Animal Nutrition

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Chapter 41

• Animal Nutrition

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• Animals are heterotrophs, therefore, their life
  depends on obtaining food.

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Diet

• A diet must provide
• Fuel for work
• Raw materials for biosynthesis
• Essential nutrients

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Fuel for work

• Comes in the form of glucose
• Used in cell respiration to generate ATP
• Glucose can be stored in the body and made
  available when levels are low

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Glucose Feedback

• Glucose levels are low ?
• Pancreas secretes glucagon
• Glucagon stimulates breakdown of glycogen into
  glucose
• Glucose levels are high ?
• Pancreas secretes insulin
• Insulin increases glucose uptake of glucose into
  liver and muscles

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Biosynthesis and Raw Materials

• Essential nutrients are ones NOT made by the body
• Example- 8 of the 20 amino acids not made in the
  human body
• How are each of the following used?
• Proteins, Carbohydrates, Lipids, Vitamins,
  Minerals, Water

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LE 41-10
Essential amino acids for adults
Beans and other legumes
Methionine
Valine
Threonine
Phenylalanine
Leucine
Corn (maize) and other grains
Isoleucine
Tryptophan
Lysine
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What happens to food?

• Four major stages
• Ingestion eating
• Digestion breaking food down into smaller pieces
• Absorption cells take up small molecules from
  the digestive system
• Elimination undigested material is excreted

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Compartments

• Intracellular digestion
• Phagocytosis or Pinocytosis leading to food
  vacuoles
• Extracellular digestion
• Breaking down food outside of cells in
  compartments (stomach)

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Differences in Animals

• Gastrovascular cavity
• Digestive sac with one opening
• Alimentary canal
• Two openings- mouth and anus

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LE 41-12
Small molecules
Pieces of food
Chemical digestion (enzymatic hydrolysis)
Nutrient molecules enter body cells
Mechanical digestion
Undigested material
Food
ELIMINATION
INGESTION
ABSORPTION
DIGESTION
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Digestion in Humans

• The mammalian digestive system consists of an
  alimentary canal and accessory glands that
  secrete digestive juices through ducts
• Accessory glands salivary glands, the pancreas,
  the liver, and the gallbladder

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LE 41-15b
Salivary glands
Mouth
Esophagus
Gall- bladder
Stomach
Small intestines
Liver
Pancreas
Large intestines
Rectum
Anus
A schematic diagram of the human digestive system
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Digestion in Humans

• Food is pushed along by peristalsis (rhythmic
  contractions of smooth muscles)
• Sections are separated by sphincters (ring-like
  valves)

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LE 41-15a
Cardiac orifice
Tongue
Oral cavity
Parotid gland
Salivary glands
Sublingual gland
Pharynx
Esophagus
Submandibular gland
Pyloric sphincter
Liver
Stomach
Ascending portion of large intestine
Gall- bladder
Pancreas
Duodenum of small intestine
Ileum of small intestine
Small intestine
Large intestine
Rectum
Anus
Appendix
Cecum
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Digestion

• Food enters oral cavity
• Food is chewed
• Saliva is produced by salivary glands
• Salivary Amylase breaks down starch and glycogen

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Digestion

• Food is formed into a bolus, which is swallowed
• Windpipe moves up, which forces the epiglottis to
  cover the glottis
• Esophagus pushes food towards the stomach

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Digestion

• Bolus passes through the cardiac orifice into
  stomach
• Stomach stores food and does some digestion

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LE 41-16_3
Bolus of food
Tongue
Epiglottis up
Epiglottis up
Pharynx
Glottis down and open
Esophageal sphincter contracted
Glottis
Esophageal sphincter relaxed
Epiglottis down
Esophageal sphincter contracted
Larynx
Glottis up and closed
Trachea
Esophagus
Relaxed muscles
To stomach
To lungs
Contracted muscles
Relaxed muscles
Stomach
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Side trip 1

• Gastric juice secreted by gastric glands (pits)
  containing
• Parietal cells (HCl)
• Chief cells (pepsinogen/pepsin)
• Mucus secreting cells (mucus)

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LE 41-17
Esophagus
Cardiac orifice
Stomach
Pyloric sphincter
5 µm
Small intestine
Folds of epithelial tissue
Interior surface of stomach
Epithelium
Pepsinogen and HCl are secreted into the lumen
of the stomach.
Pepsin (active enzyme)
Pepsinogen
HCl
Gastric gland
HCl converts pepsinogen to pepsin.
Pepsin then activates more pepsinogen, starting a
chain reaction. Pepsin begins the
chemical digestion of proteins.
Mucus cells
Chief cells
Parietal cells
Parietal cell
Chief cell
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Digestion

• Food is turned into acid chyme
• Pyloric Sphincter allows small amounts to pass
  into small intestine
• Chyme enters small intestine
• Chyme mixes with pancreatic juice, bile, and
  enzymes from small intestine

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Side Trip 2

• Prancreatic juice
• Digestive enzymes and buffer
• From pancreas
• Bile
• From liver/gall bladder
• Aids in absorption and digestion
• Pigments from broken down red blood cells

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LE 41-19
Bile
Liver
Gall- bladder
Stomach
Acid chyme
Intestinal juice
Pancreatic
juice
Pancreas
Duodenum of small intestine
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Digestion

• Duodenum- first part of small intestine
• Where most chemical digestion is
• Villi (containing microvilli) absorb nutrients

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Side Trip 3

• Most absorption is in jejunum and ileum
• Amino acids and sugars enter capillaries
• Capillaries converge into the hepatic portal vein
• That goes to liver (1st shot at sugars

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LE 41-23
Key
Nutrient absorption
Microvilli (brush border)
Vein carrying blood to hepatic portal vessel
Blood capillaries
Epithelial cells
Muscle layers
Epithelial cells
Large circular folds
Lacteal
Villi
Lymph vessel
Villi
Intestinal wall
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Digestion

• Fats are converted, combine with cholesterol and
  enter lacteal (small vessels of lymphatic system)

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LE 41-24
Fat globule
Bile salts
Fat droplets coated with bile salts
Micelles made up of fatty acids, monoglycerides, a
nd bile salts
Epithelium of small intestine
Lacteal
Epithelium of lacteal
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Digestion

• Food enters large intestine/cecum
• Water is reabsorbed
• 12-24 hours
• Bacteria eat some unabsorbed food
• Produce hydrogen sulfide, methane, and some
  vitamins
• Feces pass through rectum and out

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LE 41-26
Incisors
Canines
Molars
Premolars
Carnivore
Herbivore
Omnivore
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LE 41-27
Small intestine
Stomach
Small intestine
Cecum
Colon (large intestine)
Carnivore
Herbivore
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LE 41-28
Intestine
Rumen
Reticulum
Esophagus
Abomasum
Omasum