Biology 1108

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Lecture 20

• Biology 1108
• Chapter 41 Nutrition and Digestion

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Learning Objectives

• Define
• Herbivores, carnivores, omnivores
• Contrast
• Suspension, substrate, fluid, and bulk feeders
• Discuss
• 4 stages of digestion
• Gastric ulcers
• Advantages to digestive compartmentalization
• Explain how the esophagus works

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Dietary Preferences

• Herbivores
• Eat plants
• Carnivores
• Eat animals (includes poultry, fish, insects)
• Omnivores
• Eath both plants and animals

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4 Feeding Styles

• Suspension feeders
• Substrate feeders
• Fluid feeders
• Bulk feeders

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Suspension Feeders

• Strain material from water
• Usually have some net or comb-like feeding
  structure
• Examples
• Flamingos eat tiny shrimp
• Barnacles eat tiny plankton
• Blue whales eat krill, small shrimp

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Substrate Feeders

• Eat their way through food
• Examples
• Fruit fly larvae
• Burrow through over-ripe fruit
• Earthworms
• Eat their way through soil
• Digest bacteria

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Fluid Feeders

• Suck material out of living hosts
• Mouthparts specialized for fluid diet
• Ex
• Mosquitos eat blood
• Aphids suck plant sap

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Bulk Feeders

• Ingest large bites of food
• Ex
• Humans
• Dogs
• Sharks
• Cows

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Bulk Feeding in Action
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7th Inning Stretch
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Four Stages of Food Processing

• Ingestion
• Digestion
• Absorption
• Elimination

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Ingestion Taking Food In

• Predators
• Prey must be first captured, then disabled
• Gape-limited predators usually take prey whole
• Size of mouth (gape) is crucial
• Example bream are gape-limited
• Other predators take pieces of prey
• Examples
• Sharks
• African lion
• Herbivores
• Usually very careful in food choices
• Trying to maximize benefit for given effort

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Digestion

• 2 Phases
• Mechanical breakdown
• Chemical breakdown (hydrolysis)

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Mechanical Breakdown

• Usually occurs first
• Tearing, mashing, cutting food into smaller
  pieces
• Increases surface area for enzymes to work
• Smaller pieces move through system more easily

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Breakdown Methods

• Herbivores generally grind
• Must break down tough cellulose cell walls
• Food generally plentiful, so they can take time
• Carnivores usually cut
• Must quickly ingest before competition moves in
• Dogs, cats gulp food!
• No cell wall, so breakdown is easier

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Chemical Breakdown

• Usually involves hydrolysis
• Literally, taking polymers apart using water
• Monomers are yielded
• Animals can use these to build new polymers or
  for energy
• Ex potatoes contain starches
• We break hydrolyze them to simple sugars
• Our cells can use these for ATP production

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Absorption

• Movement of useful molecules from digestive tract
  into bloodstream
• In humans, occurs mainly in the small intestine

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Elimination

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

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Digestion in Compartments

• Body tissues must be protected from
• Acids
• Enzymes
• Proper environment must be maintained for enzyme
  reactions
• Even sponges compartmentalize digestion (in
  cells)
• Other animals use
• Gastrovascular cavity
• Alimentary canal

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Gastrovascular Cavity

• Protects body cells from enzymes
• Keeps enzymes close to prey
• Allows for relatively large food item to be taken
• Not even largest sponges can eat a Daphnia, but
  Hydra can

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Hydra Digesting
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Alimentary Canal

• Tube with 2 openings
• Mouth
• Anus
• Tube has several parts in humans
• Esophagus
• Stomach
• Large, small intestines

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Esophagus

• Two layers of muscle
• Circular layer constricts food tube
• Longitudinal layer shortens food tube
• Movement of food peristalsis
• Swallowing peristaltic wave
• Vomiting reverse peristaltic wave

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Swallowing
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Stomach

• 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

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Stomach Cross-Section
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Gastric Ulcers

• Literally, a hole in stomach
• Can cause life-threatening internal bleeding
• Once thought to be caused by excess acid, now
  known to be caused by bacterial infection

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Helicobacter pylori

• Well-suited to life in stomach acid
• Produces acid-neutralizing chemicals
• Damages mucus layer stomach lining
• Normal levels of acids and pepsin can then
  dissolve stomach wall
• Ulcer results
• Cure antibiotics bismuth (Pepto Bismol)