Animal Nutrition II (Ch. 41)

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Animal Nutrition II (Ch. 41)
Guest lecturer Letitia Reichart (Letty)
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Keywords

• Roles of mouth, stomach, sm.lg. Intestine in
  digestion
• Pepsin, pepsinogen
• Villi, microvilli
• Cecum
• Cellulose
• Cellulase

• Acid chyme
• Enzymatic hydrolysis
• Peristalsis

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Mammalian Digestive System

• Alimentary canal
• Accessory glands
• Salivary glands, pancreas, liver, gallbladder
• Food moved by peristalsis

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Mouth (oral cavity)

• Mechanical
• Teeth
• Saliva
• Enzymatic
• Salivary amylase breakdown of starch and
  glycogen

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Throat (pharynx) Esophagus

• Throat junction to esophagus trachea
• Epiglottis
• Esophagus uses peristalsis to move food to
  stomach

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Stomach

• Stores food
• Secretes gastric juices
• Acid chyme

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Digestive mechanisms in stomach

• Mechanical
• Chemical
• Enzymatic

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Mechanical

• Mixing and churning
• Smooth muscle
• Every 20 seconds

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Chemical

• Hydrochloric acid (HCl)
• pH around 2
• Also breaks food down

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Enzymatic

• Pepsin
• Breaks down proteins

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Why doesnt pepsin digest stomach?
Gastric pit
Interior surface of stomach
Gastric gland
Mucus cells
Chief cells
Parietal cells
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Activation of pepsin
Pepsinogen
Pepsin (active enzyme)
HCl
Parietal cell
Chief cell
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Stomach

• After mechanical and enzymatic digestion
• -Acid chyme (nutrient-rich broth)
• - Pyloric sphincter to the small intestine

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Small intestine

• Most of
• Enzymatic digestion occurs here
• Absorption of nutrients into the blood stream
  occurs here

Small intestine
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Figure 41.21 p. 859 in Campbell
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Figure 41.19 p. 858 in Campbell
Bile
Liver
Gall- bladder
Stomach
Acid chyme
Intestinal juice
Pancreatic
juice
Pancreas
Duodenum of small intestine
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Pancreas

• Secretes proteases into duodenum

Inactive form Active form
Trypsinogen Trypsin
Procarboxypeptidase Carboxypeptidase
Chymotrpsinogen Chymotrypsin
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Why doesnt the small intestine digest itself?
Pancreas
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Liver

• Produces bile that is stored in gallbladder
• Bile contain bile salts
• Bile salts aids digestion and absorption of fats

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Most nutrient absorption occurs in small intestine
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Structure of small intestine
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Microvilli

• Aid in nutrient transport across epithelial
  cells of sm. intestine into bloodstream

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Large intestine (colon)

• Major function is to reabsorb water

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Here are a few review questions
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What would happen if you had a defect in pepsin
production?
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What would happen if you had a defect in pepsin
production?

• A. carbohydrate would not be digested well
• B. meat would not be digested at all
• C. perhaps decreased absorption of protein

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What would happen if you had a defect in salivary
amylase production?
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What would happen if you had a defect in salivary
amylase production?

• A. You would die
• B. You would be unable to digest starch
• C. The pH of the stomach would be affected
• D. None of the above

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Which of the following would you least like to
donate to science while you are still alive?

• A. Cecum
• B. Pancreas
• C. Reproductive organs

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What would happen if you had a defect in small
intestine enteropeptidase?
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What would happen if you had a defect in small
intestine enteropeptidase?

• A. Pancreatic enzymes would not be activated
• B. Liver enzymes would increased
• C. Your small intestine would become blocked
• D. None of the above

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Variations of vertebrate digestive system

• Herbivorous mammals
• Specialized fermentation chambers

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Coyote vs. Koala
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Why does herbivory require specializations?

• Plant tissue
• Harder to break up
• Contains cellulose
• Nutrients less concentrated than meat

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Structure of cellulose
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Only bacteria and protozoa can break down
cellulose
Via the enzyme cellulase
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Cecum

• Pouch at junction between lg and sm intestine
• Large cecum in rabbits, some rodents, koala,
  horses
• Full of symbiotic bacteria

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Symbiosis

• living together

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Cecum function

• Fermentation chamber
• Bacteria breakdown cellulose
• Feces must be reingested