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Herbivores
Plant-eaters (cattle, snails, sea urchins)
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Carnivores
Meat-eaters (lions, hawks, spiders)
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Omnivores
Eating both plants and other animals (humans, roaches, crows, raccoons)
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Animals obtain and digest their food 4 ways:
- Suspension feeding
- Substrate feeding
- Fluid feeding
- Bulk feeding
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Food is processed in 4 stages:
- Ingestion
- Digestion
- Absorption
- Elimination
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Mechanical digestion
- Breaks food down into smaller pieces
- Smaller pieces are easier to swallow
- Smaller pieces have more surface area exposed to digestive fluids
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Chemical digestion
Breaks down large organic molecules into their components
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Most animals have an alimentary canal:
- Mouth
- Anus
- Specialized regions
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Sphincters
Control the movement of into and out of digestive chambers
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The pyloric sphincter
- Regulates the passage of food from the stomach to the small intestine
- Limits the upward movement of acids into the esophagus
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The trachea
Conducts air to the lungs
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Esophagus
Conducts food from the pharynx to the stomach
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Swallowing reflex
- Food moves from the pharynx into the esophagus
- Prevents food from entering the trachea
- A coughing reflex helps expel materials that accidentally enter the trachea
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Stomach
Stores food and breaks it down with acid and enzymes
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Acid
- pH 2
- Parietal cells secrete hydrogen and chloride ions, which combine to make HCl
- Acid kills bacteria and breaks apart cells in food
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Pepsinogen and HCl produce:
Pepsin
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Postive feedback
Pepsin production activates more pepsinogen production
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Heartburn
Acid reflux into esophagus
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Alkaline pancreatic juice
Neutralizes acid chyme and its enzymes digest food
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Bile
- Made in the liver and stored in the gall bladder
- Emulsifies fat for attack by pancreatic enzymes
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Surface area of absorption is increased by:
- Folds of the intestinal lining
- Fingerlike villi
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Nutrients
Pass across the epithelium and into blood
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Blood
Flows to the liver where nutrients are processed and stored
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When diarrhea occurs:
Too little water is reclaimed
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When constipation occurs:
Too much water is reclaimed
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Specializations of the gut for herbivores:
- Rumen
- Reticulum
- Omasum
- Abomasum
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A healthy diet satisfies three needs:
- Fuel to power the body
- Organic molecules to build molecules
- Essential nutrients (raw materials that animals cannot make for themselves)
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Main sources of dietary calories:
- Proteins
- Carbohydrates
- Fats
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Basal metabolic rate (BMR)
The energy a resting animal requires each day
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Metabolic rate
The BMR plus the energy needed for physical activity
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Excess energy is store as:
Glycogen or fat
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Undernourishment
Not enough calories
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Malnourishment
Missing essential nutrients
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Minerals
Simple, inorganic nutrients usually required in small amounts
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Recommended Dietary Allowances (RDA)
Excessive doses of Vitamin A, K, D, E and iron can be dangerous
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