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Transcript
Chapter 40
Basic Principles of Animal
Form and Function
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
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Physical Constraints on Animal Size and Shape
• The ability to perform certain actions depends
on an animal’s shape, size, and environment
• Evolutionary convergence reflects different
species’ adaptations to a similar environmental
challenge
• Physical laws impose constraints on animal
size and shape – cells as well as animals can
only get so big
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 40-2
(a) Tuna
(b) Penguin
(c) Seal
Exchange with the Environment
• An animal’s size and shape directly affect how
it exchanges energy and materials with its
surroundings
• Exchange occurs as substances dissolved in
the aqueous medium diffuse and are
transported across the cells’ plasma
membranes
• A single-celled protist living in water has a
sufficient surface area of plasma membrane to
service its entire volume of cytoplasm
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 40-3
Mouth
Gastrovascular
cavity
Exchange
Exchange
Exchange
0.15 mm
1.5 mm
(a) Single cell
(b) Two layers of cells
• Multicellular organisms with a sac body plan
have body walls that are only two cells thick,
facilitating diffusion of materials
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• More complex organisms have highly folded
internal surfaces for exchanging materials
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 40-4
External environment
CO2
Food
O2
Mouth
Respiratory
system
0.5 cm
50 µm
Animal
body
Lung tissue
Nutrients
Heart
Cells
Circulatory
system
10 µm
Interstitial
fluid
Digestive
system
Excretory
system
Lining of small intestine
Kidney tubules
Anus
Unabsorbed
matter (feces)
Metabolic waste products
(nitrogenous waste)
• In vertebrates, the space between cells is filled
with intercellular (interstitial) fluid, ICF,
which allows for the movement of material into
and out of cells
• Diffusion of materials into and out of cells
requires an aqueous environment
• A complex body plan helps an animal in a
variable environment to maintain a relatively
stable internal environment
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 41-10
Tongue
Sphincter
Salivary
glands
Oral cavity
Salivary glands
Mouth
Pharynx
Esophagus
Esophagus
Sphincter
Liver
Stomach
Ascending
portion of
large intestine
Gallbladder
Gallbladder
Duodenum of
small intestine
Pancreas
Liver
Small
intestine
Small
intestine
Large
intestine
Rectum
Anus
Appendix
Cecum
Pancreas
Stomach
Small
intestine
Large
intestine
Rectum
Anus
A schematic diagram of the
human digestive system
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 greatly
increases the rate of nutrient absorption
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 41-15
Microvilli (brush
border) at apical
(lumenal) surface Lumen
Vein carrying blood
to hepatic portal vein
Blood
capillaries
Muscle layers
Epithelial
cells
Basal
surface
Large
circular
folds
Villi
Epithelial cells
Lacteal
Key
Nutrient
absorption
Intestinal wall
Villi
Lymph
vessel
Concept 42.1: Circulatory systems link exchange
surfaces with cells throughout the body
• In small and/or thin animals, cells can
exchange materials directly with the
surrounding medium
• In most animals, transport systems connect the
organs of exchange with the body cells
• Most complex animals have internal transport
systems that circulate fluid
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Open and Closed Circulatory Systems
• More complex animals have either open or
closed circulatory systems
• Both systems have three basic components:
– A circulatory fluid (blood or hemolymph)
– A set of tubes (blood vessels)
– A muscular pump (the heart)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• In insects, other arthropods, and most
molluscs, blood bathes the organs directly in
an open circulatory system
• In an open circulatory system, there is no
distinction between blood and interstitial fluid,
and this general body fluid is more correctly
called hemolymph
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• In a closed circulatory system, blood is
confined to vessels and is distinct from the
interstitial fluid
• Closed systems are more efficient at
transporting circulatory fluids to tissues and
cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 42-3
Heart
Hemolymph in sinuses
surrounding organs
Pores
Heart
Blood
Interstitial
fluid
Small branch vessels
In each organ
Dorsal vessel
(main heart)
Tubular heart
(a) An open circulatory system
Auxiliary hearts
Ventral vessels
(b) A closed circulatory system
Concept 42.5: Gas exchange occurs across
specialized respiratory surfaces
• Gas exchange supplies oxygen for cellular
respiration and disposes of carbon dioxide
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Respiratory Surfaces
• Animals require large, moist respiratory
surfaces for exchange of gases between their
cells and the respiratory medium, either air or
water
• Gas exchange across respiratory surfaces
takes place by diffusion
• Respiratory surfaces vary by animal and can
include the outer surface, skin, gills, tracheae,
and lungs
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Mammalian Respiratory Systems: A Closer Look
• A system of branching ducts conveys air to the
lungs
• Air inhaled through the nostrils passes through
the pharynx via the larynx, trachea, bronchi,
bronchioles, and alveoli, where gas
exchange occurs
• Exhaled air passes over the vocal cords to
create sounds
• Secretions called surfactants coat the surface
of the alveoli
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 42-24
Branch of
pulmonary
vein
(oxygen-rich
blood)
Branch of
pulmonary
artery
(oxygen-poor
blood)
Terminal
bronchiole
Nasal
cavity
Pharynx
Larynx
Alveoli
(Esophagus)
Left
lung
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
Heart
SEM
50 µm
Colorized
SEM
50 µm
Concept 44.3: Diverse excretory systems are
variations on a tubular theme
• Excretory systems regulate solute movement
between internal fluids and the external
environment
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Excretory Processes
• Most excretory systems produce urine by
refining a filtrate derived from body fluids
• Key functions of most excretory systems:
– Filtration: pressure-filtering of body fluids
– Reabsorption: reclaiming valuable solutes
– Secretion: adding toxins and other solutes
from the body fluids to the filtrate
– Excretion: removing the filtrate from the
system
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Survey of Excretory Systems
• Systems that perform basic excretory functions
vary widely among animal groups
• They usually involve a complex network of
tubules
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Kidneys
• Kidneys, the excretory organs of vertebrates,
function in both excretion and osmoregulation
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Structure of the Mammalian Excretory System
• The mammalian excretory system centers on
paired kidneys, which are also the principal site
of water balance and salt regulation
• Each kidney is supplied with blood by a renal
artery and drained by a renal vein
• Urine exits each kidney through a duct called
the ureter
• Both ureters drain into a common urinary
bladder, and urine is expelled through a
urethra
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 44-14
Renal
medulla
Posterior
vena cava
Renal artery
and vein
Aorta
Renal
cortex
Kidney
Renal
pelvis
Ureter
Urinary
bladder
Urethra
Ureter
(a) Excretory organs and major
associated blood vessels
Juxtamedullary
nephron
Section of kidney
from a rat
(b) Kidney structure
Cortical
nephron
10 µm
4 mm
Afferent arteriole Glomerulus
from renal artery
Bowman’s capsule
SEM
Proximal tubule
Peritubular capillaries
Renal
cortex
Efferent
arteriole from
glomerulus
Collecting
duct
Renal
medulla
Branch of
renal vein
Collecting
duct
Descending
limb
To
renal
pelvis
Loop of
Henle
(c) Nephron types
Distal
tubule
Ascending
limb
(d) Filtrate and blood flow
Vasa
recta
Concept 40.2: Feedback control loops maintain the
internal environment in many animals
• Animals manage their internal environment by
regulating or conforming to the external
environment
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 40-7
40
Body temperature (°C)
River otter (temperature regulator)
30
20
Largemouth bass
(temperature conformer)
10
0
10
20
30
40
Ambient (environmental) temperature (ºC)
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Animation: Negative Feedback
Animation: Positive Feedback
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 40-8
Response:
Heater
turned
off
Room
temperature
decreases
Stimulus:
Control center
(thermostat)
reads too hot
Set
point:
20ºC
Stimulus:
Control center
(thermostat)
reads too cold
Room
temperature
increases
Response:
Heater
turned
on
Feedback Loops in Homeostasis
• The dynamic equilibrium of homeostasis is
maintained by negative feedback, which helps
to return a variable to either a normal range or
a set point
• Most homeostatic control systems function by
negative feedback, where buildup of the end
product shuts the system off
• Positive feedback loops occur in animals, but
do not usually contribute to homeostasis
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Insulin and Glucagon: Control of Blood Glucose
• Insulin and glucagon are antagonistic
hormones that help maintain glucose
homeostasis
• The pancreas has clusters of endocrine cells
called islets of Langerhans with alpha cells
that produce glucagon and beta cells that
produce insulin
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 45-12-2
Body cells
take up more
glucose.
Insulin
Beta cells of
pancreas
release insulin
into the blood.
Liver takes
up glucose
and stores it
as glycogen.
STIMULUS:
Blood glucose level
rises.
Blood glucose
level declines.
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
Fig. 45-12-4
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
STIMULUS:
Blood glucose level
falls.
Blood glucose
level rises.
Alpha cells of pancreas
release glucagon.
Liver breaks
down glycogen
and releases
glucose.
Glucagon
Fig. 45-12-5
Body cells
take up more
glucose.
Insulin
Beta cells of
pancreas
release insulin
into the blood.
Liver takes
up glucose
and stores it
as glycogen.
STIMULUS:
Blood glucose level
rises.
Blood glucose
level declines.
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
STIMULUS:
Blood glucose level
falls.
Blood glucose
level rises.
Alpha cells of pancreas
release glucagon.
Liver breaks
down glycogen
and releases
glucose.
Glucagon
Diabetes Mellitus
• Diabetes mellitus is perhaps the best-known
endocrine disorder
• It is caused by a deficiency of insulin or a
decreased response to insulin in target tissues
• It is marked by elevated blood glucose levels
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Type I diabetes mellitus (insulin-dependent) is
an autoimmune disorder in which the immune
system destroys pancreatic beta cells
• Type II diabetes mellitus (non-insulindependent) involves insulin deficiency or
reduced response of target cells due to change
in insulin receptors
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Feedback Loops in Homeostasis
• Positive feedback loops occur in animals, but
do not usually contribute to homeostasis
• Some examples are:
– Lactation in mammals
– Onset of labor in childbirth
– Ripening of fruit
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• 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
• Countercurrent heat exchangers are an
important mechanism for reducing heat loss
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 40-12
Canada goose
Bottlenose
dolphin
Blood flow
Artery Vein
Vein
Artery
35ºC
33º
30º
27º
20º
18º
10º
9º
• 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Cooling by Evaporative Heat Loss
• Many types of animals lose heat through
evaporation of water in sweat
• Panting increases the cooling effect in birds
and many mammals
• Sweating or bathing moistens the skin, helping
to cool an animal down
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 40-16
Sweat glands secrete
sweat, which evaporates,
cooling the body.
Body temperature
decreases;
thermostat
shuts off cooling
mechanisms.
Thermostat in hypothalamus
activates cooling mechanisms.
Blood vessels
in skin dilate:
capillaries fill;
heat radiates
from skin.
Increased body
temperature
Homeostasis:
Internal temperature
of 36–38°C
Body temperature
increases; thermostat
shuts off warming
mechanisms.
Decreased body
temperature
Blood vessels in skin
constrict, reducing
heat loss.
Skeletal muscles contract;
shivering generates heat.
Thermostat in
hypothalamus
activates warming
mechanisms.
Alterations in Homeostasis
• Set points and normal ranges can change with
age or show cyclic variation
• Acclimatization is the process by which an
animal adjusts to changes in its external
environment
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Metabolic rate
(kcal per day)
Fig. 40-21
200
Actual
metabolism
100
0
35
30
Temperature (°C)
Additional metabolism that would be
necessary to stay active in winter
Arousals
Body
temperature
25
20
15
10
5
0
–5
Outside
temperature
Burrow
temperature
–10
–15
June
August
October
December
February
April
• Estivation, or summer torpor, enables animals
to survive long periods of high temperatures
and scarce water supplies
• Daily torpor is exhibited by many small
mammals and birds and seems adapted to
feeding patterns
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Digestive Compartments
• Most animals process food in specialized
compartments
• These compartments reduce the risk of an
animal digesting its own cells and tissues
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Intracellular Digestion
• In intracellular digestion, food particles are
engulfed by endocytosis and digested within
food vacuoles
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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
• This is what people do
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 41-8
Tentacles
Food
Mouth
Epidermis
Gastrodermis
Gastrovascular
cavity
• Animals with simple body plans have a
gastrovascular cavity that functions in both
digestion and distribution of nutrients
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• 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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 41-9
Crop
Esophagus
Gizzard
Intestine
Pharynx
Anus
Mouth
Typhlosole
Lumen of intestine
(a) Earthworm
Foregut
Midgut
Esophagus
Hindgut
Rectum
Anus
Crop
Mouth
Gastric cecae
(b) Grasshopper
Stomach
Gizzard
Intestine
Mouth
Esophagus
Crop
Anus
(c) Bird
Concept 42.5: Gas exchange occurs across
specialized respiratory surfaces
• Gas exchange supplies oxygen for cellular
respiration and disposes of carbon dioxide
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Respiratory Media
• Animals can use air or water as a source of O2,
or respiratory medium
• In a given volume, there is less O2 available in
water than in air
• Obtaining O2 from water requires greater
efficiency than air breathing
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Respiratory Surfaces
• Animals require large, moist respiratory
surfaces for exchange of gases between their
cells and the respiratory medium, either air or
water
• Gas exchange across respiratory surfaces
takes place by diffusion
• Respiratory surfaces vary by animal and can
include the outer surface, skin, gills, tracheae,
and lungs
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Gills in Aquatic Animals
• Gills are outfoldings of the body that create a
large surface area for gas exchange
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 42-21
Coelom
Gills
Gills
Parapodium (functions as gill)
(a) Marine worm
Tube foot
(b) Crayfish
(c) Sea star
• Ventilation moves the respiratory medium over
the respiratory surface
• Aquatic animals move through water or move
water over their gills for ventilation
• Fish gills use a countercurrent exchange
system, where blood flows in the opposite
direction to water passing over the gills; blood
is always less saturated with O2 than the water
it meets
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 42-22
Fluid flow
through
gill filament
Oxygen-poor blood
Anatomy of gills
Oxygen-rich blood
Gill
arch
Lamella
Gill
arch
Gill filament
organization
Blood
vessels
Water
flow
Operculum
Water flow
between
lamellae
Blood flow through
capillaries in lamella
Countercurrent exchange
PO2 (mm Hg) in water
150 120 90 60 30
Gill filaments
Net diffusion of O2
from water
to blood
140 110 80 50 20
PO2 (mm Hg) in blood
Tracheal Systems in Insects
• The tracheal system of insects consists of tiny
branching tubes that penetrate the body
• The tracheal tubes supply O2 directly to body
cells
• The respiratory and circulatory systems are
separate
• Larger insects must ventilate their tracheal
system to meet O2 demands
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 42-23
Air sacs
Tracheae
External
opening
Tracheoles
Mitochondria
Muscle fiber
Body
cell
Air
sac
Tracheole
Trachea
Air
Body wall
2.5 µm
Lungs
• Lungs are an infolding of the body surface
• The circulatory system (open or closed)
transports gases between the lungs and the
rest of the body
• The size and complexity of lungs correlate with
an animal’s metabolic rate
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 42-24
Branch of
pulmonary
vein
(oxygen-rich
blood)
Branch of
pulmonary
artery
(oxygen-poor
blood)
Terminal
bronchiole
Nasal
cavity
Pharynx
Larynx
Alveoli
(Esophagus)
Left
lung
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
Heart
SEM
50 µm
Colorized
SEM
50 µm
Overview: A Balancing Act
• Physiological systems of animals operate in a
fluid environment
• Relative concentrations of water and solutes
must be maintained within fairly narrow limits
• Osmoregulation regulates solute
concentrations and balances the gain and loss
of water
• Your notes and book discuss examples
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• Freshwater animals show adaptations that
reduce water uptake and conserve solutes
• Desert and marine animals face desiccating
environments that can quickly deplete body
water
• Excretion gets rid of nitrogenous metabolites
and other waste products
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Concept 44.2: An animal’s nitrogenous wastes
reflect its phylogeny and habitat
• The type and quantity of an animal’s waste
products may greatly affect its water balance
• Among the most important wastes are
nitrogenous breakdown products of proteins
and nucleic acids
• Some animals convert toxic ammonia (NH3) to
less toxic compounds prior to excretion
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 44-9
Proteins
Nucleic acids
Amino
acids
Nitrogenous
bases
Amino groups
Most aquatic
animals, including
most bony fishes
Ammonia
Mammals, most
Many reptiles
amphibians, sharks, (including birds),
some bony fishes
insects, land snails
Urea
Uric acid
Forms of Nitrogenous Wastes
• Different animals excrete nitrogenous wastes in
different forms: ammonia, urea, or uric acid
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Ammonia
• Animals that excrete nitrogenous wastes as
ammonia need lots of water
• They release ammonia across the whole body
surface or through gills
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Urea
• The liver of mammals and most adult
amphibians converts ammonia to less toxic
urea
• The circulatory system carries urea to the
kidneys, where it is excreted
• Conversion of ammonia to urea is energetically
expensive; excretion of urea requires less
water than ammonia
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Uric Acid
• Insects, land snails, and many reptiles,
including birds, mainly excrete uric acid
• Uric acid is largely insoluble in water and can
be secreted as a paste with little water loss
• Uric acid is more energetically expensive to
produce than urea
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Concept 44.3: Diverse excretory systems are
variations on a tubular theme
• Excretory systems regulate solute movement
between internal fluids and the external
environment
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Excretory Processes
• Most excretory systems produce urine by
refining a filtrate derived from body fluids
• Key functions of most excretory systems:
– Filtration: pressure-filtering of body fluids
– Reabsorption: reclaiming valuable solutes
– Secretion: adding toxins and other solutes
from the body fluids to the filtrate
– Excretion: removing the filtrate from the
system
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 44-10
Filtration
Capillary
Excretory
tubule
Reabsorption
Secretion
Urine
Excretion
Survey of Excretory Systems
• Systems that perform basic excretory functions
vary widely among animal groups
• They usually involve a complex network of
tubules
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Protonephridia
• A protonephridium is a network of dead-end
tubules connected to external openings
• The smallest branches of the network are
capped by a cellular unit called a flame bulb
• These tubules excrete a dilute fluid and
function in osmoregulation
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 44-11
Nucleus
of cap cell
Cilia
Flame
bulb
Interstitial
fluid flow
Tubule
Tubules of
protonephridia
Opening in
body wall
Tubule cell
Metanephridia
• Each segment of an earthworm has a pair of
open-ended metanephridia
• Metanephridia consist of tubules that collect
coelomic fluid and produce dilute urine for
excretion
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Fig. 44-12
Coelom
Capillary
network
Components of
a metanephridium:
Internal opening
Collecting tubule
Bladder
External opening
Kidneys
• Kidneys, the excretory organs of vertebrates,
function in both excretion and osmoregulation
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Structure of the Mammalian Excretory System
• The mammalian excretory system centers on
paired kidneys, which are also the principal site
of water balance and salt regulation
• Each kidney is supplied with blood by a renal
artery and drained by a renal vein
• Urine exits each kidney through a duct called
the ureter
• Both ureters drain into a common urinary
bladder, and urine is expelled through a
urethra
Animation: Nephron Introduction
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Fig. 44-14
Renal
medulla
Posterior
vena cava
Renal artery
and vein
Aorta
Renal
cortex
Kidney
Renal
pelvis
Ureter
Urinary
bladder
Urethra
Ureter
(a) Excretory organs and major
associated blood vessels
Juxtamedullary
nephron
Section of kidney
from a rat
(b) Kidney structure
Cortical
nephron
10 µm
4 mm
Afferent arteriole Glomerulus
from renal artery
Bowman’s capsule
SEM
Proximal tubule
Peritubular capillaries
Renal
cortex
Efferent
arteriole from
glomerulus
Collecting
duct
Renal
medulla
Branch of
renal vein
Collecting
duct
Descending
limb
To
renal
pelvis
Loop of
Henle
(c) Nephron types
Distal
tubule
Ascending
limb
(d) Filtrate and blood flow
Vasa
recta
Fig. 44-14d
10 µm
Afferent arteriole
from renal artery
SEM
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubular capillaries
Efferent
arteriole from
glomerulus
Distal
tubule
Branch of
renal vein
Collecting
duct
Descending
limb
Loop of
Henle
(d) Filtrate and blood flow
Ascending
limb
Vasa
recta
Open and Closed Circulatory Systems
• More complex animals have either open or
closed circulatory systems
• Both systems have three basic components:
– A circulatory fluid (blood or hemolymph)
– A set of tubes (blood vessels)
– A muscular pump (the heart)
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• In insects, other arthropods, and most
molluscs, blood bathes the organs directly in
an open circulatory system
• In an open circulatory system, there is no
distinction between blood and interstitial fluid,
and this general body fluid is more correctly
called hemolymph
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• In a closed circulatory system, blood is
confined to vessels and is distinct from the
interstitial fluid
• Closed systems are more efficient at
transporting circulatory fluids to tissues and
cells
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Fig. 42-3
Heart
Hemolymph in sinuses
surrounding organs
Pores
Heart
Blood
Interstitial
fluid
Small branch vessels
In each organ
Dorsal vessel
(main heart)
Tubular heart
(a) An open circulatory system
Auxiliary hearts
Ventral vessels
(b) A closed circulatory system
Organization of Vertebrate Circulatory Systems
• Humans and other vertebrates have a closed
circulatory system, often called the
cardiovascular system
• The three main types of blood vessels are
arteries, veins, and capillaries
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• Arteries branch into arterioles and carry blood
to capillaries
• Networks of capillaries called capillary beds
are the sites of chemical exchange between
the blood and interstitial fluid
• Venules converge into veins and return blood
from capillaries to the heart
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• Vertebrate hearts contain two or more
chambers
• Blood enters through an atrium and is pumped
out through a ventricle
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Single Circulation
• Bony fishes, rays, and sharks have single
circulation with a two-chambered heart
• In single circulation, blood leaving the heart
passes through two capillary beds before
returning
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Fig. 42-4
Gill capillaries
Artery
Gill
circulation
Ventricle
Heart
Atrium
Vein
Systemic
circulation
Systemic capillaries
Double Circulation
• Amphibian, reptiles, and mammals have
double circulation
• Oxygen-poor and oxygen-rich blood are
pumped separately from the right and left sides
of the heart
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Fig. 42-5
Amphibians
Reptiles (Except Birds)
Mammals and Birds
Lung and skin capillaries
Lung capillaries
Lung capillaries
Pulmocutaneous
circuit
Atrium (A)
Right
systemic
aorta
Atrium (A)
Ventricle (V)
Left
Right
Systemic
circuit
Systemic capillaries
Pulmonary
circuit
A
V
Right
Pulmonary
circuit
A
A
V
Left
Systemic capillaries
Left
systemic
aorta
A
V
V
Right
Left
Systemic
circuit
Systemic capillaries
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
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Fig. 40-17
External
environment
Animal
body
Organic molecules
in food
Digestion and
absorption
Heat
Energy lost
in feces
Nutrient molecules
in body cells
Carbon
skeletons
Cellular
respiration
Energy lost in
nitrogenous
waste
Heat
ATP
Biosynthesis
Cellular
work
Heat
Heat
Quantifying Energy Use
• Metabolic rate is the amount of energy an
animal uses in a unit of time
• One way to measure it is to determine the
amount of oxygen consumed or carbon dioxide
produced
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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
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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
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Size and Metabolic Rate
• Metabolic rate per gram is inversely related to
body size among similar animals
• Researchers continue to search for the causes
of this relationship
• 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
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Chapter 43
The Immune System
PowerPoint® Lecture Presentations for
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Overview: Reconnaissance, Recognition, and
Response
• Barriers help an animal to defend itself from the
many dangerous pathogens it may encounter
• The immune system recognizes foreign
bodies and responds with the production of
immune cells and proteins
• Two major kinds of defense have evolved:
innate immunity and acquired immunity
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• Innate immunity is present before any
exposure to pathogens and is effective from
the time of birth
• It involves nonspecific responses to pathogens
• Innate immunity consists of external barriers
plus internal cellular and chemical defenses
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• Acquired immunity, or adaptive immunity,
develops after exposure to agents such as
microbes, toxins, or other foreign substances
• It involves a very specific response to
pathogens
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Fig. 43-2
Pathogens
(microorganisms
and viruses)
INNATE IMMUNITY
• Recognition of traits
shared by broad ranges
of pathogens, using a
small set of receptors
• Rapid response
ACQUIRED IMMUNITY
• Recognition of traits
specific to particular
pathogens, using a vast
array of receptors
• Slower response
Barrier defenses:
Skin
Mucous membranes
Secretions
Internal defenses:
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells
Humoral response:
Antibodies defend against
infection in body fluids.
Cell-mediated response:
Cytotoxic lymphocytes defend
against infection in body cells.
Concept 43.1: In innate immunity, recognition and
response rely on shared traits of pathogens
• Both invertebrates and vertebrates depend on
innate nonspecific immunity to fight infection
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Innate Immunity of Invertebrates
• In insects, an exoskeleton made of chitin forms
the first barrier to pathogens
• The digestive system is protected by low pH
and lysozyme, an enzyme that digests
microbial cell walls
• Hemocytes circulate within hemolymph and
carry out phagocytosis, the ingestion and
digestion of foreign substances including
bacteria
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• Hemocytes also secrete antimicrobial peptides
that disrupt the plasma membranes of bacteria
• The immune system recognizes bacteria and
fungi by structures on their cell walls
• An immune response varies with the class of
pathogen encountered
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Innate Immunity of Vertebrates
• The immune system of mammals is the best
understood of the vertebrates
• Innate defenses include barrier defenses,
phagocytosis, antimicrobial peptides
• Additional defenses are unique to vertebrates:
the inflammatory response and natural killer
cells
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Barrier Defenses
• Barrier defenses include the skin and mucous
membranes of the respiratory, urinary, and
reproductive tracts
• Mucus traps and allows for the removal of
microbes
• Many body fluids including saliva, mucus, and
tears are hostile to microbes
• The low pH of skin and the digestive system
prevents growth of microbes
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Cellular Innate Defenses
• White blood cells (leukocytes) engulf
pathogens in the body
• A white blood cell engulfs a microbe, then
fuses with a lysosome to destroy the microbe
• Peptides and proteins function in innate
defense by attacking microbes directly or
impeding their reproduction
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Inflammatory Responses
• Following an injury, mast cells release
histamine, which promotes changes in blood
vessels; this is part of the inflammatory
response
• These changes increase local blood supply
and allow more phagocytes and antimicrobial
proteins to enter tissues. This causes swelling.
• Pus, a fluid rich in white blood cells, dead
microbes, and cell debris, accumulates at the
site of inflammation
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Fig. 43-8-3
Pathogen
Splinter
Chemical Macrophage
signals
Mast cell
Capillary
Red blood cells Phagocytic cell
Fluid
Phagocytosis
• Inflammation can be either local or systemic
(throughout the body)
• Fever is a systemic inflammatory response
triggered by pyrogens released by
macrophages, and toxins from pathogens
• Septic shock is a life-threatening condition
caused by an overwhelming inflammatory
response
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Natural Killer Cells
• All cells in the body (except red blood cells)
have a class 1 MHC protein on their surface
• Cancerous or infected cells no longer express
this protein; natural killer (NK) cells attack
these damaged cells
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Innate Immune System Evasion by Pathogens
• Some pathogens avoid destruction by
modifying their surface to prevent recognition
or by resisting breakdown following
phagocytosis
• Tuberculosis (TB) is one such disease and kills
more than a million people a year
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Concept 43.2: In acquired immunity, lymphocyte
receptors provide pathogen-specific recognition
• White blood cells called lymphocytes
recognize and respond to antigens, foreign
molecules
• Lymphocytes that mature in the thymus above
the heart are called T cells, and those that
mature in bone marrow are called B cells
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Acquired Immunity: An Overview
• B cells and T cells have receptor proteins that
can bind to foreign molecules
• Each individual lymphocyte is specialized to
recognize a specific type of molecule
• Lymphocytes contribute to immunological
memory, an enhanced response to a foreign
molecule encountered previously
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Antigen Recognition by Lymphocytes
• An antigen is any foreign molecule to which a
lymphocyte responds
• A single B cell or T cell has about 100,000
identical antigen receptors
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Fig. 43-9
Antigenbinding
site
Antigenbinding site
Antigenbinding
site
Disulfide
bridge
C
C
Light
chain
Variable
regions
V
V
Constant
regions
C
C
Transmembrane
region
Plasma
membrane
Heavy chains
 chain
 chain
Disulfide bridge
B cell
(a) B cell receptor
Cytoplasm of B cell
Cytoplasm of T cell
(b) T cell receptor
T cell
• All antigen receptors on a single lymphocyte
recognize the same antigen
• B cells give rise to plasma cells, which secrete
proteins called antibodies or
immunoglobulins
• Secreted antibodies, or immunoglobulins, are
structurally similar to B cell receptors but lack
transmembrane regions that anchor receptors
in the plasma membrane
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CELL-MEDIATED RESPONSE
• T cells bind to antigen fragments presented on
a host cell
• These antigen fragments are bound to cellsurface proteins called MHC molecules
• MHC molecules are so named because they
are encoded by a family of genes called the
major histocompatibility complex
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The Role of the MHC
• In infected cells, MHC molecules bind and
transport antigen fragments to the cell surface,
a process called antigen presentation
• A nearby T cell can then detect the antigen
fragment displayed on the cell’s surface
• Depending on their source, peptide antigens
are handled by different classes of MHC
molecules
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• Class I MHC molecules are found on almost
all nucleated cells of the body
• They display peptide antigens to cytotoxic T
cells
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Fig. 43-12
Infected cell
Microbe
Antigenpresenting
cell
1 Antigen
associates
with MHC
molecule
Antigen
fragment
Antigen
fragment
1
Class I MHC
molecule
1
T cell
receptor
(a)
2
2
Cytotoxic T cell
Class II MHC
molecule
T cell
receptor
2 T cell
recognizes
combination
(b)
Helper T cell
• Class II MHC molecules are located mainly on
dendritic cells, macrophages, and B cells
• Dendritic cells, macrophages, and B cells are
antigen-presenting cells that display antigens
to cytotoxic T cells and helper T cells
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• The first exposure to a specific antigen
represents the primary immune response
• During this time, effector B cells called plasma
cells are generated, and T cells are activated
to their effector forms
• In the secondary immune response, memory
cells facilitate a faster, more efficient response
Animation: Role of B Cells
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Concept 43.3: Acquired immunity defends against
infection of body cells and fluids
• Acquired immunity has two branches: the
humoral immune response and the cellmediated immune response
• Humoral immune response involves
activation and clonal selection of B cells,
resulting in production of secreted antibodies
• Cell-mediated immune response involves
activation and clonal selection of cytotoxic T
cells
• Helper T cells aid both responses
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Fig. 43-16
Humoral (antibody-mediated) immune response
Cell-mediated immune response
Key
Antigen (1st exposure)
+
Engulfed by
Gives rise to
Antigenpresenting cell
+
Stimulates
+
+
B cell
Helper T cell
+
Cytotoxic T cell
+
Memory
Helper T cells
+
+
+
Antigen (2nd exposure)
Plasma cells
Memory B cells
+
Memory
Cytotoxic T cells
Active
Cytotoxic T cells
Secreted
antibodies
Defend against extracellular pathogens by binding to antigens,
thereby neutralizing pathogens or making them better targets
for phagocytes and complement proteins.
Defend against intracellular pathogens
and cancer by binding to and lysing the
infected cells or cancer cells.
Helper T Cells: A Response to Nearly All Antigens
• A surface protein called CD4 binds the class II
MHC molecule
• This binding keeps the helper T cell joined to
the antigen-presenting cell while activation
occurs
• Activated helper T cells secrete cytokines that
stimulate other lymphocytes
Animation: Helper T Cells
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Cytotoxic T Cells: A Response to Infected Cells
• Cytotoxic T cells are the effector cells in cellmediated immune response
• Cytotoxic T cells make CD8, a surface protein
that greatly enhances interaction between a
target cell and a cytotoxic T cell
• Binding to a class I MHC complex on an
infected cell activates a cytotoxic T cell and
makes it an active killer
• The activated cytotoxic T cell secretes proteins
that destroy the infected target cell
Animation: Cytotoxic T Cells
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B Cells: A Response to Extracellular Pathogens
• The humoral response is characterized by
secretion of antibodies by B cells
• Activation of B cells is aided by cytokines and
antigen binding to helper T cells
• Clonal selection of B cells generates antibodysecreting plasma cells, the effector cells of
humoral immunity
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Active and Passive Immunization
• Active immunity develops naturally in
response to an infection
• It can also develop following immunization,
also called vaccination
• In immunization, a nonpathogenic form of a
microbe or part of a microbe elicits an immune
response to an immunological memory
• This type of immunity is considered permanent
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• Passive immunity provides immediate, shortterm protection
• It is conferred naturally when IgG crosses the
placenta from mother to fetus or when IgA
passes from mother to infant in breast milk
• It can be conferred artificially by injecting
antibodies into a nonimmune person
• This immunity is temporary
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Immune Rejection
• Cells transferred from one person to another
can be attacked by immune defenses
• This complicates blood transfusions or the
transplant of tissues or organs
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Blood Groups
• Antigens on red blood cells determine whether
a person has blood type A (A antigen), B (B
antigen), AB (both A and B antigens), or O
(neither antigen) See CH 14 pg. 273
• Antibodies to nonself blood types exist in the
body
• Transfusion with incompatible blood leads to
destruction of the transfused cells
• Recipient-donor combinations can be fatal or
safe
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Tissue and Organ Transplants
• MHC molecules are different among genetically
nonidentical individuals
• Differences in MHC molecules stimulate
rejection of tissue grafts and organ transplants
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• Chances of successful transplantation increase
if donor and recipient MHC tissue types are
well matched
• Immunosuppressive drugs facilitate
transplantation
• Lymphocytes in bone marrow transplants may
cause the donor tissue to reject the recipient
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Concept 43.4: Disruption in immune system
function can elicit or exacerbate disease
• Some pathogens have evolved to diminish the
effectiveness of host immune responses
• If the delicate balance of the immune system is
disrupted, effects range from minor to often
fatal
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Allergies
• Allergies are exaggerated (hypersensitive)
responses to antigens called allergens
• In localized allergies such as hay fever, IgE
antibodies produced after first exposure to an
allergen attach to receptors on mast cells
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Fig. 43-23
IgE
Histamine
Allergen
Granule
Mast cell
• The next time the allergen enters the body, it
binds to mast cell–associated IgE molecules
• Mast cells release histamine and other
mediators that cause vascular changes leading
to typical allergy symptoms
• An acute allergic response can lead to
anaphylactic shock, a life-threatening reaction
that can occur within seconds of allergen
exposure
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Autoimmune Diseases
• In individuals with autoimmune diseases, the
immune system loses tolerance for self and
turns against certain molecules of the body
• Autoimmune diseases include systemic lupus
erythematosus, rheumatoid arthritis, insulindependent diabetes mellitus, and multiple
sclerosis
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Immunodeficiency Diseases
• Inborn immunodeficiency results from
hereditary or developmental defects that
prevent proper functioning of innate, humoral,
and/or cell-mediated defenses
• Acquired immunodeficiency results from
exposure to chemical and biological agents
• Acquired immunodeficiency syndrome
(AIDS) is caused by a virus
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Acquired Immune System Evasion by Pathogens
• Pathogens have evolved mechanisms to attack
immune responses
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Antigenic Variation
• Through antigenic variation, some pathogens
are able to change epitope expression and
prevent recognition
• The human influenza virus mutates rapidly, and
new flu vaccines must be made each year
• Human viruses occasionally exchange genes
with the viruses of domesticated animals
• This poses a danger as human immune
systems are unable to recognize the new viral
strain
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Latency
• Some viruses may remain in a host in an
inactive state called latency
• Herpes simplex viruses can be present in a
human host without causing symptoms
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Attack on the Immune System: HIV
• Human immunodeficiency virus (HIV) infects
helper T cells
• The loss of helper T cells impairs both the
humoral and cell-mediated immune responses
and leads to AIDS
• HIV eludes the immune system because of
antigenic variation and an ability to remain
latent while integrated into host DNA
Animation: HIV Reproductive Cycle
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Chapter 48
Neurons, Synapses, and
Signaling
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Overview: Lines of Communication
• The cone snail kills prey with venom that
disables neurons
• Neurons are nerve cells that transfer
information within the body
• Neurons use two types of signals to
communicate: electrical signals (long-distance)
and chemical signals (short-distance)
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• The transmission of information depends on
the path of neurons along which a signal
travels
• Processing of information takes place in simple
clusters of neurons called ganglia or a more
complex organization of neurons called a brain
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Introduction to Information Processing
• Nervous systems process information in three
stages: sensory input, integration, and motor
output
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Neuron Structure and Function
• Most of a neuron’s organelles are in the cell
body
• Most neurons have dendrites, highly branched
extensions that receive signals from other
neurons
• The axon is typically a much longer extension
that transmits signals to other cells at synapses
• An axon joins the cell body at the axon hillock
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Fig. 48-4
Dendrites
Stimulus
Nucleus
Cell
body
Axon
hillock
Presynaptic
cell
Axon
Synapse
Synaptic terminals
Postsynaptic cell
Neurotransmitter
• A synapse is a junction between an axon and
another cell
• The synaptic terminal of one axon passes
information across the synapse in the form of
chemical messengers called
neurotransmitters
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Concept 48.2: Ion pumps and ion channels
maintain the resting potential of a neuron
• Every cell has a voltage (difference in electrical
charge) across its plasma membrane called a
membrane potential
• Messages are transmitted as changes in
membrane potential
• The resting potential is the membrane
potential of a neuron not sending signals
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Formation of the Resting Potential
• In a mammalian neuron at resting potential, the
concentration of K+ is greater inside the cell,
while the concentration of Na+ is greater outside
the cell
• Sodium-potassium pumps use the energy of
ATP to maintain these K+ and Na+ gradients
across the plasma membrane
• These concentration gradients represent
chemical potential energy
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• The opening of ion channels in the plasma
membrane converts chemical potential to
electrical potential
• A neuron at resting potential contains many
open K+ channels and fewer open Na+
channels; K+ diffuses out of the cell
• Anions trapped inside the cell contribute to the
negative charge within the neuron
Animation: Resting Potential
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-6
Key
Na+
K+
OUTSIDE
CELL
OUTSIDE [K+]
CELL
5 mM
INSIDE [K+]
CELL 140 mM
[Na+]
[Cl–]
150 mM 120 mM
[Na+]
15 mM
[Cl–]
10 mM
[A–]
100 mM
INSIDE
CELL
(a)
(b)
Sodiumpotassium
pump
Potassium
channel
Sodium
channel
Concept 48.3: Action potentials are the signals
conducted by axons
• Neurons contain gated ion channels that
open or close in response to stimuli
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• Membrane potential changes in response to
opening or closing of these channels
• When gated K+ channels open, K+ diffuses out,
making the inside of the cell more negative
• This is hyperpolarization, an increase in
magnitude of the membrane potential
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-9a
Stimuli
Membrane potential (mV)
+50
0
–50 Threshold
Resting
potential
–100
Hyperpolarizations
0
1 2 3 4 5
Time (msec)
(a) Graded hyperpolarizations
• Other stimuli trigger a depolarization, a
reduction in the magnitude of the membrane
potential
• For example, depolarization occurs if gated
Na+ channels open and Na+ diffuses into the
cell
• Graded potentials are changes in polarization
where the magnitude of the change varies with
the strength of the stimulus
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-9b
Stimuli
Membrane potential (mV)
+50
0
–50 Threshold
Resting
potential
Depolarizations
–100
0 1 2 3 4 5
Time (msec)
(b) Graded depolarizations
Production of Action Potentials
• Voltage-gated Na+ and K+ channels respond
to a change in membrane potential
• When a stimulus depolarizes the membrane,
Na+ channels open, allowing Na+ to diffuse into
the cell
• The movement of Na+ into the cell increases
the depolarization and causes even more Na+
channels to open
• A strong stimulus results in a massive change
in membrane voltage called an action
potential
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Fig. 48-9c
Strong depolarizing stimulus
+50
Membrane potential (mV)
Action
potential
0
–50 Threshold
Resting
potential
–100
0
(c) Action potential
1 2 3 4 5
Time (msec)
6
• An action potential occurs if a stimulus causes
the membrane voltage to cross a particular
threshold
• An action potential is a brief all-or-none
depolarization of a neuron’s plasma membrane
• Action potentials are the nerve impulses, or
signals, that carry information along axons
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-9
Stimuli
Stimuli
Strong depolarizing stimulus
+50
+50
+50
0
–50
Threshold
Membrane potential (mV)
Membrane potential (mV)
Membrane potential (mV)
Action
potential
0
–50
Resting
potential
Threshold
0
–50
Resting
potential
Resting
potential
Depolarizations
Hyperpolarizations
–100
–100
0
1
2 3 4 5
Time (msec)
(a) Graded hyperpolarizations
Threshold
–100
0
1 2 3 4
Time (msec)
(b) Graded depolarizations
5
0
(c) Action potential
1
2 3 4 5
Time (msec)
6
Generation of Action Potentials: A Closer Look
• A neuron can produce hundreds of action
potentials per second
• The frequency of action potentials can reflect
the strength of a stimulus
• An action potential can be broken down into a
series of stages
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Fig. 48-10-5
Key
Na+
K+
3
4
Rising phase of the action potential
Falling phase of the action potential
Membrane potential
(mV)
+50
Action
potential
–50
2
2
4
Threshold
1
1
5
Resting potential
Depolarization
Extracellular fluid
3
0
–100
Sodium
channel
Time
Potassium
channel
Plasma
membrane
Cytosol
Inactivation loop
5
1
Resting state
Undershoot
• During the refractory period after an action
potential, a second action potential cannot be
initiated
• The refractory period is a result of a temporary
inactivation of the Na+ channels
BioFlix: How Neurons Work
Animation: Action Potential
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Conduction of Action Potentials
• An action potential can travel long distances by
regenerating itself along the axon
• At the site where the action potential is
generated, usually the axon hillock, an
electrical current depolarizes the neighboring
region of the axon membrane
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• Inactivated Na+ channels behind the zone of
depolarization prevent the action potential from
traveling backwards
• Action potentials travel in only one direction:
toward the synaptic terminals
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 48-11-3
Axon
Plasma
membrane
Action
potential
Cytosol
Na+
K+
Action
potential
Na+
K+
K+
Action
potential
Na+
K+
Conduction Speed
• The speed of an action potential increases with
the axon’s diameter
• In vertebrates, axons are insulated by a myelin
sheath, which causes an action potential’s
speed to increase
• Myelin sheaths are made by glia—
oligodendrocytes in the CNS and Schwann
cells in the PNS
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Fig. 48-12a
Node of Ranvier
Layers of myelin
Axon
Schwann
cell
Axon
Nodes of
Myelin sheath Ranvier
Schwann
cell
Nucleus of
Schwann cell
• Action potentials are formed only at nodes of
Ranvier, gaps in the myelin sheath where
voltage-gated Na+ channels are found
• Action potentials in myelinated axons jump
between the nodes of Ranvier in a process
called saltatory conduction
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Fig. 48-13
Schwann cell
Depolarized region
(node of Ranvier)
Cell body
Myelin
sheath
Axon
Concept 48.4: Neurons communicate with other
cells at synapses
• At electrical synapses, the electrical current
flows from one neuron to another
• At chemical synapses, a chemical
neurotransmitter carries information across
the gap junction
• Most synapses are chemical synapses
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• The presynaptic neuron synthesizes and
packages the neurotransmitter in synaptic
vesicles located in the synaptic terminal
• The action potential causes the release of the
neurotransmitter
• The neurotransmitter diffuses across the
synaptic cleft and is received by the
postsynaptic cell
Animation: Synapse
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Fig. 48-15
5
Synaptic vesicles
containing
neurotransmitter
Voltage-gated
Ca2+ channel
Postsynaptic
membrane
1 Ca2+
4
2
Synaptic
cleft
Presynaptic
membrane
3
Ligand-gated
ion channels
6
K+
Na+
Generation of Postsynaptic Potentials
• Direct synaptic transmission involves binding of
neurotransmitters to ligand-gated ion channels
in the postsynaptic cell
• Neurotransmitter binding causes ion channels
to open, generating a postsynaptic potential
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• Postsynaptic potentials fall into two categories:
– Excitatory postsynaptic potentials (EPSPs)
are depolarizations that bring the membrane
potential toward threshold
– Inhibitory postsynaptic potentials (IPSPs)
are hyperpolarizations that move the
membrane potential farther from threshold
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• After release, the neurotransmitter
– May diffuse out of the synaptic cleft
– May be taken up by surrounding cells
– May be degraded by enzymes
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Neurotransmitters
• The same neurotransmitter can produce
different effects in different types of cells
• There are five major classes of
neurotransmitters: acetylcholine, biogenic
amines, amino acids, neuropeptides, and
gases
• Neuropeptides include substance P and
endorphins, which both affect our perception
of pain
• Opiates bind to the same receptors as
endorphins and can be used as painkillers
Chapter 49
Nervous Systems
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
Concept 49.1: Nervous systems consist of circuits
of neurons and supporting cells
• The simplest animals with nervous systems,
the cnidarians, have neurons arranged in nerve
nets
• A nerve net is a series of interconnected nerve
cells
• More complex animals have nerves
• Nerves are bundles that consist of the axons of
multiple nerve cells
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• In vertebrates
– The central nervous system (CNS) is
composed of the brain and spinal cord
– The peripheral nervous system (PNS) is
composed of nerves and ganglia
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Organization of the Vertebrate Nervous System
• The spinal cord conveys information from the
brain to the PNS
• The spinal cord also produces reflexes
independently of the brain
• A reflex is the body’s automatic response to a
stimulus
– For example, a doctor uses a mallet to trigger
a knee-jerk reflex
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• The central canal of the spinal cord and the
ventricles of the brain are hollow and filled
with cerebrospinal fluid
• The cerebrospinal fluid is filtered from blood
and functions to cushion the brain and spinal
cord
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Fig. 49-5
Gray matter
White
matter
Ventricles
• The brain and spinal cord contain
– Gray matter, which consists of neuron cell
bodies, dendrites, and unmyelinated axons
– White matter, which consists of bundles of
myelinated axons
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Concept 49.2: The vertebrate brain is regionally
specialized
• All vertebrate brains develop from three
embryonic regions: forebrain, midbrain, and
hindbrain
• By the fifth week of human embryonic
development, five brain regions have formed
from the three embryonic regions
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The Brainstem
• The brainstem coordinates and conducts
information between brain centers
• The brainstem has three parts: the midbrain,
the pons, and the medulla oblongata
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Fig. 49-UN1
MIDBRAIN
PONS
MEDULLA
OBLONGATA
• The midbrain contains centers for receipt and
integration of sensory information
• The pons regulates breathing centers in the
medulla
• The medulla oblongata contains centers that
control several functions including breathing,
cardiovascular activity, swallowing, vomiting,
and digestion
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The Cerebellum
• The cerebellum is important for coordination
and error checking during motor, perceptual,
and cognitive functions
• It is also involved in learning and remembering
motor skills
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Fig. 49-UN2
CEREBELLUM
The Cerebrum
• The cerebrum develops from the embryonic
telencephalon
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Fig. 49-UN4
CEREBRUM
Outer part where gray matter
is, is called the cortex.
• The cerebrum has right and left cerebral
hemispheres
• Each cerebral hemisphere consists of a
cerebral cortex (gray matter) overlying white
matter and basal nuclei
• In humans, the cerebral cortex is the largest
and most complex part of the brain
• The basal nuclei are important centers for
planning and learning movement sequences
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• A thick band of axons called the corpus
callosum provides communication between
the right and left cerebral cortices
• The right half of the cerebral cortex controls the
left side of the body, and vice versa
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 49-13
Left cerebral
hemisphere
Right cerebral
hemisphere
Corpus
callosum
Thalamus
Cerebral
cortex
Basal
nuclei
Concept 49.3: The cerebral cortex controls
voluntary movement and cognitive functions
• Each side of the cerebral cortex has four lobes:
frontal, temporal, occipital, and parietal
• Each lobe contains primary sensory areas and
association areas where information is
integrated
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Fig. 49-15
Frontal lobe
Parietal lobe
Speech
Frontal
association
area
Somatosensory
association
area
Taste
Reading
Speech
Hearing
Smell
Auditory
association
area
Visual
association
area
Vision
Temporal lobe
Occipital lobe
Lateralization of Cortical Function
• The corpus callosum transmits information
between the two cerebral hemispheres
• The left hemisphere is more adept at language,
math, logic, and processing of serial
sequences
• The right hemisphere is stronger at pattern
recognition, nonverbal thinking, and emotional
processing
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• The differences in hemisphere function are
called lateralization
• Lateralization is linked to handedness
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