, longer tract seems to be to allow more time for digestion and reabsorption.

• Most energy in plants comes from cell walls.

• Cellulose cannot be digested by many organisms.

• Symbiotic microbes can digest it. Location of symbiotic microbes in herbivores’ digestive tracts varies depending on species.

http://www.nature.com/news/2001/010118/images/cellulose_200.jpg

• Most elaborate adaptations for herbivorous diet have evolved in ruminants (deer, cattle, sheep).

• When cow first chews and swallows mouthful of grass, boluses enter rumen and reticulum.

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• Symbiotic bacteria, protists digest cellulose-rich meal, secreting fatty acids. Cow regurgitates, rechews cud, which further breaks down cellulose fibers. Cow reswallows cud, water removed.

• Cud, with many microorganisms digested by cow’s enzymes.