Nutrition and Digestion

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Chapter 21

• Nutrition and Digestion

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Learning Objectives

• Ingestion versus absorptive feeding
• Mechanisms of ingestion
• Four stages of bulk feeding
• Compartmentalization
• Human digestion details
• Cause of ulcers
• Herbivores versus carnivores
• Ruminant versus non-ruminant herbivores
• Ruminant digestion details
• Nutrition and types of nutrients
• Energy
• Essential nutrients

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Nutritional Diversity

• Ingestive versus Absorptive
• Humans versus bacteria
• Ingestive involves digestion and absorption
• Absorptive involves absorption of simple
  nutrients
• Ingestive types
• Herbivores
• Carnivores
• Omnivores

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Ingestive Feeding Styles

• Suspension feeders
• Straining effect
• Pelicans
• Substrate feeders
• Eat as they move through
• earthworms
• Fluid feeders
• Suck fluid food from source
• mosquitoes
• Bulk feeders
• Ingest and macerate large particles
• humans

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Four General Stages of Eating

• Ingestion
• Digestion
• Absorption
• Elimination

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Digestion

• 2 Phases
• Breakdown from larger macromolecules to smaller
  macromolecules
• Increases surface area for further breakdown by
  enzymes
• Beans into proteins and polysaccharides
• Mechanical and enzymatic
• Macromolecules into monomers
• Proteins into amino acids, lipids into fatty
  acids and glycerol, and polysaccharides into
  simple sugars
• Hydrolysis?enzymatic only

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Absorption

• Movement of useful monomers from digestive tract
  into bloodstream
• In humans, occurs mainly in the small intestine
• Incorporated or used for energy at cellular level
• Examples
• Amino acids (monomer) to assemble proteins
  (polymer)?incorporated
• Glucose metabolized to make ATP?energy

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Elimination

• Feces material left after absorption
• Animal cannot use this
• Example cellulose in humans
• In humans, works best if theres high volume
• Fiber!

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Digestion in Compartments

• Body tissues must be protected from acids and
  enzymes
• Proper environment (optimal conditions) must be
  maintained for enzyme reactions
• Single celled or primitive ingestive organisms
  use a vacuole
• Simple organisms (hydra) use gastrovascular
  cavity
• More complex organisms use alimentary canal
• Mammals use gastrointestinal tract

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Gastrovascular Cavity

• One opening
• Ingestion?mouth
• Elimination?mouth
• Cavity
• Digestion and Absorption
• Protects body cells from enzymes
• Keeps enzymes close to prey
• Allows for relatively large food item to be taken

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Hydra Digesting
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Alimentary Canal

• Tube with 2 openings
• Mouth
• Anus
• More specialized portions than GC

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Four Stages in Alimentary Canal

• Ingestion Mouth, Buccal cavity, pharynx and
  esophagus
• Digestion microorganisms, crop, and gizzard
• Microbes secrete enzymes to break material into
  monomers
• Crop mixes, softens and stores food
• Gizzard grinds food
• Absorption intestine
• Elimination anus

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Four Stages In Human GI Tract

• Ingestion mouth, tongue, teeth, pharynx,
  esophagus
• Digestion enzymes, saliva, stomach, gall bladder
  (bile), liver, duodenum, pancreas
• Absorption anterior small intestine, large
  intestine, liver
• Elimination Large intestine, rectum and anus

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Passage Through GI
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Ingestion

• Mouth/Tongue
• Maceration, bolus formation, saliva secretion
• Initial digestion of starch
• Amylase enzyme in saliva
• Pharynx
• Entrance into esophagus
• Larynx closes epiglottis as food passes to
  esophagus
• After passage larynx opens epiglottis and
  esophageal sphincter closes esophagus
• Down the wrong hole!

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Ingestion Mouth/Tongue/Pharynx
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Ingestion Esophagus

• Two layers of muscle
• Circular layer constricts
• Longitudinal layer shortens
• Wavelike movement peristalsis
• Swallowing peristaltic wave
• Vomiting reverse peristaltic wave

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Digestion Stomach

• Mechanical breakdown and enzymatic digestion of
  proteins
• Folds to increase surface area
• Lined with pits, which have gastric glands
• 3 cell types in glands
• Mucous cells (help protect stomach)
• Parietal cells (make hydrochloric acid)
• Chief cells (make pepsinogen)
• Pepsinogen inactive form of pepsin digestive
  enzyme
• Glands secrete gastrin (mucous, HCl, pepsinogen)

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Stomach Cross-Section
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Digestion Stomach

• Pepsinogen versus pepsin
• How to activate pepsinogen?low pH
• Gastrin secreted in response to signals from
  nerves or other glands?low pH
• Acid chyme after mixing with food during
  peristalsis
• Secretion stopped when pH gets too low?no food
• 2-6 hours
• Pyloric sphincter regulates passage of food to
  duodenum
• Why dont we digest our own stomach?

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Digestion Duodenum

• Final Chemical Breakdown?monomers
• Digestive enzymes come from pancreas
• Sugar enzymes
• Amylase?starch to maltose
• Maltase?maltose to glucose
• Sucrase?sucrose to glucose and fructose
• Lactase?lactose to glucose and galactose
• Protein enzymes
• Trypsin and chymotrypsin?longer to shorter
  polypeptides
• Peptidases?short polypeptides to amino acids

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Duodenum
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Duodenum More Digestive Enzymes

• Fats
• Bile made by liver and released by gall bladder
• Emulsifies fats?more surface area to break them
  down?like a detergent
• Lipase released from pancreas acids and glycerol
• Nucleic acids (DNA/RNA)
• Nucleases released from pancreas

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Absorption Small Intestine

• Huge surface area
• 300 m2 (tennis court)
• 6 m long
• How is this possible?
• Folds and projections
• Villi
• Microvilli
• Blood vessels carry nutrients to liver for
  processing

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Small Intestine
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Absorption and Elimination Colon

• Short, but fat
• 1.5m by 5 cm
• Main job to absorb water and concentrate
  indigestible food (feces)
• Recycles 90 of the 7 liters of water used during
  digestion in 1 day
• Cecum and appendix
• Rectum 2 sphincters
• Constipation versus diarrhea
• Secondary job absorb vitamins produced by colon
  bacteria (normal flora)

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Colon
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E. coli the Gut Bacterium

• Normal strains of E. coli very helpful
• Make vitamins
• Folic acid
• Biotin
• B (several kinds)
• K
• Mutant pathogenic strains of E. coli cause
  sickness
• Prevent water absorption in colon

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The Glands

• Liver
• Production of bile
• Conversion of monomers to functional products or
  storage products
• Glucose?glycogen
• Breaks down some toxins absorbed by blood
• Activates carcinogens!!
• Salivary glands
• Buffers, amylase and glycoprotein
• Maintain neutral pH, digestion of starch,
  lubrication
• Pancreas
• Production and release of digestive enzymes to
  duodenum

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Peptic Ulcers

• Damage to mucus layer stomach lining
• 50 of population
• Mediated by Helicobacter pylori
• Bacteria that can colonize the stomach
• Resistant to low pH (produces acid neutralizing
  chemicals around it)
• Damages mucous cells and makes stomach cells
  susceptible to damage by pepsin/acid
• White blood cells defense and gastritis
• Damage is exponential
• Cure antibiotics bismuth (Pepto Bismol)

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Vertebrate Digestive Systems

• Herbivores versus carnivores
• Herbivores Longer intestines
• More time for herbivores to extract nutrients
  (plant cell walls)
• Nutrients less concentrated than carnivores
• Herbivores require microbes to help digest
  cellulose
• non-ruminants (horses, elephants, rodents, and
  rabbits)
• Microbes in cecum
• Lose a lot of nutrients!
• Rabbits and rodents are copraphageous!!!
• Ruminants
• Most efficient digestion of cellulose
• Dont lose many nutrients

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Ruminant Digestion Components

• Rumen (4 part stomach) possessed by deer, cattle,
  sheep
• Rumen?microbe digestion of starch
• Reticulum? microbe digestion of starch and
  mediates passage of cud (to mouth or to omasum)
• Omasum?water absorption
• Abomasum?cow enzymes digest microbes and
  microbial products
• Intestines?nutrient absorption and more water
  absorption
• Cud (partially digested food) regurgitated and
  chewed
• Helps mechanical break-up of large particles
• Increases surface area for enzymes, bacteria to
  attack

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The Rumen
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Nutrition

• Purpose of eating
• Energy
• Macromolecules to make cell componenets
• Essential nutrients (things we cannot synthesize,
  but need desperately)
• Energy
• Calorie versus kilocalorie
• BMR energy needed to do basic bodily functions
  (breath, heart beat, digest, etc.)
• 1,300-1,800 kcal/day
• Activities (movements of any sort or thinking)
  increase the demand for energy above the BMR

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Energy

• How do you turn calories associated with
  molecules into ATP?
• Sources of calories (energy)
• Carbohydrates
• Fat
• Protein
• Use of Oxygen
• 4.83 kcal/liter of O2
• Excess calorie containing molecules are turned
  into glycogen and fat
• Stored and used during famine

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Fat

• Normal amounts of body fat
• W 20-25
• M 15-19
• Fatty acids
• Can make most of them from other molecules
• Some Essential Fatty acids (required in diet)
• Carbs are used first for energy and fat is used
  when carbs are used up
• Fat that is not used in diet is stored
• If excess carb then it is turned to fat and
  stored
• Why do we hoard fat?

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Fat Continued

• Saturated versus nonsaturated fat
• cholesterol
• LDL and heart disease
• Cant make it to liver for processing and clogs
  vessels
• Saturated fats increase LDLs
• HDL
• Can travel to liver and is processed into
  important cellular components
• Unsaturated fats increase HDLs
• Fish oils, olive oil, canola

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The 9 Essential Amino Acids

• Our cells need 20 amino acids
• We can synthesize all but 9
• we must get from diet?essential
• Cannot store excess amino acids
• No constant supply of all 20 then problems
• Meat sources versus veggie sources
• Meat?easier to obtain all
• Veggies?require a wide variety of different
  veggies
• Beans and corn and the balanced veggie diet

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Vitamins

• Necessary organic compounds other than amino
  acids
• Required in smaller amounts than amino acids
• Assist in enzyme catalysis
• Water soluble vitamins
• EX) b vitamins
• Excess passed through urine
• Fat soluble vitamins
• EX) Vitamin A
• Dangerous in excess because excess are stored in
  fat

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Minerals

• Inorganic nutrients
• Required in really small amounts
• Assist in catalysis
• Iron required by blood to carry oxygen
• Calcium required by bones to maintain structure
• Sodium required by muscles and nerves to function
  properly.
• All are elements