Biology in Focus - Chapter 33

CAMPBELL BIOLOGY IN FOCUS
© 2014 Pearson Education, Inc.
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
33
Animal
Nutrition

 Food is taken in, taken apart, and taken up in the
process of animal nutrition
 In general, animals fall into three categories
 Herbivores eat mainly plants and algae
 Carnivores eat other animals
 Omnivores regularly consume animals as well as
plants or algae
 Most animals are also opportunistic feeders
Overview: The Need to Feed

Figure 33.1

Concept 33.1: An animal’s diet must supply
chemical energy, organic molecules, and essential
nutrients
 An animal’s diet provides
 Chemical energy, which is converted into ATP to
power cellular processes
 Organic building blocks, such as organic carbon and
organic nitrogen, to synthesize a variety of organic
molecules
 Essential nutrients, which are required by cells and
must be obtained from dietary sources

Essential Nutrients
 Essential nutrients must be obtained from an
animal’s diet
 There are four classes of essential nutrients
 Essential amino acids
 Essential fatty acids
 Vitamins
 Minerals

Figure 33.2
Iron cofactor
Essential
amino
acids
NADH coenzyme
(vitamin B3)
NADH
Fatty acid desaturase
γ-Linoleic acid
Phospholipids
Prostaglandins
Gly
Ile
Leu
Phe
Phe
Tyr
Glu
Linoleic acid

 In animals, fatty acids are converted into a variety of
cellular components, such as membrane
phospholipids, signaling molecules, and storage fats
 Essential fatty acids can be synthesized by plants
 Deficiencies of essential fatty acids are rare
Essential Fatty Acids and 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
 Meat, eggs, and cheese provide all the essential
amino acids and are thus “complete” proteins

 Most plant proteins are incomplete in amino acid
composition
 Individuals who eat only plant proteins need to eat
specific plant combinations to get all the essential
amino acids

Vitamins
 Vitamins are organic molecules required in the diet
in small amounts
 Thirteen vitamins are essential for humans
 Vitamins are grouped into two categories: fat-soluble
and water-soluble

Minerals
 Minerals are simple inorganic nutrients, usually
required in small amounts
 Ingesting large amounts of some minerals can
upset homeostatic balance

Dietary Deficiencies
 Malnutrition results from the long-term absence
from the diet of one or more essential nutrients

Deficiencies in Essential Nutrients
 Deficiencies in essential nutrients can cause
deformities, disease, and death
 Animals may consume salt, minerals, shells, or
stones to prevent mineral deficiencies

Figure 33.3

 A diet with insufficient amounts of one or more
amino acids is the most common type of
malnutrition among humans
 Individuals subsisting on simple rice diets are often
deficient in vitamin A
 To overcome this, scientists have engineered a
strain of rice that synthesizes beta-carotene, which
is converted to vitamin A in the body

 Undernutrition results when a diet does not provide
enough chemical energy
 An undernourished individual will
 Use up stored fat and carbohydrates
 Break down its own proteins
 Lose muscle mass
 Suffer protein deficiency of the brain
 Die or suffer irreversible damage
Undernutrition

Assessing Nutritional Needs
 Genetic defects that disrupt food uptake provide
information about human nutrition
 For example, hemochromatosis causes iron buildup
without excessive iron intake
 Insights into human nutrition have come from
epidemiology, the study of human health and
disease in populations
 Neural tube defects were found to be the result of a
deficiency in folic acid in pregnant mothers

Concept 33.2: The main stages of food processing
are ingestion, digestion, absorption, and
elimination
 Food processing can be divided into four distinct
stages

Figure 33.4
Mechanical
digestion
Nutrient molecules
enter body cells
Chemical
digestion
(enzymatic
hydrolysis)
Undigested
material
EliminationAbsorptionDigestionIngestion1 2 3 4

 Ingestion is the act of eating or feeding
 Strategies for extracting resources from food differ
widely among animals
Video: Shark Eating a Seal

Figure 33.5
Filter feeders Substrate feeders Fluid feeders
Bulk feeders
Caterpillar Feces
Baleen

Figure 33.5a
Filter feeders
Baleen

Figure 33.5b
Substrate feeders
Caterpillar Feces

Figure 33.5c
Fluid feeders

Figure 33.5d
Bulk feeders

 Digestion is the process of breaking food down into
molecules small enough to absorb
 Mechanical digestion, including chewing, increases
the surface area of food
 Chemical digestion splits food into small molecules
that can pass through membranes
 In chemical digestion, the process of enzymatic
hydrolysis splits bonds in molecules with the addition
of water

 Absorption is uptake of nutrients by body cells
 Elimination is the passage of undigested material
out of the digestive system

Digestive Compartments
 Most animals process food in specialized
compartments
 These compartments reduce the risk of an animal
digesting its own cells and tissues

Intracellular Digestion
 In intracellular digestion, food particles are engulfed
by phagocytosis
 Food vacuoles, containing food, fuse with
lysosomes containing hydrolytic enzymes

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
 Animals with simple body plans have a
gastrovascular cavity that functions in both
digestion and distribution of nutrients
Video: Hydra Eating

Figure 33.6
Mouth
Tentacles
Digestive enzymes
released
Food particles
broken down
Food particles
engulfed and digested
GastrodermisEpidermis
Food
1
2
3

 More complex animals have a complete digestive
tract or an alimentary canal with a mouth and an
anus
 The alimentary canal can have specialized regions
that carry out digestion and absorption in a stepwise
fashion

Figure 33.7
Crop
Gizzard
Intestine
Anus
Esophagus
Pharynx
Mouth
(a) Earthworm
Esophagus
Crop
Stomach
Gizzard
Intestine
Anus
Mouth
(c) Bird(b) Grasshopper
Mouth
Crop Gastric
cecae
Anus
RectumEsophagus
Foregut Midgut Hindgut

Concept 33.3: 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

Figure 33.8
Tongue
Salivary
glands
Liver
Gall-
bladder
Pancreas
Small
intestine
Large
intestine
Rectum
Anus
Oral cavity
Pharynx
Esophagus
Sphincter
Sphincter
Stomach
Liver
Pancreas
Gallbladder
Duodenum of
small intestine
Stomach
Small
intestine
Large
intestine
Rectum
Anus
Salivary
glands
Esophagus
Mouth

Figure 33.8a
Liver
Pancreas
Gallbladder
Stomach
Small
intestine
Large
intestine
Rectum
Anus
Salivary
glands
Esophagus
Mouth

 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

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 the oral cavity
through ducts
 Teeth chew food into smaller particles that are
exposed to salivary amylase, initiating breakdown
of glucose polymers
 Saliva also contains mucus, a viscous mixture of
water, salts, cells, and glycoproteins

 The tongue shapes food into a bolus and provides
help with swallowing
 The throat, or pharynx, is the junction that opens to
both the esophagus and the trachea
 The esophagus connects to the stomach
 The trachea (windpipe) leads to the lungs

 Swallowing must be carefully choreographed to
avoid choking
 The esophagus conducts food from the pharynx
down to the stomach through rhythmic cycles of
contraction
 The form of the esophagus fits its function and
varies among species

Digestion in the Stomach
 The stomach stores food and secretes gastric
juice, which converts a meal to a mixture of food
and digestive juice called chyme

Figure 33.9
Esophagus
Sphincter
Sphincter
Stomach
Folds of
epithelial
tissue
Small
intestine
Epithelium
Production of gastric
juice
Pepsinogen and
HCI secreted into
lumen
HCI converts
pepsinogen to
pepsin.
Pepsin activates
more pepsinogen,
starting a chain
reaction.
Parietal
cell
Pepsin
(active
enzyme)
Chief
cell
Pepsinogen
1
2
3
1
2
3
Gastric gland
Mucous cell
Chief cell
Parietal cell
Gastric pit
on the interior
surface of
stomach
10µm
HCI
H+
Cl−

Figure 33.9a
Gastric gland
Mucous cell
Chief cell
Parietal cell
Gastric pit
on the interior
surface of
stomach
Epithelium
Parietal
cell
Pepsin
(active
enzyme)
Chief
cell
HCI
H+
Cl−
Pepsinogen
1
2
3

Figure 33.9b-1
juice
Pepsinogen and
HCI secreted into
lumen
Parietal
cell
Chief
cell
HCI
H+
Cl−
Pepsinogen
1
1

Figure 33.9b-2
juice
Pepsinogen and
HCI secreted into
lumen
HCI converts
pepsinogen to
pepsin.
Parietal
cell
Pepsin
(active
enzyme)
Chief
cell
HCI
H+
Pepsinogen
2
1
1
2
Cl−

Figure 33.9b-3
juice
Pepsinogen and
HCI secreted into
lumen
HCI converts
pepsinogen to
pepsin.
Pepsin activates
more pepsinogen,
starting a chain
reaction.
Parietal
cell
Pepsin
(active
enzyme)
Chief
cell
HCI
H+
Pepsinogen
3
2
1
1
2
3
Cl−

Figure 33.9c
Gastric pit on the interior
surface of stomach
10µm

Chemical Digestion in the Stomach
 Gastric juice has a low pH of about 2, which kills
bacteria and denatures proteins
 Gastric juice is made up of hydrochloric acid (HCl)
and pepsin
 Pepsin is a protease, or protein-digesting enzyme,
that cleaves proteins into smaller peptides

Figure 33.10
Fat digestion
Fat
(triglycerides)
Glycerol,
fatty acids,
monoglycerides
Pancreatic
lipase
Pancreatic
nucleases
Nucleotidases
Pepsin
Pancreatic trypsin
and chymotrypsin
Pancreatic
carboxypeptidase
Dipeptidases,
carboxypeptidase,
and aminopeptidaseDisaccharidases
Pancreatic amylases
Disaccharides
Monosaccharides Amino acids
Small peptides
Smaller
polypeptides
Small polypeptides
Nucleotides
Nucleosides
Nitrogenous bases,
sugars, phosphates
Nucleosidases
and
phosphatases
DNA, RNA
Nucleic acid
digestion
Protein digestion
Proteins
MaltoseSmaller
polysaccharides
Polysaccharides
(starch, glycogen)
Disaccharides
(sucrose,
lactose)
Carbohydrate digestion
Oral cavity,
pharynx,
esophagus
Small
intestine
(enzymes
from
pancreas)
Stomach
Small
intestine
(enzymes
from
epithelium)
Salivary amylase

Figure 33.10a
MaltoseSmaller
polysaccharides
Polysaccharides
Oral cavity, pharynx, esophagus
Salivary amylase
Disaccharides

Figure 33.10b
Pepsin
Small polypeptides
Protein digestion
Proteins
Stomach
DisaccharidesMaltoseSmaller
polysaccharides

Figure 33.10c
Fat digestion
Fat
(triglycerides)
Glycerol,
fatty acids,
monoglycerides
Pancreatic
lipase
Pancreatic
nucleases
Pancreatic trypsin
and chymotrypsin
Pancreatic
carboxypeptidase
Pancreatic amylases
Disaccharides
Small
peptides
Smaller
polypeptides
Small polypeptides
Nucleotides
DNA, RNA
Small intestine (enzymes from pancreas)
Nucleic acid
digestion
Protein digestion
Polysaccharides Disaccha-
rides
Amino
acids

Figure 33.10d
NucleotidasesDipeptidases,
carboxypeptidase,
and aminopeptidase
Disaccharidases
Monosaccharides Amino acids
Nucleosides
Nitrogenous bases,
sugars, phosphates
Nucleosidases
and
phosphatases
Small intestine (enzymes from epithelium)
Nucleic acid
digestion
Protein digestionCarbohydrate digestion
Disaccharides Amino acidsSmall
peptides
Nucleotides

 Mucus protects the stomach lining from gastric juice
 Also, cell division adds a new epithelial layer every
three days, to replace any cells damaged by
digestive juices
 Gastric ulcers, lesions in the stomach lining, are
caused mainly by the bacterium Helicobacter pylori

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
 Stomach contents typically pass into the small
intestine 2–6 hours after a meal

Digestion in the Small Intestine
 The small intestine is the longest section of the
alimentary canal
 It is the major organ of digestion and absorption
 The first portion of the small intestine is the
duodenum
 Here, chyme from the stomach mixes with digestive
juices from the pancreas, liver, gallbladder, and the
intestinal wall

Pancreatic Secretions
 The pancreas produces proteases trypsin and
chymotrypsin, which are activated in the lumen of
the duodenum
 Its solution is alkaline and neutralizes the acidic
chyme

Bile Production by the Liver
 In the small intestine, bile aids in digestion and
absorption of fats
 Bile is made in the liver and stored in the
gallbladder
 Bile also destroys nonfunctional red blood cells

Secretions of the Small Intestine
 The epithelial lining of the duodenum 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

Figure 33.11
Vein carrying
blood to liver
Microvilli (brush
border) at apical
(lumenal) surface
Villi
Lumen
Basal
surface
Lymph
vessel
Capillary
Epithelial
cells
(toward
capillary)
Blood
capillaries
Epithelial
cells
Large
circular
folds
Muscle layers
Villi
Intestinal
wall
Nutrient
absorption
Lacteal

Figure 33.11a
Vein carrying
blood to liver
Large
circular
folds
Muscle layers
Villi
Intestinal
wall
Nutrient
absorption

Figure 33.11b
Microvilli (brush
border) at apical
(lumenal) surface
Villi
Lumen
Basal
surface
Lymph
vessel
Capillary
Epithelial
cells
(toward
capillary)
Blood
capillaries
Epithelial
cells
Lacteal
Nutrient
absorption

Absorption in the Small Intestine
 The small intestine has a huge surface area, due to
villi and microvilli that project into the intestinal
lumen
 The enormous microvillar surface creates a brush
border that greatly increases the rate of nutrient
absorption
 Transport across the epithelial cells can be passive
or active depending on the nutrient
Animation: Membrane Transport

Figure 33.12
Triglycerides
are broken down
to fatty acids and
monoglycerides
by lipase.
Monoglycerides
and fatty acids diffuse
into epithelial cells
and are re-formed into
triglycerides.
Triglycerides are
incorporated into
chylomicrons.
Chylomicrons enter
lacteals and are carried
away by lymph.
4
3
2
1
Triglycerides
Chylomicron
Lacteal
Phospholipids,
cholesterol,
and proteins
Triglycerides
Fatty acids
Mono-
glycerides
Epithelial
cell
LUMEN
OF SMALL
INTESTINE

Figure 33.12a
Triglycerides
are broken down
to fatty acids and
monoglycerides
by lipase.
Monoglycerides
and fatty acids diffuse
into epithelial cells
and are re-formed into
triglycerides.
1
Triglycerides
Fatty acids
Mono-
glycerides
Epithelial
cell
LUMEN
OF SMALL
INTESTINE
Triglycerides
2

Figure 33.12b
Triglycerides are
incorporated into
chylomicrons.
Chylomicrons enter
lacteals and are carried
away by lymph.
Chylomicron
Lacteal
Phospholipids,
cholesterol,
and proteins
Triglycerides
3
4

 The hepatic portal vein carries nutrient-rich blood
from the capillaries of the villi to the liver, then to
the heart
 The liver regulates nutrient distribution,
interconverts many organic molecules, and
detoxifies many organic molecules

 Epithelial cells absorb fatty acids and monoglycerides
and recombine them into triglycerides
 These fats are coated with phospholipids,
cholesterol, and proteins to form water-soluble
chylomicrons
 Chylomicrons are transported into a lacteal, a
lymphatic vessel in each villus
 Lymphatic vessels deliver chylomicron-containing
lymph to large veins that return blood to the heart

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

Figure 33.13
Ascending
portion
of colon
Small
intestine
Appendix
Cecum
Junction of the small and
large intestines

 A major function of the colon is to recover water
that has entered the alimentary canal
 The colon houses bacteria (e.g., Escherichia coli)
that live on unabsorbed organic material; some
produce vitamins
 Feces, including undigested material and bacteria,
become more solid as they move through the
colon

 Feces are stored in the rectum until they can be
eliminated through the anus
 Two sphincters between the rectum and anus
control bowel movements

Concept 33.4: Evolutionary adaptations of
vertebrate digestive systems correlate with diet
 Digestive systems of vertebrates are variations on
a common plan
 However, there are intriguing adaptations, often
related to diet

Dental Adaptations
 Dentition, an animal’s assortment of teeth, is one
example of structural variation reflecting diet
 The success of mammals is due in part to their
dentition, which is specialized for different diets
 Nonmammalian vertebrates have less specialized
teeth, though exceptions exist
 For example, the teeth of poisonous snakes are
modified as fangs for injecting venom

Figure 33.14
Carnivore Herbivore
Omnivore
Incisors Canines Premolars Molars

Mutualistic Adaptations
 Many herbivores have fermentation chambers in
their alimentary canals, where mutualistic
microorganisms digest cellulose
 Rabbits and some rodents harbor mutualistic
bacteria in their large intestines and ceca
 The most elaborate adaptations for an herbivorous
diet have evolved in the animals called ruminants,
including deer, sheep, and cattle

Figure 33.15
Rumen Reticulum
Esophagus
Omasum
Abomasum
Intestine

Stomach and Intestinal Adaptations
 Many carnivores have large, expandable stomachs
 Herbivores and omnivores generally have longer
alimentary canals than carnivores, reflecting the
longer time needed to digest vegetation

Figure 33.16
Small
intestine
Small intestine
Stomach
Cecum
Colon
(large
Intestine)Carnivore
Herbivore

Figure 33.16a

Figure 33.16b

Concept 33.5: Feedback circuits regulate
digestion, energy allocation, and appetite
 An animal’s intake of food and use of nutrients are
matched to circumstance and need

Regulation of Digestion
 Each step in the digestive system is activated as
needed
 The enteric division of the nervous system helps to
regulate the digestive process
 The endocrine system also regulates digestion
through the release and transport of hormones

Figure 33.17
Food
Stomach
GastrinGastric
juices
Pancreas
Liver
Gallbladder
Stimulation
Inhibition
1
Duodenum of
small intestine
Bile
Chyme
HCO3
−
, enzymes
32
CCK
CCK
Secretin
and CCK
Secretin
Gastric
juices

Figure 33.17a
Food
Stomach
GastrinGastric
juices
Pancreas
Liver
Gallbladder
Stimulation
Inhibition
1
Duodenum of
small intestine

Figure 33.17b
Bile
Chyme
HCO3
−
, enzymes
CCK
CCK
SecretinStimulation
Inhibition
2

Figure 33.17c
Secretin
and CCK
Gastric
juices
3
Stimulation
Inhibition

Energy Allocation
 The flow and transformation of energy in an animal
—its bioenergetics—determine nutritional needs
 An animal’s energy use per unit of time is called its
metabolic rate
 Metabolic rate can be determined by monitoring an
animal’s rate of heat loss, the amount of O2
consumed, or the amount of CO2 produced

Figure 33.18-1
Organic molecules
in food
Animal
body
External
environment

Figure 33.18-2
Organic molecules
in food
Heat
Energy
lost in
feces
Digestion and
absorption
Nutrient molecules
in body cells
Animal
body
External
environment

Figure 33.18-3
Organic molecules
in food
Heat
Energy
lost in
feces
Energy
lost in
nitrogenous
waste
Heat
Cellular
respiration
Digestion and
absorption
Nutrient molecules
in body cells
Animal
body
External
environment
Carbon
skeletons
ATP

Figure 33.18-4
Organic molecules
in food
Heat
Energy
lost in
feces
Energy
lost in
nitrogenous
waste
Heat
Cellular
respiration
Digestion and
absorption
Nutrient molecules
in body cells
Animal
body
External
environment
Carbon
skeletons
ATP
Bio-
synthesis
Cellular
work
Heat
Heat

Minimum Metabolic Rate
 Animals must maintain a minimum metabolic rate
for basic cell functions
 Basal metabolic rate, BMR, is the minimum
metabolic rate of a nongrowing endotherm that is at
rest, has an empty stomach, and is not experiencing
stress
 The metabolic rate of a fasting, nonstressed
ectotherm at a particular temperature is called
standard metabolic rate, SMR

 Endothermy is more energetically costly than
ectothermy
 For ectotherms and endotherms, activity greatly
affects metabolic rate

Regulation of Energy Storage
 When an animal takes in more energy than is needed
for metabolism and activity, excess energy is stored
 In humans, the liver and muscle cells are used first;
energy is stored as glycogen
 When glycogen depots are full, additional excess
energy is stored as fat in adipose cells
 When fewer calories are taken in than expended, the
body expends liver glycogen, muscle glycogen, and
then fat, in that order

Glucose Homeostasis
 Insulin and glucagon together maintain glucose
levels
 Insulin levels rise after a carbohydrate-rich meal, and
glucose entering the liver through the hepatic portal
vein is used to synthesize glycogen
 When glucose concentration is low in the hepatic
portal vein, glucagon stimulates the liver to break
down glycogen and release glucose into the blood
 Insulin and glucagon are produced in the pancreas in
beta cells and alpha cells, respectively
Animation: Homeostasis

Figure 33.19
Transport of
glucose into
body cells
and storage
of glucose
as glycogen
Breakdown of
glycogen and
release of
glucose into
blood
Secretion
of insulin by
pancreas
Secretion
of glucagon
by pancreas
Stimulus:
Blood glucose
level drops
below set point.
Stimulus:
Blood glucose
level rises
after eating.
Homeostasis:
70–110 mg glucose/
100 mL blood

Diabetes Mellitus
 Diabetes mellitus is a disease caused by a deficiency
of insulin or a decreased response to insulin in target
tissues
 Cells are unable to take up glucose to meet their
metabolic needs
 Fat becomes the main substrate for cellular
respiration

 Type 1 diabetes is an autoimmune disorder in which
the immune system destroys the pancreatic beta
cells
 Type 2 diabetes is characterized by a failure of
target cells to respond normally to insulin
 Heredity is a factor in type 2 diabetes
 Excess body weight and lack of exercise increase
the risk

Regulation of Appetite and Consumption
 Overnourishment causes obesity, which results from
excessive intake of food energy with the excess
stored as fat
 Obesity contributes to diabetes (type 2), cancer of
the colon and breasts, heart attacks, and strokes
 Researchers have discovered several of the
mechanisms that help regulate body weight

 Ghrelin, a hormone secreted by the stomach wall,
triggers a feeling of hunger before meals
 Insulin and PYY, a hormone secreted by the small
intestine after eating, both suppress appetite
 Leptin, a hormone produced by adipose (fat) tissue,
also suppresses appetite and may regulate body fat
levels

Figure 33.UN01a

Figure 33.UN01b

Figure 33.UN02
Veins to heart
Lymphatic system
Stomach
Lipids
Mouth
Esophagus
Small intestine
Hepatic portal vein
Liver
Absorbed
water
Absorbed food
(except lipids)
Anus
RectumLarge
intestine
Secretions from liver
Secretions from pancreas
Secretions
from gastric
glands
Secretions
from salivary
glands

Biology in Focus - Chapter 33

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