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Chapter 41
Animal Nutrition
Pages 884-890
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 41-1
Concept 41.3: Organs specialized for sequential
stages of food processing form the mammalian
digestive system
• The mammalian digestive system consists of
an alimentary canal and accessory glands that
secrete digestive juices through ducts
• Mammalian accessory glands are the salivary
glands, the pancreas, the liver, and the
gallbladder
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• Food is pushed along by peristalsis, rhythmic
contractions of muscles in the wall of the canal
• Valves called sphincters regulate the
movement of material between compartments
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 41-10a
Tongue
Sphincter
Oral cavity
Salivary glands
Pharynx
Esophagus
Sphincter
Liver
Stomach
Ascending
portion of
large intestine
Gallbladder
Duodenum of
small intestine
Pancreas
Small
intestine
Small
intestine
Large
intestine
Rectum
Anus
Appendix
Cecum
Fig. 41-10b
Salivary
glands
Mouth
Esophagus
Gallbladder
Liver
Pancreas
Stomach
Small
intestine
Large
intestine
Rectum
Anus
A schematic diagram of the
human digestive system
The Oral Cavity, Pharynx, and Esophagus
• The first stage of digestion is mechanical and
takes place in the oral cavity
• Salivary glands deliver saliva to lubricate food
• Teeth chew food into smaller particles that are
exposed to salivary amylase, initiating
breakdown of glucose polymers
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• The tongue shapes food into a bolus and
provides help with swallowing
• The region we call our throat is the pharynx, a
junction that opens to both the esophagus and
the trachea (windpipe)
• The trachea leads to the lungs
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• The esophagus conducts food from the
pharynx down to the stomach by peristalsis
• Swallowing causes the epiglottis to block
entry to the trachea, and the bolus is guided by
the larynx, the upper part of the respiratory
tract
• Coughing occurs when the swallowing reflex
fails and food or liquids reach the windpipe
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 41-11-1
Food
Epiglottis
up
Tongue
Pharynx
Esophageal
sphincter
contracted
Glottis
Larynx
Trachea
Esophagus
To To
lungs stomach
Fig. 41-11-2
Food
Epiglottis
up
Tongue
Pharynx
Esophageal
sphincter
contracted
Glottis
Larynx
Trachea
Epiglottis
down
Esophagus
To To
lungs stomach
Glottis up
and closed
Esophageal
sphincter
relaxed
Fig. 41-11-3
Food
Epiglottis
up
Tongue
Epiglottis
up
Pharynx
Esophageal
sphincter
contracted
Glottis
Larynx
Trachea
Epiglottis
down
Esophagus
To To
lungs stomach
Glottis up
and closed
Esophageal
sphincter
relaxed
Glottis
down
and open
Esophageal
sphincter
contracted
Relaxed
muscles
Relaxed
muscles
Contracted
muscles
Sphincter
relaxed
Stomach
Digestion in the Stomach
• The stomach stores food and secretes gastric
juice, which converts a meal to acid chyme
(ingested food and digestive juice)
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Chemical Digestion in the Stomach
• Gastric juice is made up of hydrochloric acid and the enzyme
pepsin ( a protease: an enzyme that digest proteins)
• pH of gastric juice is highly acidic (~2)
• The ingredients of gastric juice are kept inactive until released
into the lumen (cavity of the stomach)
• Parietal cells secrete hydrogen and chloride ions separately
• Chief cells secrete inactive pepsinogen, which is activated to
pepsin when mixed with hydrochloric acid in the stomach (by
clipping off a small portion and exposing its active site)
• Mucus: a viscous and slippery mixture of glycoproteins, cells,
salts and water.
• Mucus protects the stomach lining from gastric juice as well as to
acid-tolerant pathogens in food
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Fig. 41-12a
Esophagus
Sphincter
Stomach
5 µm
Sphincter
Interior surface
of stomach
Small
intestine
Folds of
epithelial
tissue
Fig. 41-12b
Interior surface
of stomach
Epithelium
3
Pepsinogen
2
1 Pepsinogen and HCl
are secreted.
HCl
Gastric gland
1
Mucus cells
Pepsin
H+
–
Cl
2 HCl converts
pepsinogen to pepsin.
3 Pepsin activates
more pepsinogen.
Chief cells
Chief cell
Parietal cells
Parietal cell
• Barry Marshall and Robin Warren, 1982
• Gastric ulcers, lesions in the stomach lining,
are caused mainly by the bacterium
Helicobacter pylori
• Nobel prize in 2005
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Stomach Dynamics
• Coordinated contraction and relaxation of
stomach muscle churn the stomach’s contents
• Sphincters prevent chyme from entering the
esophagus and regulate its entry into the small
intestine
• Acid reflux: a backflow of chyme from the
stomach to lower end of esophagus.
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Digestion in the Small Intestine
• Most enzymatic hydrolysis of macromolecules
from food occurs in the small intestine
• The small intestine is the longest section of
the alimentary canal (> 6 m)
• It is the major organ of digestion and
absorption
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Fig. 41-13
Carbohydrate digestion
Oral cavity,
pharynx,
esophagus
Protein digestion
Nucleic acid digestion
Fat digestion
Polysaccharides Disaccharides
(starch, glycogen)
(sucrose, lactose)
Salivary amylase
Smaller polysaccharides,
maltose
Stomach
Proteins
Pepsin
Small polypeptides
Lumen of
small intestine
Polysaccharides
Pancreatic amylases
Polypeptides
Pancreatic trypsin and
chymotrypsin
DNA, RNA
Fat globules
Pancreatic
nucleases
Bile salts
Maltose and other
disaccharides
Nucleotides
Fat droplets
Smaller
polypeptides
Pancreatic lipase
Pancreatic carboxypeptidase
Glycerol, fatty
acids, monoglycerides
Amino acids
Epithelium
of small
intestine
(brush
border)
Small peptides
Disaccharidases
Monosaccharides
Nucleotidases
Nucleosides
Dipeptidases, carboxypeptidase,
and aminopeptidase
Amino acids
Nucleosidases
and
phosphatases
Nitrogenous bases,
sugars, phosphates
Fig. 41-13a
Carbohydrate digestion
Oral cavity,
pharynx,
esophagus
Polysaccharides
Disaccharides
(starch, glycogen)
(sucrose, lactose)
Salivary amylase
Smaller polysaccharides,
maltose
Stomach
Polysaccharides
Lumen of
small
intestine
Epithelium
of small
intestine
(brush
border)
Pancreatic amylases
Maltose and other
disaccharides
Disaccharidases
Monosaccharides
Fig. 41-13b
Protein digestion
Stomach
Proteins
Pepsin
Small polypeptides
Polypeptides
Pancreatic trypsin and
chymotrypsin
Lumen of
small
intestine
Smaller
polypeptides
Pancreatic carboxypeptidase
Amino acids
Small peptides
Epithelium
of small
intestine
(brush
border)
Dipeptidases, carboxypeptidase,
and aminopeptidase
Monosaccharides
Amino acids
Fig. 41-13c
Nucleic acid digestion
DNA, RNA
Lumen of
small
intestine
Pancreatic
nucleases
Nucleotides
Nucleotidases
Epithelium
of small
intestine
(brush
border)
Nucleosides
Nucleosidases
and
phosphatases
Nitrogenous bases,
sugars, phosphates
Fig. 41-13d
Fat digestion
Fat globules
Bile salts
Lumen of
small
intestine
Fat droplets
Pancreatic lipase
Glycerol, fatty
acids, monoglycerides
• The first portion of the small intestine is the
duodenum, where acid chyme from the
stomach mixes with digestive juices from the
pancreas, liver, gallbladder, and the small
intestine itself
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Fig. 41-14
Liver
Gallbladder
Bile
When chyme rich in fats enters the
Duodenum , secretin and CCK inhibit
peristalsis and acid secretion thereby
slowing digestion
Stomach
Circulates back to the
stomach and stimulates
production of gastric
juices
Secretin
and CCK
–
Gastrin
+
CCK
+
Pancreas
Duodenum of
small intestine
Amino acids or fatty
acids trigger the release
of cholecytokinin (CCK)
which stimulates the
release of enzymes from
the pancreas and of bile
from the gallbladder
Secretin stimulates the
pancreas to release
sodium bicarbonate which
neutralizes chyme, act as
a buffer
Secretin
+
Key
CCK
+
+
–
Stimulation
Inhibition
Pancreatic Secretions
• The pancreas produces proteases trypsin and
chymotrypsin, protein-digesting enzymes that
are activated after entering the duodenum
• Its solution is alkaline (rich in bicarbonate) and
neutralizes the acidic chyme
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Bile Production by the Liver
• Bile is contains bile salts which act as
detergents that aid in digestion and absorption
of lipids in small intestine.
• Bile is made in the liver and stored and
concentrated in the gallbladder
• Liver breaks down toxins and helps balance
nutrient utilization
• Bile is important in the liver in destruction of red
blood cells that are no longer functional
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Secretions of the Small Intestine
• The epithelial lining of the duodenum, called
the brush border, produces several digestive
enzymes
• Enzymatic digestion is completed as peristalsis
moves the chyme and digestive juices along
the small intestine
• Most digestion occurs in the duodenum; the
jejunum and ileum function mainly in
absorption of nutrients and water
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Absorption in the Small Intestine
• The small intestine has a huge surface area,
due to villi (finger-like projections) and
microvilli that are exposed to the intestinal
lumen
• The enormous microvillar surface greatly
increases the rate of nutrient absorption
• Surface area ~ 300 m2.
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Fig. 41-15a
Vein carrying blood
to hepatic portal vein
Muscle layers
Large
circular
folds
Villi
Key
Nutrient
absorption
Intestinal wall
Fig. 41-15b
Microvilli (brush
border) at apical
(lumenal) surface Lumen
Blood
capillaries
Epithelial
cells
Basal
surface
Epithelial cells
Lacteal
Villi
Key
Nutrient
absorption
Lymph
vessel
• Each villus contains a network of blood vessels
and a small lymphatic vessel called a lacteal
• After glycerol and fatty acids are absorbed by
epithelial cells, they are recombined into fats
within these cells
• These fats are mixed with cholesterol and
coated with protein, forming molecules called
chylomicrons, which are transported into
lacteals
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Fig. 41-16
Lumen
of small
intestine
Triglycerides
Fatty acids
Monoglycerides
1. In the lumen, bile salts keep fat droplets
from coalescing. Within the droplets, fats are
broken down by the enzyme lipase
Epithelial
cell
2. After diffusing into epithelial cells,
monoglycerides and fatty acids are
reformed into fats
Triglycerides
Phospholipids,
cholesterol,
and proteins
Chylomicron
Lacteal
3. Triglycerides are incorporated into
water-soluble globules called chylomicrons
4. Chylomicrons leave epithelial cells by
exocytosis and enter lacteals, where they are
carried away by the lymph and later pass into
large veins
• Amino acids and sugars pass through the
epithelium of the small intestine and enter the
bloodstream (by active transport)
• Capillaries and veins from the lacteals
converge in the hepatic portal vein and
deliver blood to the liver and then on to the
heart
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Absorption in the Large Intestine
• The colon of the large intestine is connected
to the small intestine
• The cecum aids in the fermentation of plant
material and connects where the small and
large intestines meet
• The human cecum has an extension called the
appendix, which plays a very minor role in
immunity
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Fig. 41-17
• A major function of the colon is to recover
water that has entered the alimentary canal
• Wastes of the digestive tract, the feces,
become more solid as they move through the
colon
• Feces pass through the rectum and exit via the
anus
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• The colon houses strains of the bacterium
Escherichia coli, some of which produce
vitamins
• Feces are stored in the rectum until they can
be eliminated
• Two sphincters between the rectum and anus
control bowel movements
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The END
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings