Transcript small intestine - HCC Learning Web

LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 40
Basic Principles of Animal Form
and Function
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: Diverse Forms, Common
Challenges
• Anatomy is the study of the biological form of an
organism
• Physiology is the study of the biological
functions an organism performs
• The comparative study of animals reveals that
form and function are closely correlated
© 2011 Pearson Education, Inc.
Concept 40.1: Animal form and function
are correlated at all levels of organization
• Size and shape affect the way an animal interacts
with its environment
• Many different animal body plans have evolved
and are determined by the genome
© 2011 Pearson Education, Inc.
Evolution of Animal Size and Shape
• Physical laws constrain strength, diffusion,
movement, and heat exchange
• As animals increase in size, their skeletons must
be proportionately larger to support their mass
• Evolutionary convergence reflects different
species’ adaptations to a similar environmental
challenge
© 2011 Pearson Education, Inc.
Figure 40.2
Seal
Penguin
Tuna
Exchange with the Environment
• Materials such as nutrients, waste products, and
gases must be exchanged across the cell
membranes of animal cells
• Rate of exchange is proportional to a cell’s
surface area while amount of exchange material
is proportional to a cell’s volume
© 2011 Pearson Education, Inc.
• A single-celled protist living in water has a
sufficient surface area of plasma membrane to
service its entire volume of cytoplasm
• Multicellular organisms with a saclike body plan
have body walls that are only two cells thick,
facilitating diffusion of materials
© 2011 Pearson Education, Inc.
Figure 40.3
Mouth
Gastrovascular
cavity
Exchange
Exchange
Exchange
0.1 mm
1 mm
(a) Single cell
(b) Two layers of cells
• In flat animals such as tapeworms, the distance
between cells and the environment is minimized
• More complex organisms have highly folded
internal surfaces for exchanging materials
© 2011 Pearson Education, Inc.
Figure 40.4
External environment
CO2 O
Food
2
Mouth
Respiratory
system
Heart
Interstitial
fluid
Circulatory
system
Anus
Unabsorbed
matter (feces)
Metabolic waste products
(nitrogenous waste)
50 m
Excretory
system
100 m
Lining of small
intestine (SEM)
Lung tissue (SEM)
Cells
Digestive
system
Nutrients
250 m
Animal
body
Blood vessels in
kidney (SEM)
• In vertebrates, the space between cells is filled
with interstitial fluid, which allows for the
movement of material into and out of cells
• A complex body plan helps an animal living in a
variable environment to maintain a relatively
stable internal environment
© 2011 Pearson Education, Inc.
Hierarchical Organization of Body Plans
• Most animals are composed of specialized cells
organized into tissues that have different
functions
• Tissues make up organs, which together make
up organ systems
• Some organs, such as the pancreas, belong to
more than one organ system
© 2011 Pearson Education, Inc.
Table 40.1
Exploring Structure and Function in
Animal Tissues
• Different tissues have different structures that are
suited to their functions
• Tissues are classified into four main categories:
epithelial, connective, muscle, and nervous
© 2011 Pearson Education, Inc.
Epithelial Tissue
• Epithelial tissue covers the outside of the body
and lines the organs and cavities within the body
• It contains cells that are closely joined
• The shape of epithelial cells may be cuboidal (like
dice), columnar (like bricks on end), or squamous
(like floor tiles)
© 2011 Pearson Education, Inc.
• The arrangement of epithelial cells may be simple
(single cell layer), stratified (multiple tiers of
cells), or pseudostratified (a single layer of cells
of varying length)
© 2011 Pearson Education, Inc.
Figure 40.5aa
Epithelial Tissue
Stratified squamous
epithelium
Cuboidal
epithelium
Simple columnar
epithelium
Simple squamous
epithelium
Pseudostratified
columnar
epithelium
Figure 40.5ab
Apical surface
Basal surface
40 m
Basal lamina
Polarity of epithelia
Connective Tissue
• Connective tissue mainly binds and supports
other tissues
• It contains sparsely packed cells scattered
throughout an extracellular matrix
• The matrix consists of fibers in a liquid, jellylike,
or solid foundation
© 2011 Pearson Education, Inc.
• There are three types of connective tissue fiber,
all made of protein:
– Collagenous fibers provide strength and
flexibility
– Elastic fibers stretch and snap back to their
original length
– Reticular fibers join connective tissue to
adjacent tissues
© 2011 Pearson Education, Inc.
• Connective tissue contains cells, including
– Fibroblasts that secrete the protein of
extracellular fibers
– Macrophages that are involved in the
immune system
© 2011 Pearson Education, Inc.
• In vertebrates, the fibers and foundation combine
to form six major types of connective tissue:
– Loose connective tissue binds epithelia to
underlying tissues and holds organs in place
– Cartilage is a strong and flexible support
material
– Fibrous connective tissue is found in
tendons, which attach muscles to bones,
and ligaments, which connect bones at joints
© 2011 Pearson Education, Inc.
– Adipose tissue stores fat for insulation
and fuel
– Blood is composed of blood cells and cell
fragments in blood plasma
– Bone is mineralized and forms the
skeleton
© 2011 Pearson Education, Inc.
Figure 40.5ba
Connective Tissue
Loose connective tissue
Blood
Collagenous fiber
Plasma
55 m
120 m
White
blood cells
Elastic fiber
Red blood cells
Cartilage
Fibrous connective tissue
30 m
100 m
Chondrocytes
Chondroitin sulfate
Nuclei
Adipose tissue
Central
canal
Fat droplets
Osteon
150 m
700 m
Bone
Muscle Tissue
• Muscle tissue consists of long cells called
muscle fibers, which contract in response to
nerve signals
© 2011 Pearson Education, Inc.
• It is divided in the vertebrate body into three
types:
– Skeletal muscle, or striated muscle, is
responsible for voluntary movement
– Smooth muscle is responsible for involuntary
body activities
– Cardiac muscle is responsible for contraction
of the heart
© 2011 Pearson Education, Inc.
Figure 40.5ca
Muscle Tissue
Skeletal muscle
Nuclei
Muscle
fiber
Sarcomere
100 m
Smooth muscle
Nucleus
Muscle fibers
Cardiac muscle
25 m
Nucleus
Intercalated disk
50 m
Nervous Tissue
• Nervous tissue senses stimuli and transmits
signals throughout the animal
• Nervous tissue contains
– Neurons, or nerve cells, that transmit nerve
impulses
– Glial cells, or glia, that help nourish,
insulate, and replenish neurons
© 2011 Pearson Education, Inc.
Figure 40.5da
Nervous Tissue
Neurons
Glia
Glia
Neuron:
Dendrites
Cell body
Axons of
neurons
40 m
Axon
Blood
vessel
(Fluorescent LM)
(Confocal LM)
15 m
Coordination and Control
• Control and coordination within a body depend on
the endocrine system and the nervous system
• The endocrine system transmits chemical signals
called hormones to receptive cells throughout
the body via blood
• A hormone may affect one or more regions
throughout the body
• Hormones are relatively slow acting, but can
have long-lasting effects
© 2011 Pearson Education, Inc.
Figure 40.6
• The nervous system transmits information
between specific locations
• The information conveyed depends on a signal’s
pathway, not the type of signal
• Nerve signal transmission is very fast
• Nerve impulses can be received by neurons,
muscle cells, endocrine cells, and exocrine cells
© 2011 Pearson Education, Inc.
Concept 40.2: Feedback control maintains
the internal environment in many animals
• Animals manage their internal environment by
regulating or conforming to the external
environment
© 2011 Pearson Education, Inc.
Regulating and Conforming
• A regulator uses internal control mechanisms to
moderate internal change in the face of external,
environmental fluctuation
• A conformer allows its internal condition to vary
with certain external changes
• Animals may regulate some environmental
variables while conforming to others
© 2011 Pearson Education, Inc.
Figure 40.7
Homeostasis
• Organisms use homeostasis to maintain a
“steady state” or internal balance regardless of
external environment
• In humans, body temperature, blood pH, and
glucose concentration are each maintained at a
constant level
© 2011 Pearson Education, Inc.
Mechanisms of Homeostasis
• Mechanisms of homeostasis moderate changes
in the internal environment
• For a given variable, fluctuations above or below
a set point serve as a stimulus; these are
detected by a sensor and trigger a response
• The response returns the variable to the set point
© 2011 Pearson Education, Inc.
Figure 40.8
Feedback Control in Homeostasis
• The dynamic equilibrium of homeostasis is
maintained by negative feedback, which helps to
return a variable to a normal range
• Most homeostatic control systems function by
negative feedback, where buildup of the end
product shuts the system off
• Positive feedback amplifies a stimulus and does
not usually contribute to homeostasis in animals
© 2011 Pearson Education, Inc.
Alterations in Homeostasis
• Set points and normal ranges can change with
age or show cyclic variation
• In animals and plants, a circadian rhythm
governs physiological changes that occur roughly
every 24 hours
© 2011 Pearson Education, Inc.
Figure 40.9
• Homeostasis can adjust to changes in external
environment, a process called acclimatization
© 2011 Pearson Education, Inc.
Concept 40.3: Homeostatic processes for
thermoregulation involve form, function,
and behavior
• Thermoregulation is the process by which
animals maintain an internal temperature within a
tolerable range
© 2011 Pearson Education, Inc.
Endothermy and Ectothermy
• Endothermic animals generate heat by
metabolism; birds and mammals are endotherms
• Ectothermic animals gain heat from external
sources; ectotherms include most invertebrates,
fishes, amphibians, and nonavian reptiles
© 2011 Pearson Education, Inc.
• In general, ectotherms tolerate greater variation
in internal temperature, while endotherms are
active at a greater range of external temperatures
• Endothermy is more energetically expensive than
ectothermy
© 2011 Pearson Education, Inc.
Figure 40.10
Variation in Body Temperature
• The body temperature of a poikilotherm varies
with its environment
• The body temperature of a homeotherm is
relatively constant
• The relationship between heat source and body
temperature is not fixed (that is, not all
poikilotherms are ectotherms)
© 2011 Pearson Education, Inc.
Balancing Heat Loss and Gain
• Organisms exchange heat by four physical
processes: radiation, evaporation, convection,
and conduction
© 2011 Pearson Education, Inc.
Figure 40.11
• Heat regulation in mammals often involves the
integumentary system: skin, hair, and nails
• Five adaptations help animals thermoregulate:
–
–
–
–
–
Insulation
Circulatory adaptations
Cooling by evaporative heat loss
Behavioral responses
Adjusting metabolic heat production
© 2011 Pearson Education, Inc.
Insulation
• Insulation is a major thermoregulatory adaptation
in mammals and birds
• Skin, feathers, fur, and blubber reduce heat flow
between an animal and its environment
• Insulation is especially important in marine
mammals such as whales and walruses
© 2011 Pearson Education, Inc.
Circulatory Adaptations
• Regulation of blood flow near the body surface
significantly affects thermoregulation
• Many endotherms and some ectotherms can alter
the amount of blood flowing between the body
core and the skin
• In vasodilation, blood flow in the skin increases,
facilitating heat loss
• In vasoconstriction, blood flow in the skin
decreases, lowering heat loss
© 2011 Pearson Education, Inc.
• The arrangement of blood vessels in many
marine mammals and birds allows for
countercurrent exchange
• Countercurrent heat exchangers transfer heat
between fluids flowing in opposite directions and
reduce heat loss
© 2011 Pearson Education, Inc.
Figure 40.12
• Some bony fishes and sharks also use
countercurrent heat exchanges
• Many endothermic insects have countercurrent
heat exchangers that help maintain a high
temperature in the thorax
© 2011 Pearson Education, Inc.
Cooling by Evaporative Heat Loss
• Many types of animals lose heat through
evaporation of water from their skin
• Panting increases the cooling effect in birds and
many mammals
• Sweating or bathing moistens the skin, helping to
cool an animal down
© 2011 Pearson Education, Inc.
Behavioral Responses
• Both endotherms and ectotherms use behavioral
responses to control body temperature
• Some terrestrial invertebrates have postures that
minimize or maximize absorption of solar heat
© 2011 Pearson Education, Inc.
Figure 40.13
Adjusting Metabolic Heat Production
• Thermogenesis is the adjustment of metabolic
heat production to maintain body temperature
• Thermogenesis is increased by muscle activity
such as moving or shivering
• Nonshivering thermogenesis takes place when
hormones cause mitochondria to increase their
metabolic activity
• Some ectotherms can also shiver to increase
body temperature
© 2011 Pearson Education, Inc.
Acclimatization in Thermoregulation
• Birds and mammals can vary their insulation to
acclimatize to seasonal temperature changes
• When temperatures are subzero, some
ectotherms produce “antifreeze” compounds to
prevent ice formation in their cells
© 2011 Pearson Education, Inc.
Physiological Thermostats and Fever
• Thermoregulation is controlled by a region of
the brain called the hypothalamus
• The hypothalamus triggers heat loss or heat
generating mechanisms
• Fever is the result of a change to the set point
for a biological thermostat
© 2011 Pearson Education, Inc.
Figure 40.16
Concept 40.4: Energy requirements are
related to animal size, activity, and
environment
• Bioenergetics is the overall flow and
transformation of energy in an animal
• It determines how much food an animal needs
and it relates to an animal’s size, activity, and
environment
© 2011 Pearson Education, Inc.
Energy Allocation and Use
• Animals harvest chemical energy from food
• Energy-containing molecules from food are
usually used to make ATP, which powers cellular
work
• After the needs of staying alive are met,
remaining food molecules can be used in
biosynthesis
• Biosynthesis includes body growth and repair,
synthesis of storage material such as fat, and
production of gametes
© 2011 Pearson Education, Inc.
Figure 40.17
Quantifying Energy Use
• Metabolic rate is the amount of energy an
animal uses in a unit of time
• Metabolic rate can be determined by
– An animal’s heat loss
– The amount of oxygen consumed or carbon
dioxide produced
© 2011 Pearson Education, Inc.
Minimum Metabolic Rate and
Thermoregulation
• Basal metabolic rate (BMR) is the metabolic
rate of an endotherm at rest at a “comfortable”
temperature
• Standard metabolic rate (SMR) is the metabolic
rate of an ectotherm at rest at a specific
temperature
• Both rates assume a nongrowing, fasting, and
nonstressed animal
• Ectotherms have much lower metabolic rates
than endotherms of a comparable size
© 2011 Pearson Education, Inc.
Influences on Metabolic Rate
• Metabolic rates are affected by many factors
besides whether an animal is an endotherm or
ectotherm
• Two of these factors are size and activity
© 2011 Pearson Education, Inc.
Size and Metabolic Rate
• Metabolic rate is proportional to body mass to the
power of three quarters (m3/4)
• Smaller animals have higher metabolic rates per
gram than larger animals
• The higher metabolic rate of smaller animals
leads to a higher oxygen delivery rate, breathing
rate, heart rate, and greater (relative) blood
volume, compared with a larger animal
© 2011 Pearson Education, Inc.
Figure 40.19
Activity and Metabolic Rate
• Activity greatly affects metabolic rate for
endotherms and ectotherms
• In general, the maximum metabolic rate an
animal can sustain is inversely related to the
duration of the activity
© 2011 Pearson Education, Inc.
Energy Budgets
• Different species use energy and materials in
food in different ways, depending on their
environment
• Use of energy is partitioned to BMR (or SMR),
activity, thermoregulation, growth, and
reproduction
© 2011 Pearson Education, Inc.
Figure 40.20
Torpor and Energy Conservation
• Torpor is a physiological state in which activity is
low and metabolism decreases
• Torpor enables animals to save energy while
avoiding difficult and dangerous conditions
• Hibernation is long-term torpor that is an
adaptation to winter cold and food scarcity
© 2011 Pearson Education, Inc.
Figure 40.21
• Summer torpor, called estivation, enables
animals to survive long periods of high
temperatures and scarce water
• Daily torpor is exhibited by many small mammals
and birds and seems adapted to feeding patterns
© 2011 Pearson Education, Inc.
LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 41
Animal Nutrition
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: The Need to Feed
• 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
© 2011 Pearson Education, Inc.
Concept 41.1: 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
© 2011 Pearson Education, Inc.
Essential Nutrients
• There are four classes of essential nutrients:
–
–
–
–
Essential amino acids
Essential fatty acids
Vitamins
Minerals
© 2011 Pearson Education, Inc.
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
• Meat, eggs, and cheese provide all the essential
amino acids and are thus “complete” proteins
© 2011 Pearson Education, Inc.
• 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
• Some animals have adaptations that help them
through periods when their bodies demand
extraordinary amounts of protein
© 2011 Pearson Education, Inc.
Essential Fatty Acids
• Animals can synthesize most of the fatty acids
they need
• The essential fatty acids must be obtained from
the diet and include certain unsaturated fatty
acids (i.e., fatty acids with one or more double
bonds)
• Deficiencies in fatty acids are rare
© 2011 Pearson Education, Inc.
Vitamins
• Vitamins are organic molecules required in the
diet in small amounts
• Thirteen vitamins are essential for humans
• Vitamins are grouped into two categories: fatsoluble and water-soluble
© 2011 Pearson Education, Inc.
Table 41.1
Minerals
• Minerals are simple inorganic nutrients, usually
required in small amounts
• Ingesting large amounts of some minerals can
upset homeostatic balance
© 2011 Pearson Education, Inc.
Table 41.2
Dietary Deficiencies
• Malnourishment is the long-term absence from
the diet of one or more essential nutrients
© 2011 Pearson Education, Inc.
Deficiencies in Essential Nutrients
• Deficiencies in essential nutrients can cause
deformities, disease, and death
• “Golden Rice” is an engineered strain of rice
with beta-carotene, which is converted to
vitamin A in the body
© 2011 Pearson Education, Inc.
Undernutrition
• 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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Concept 41.2: The main stages of food
processing are ingestion, digestion,
absorption, and elimination
• Ingestion is the act of eating
© 2011 Pearson Education, Inc.
Figure 41.5
Mechanical
digestion
1 Ingestion
Nutrient molecules
enter body cells
Chemical
digestion
(enzymatic
hydrolysis)
2 Digestion
Undigested
material
3 Absorption
4 Elimination
Suspension Feeders
• Many aquatic animals are suspension feeders,
which sift small food particles from the water
© 2011 Pearson Education, Inc.
Figure 41.6
Suspension Feeders and Filter Feeders
Baleen
Substrate
Feeders
Fluid Feeders
Caterpillar Feces
Bulk Feeders
Bulk Feeders
• Bulk feeders eat relatively large pieces of food
© 2011 Pearson Education, Inc.
Figure 41.6d
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;
these are used to build larger molecules
• In chemical digestion, the process of enzymatic
hydrolysis splits bonds in molecules with the
addition of water
© 2011 Pearson Education, Inc.
• Absorption is uptake of nutrients by body cells
• Elimination is the passage of undigested
material out of the digestive system
© 2011 Pearson Education, Inc.
Digestive Compartments
• Most animals process food in specialized
compartments
• These compartments reduce the risk of an
animal digesting its own cells and tissues
© 2011 Pearson Education, Inc.
Intracellular Digestion
• In intracellular digestion, food particles are
engulfed by phagocytosis
• Food vacuoles, containing food, fuse with
lysosomes containing hydrolytic enzymes
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 41.7
Mouth
Tentacles
Food
1 Digestive
enzymes released
2 Food
particles broken
down
3 Food particles
engulfed and
digested
Epidermis
Gastrodermis
• 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
© 2011 Pearson Education, Inc.
Figure 41.8
Esophagus
Crop
Gizzard
Intestine
Pharynx
Anus
Mouth
(a) Earthworm
Foregut Midgut Hindgut
Esophagus
Rectum
Anus
Esophagus
Crop
Stomach
Gizzard
Intestine
Mouth
Anus
Crop
Gastric cecae
Mouth
(b) Grasshopper
(c) Bird
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
© 2011 Pearson Education, Inc.
• 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
© 2011 Pearson Education, Inc.
Figure 41.9
Tongue
Oral cavity
Salivary
glands
Mouth
Pharynx
Esophagus
Salivary
glands
Esophagus
Liver
Sphincter
Gallbladder
Pancreas
Small
intestine
Large
intestine
Rectum
Anus
Sphincter
Stomach
Gallbladder
Liver
Pancreas
Stomach
Small
intestine
Large
intestine
Rectum
Anus
Schematic diagram
Duodenum of
small intestine
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
• Saliva also contains mucus, a viscous mixture of
water, salts, cells, and glycoproteins
© 2011 Pearson Education, Inc.
• 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
© 2011 Pearson Education, Inc.
• 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
© 2011 Pearson Education, Inc.
Figure 41.10-3
Tongue
Bolus of
food
Pharynx
Epiglottis
up
Glottis
Larynx
Trachea
Esophageal
sphincter
contracted
Esophagus
To lungs To stomach
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
• Parietal cells secrete hydrogen and chloride ions
separately into the lumen (cavity) of the stomach
• Chief cells secrete inactive pepsinogen, which
is activated to pepsin when mixed with
hydrochloric acid in the stomach
• Mucus protects the stomach lining from gastric
juice
© 2011 Pearson Education, Inc.
Figure 41.11
Esophagus
Sphincter
Stomach
10 m
Sphincter
Gastric pits on
interior surface
of stomach
Small
intestine
Folds of
epithelial
tissue
Epithelium
3
Pepsinogen
Pepsin
2
Gastric gland
Mucous cell
Chief cell
Parietal cell
HCl
Chief
cell
1
Cl
H
Parietal
cell
• Gastric ulcers, lesions in the lining, are caused
mainly by the bacterium Heliobacter pylori
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 41.12-4
Carbohydrate digestion
Oral cavity,
Polysaccharides Disaccharides
pharynx,
esophagus
Salivary amylase
Smaller
Maltose
polysaccharides
Stomach
Protein digestion
Proteins
Pepsin
Small polypeptides
Small
intestine
(enzymes
from
pancreas)
Pancreatic amylases
Pancreatic trypsin and
chymotrypsin
Nucleic acid digestion
Fat digestion
DNA, RNA
Fat (triglycerides)
Pancreatic
nucleases
Disaccharides
Smaller
polypeptides
Nucleotides
Pancreatic lipase
Pancreatic carboxypeptidase
Glycerol, fatty acids,
monoglycerides
Small peptides
Small
intestine
(enzymes
from
epithelium)
Disaccharidases
Dipeptidases, carboxypeptidase, and
aminopeptidase
Nucleotidases
Nucleosides
Nucleosidases
and
phosphatases
Monosaccharides
Amino acids
Nitrogenous bases,
sugars, phosphates
• The first portion of the small intestine is the
duodenum, where chyme from the stomach
mixes with digestive juices from the pancreas,
liver, gallbladder, and the small intestine itself
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Pancreatic Secretions
• The pancreas produces proteases trypsin and
chymotrypsin that are activated in the lumen of
the duodenum
• Its solution is alkaline and neutralizes the acidic
chyme
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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
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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
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Absorption in the Small Intestine
• The small intestine has a huge surface area,
due to villi and microvilli that are exposed to
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
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Figure 41.13
Vein carrying
blood to liver
Villi
Microvilli (brush
border) at apical
(lumenal) surface
Epithelial
cells
Blood
capillaries
Muscle layers
Villi
Intestinal wall
Epithelial
cells
Large
circular
folds
Basal
surface
Lacteal
Key
Nutrient
absorption
Lymph
vessel
Lumen
• 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
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• 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
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Figure 41.14
LUMEN
Triglycerides
OF SMALL
INTESTINE
Epithelial
cell
Fatty acids
Monoglycerides
Triglycerides
Phospholipids,
cholesterol,
and proteins
Chylomicron
Lacteal
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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Figure 41.15
Ascending
portion
of colon
Small
intestine
Cecum
Appendix
• A major function of the colon is to recover water
that has entered the alimentary canal
• The colon houses bacteria (e.g., Escherichia
coli) which live on unabsorbed organic material;
some produce vitamins
• Feces, including undigested material and
bacteria, become more solid as they move
through the colon
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• Feces are stored in the rectum until they can be
eliminated through the anus
• Two sphincters between the rectum and anus
control bowel movements
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Concept 41.4: 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
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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
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Figure 41.16
Carnivore
Herbivore
Key
Incisors
Omnivore
Canines
Premolars
Molars
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
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Figure 41.17
Small intestine
Small
intestine
Stomach
Cecum
Carnivore
Colon
(large
intestine)
Herbivore
Mutualistic Adaptations
• Many herbivores have fermentation chambers,
where mutualistic microorganisms digest
cellulose
• The most elaborate adaptations for an
herbivorous diet have evolved in the animals
called ruminants
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Figure 41.18
2 Reticulum
1 Rumen
Esophagus
Intestine
4 Abomasum
3 Omasum
Concept 41.5: Feedback circuits regulate
digestion, energy storage, and appetite
• The intake of food and the use of nutrients
varies with an animal’s diet and environment
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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
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Figure 41.19
1
2
Food
3
Bile
Liver
Stomach
Secretin
and CCK
Chyme
Gallbladder
Gastric
juices

Gastric
juices
CCK

Pancreas
Duodenum
of small intestine
HCO3, enzymes
Secretin

Key
 Stimulation
 Inhibition

Gastrin
CCK

Regulation of Energy Storage
• The body stores energy-rich molecules that are
not needed right away for metabolism
• In humans, energy is stored first in the liver and
muscle cells in the polymer glycogen
• Excess energy is stored in adipose tissue, the
most space-efficient storage tissue
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Glucose Homeostasis
• Oxidation of glucose generates ATP to fuel
cellular processes
• The hormones insulin and glucagon regulate the
breakdown of glycogen into glucose
• The liver is the site for glucose homeostasis
– A carbohydrate-rich meal raises insulin levels,
which triggers the synthesis of glycogen
– Low blood sugar causes glucagon to stimulate
the breakdown of glycogen and release glucose
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Figure 41.20
Transport of
glucose into
body cells
and storage
of glucose
as glycogen
Pancreas
secretes
insulin.
Stimulus:
Blood glucose
level rises
after eating.
Homeostasis:
70–110 mg glucose/
100 mL blood
Breakdown
of glycogen
and release
of glucose
into blood
Stimulus:
Blood glucose
level drops
below set point.
Pancreas
secretes
glucagon.
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
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Figure 41.21
Satiety
center
Ghrelin

Insulin

Leptin

PYY

• Hormones regulate long-term and short-term
appetite by affecting a “satiety center” in the brain
• Studies on mice revealed that the hormone leptin
plays an important role in regulating obesity
• Leptin is produced by adipose tissue and can
help to suppress appetite
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Obesity and Evolution
• A species of birds called petrels become obese
as chicks; in order to consume enough protein
from high-fat food, chicks need to consume more
calories than they burn
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• The problem of maintaining weight partly stems
from our evolutionary past, when fat hoarding
was a means of survival
• Individuals who were more likely to eat fatty food
and store energy as adipose tissue may have
been more likely to survive famines
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