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Chapter 41
Animal Nutrition
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: The Need to Feed
• Every meal reminds us that we are heterotrophs,
dependent on a regular supply of food
• In general, animals fall into three categories:
– Herbivores eat mainly autotrophs (plants and
algae)
– Carnivores eat other animals
– Omnivores regularly consume animals as well
as plants or algal matter
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• An adequate diet must satisfy three needs:
– Fuel for all cellular work
– Organic raw materials for biosynthesis
– Essential nutrients, substances that the animal
cannot make for itself
• Main feeding mechanisms: suspension feeding,
substrate feeding, fluid feeding, bulk feeding
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 41-2a
Baleen
LE 41-2b
Caterpillar
Feces
Video: Lobster Mouth Parts
Video: Shark Eating a Seal
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Concept 41.1: Homeostatic mechanisms manage
an animal’s energy budget
• Nearly all of an animal’s ATP generation is based
on oxidation of energy-rich molecules:
carbohydrates, proteins, and fats
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Glucose Regulation as an Example of Homeostasis
• Animals store excess calories as glycogen in the
liver and muscles and as fat
• Glucose is a major fuel for cells
• Hormones regulate glucose metabolism
• When fewer calories are taken in than are
expended, fuel is taken from storage and oxidized
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LE 41-3
STIMULUS:
Blood glucose
level rises
after eating.
Homeostasis:
90 mg glucose/
100 mL blood
STIMULUS:
Blood glucose
level drops
below set point.
Caloric Imbalance
• Undernourishment occurs in animals when their
diets are chronically deficient in calories
• Overnourishment, or obesity, results from
excessive intake, with excess stored as fat
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LE 41-4
100 µm
Obesity as a Human Health Problem
• The World Health Organization now recognizes
obesity as a major global health problem
• Obesity contributes to a number of health
problems, including diabetes, cardiovascular
disease, and colon and breast cancer
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• Researchers have discovered several of the
mechanisms that help regulate body weight
• Over the long term, homeostatic mechanisms are
feedback circuits that control the body’s storage
and metabolism of fat
• Hormones regulate long-term and short-term
appetite by affecting a “satiety center” in the brain
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LE 41-5
Ghrelin
Insulin
Leptin
PYY
• The complexity of weight control in humans is
evident from studies of the hormone leptin
• Mice that inherit a defect in the gene for leptin
become very obese
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Obesity and Evolution
• The problem of maintaining weight partly stems
from our evolutionary past, when fat hoarding was
a means of survival
• A species of birds called petrels become obese as
chicks due to the need to consume more calories
than they burn
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 41.2: An animal’s diet must supply
carbon skeletons and essential nutrients
• An animal must obtain carbon skeletons from its
food to build complex molecules
• Besides fuel and carbon skeletons, a diet must
supply essential nutrients in preassembled form
• A malnourished animal is missing one or more
essential nutrients in its diet
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• Herbivores may suffer mineral deficiencies if they
graze on plants in soil lacking key minerals
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Malnutrition is much more common than
undernutrition in human populations
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Essential Amino Acids
• Animals require 20 amino acids and can
synthesize about half from molecules in their diet
• The remaining amino acids, the essential amino
acids, must be obtained from food in
preassembled form
• A diet that provides insufficient essential amino
acids causes malnutrition called protein deficiency
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Most plant proteins are incomplete in amino acid
makeup
• Individuals who eat only plant proteins need to eat
a variety to get all essential amino acids
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LE 41-10
Essential amino acids for adults
Methionine
Valine
Threonine
Phenylalanine
Leucine
Corn (maize)
and other grains
Isoleucine
Tryptophan
Lysine
Beans
and other
legumes
• Some animals have adaptations that help them
through periods when their bodies demand
extraordinary amounts of protein
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Essential Fatty Acids
• Animals can synthesize most of the fatty acids
they need
• The essential fatty acids are certain unsaturated
fatty acids
• Deficiencies in fatty acids are rare
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Vitamins
• Vitamins are organic molecules required in the diet
in small amounts
• 13 vitamins essential to humans have been
identified
• Vitamins are grouped into two categories: fatsoluble and water-soluble
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Minerals
• Minerals are simple inorganic nutrients, usually
required in small amounts
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 41.3: The main stages of food processing
are ingestion, digestion, absorption, and elimination
• Ingestion is the act of eating
• Digestion is the process of breaking food down
into molecules small enough to absorb
• Absorption is uptake of nutrients by body cells
• Elimination is the passage of undigested material
out of the digestive compartment
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LE 41-12
Small
molecules
Pieces
of food
Mechanical
digestion
Chemical digestion
Nutrient
(enzymatic hydrolysis) molecules
enter body
cells
Undigested
material
Food
INGESTION
DIGESTION
ABSORPTION
ELIMINATION
Digestive Compartments
• Most animals process food in specialized
compartments
• These compartments reduce risk of self-digestion
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Intracellular Digestion
• In intracellular digestion, food particles are
engulfed by endocytosis and digested within food
vacuoles
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Extracellular Digestion
• Extracellular digestion is the breakdown of food
particles outside of cells
• It occurs in compartments that are continuous with
the outside of the animal’s body
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• Animals with simple body plans have a
gastrovascular cavity that functions in both
digestion and distribution of nutrients
Video: Hydra Eating Daphnia
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 41-13
Mouth
Tentacles
Gastrovascular
Food cavity
Epidermis
Mesoglea
Gastrodermis
Nutritive
muscular
cells
Flagella
Gland cells
Food vacuoles
Mesoglea
• More complex animals have a digestive tube with
two openings, a mouth and an anus
• This digestive tube is called a complete digestive
tract or an alimentary canal
• It can have specialized regions that carry out
digestion and absorption in a stepwise fashion
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LE 41-14a
Crop Gizzard
Intestine
Esophagus
Pharynx
Anus
Mouth
Typhlosole
Lumen of intestine
Earthworm
LE 41-14b
Foregut
Midgut
Esophagus
Hindgut
Rectum
Anus
Crop
Mouth
Grasshopper
Gastric ceca
LE 41-14c
Esophagus
Stomach
Gizzard
Intestine
Mouth
Crop
Anus
Bird
Concept 41.4: Each organ of the mammalian digestive
system has specialized food-processing functions
• 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
• Food is pushed along by peristalsis, rhythmic
contractions of muscles in the wall of the canal
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 41-15a
Cardiac
orifice
Tongue
Salivary
glands
Oral cavity
Parotid gland
Sublingual gland
Pharynx
Esophagus
Submandibular gland
Pyloric
sphincter
Liver
Stomach
Ascending
portion of
large intestine
Gallbladder
Pancreas
Ileum
of small
intestine
Small
intestine
Large
intestine
Rectum
Anus
Appendix
Cecum
Duodenum of
small intestine
LE 41-15b
Salivary
glands
Mouth
Esophagus
Gallbladder
Liver
Pancreas
Stomach
Small
intestines
Large
intestines
Rectum
Anus
A schematic diagram of the
human digestive system
The Oral Cavity, Pharynx, and Esophagus
• In the oral cavity, food is lubricated and digestion
begins
• Teeth chew food into smaller particles that are
exposed to salivary amylase, initiating breakdown
of glucose polymers
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• The region we call our throat is the pharynx, a
junction that opens to both the esophagus and the
windpipe (trachea)
• The esophagus conducts food from the pharynx
down to the stomach by peristalsis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 41-16_3
Bolus of food
Tongue
Epiglottis
up
Epiglottis
up
Pharynx
Glottis
Larynx
Trachea
Glottis
down
and open
Esophageal
sphincter
contracted
Epiglottis
down
Esophagus
Glottis up
and closed
Esophageal
sphincter
relaxed
Esophageal
sphincter
contracted
Relaxed
muscles
To lungs To stomach
Contracted
muscles
Relaxed
muscles
Stomach
The Stomach
• The stomach stores food and secretes gastric
juice, which converts a meal to acid chyme
• Gastric juice is made up of hydrochloric acid and
the enzyme pepsin
• Pepsin is secreted as inactive pepsinogen; pepsin
is activated when mixed with hydrochloric acid in
the stomach
• Mucus protects the stomach lining from gastric
juice
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 41-17
Esophagus
Cardiac orifice
Stomach
5 µm
Pyloric sphincter
Interior surface of stomach
Small
intestine
Folds of
epithelial
tissue
Epithelium
Pepsinogen
Gastric gland
Pepsin
(active enzyme)
HCl
Pepsinogen and HCl
are secreted into the
lumen of the stomach.
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
Chief cell
Parietal cell
• Gastric ulcers, lesions in the lining, are caused
mainly by the bacterium Helicobacter pylori
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LE 41-18
Bacteria
1 µm
Mucus
layer of
stomach
The Small Intestine
• The small intestine is the longest section of the
alimentary canal
• It is the major organ of digestion and absorption
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Enzymatic Action in the Small Intestine
• 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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LE 41-19
Liver
Bile
Gallbladder
Stomach
Acid chyme
Intestinal
juice
Pancreas
Duodenum of
small intestine
• The pancreas produces proteases, proteindigesting enzymes that are activated after entering
the duodenum
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 41-20
Pancreas
Membrane-bound
enteropeptidase
Inactive
trypsinogen
Other inactive
proteases
Lumen of duodenum
Trypsin
Active
proteases
• The liver produces bile, which aids in digestion
and absorption of fats
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 41-21
Carbohydrate digestion
Protein digestion
Nucleic acid digestion
Fat digestion
Oral cavity, Polysaccharides Disaccharides
pharynx,
Salivary amylase
esophagus
Smaller polysaccharides, maltose
Stomach
Proteins
Pepsin
Small polypeptides
Lumen of
small intestine
Polysaccharides
Polypeptides
Pancreatic amylases
Pancreatic trypsin
and chymotrypsin
Maltose and other
disaccharides
DNA, RNA
Pancreatic
nucleases
Nucleotides
Pancreatic carboxypeptidase
Pancreatic lipase
Amino acids
Disaccharidases
Monosaccharides
Bile salts
Fat droplets
Smaller polypeptides
Epithelium
of small
intestine
(brush
border)
Fat globules
Glycerol, fatty
acids, glycerides
Small peptides
Nucleotidases
Dipeptidases, carboxypeptidase, and
aminopeptidase
Nucleosides
Amino acids
Nucleosidases
and phosphatases
Nitrogenous bases,
sugars, phosphates
• Hormones help coordinate the secretion of
digestive juices into the alimentary canal
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 41-22
Key
Liver
Stimulation
Enterogastrone
Inhibition
Gallbladder
Gastrin
CCK
Stomach
Pancreas
Secretin
Duodenum
CCK
Absorption of Nutrients
• The small intestine has a huge surface area, due
to villi and microvilli that are exposed to the
intestinal lumen
• The enormous microvillar surface greatly
increases the rate of nutrient absorption
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 41-23
Key
Vein carrying blood
to hepatic portal
vessel
Nutrient
absorption
Microvilli
(brush border)
Blood
capillaries
Epithelial
cells
Muscle layers
Epithelial cells
Large
circular
folds
Villi
Lacteal
Villi
Intestinal wall
Lymph
vessel
• Each villus contains a network of blood vessels
and a small lymphatic vessel called a lacteal
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Amino acids and sugars pass through the
epithelium of the small intestine and enter the
bloodstream
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 41-24
Fat globule
Bile salts
Fat droplets
coated with
bile salts
Micelles made
up of fatty acids,
monoglycerides,
and bile salts
Epithelium
of small
intestine
Epithelium
of lacteal
Lacteal
The Large Intestine
• The large intestine, or colon, is connected to the
small intestine
• Its major function 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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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The colon houses strains of the bacterium
Escherichia coli, some of which produce vitamins
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Concept 41.5: Evolutionary adaptations of vertebrate
digestive systems are often associated with diet
• Digestive systems of vertebrates are variations on
a common plan
• However, there are intriguing adaptations, often
related to diet
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Some Dental Adaptations
• Dentition, an animal’s assortment of teeth, is one
example of structural variation reflecting diet
• Mammals have specialized dentition that best
enables them to ingest their usual diet
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LE 41-26
Incisors
Molars
Canines
Premolars
Carnivore
Herbivore
Omnivore
Stomach and Intestinal Adaptations
• Herbivores generally have longer alimentary
canals than carnivores, reflecting the longer time
needed to digest vegetation
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LE 41-27
Small intestine
Stomach
Small
intestine
Cecum
Colon
(large
intestine)
Carnivore
Herbivore
Symbiotic Adaptations
• Many herbivores have fermentation chambers,
where symbiotic microorganisms digest cellulose
• The most elaborate adaptations for an herbivorous
diet have evolved in the animals called ruminants
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LE 41-28
Intestine
Rumen
Reticulum
Esophagus
Abomasum
Omasum