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Overview: Trading Places
• Every organism must exchange materials
with its environment
• Exchanges ultimately occur at the cellular
level by crossing the plasma membrane
• In unicellular organisms, these exchanges
occur directly with the environment
• For most cells making up multicellular
organisms, direct exchange with the
environment is not possible
• Gills are an example of a specialized
exchange system in animals
– O2 diffuses from the water into blood vessels
– CO2 diffuses from blood into the water
• Internal transport and gas exchange are
functionally related in most animals
Concept 42.1: Circulatory systems link
exchange surfaces with cells throughout the
body
• Diffusion time is proportional to the square of
the distance
• Diffusion is only efficient over small distances
• In small and/or thin animals, cells can
exchange materials directly with the
surrounding medium
• In most animals, cells exchange materials with
the environment via a fluid-filled circulatory
system
Gastrovascular Cavities
• Some animals lack a circulatory system
• Some cnidarians, such as jellies, have
elaborate gastrovascular cavities
• A gastrovascular cavity functions in both
digestion and distribution of substances
throughout the body
• The body wall that encloses the
gastrovascular cavity is only two cells thick
• Flatworms have a gastrovascular cavity and a
large surface area to volume ratio
Figure 42.2
Circular
canal
Mouth
Gastrovascular
cavity
Mouth
Pharynx
Radial canals
5 cm
(a) The moon jelly Aurelia, a cnidarian
2 mm
(b) The planarian Dugesia, a flatworm
Evolutionary Variation in Circulatory
Systems
• A circulatory system minimizes the diffusion
distance in animals with many cell layers
General Properties of Circulatory Systems
• A circulatory system has
– A circulatory fluid
– A set of interconnecting vessels
– A muscular pump, the heart
• The circulatory system connects the fluid that
surrounds cells with the organs that exchange
gases, absorb nutrients, and dispose of
wastes
• Circulatory systems can be open or closed,
and vary in the number of circuits in the body
Open and Closed Circulatory Systems
• 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 called
hemolymph
Figure 42.3
(a) An open circulatory system
(b) A closed circulatory system
Heart
Heart
Interstitial fluid
Hemolymph in sinuses
surrounding organs
Pores
Blood
Small branch
vessels in
each organ
Dorsal
Auxiliary
vessel
hearts
(main heart)
Tubular heart
Ventral vessels
Figure 42.3a
(a) An open circulatory system
Heart
Hemolymph in sinuses
surrounding organs
Pores
Tubular heart
• 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
• Annelids, cephalopods, and vertebrates
have closed circulatory systems
Figure 42.3b
(b) A closed circulatory system
Heart
Interstitial fluid
Blood
Small branch
vessels in
each organ
Dorsal
Auxiliary
vessel
hearts
(main heart)
Ventral vessels
Organization of Vertebrate Circulatory
Systems
• Humans and other vertebrates have a
closed circulatory system called the
cardiovascular system
• The three main types of blood vessels are
arteries, veins, and capillaries
• Blood flow is one way in these vessels
• Arteries branch into arterioles and carry
blood away from the heart 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
© 2011 Pearson Education, Inc.
• Arteries and veins are distinguished by the
direction of blood flow, not by O2 content
• Vertebrate hearts contain two or more
chambers
• Blood enters through an atrium and is
pumped out through a ventricle
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
Figure 42.4
(a) Single circulation
(b) Double circulation
Pulmonary circuit
Gill
capillaries
Lung
capillaries
Artery
Heart:
A
Atrium (A)
V
Right
Ventricle (V)
A
V
Left
Vein
Systemic
capillaries
Body
capillaries
Systemic circuit
Key
Oxygen-rich blood
Oxygen-poor blood
Figure 42.4a
(a) Single circulation
Gill
capillaries
Artery
Heart:
Atrium (A)
Ventricle (V)
Vein
Body
capillaries
Key
Oxygen-rich blood
Oxygen-poor blood
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
Figure 42.4b
(b) Double circulation
Pulmonary circuit
Lung
capillaries
A
V
Right
A
V
Left
Systemic
capillaries
Key
Systemic circuit
Oxygen-rich blood
Oxygen-poor blood
• In reptiles and mammals, oxygen-poor blood
flows through the pulmonary circuit to pick
up oxygen through the lungs
• In amphibians, oxygen-poor blood flows
through a pulmocutaneous circuit to pick
up oxygen through the lungs and skin
• Oxygen-rich blood delivers oxygen through
the systemic circuit
• Double circulation maintains higher blood
pressure in the organs than does single
circulation
Adaptations of Double Circulatory Systems
• Hearts vary in different vertebrate groups
Amphibians
• Frogs and other amphibians have a threechambered heart: two atria and one
ventricle
• The ventricle pumps blood into a forked
artery that splits the ventricle’s output into
the pulmocutaneous circuit and the systemic
circuit
• When underwater, blood flow to the lungs is
nearly shut off
Figure 42.5a
Amphibians
Pulmocutaneous circuit
Lung
and skin
capillaries
Atrium
(A)
Atrium
(A)
Right
Left
Ventricle (V)
Systemic
capillaries
Systemic circuit
Key
Oxygen-rich blood
Oxygen-poor blood
Reptiles (Except Birds)
• Turtles, snakes, and lizards have a threechambered heart: two atria and one
ventricle
• In alligators, caimans, and other crocodilians
a septum divides the ventricle
• Reptiles have double circulation, with a
pulmonary circuit (lungs) and a systemic
circuit
Figure 42.5b
Reptiles (Except Birds)
Pulmonary circuit
Lung
capillaries
Right
systemic
aorta
Atrium
(A)
Ventricle
(V)
A
Right
V
Left
Left
systemic
aorta
Incomplete
septum
Systemic
capillaries
Systemic circuit
Key
Oxygen-rich blood
Oxygen-poor blood
Mammals and Birds
• Mammals and birds have a four-chambered
heart with two atria and two ventricles
• The left side of the heart pumps and
receives only oxygen-rich blood, while the
right side receives and pumps only oxygenpoor blood
• Mammals and birds are endotherms and
require more O2 than ectotherms
Figure 42.5c
Mammals and Birds
Pulmonary circuit
Lung
capillaries
A
Atrium
(A)
Ventricle
(V)
Right
V
Left
Systemic
capillaries
Systemic circuit
Key
Oxygen-rich blood
Oxygen-poor blood
Figure 42.5
Amphibians
Pulmocutaneous circuit
Pulmonary circuit
Lung
and skin
capillaries
Atrium
(A)
Atrium
(A)
Right
Pulmonary circuit
Lung
capillaries
Lung
capillaries
Right
systemic
aorta
A
V
Right
Left
Mammals and Birds
Reptiles (Except Birds)
A
V
Left
Left
systemic
aorta
Incomplete
septum
A
V
Right
A
V
Left
Ventricle (V)
Systemic circuit
Key
Oxygen-rich blood
Oxygen-poor blood
Systemic
capillaries
Systemic
capillaries
Systemic
capillaries
Systemic circuit
Systemic circuit
Concept 42.2: Coordinated cycles of heart
contraction drive double circulation in
mammals
• The mammalian cardiovascular system meets the
body’s continuous demand for O2
Mammalian Circulation
• Blood begins its flow with the right ventricle
pumping blood to the lungs
• In the lungs, the blood loads O2 and unloads
CO2
• Oxygen-rich blood from the lungs enters the
heart at the left atrium and is pumped
through the aorta to the body tissues by the
left ventricle
• The aorta provides blood to the heart
through the coronary arteries
• Blood returns to the heart through the
superior vena cava (blood from head, neck,
and forelimbs) and inferior vena cava (blood
from trunk and hind limbs)
• The superior vena cava and inferior vena
cava flow into the right atrium
Animation: Path of Blood Flow in Mammals
Animation: Path of Blood Flow in Mammals
Right-click slide / select “Play”
Figure 42.6
Capillaries of
head and forelimbs
Superior vena cava
Pulmonary
artery
Capillaries
of right lung
Pulmonary
vein
Right atrium
Right ventricle
Pulmonary
artery
Aorta
Capillaries
of left lung
Pulmonary vein
Left atrium
Left ventricle
Aorta
Inferior
vena cava
Capillaries of
abdominal organs
and hind limbs
The Mammalian Heart: A Closer Look
• A closer look at the mammalian heart
provides a better understanding of double
circulation
Figure 42.7
Aorta
Pulmonary artery
Pulmonary
artery
Right
atrium
Left
atrium
Semilunar
valve
Semilunar
valve
Atrioventricular
valve
Atrioventricular
valve
Right
ventricle
Left
ventricle
• The heart contracts and relaxes in a
rhythmic cycle called the cardiac cycle
• The contraction, or pumping, phase is called
systole
• The relaxation, or filling, phase is called
diastole
Figure 42.8-3
2 Atrial systole and ventricular
diastole
1 Atrial and
ventricular diastole
0.1
sec
0.4
sec
0.3 sec
3 Ventricular systole and atrial
diastole
• The heart rate, also called the pulse, is the
number of beats per minute
• The stroke volume is the amount of blood
pumped in a single contraction
• The cardiac output is the volume of blood
pumped into the systemic circulation per
minute and depends on both the heart rate
and stroke volume
• Four valves prevent backflow of blood in the
heart
• The atrioventricular (AV) valves separate
each atrium and ventricle
• The semilunar valves control blood flow to
the aorta and the pulmonary artery
• The “lub-dup” sound of a heart beat is
caused by the recoil of blood against the AV
valves (lub) then against the semilunar (dup)
valves
• Backflow of blood through a defective valve
causes a heart murmur
Maintaining the Heart’s Rhythmic Beat
• Some cardiac muscle cells are self-excitable,
meaning they contract without any signal from the
nervous system
• The sinoatrial (SA) node, or pacemaker, sets the
rate and timing at which cardiac muscle cells
contract
• Impulses that travel during the cardiac cycle can
be recorded as an electrocardiogram (ECG or
EKG)
Figure 42.9-4
1
SA node
(pacemaker)
ECG
2
AV
node
3
Bundle
branches
4
Heart
apex
Purkinje
fibers
• Impulses from the SA node travel to the
atrioventricular (AV) node
• At the AV node, the impulses are delayed
and then travel to the Purkinje fibers that
make the ventricles contract
• The pacemaker is regulated by two portions
of the nervous system: the sympathetic and
parasympathetic divisions
• The sympathetic division speeds up the
pacemaker
• The parasympathetic division slows down
the pacemaker
• The pacemaker is also regulated by
hormones and temperature
Concept 42.3: Patterns of blood pressure and
flow reflect the structure and arrangement
of blood vessels
• The physical principles that govern
movement of water in plumbing systems
also influence the functioning of animal
circulatory systems
Blood Vessel Structure and Function
• A vessel’s cavity is called the central lumen
• The epithelial layer that lines blood vessels
is called the endothelium
• The endothelium is smooth and minimizes
resistance
Figure 42.10
Vein
LM
Artery
Red blood cells
100 m
Valve
Basal lamina
Endothelium
Smooth
muscle
Connective
tissue
Endothelium
Capillary
Smooth
muscle
Connective
tissue
Artery
Vein
Capillary
15 m
Red blood cell
Venule
LM
Arteriole
Figure 42.10a
Valve
Basal lamina
Endothelium
Smooth
muscle
Connective
tissue
Endothelium
Capillary
Smooth
muscle
Connective
tissue
Artery
Vein
Arteriole
Venule
Figure 42.10b
Vein
LM
Artery
Red blood cells
100 m
Capillary
LM
Red blood cell
15 m
Figure 42.10c
• Capillaries have thin walls, the endothelium
plus its basal lamina, to facilitate the
exchange of materials
• Arteries and veins have an endothelium,
smooth muscle, and connective tissue
• Arteries have thicker walls than veins to
accommodate the high pressure of blood
pumped from the heart
• In the thinner-walled veins, blood flows back
to the heart mainly as a result of muscle
action
Blood Flow Velocity
• Physical laws governing movement of fluids
through pipes affect blood flow and blood
pressure
• Velocity of blood flow is slowest in the
capillary beds, as a result of the high
resistance and large total cross-sectional
area
• Blood flow in capillaries is necessarily slow
for exchange of materials
Velocity
(cm/sec)
5,000
4,000
3,000
2,000
1,000
0
50
40
30
20
10
0
Pressure
(mm Hg)
Area (cm2)
Figure 42.11
120
100
80
60
40
20
0
Systolic
pressure
Diastolic
pressure
Blood Pressure
• Blood flows from areas of higher pressure to
areas of lower pressure
• Blood pressure is the pressure that blood
exerts against the wall of a vessel
• In rigid vessels blood pressure is
maintained; less rigid vessels deform and
blood pressure is lost
Changes in Blood Pressure During the
Cardiac Cycle
• Systolic pressure is the pressure in the
arteries during ventricular systole; it is the
highest pressure in the arteries
• Diastolic pressure is the pressure in the
arteries during diastole; it is lower than
systolic pressure
• A pulse is the rhythmic bulging of artery
walls with each heartbeat
Regulation of Blood Pressure
• Blood pressure is determined by cardiac
output and peripheral resistance due to
constriction of arterioles
• Vasoconstriction is the contraction of
smooth muscle in arteriole walls; it
increases blood pressure
• Vasodilation is the relaxation of smooth
muscles in the arterioles; it causes blood
pressure to fall
• Vasoconstriction and vasodilation help
maintain adequate blood flow as the body’s
demands change
• Nitric oxide is a major inducer of
vasodilation
• The peptide endothelin is an important
inducer of vasoconstriction
Blood Pressure and Gravity
• Blood pressure is generally measured for an
artery in the arm at the same height as the
heart
• Blood pressure for a healthy 20 year old at
rest is 120 mm Hg at systole and 70 mm Hg
at diastole
Figure 42.12
Blood pressure reading: 120/70
1
3
2
120
120
70
Artery
closed
Sounds
audible in
stethoscope
Sounds
stop
• Fainting is caused by inadequate blood flow
to the head
• Animals with longer necks require a higher
systolic pressure to pump blood a greater
distance against gravity
• Blood is moved through veins by smooth
muscle contraction, skeletal muscle
contraction, and expansion of the vena cava
with inhalation
• One-way valves in veins prevent backflow of
blood
Figure 42.13
Direction of blood flow
in vein (toward heart)
Valve (open)
Skeletal muscle
Valve (closed)
Capillary Function
• Blood flows through only 510% of the
body’s capillaries at a time
• Capillaries in major organs are usually filled
to capacity
• Blood supply varies in many other sites
• Two mechanisms regulate distribution of
blood in capillary beds
– Contraction of the smooth muscle layer in the
wall of an arteriole constricts the vessel
– Precapillary sphincters control flow of blood
between arterioles and venules
• Blood flow is regulated by nerve impulses,
hormones, and other chemicals
Figure 42.14
Precapillary
sphincters
Thoroughfare
channel
Arteriole
(a) Sphincters relaxed
Arteriole
(b) Sphincters contracted
Capillaries
Venule
Venule
• The exchange of substances between the
blood and interstitial fluid takes place across
the thin endothelial walls of the capillaries
• The difference between blood pressure and
osmotic pressure drives fluids out of
capillaries at the arteriole end and into
capillaries at the venule end
• Most blood proteins and all blood cells are
too large to pass through the endothelium
Figure 42.15
INTERSTITIAL
FLUID
Net fluid movement out
Body cell
Blood
pressure
Osmotic
pressure
Arterial end
of capillary
Direction of blood flow
Venous end
of capillary
Fluid Return by the Lymphatic System
• The lymphatic system returns fluid that
leaks out from the capillary beds
• Fluid, called lymph, reenters the circulation
directly at the venous end of the capillary
bed and indirectly through the lymphatic
system
• The lymphatic system drains into veins in
the neck
• Valves in lymph vessels prevent the
backflow of fluid
• Lymph nodes are organs that filter lymph
and play an important role in the body’s
defense
• Edema is swelling caused by disruptions in
the flow of lymph
Figure 42.16
Concept 42.4: Blood components contribute
to exchange, transport, and defense
• With open circulation, the fluid that is
pumped comes into direct contact with all
cells
• The closed circulatory systems of
vertebrates contain blood, a specialized
connective tissue
Blood Composition and Function
• Blood consists of several kinds of cells
suspended in a liquid matrix called plasma
• The cellular elements occupy about 45% of
the volume of blood
Figure 42.17
Cellular elements 45%
Plasma 55%
Constituent
Water
Solvent for
carrying other
substances
Ions (blood
electrolytes)
Sodium
Potassium
Calcium
Magnesium
Chloride
Bicarbonate
Osmotic balance,
pH buffering,
and regulation
of membrane
permeablity
Plasma proteins
Albumin
Fibrinogen
Leukocytes (white blood cells)
Separated
blood
elements
5,000–10,000
Functions
Defense and
immunity
Lymphocytes
Basophils
Eosinophils
Neutrophils
Osmotic balance,
pH buffering
Monocytes
Platelets
250,000–400,000
Clotting
Immunoglobulins Defense
(antibodies)
Substances transported by blood
Nutrients
Waste products
Respiratory gases
Hormones
Number per L
(mm3) of blood
Cell type
Major functions
Erythrocytes (red blood cells)
5–6 million
Blood
clotting
Transport
of O2 and
some CO2
Figure 42.17a
Plasma 55%
Constituent
Major functions
Water
Solvent for
carrying other
substances
Ions (blood
electrolytes)
Sodium
Potassium
Calcium
Magnesium
Chloride
Bicarbonate
Osmotic balance,
pH buffering,
and regulation
of membrane
permeablity
Plasma proteins
Albumin
Fibrinogen
Immunoglobulins (antibodies)
Osmotic balance, pH buffering
Clotting
Defense
Substances transported by blood
Nutrients
Waste products
Respiratory gases
Hormones
Separated
blood
elements
Figure 42.17b
Cellular elements 45%
Number per L
(mm3) of blood
Cell type
Leukocytes (white blood cells)
Separated
blood
elements
5,000–10,000
Functions
Defense and
immunity
Lymphocytes
Basophils
Eosinophils
Neutrophils
Monocytes
Platelets
Erythrocytes (red blood cells)
250,000–400,000
5–6 million
Blood
clotting
Transport
of O2 and
some CO2
Plasma
• Blood plasma is about 90% water
• Among its solutes are inorganic salts in the
form of dissolved ions, sometimes called
electrolytes
• Another important class of solutes is the
plasma proteins, which influence blood pH,
osmotic pressure, and viscosity
• Various plasma proteins function in lipid
transport, immunity, and blood clotting
Cellular Elements
• Suspended in blood plasma are two types of
cells
– Red blood cells (erythrocytes) transport
oxygen O2
– White blood cells (leukocytes) function in
defense
• Platelets, a third cellular element, are
fragments of cells that are involved in
clotting
Erythrocytes
• Red blood cells, or erythrocytes, are by far
the most numerous blood cells
• They contain hemoglobin, the ironcontaining protein that transports O2
• Each molecule of hemoglobin binds up to
four molecules of O2
• In mammals, mature erythrocytes lack
nuclei and mitochondria
• Sickle-cell disease is caused by abnormal
hemoglobin proteins that form aggregates
• The aggregates can deform an erythrocyte
into a sickle shape
• Sickled cells can rupture, or block blood
vessels
Leukocytes
• There are five major types of white blood
cells, or leukocytes: monocytes,
neutrophils, basophils, eosinophils, and
lymphocytes
• They function in defense by phagocytizing
bacteria and debris or by producing
antibodies
• They are found both in and outside of the
circulatory system
Platelets
• Platelets are fragments of cells and function
in blood clotting
Blood Clotting
• Coagulation is the formation of a solid clot
from liquid blood
• A cascade of complex reactions converts
inactive fibrinogen to fibrin, forming a clot
• A blood clot formed within a blood vessel is
called a thrombus and can block blood flow
Figure 42.18
2
1
3
Collagen fibers
Platelet
plug
Platelet
Fibrin
clot
Clotting factors from:
Platelets
Damaged cells
Plasma (factors include calcium, vitamin K)
Enzymatic cascade
Prothrombin

Thrombin
Fibrinogen
Fibrin
Red blood cell
Fibrin clot formation
5 m
Figure 42.18a
3
2
1
Collagen fibers
Platelet
plug
Platelet
Fibrin
clot
Clotting factors from:
Platelets
Damaged cells
Plasma (factors include calcium, vitamin K)
Enzymatic cascade
Prothrombin

Thrombin
Fibrinogen
Fibrin
Fibrin clot
formation
Figure 42.18b
Fibrin
clot
Red blood cell
5 m
Stem Cells and the Replacement of Cellular
Elements
• The cellular elements of blood wear out and are
being replaced constantly
• Erythrocytes, leukocytes, and platelets all develop
from a common source of stem cells in the red
marrow of bones, especially ribs, vertebrae,
sternum, and pelvis
• The hormone erythropoietin (EPO) stimulates
erythrocyte production when O2 delivery is low
Figure 42.19
Stem cells
(in bone marrow)
Myeloid
stem cells
Lymphoid
stem cells
B cells T cells
Erythrocytes
Neutrophils
Basophils
Lymphocytes
Monocytes
Platelets
Eosinophils
Cardiovascular Disease
• Cardiovascular diseases are disorders of
the heart and the blood vessels
• Cardiovascular diseases account for more
than half the deaths in the United States
• Cholesterol, a steroid, helps maintain
membrane fluidity
• Low-density lipoprotein (LDL) delivers
cholesterol to cells for membrane
production
• High-density lipoprotein (HDL)
scavenges cholesterol for return to the
liver
• Risk for heart disease increases with a
high LDL to HDL ratio
• Inflammation is also a factor in
cardiovascular disease
Atherosclerosis, Heart Attacks, and Stroke
• One type of cardiovascular disease,
atherosclerosis, is caused by the buildup
of plaque deposits within arteries
Figure 42.20
Lumen of artery
Endothelium
Smooth
muscle
1
LDL
Foam cell
Macrophage
Plaque
2
Extracellular
matrix
Plaque rupture
4
3
Fibrous cap
Cholesterol
Smooth
muscle
cell
T lymphocyte
• A heart attack, or myocardial infarction, is
the death of cardiac muscle tissue resulting
from blockage of one or more coronary
arteries
• Coronary arteries supply oxygen-rich blood
to the heart muscle
• A stroke is the death of nervous tissue in
the brain, usually resulting from rupture or
blockage of arteries in the head
• Angina pectoris is caused by partial
blockage of the coronary arteries and results
in chest pains
Risk Factors and Treatment of
Cardiovascular Disease
• A high LDL to HDL ratio increases the risk
of cardiovascular disease
• The proportion of LDL relative to HDL can
be decreased by exercise, not smoking, and
avoiding foods with trans fats
• Drugs called statins reduce LDL levels and
risk of heart attacks
Figure 42.21
Average  105 mg/dL
30
20
10
0
0
50
100
150
200
250
300
Plasma LDL cholesterol (mg/dL)
Individuals with two functional copies of
PCSK9 gene (control group)
Percent of individuals
Percent of individuals
RESULTS
Average  63 mg/dL
30
20
10
0
0
50
100
150
200
250
300
Plasma LDL cholesterol (mg/dL)
Individuals with an inactivating mutation in
one copy of PCSK9 gene
• Inflammation plays a role in atherosclerosis
and thrombus formation
• Aspirin inhibits inflammation and reduces
the risk of heart attacks and stroke
• Hypertension, or high blood pressure,
promotes atherosclerosis and increases the
risk of heart attack and stroke
• Hypertension can be reduced by dietary
changes, exercise, and/or medication
Concept 42.5: Gas exchange occurs across
specialized respiratory surfaces
• Gas exchange supplies O2 for cellular respiration
and disposes of CO2
Partial Pressure Gradients in Gas Exchange
• A gas diffuses from a region of higher partial
pressure to a region of lower partial
pressure
• Partial pressure is the pressure exerted by
a particular gas in a mixture of gases
• Gases diffuse down pressure gradients in
the lungs and other organs as a result of
differences in partial pressure
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
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
Gills in Aquatic Animals
• Gills are outfoldings of the body that create
a large surface area for gas exchange
Figure 42.22a
Parapodium (functions as gill)
(a) Marine worm
Figure 42.22b
Gills
(b) Crayfish
Figure 42.22c
Coelom
Gills
Tube foot
(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
Figure 42.23
O2-poor blood
Gill
arch
O2-rich blood
Lamella
Blood
vessels
Gill arch
Water
flow
Operculum
Water flow
Blood flow
Countercurrent exchange
PO (mm Hg) in water
2
150 120 90 60 30
Gill filaments
Net diffusion of O2
140 110 80 50 20
PO (mm Hg)
2
in blood
Figure 42.23a
Gill
arch
Blood
vessels
Gill arch
Water
flow
Operculum
Gill filaments
Figure 42.23b
O2-poor blood
O2-rich blood
Lamella
Water flow
Blood flow
Countercurrent exchange
PO (mm Hg) in water
2
150 120 90 60 30
Net diffusion of O2
140 110 80 50 20
PO (mm Hg)
2
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
© 2011 Pearson Education, Inc.
Tracheoles Mitochondria
Muscle fiber
2.5 m
Figure 42.24
Tracheae
Air sacs
Body
cell
Air
sac
Tracheole
Trachea
External opening
Air
Figure 42.24a
Muscle fiber
2.5 m
Tracheoles Mitochondria
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
© 2011 Pearson Education, Inc.
Mammalian Respiratory Systems: A Closer
Look
• A system of branching ducts conveys air to the
lungs
• Air inhaled through the nostrils is warmed,
humidified, and sampled for odors
• The pharynx directs air to the lungs and food to
the stomach
• Swallowing tips the epiglottis over the glottis in the
pharynx to prevent food from entering the trachea
© 2011 Pearson Education, Inc.
Figure 42.25
Branch of
pulmonary vein
(oxygen-rich
blood)
Terminal
bronchiole
Branch of
pulmonary artery
(oxygen-poor
blood)
Nasal
cavity
Pharynx
Left
lung
Larynx
(Esophagus)
Alveoli
50 m
Trachea
Right lung
Capillaries
Bronchus
Bronchiole
Diaphragm
(Heart)
Dense capillary bed
enveloping alveoli (SEM)
Figure 42.25a
Nasal
cavity
Pharynx
Left
lung
Larynx
(Esophagus)
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
(Heart)
Figure 42.25b
Branch of
pulmonary vein
(oxygen-rich
blood)
Terminal
bronchiole
Branch of
pulmonary artery
(oxygen-poor
blood)
Alveoli
Capillaries
Figure 42.25c
50 m
Dense capillary bed
enveloping alveoli (SEM)
• Air passes through the pharynx, larynx,
trachea, bronchi, and bronchioles to the
alveoli, where gas exchange occurs
• Exhaled air passes over the vocal cords in
the larynx to create sounds
• Cilia and mucus line the epithelium of the air
ducts and move particles up to the pharynx
• This “mucus escalator” cleans the
respiratory system and allows particles to be
swallowed into the esophagus
• Gas exchange takes place in alveoli, air
sacs at the tips of bronchioles
• Oxygen diffuses through the moist film of
the epithelium and into capillaries
• Carbon dioxide diffuses from the capillaries
across the epithelium and into the air space
• Alveoli lack cilia and are susceptible to
contamination
• Secretions called surfactants coat the
surface of the alveoli
• Preterm babies lack surfactant and are
vulnerable to respiratory distress syndrome;
treatment is provided by artificial surfactants
Figure 42.26
RDS deaths
Surface tension (dynes/cm)
RESULTS
Deaths from other causes
40
30
20
10
0
0
800
1,600
2,400
3,200
Body mass of infant (g)
4,000
Concept 42.6: Breathing ventilates the lungs
• The process that ventilates the lungs is
breathing, the alternate inhalation and
exhalation of air
How an Amphibian Breathes
• An amphibian such as a frog ventilates its
lungs by positive pressure breathing,
which forces air down the trachea
How a Bird Breathes
• Birds have eight or nine air sacs that
function as bellows that keep air flowing
through the lungs
• Air passes through the lungs in one direction
only
• Every exhalation completely renews the air
in the lungs
Figure 42.27
Anterior
air sacs
Posterior
air sacs
Lungs
Airflow
Air tubes
(parabronchi)
in lung
1 mm
Posterior
air sacs
Lungs
3
Anterior
air sacs
2
4
1
1 First inhalation
3 Second inhalation
2 First exhalation
4 Second exhalation
How a Mammal Breathes
• Mammals ventilate their lungs by negative
pressure breathing, which pulls air into the
lungs
• Lung volume increases as the rib muscles
and diaphragm contract
• The tidal volume is the volume of air
inhaled with each breath
Figure 42.28
1
Rib cage
expands.
2
Air
inhaled.
Lung
Diaphragm
Rib cage gets
smaller.
Air
exhaled.
• The maximum tidal volume is the vital
capacity
• After exhalation, a residual volume of air
remains in the lungs
Control of Breathing in Humans
• In humans, the main breathing control
centers are in two regions of the brain, the
medulla oblongata and the pons
• The medulla regulates the rate and depth of
breathing in response to pH changes in the
cerebrospinal fluid
• The medulla adjusts breathing rate and
depth to match metabolic demands
• The pons regulates the tempo
• Sensors in the aorta and carotid arteries
monitor O2 and CO2 concentrations in the
blood
• These sensors exert secondary control over
breathing
Figure 42.29
Homeostasis:
Blood pH of about 7.4
CO2 level
decreases.
Response:
Rib muscles
and diaphragm
increase rate
and depth of
ventilation.
Stimulus:
Rising level of
CO2 in tissues
lowers blood pH.
Carotid
arteries
Sensor/control center:
Cerebrospinal fluid
Medulla
oblongata
Aorta
Concept 42.7: Adaptations for gas exchange
include pigments that bind and transport
gases
• The metabolic demands of many organisms
require that the blood transport large
quantities of O2 and CO2
Coordination of Circulation and Gas
Exchange
• Blood arriving in the lungs has a low partial
pressure of O2 and a high partial pressure of
CO2 relative to air in the alveoli
• In the alveoli, O2 diffuses into the blood and
CO2 diffuses into the air
• In tissue capillaries, partial pressure
gradients favor diffusion of O2 into the
interstitial fluids and CO2 into the blood
Figure 42.30
Alveolar
epithelial
cells
2 Alveolar
spaces
CO2
O2
Alveolar
capillaries
7 Pulmonary
arteries
3 Pulmonary
veins
6 Systemic
veins
4 Systemic
arteries
Heart
CO2
Partial pressure (mm Hg)
1 Inhaled air
8 Exhaled air
160
O2
5 Body tissue
(a) The path of respiratory gases in the circulatory
system
2
Exhaled
air
120
80
40
0
1
Systemic
capillaries
PO
2
PCO
Inhaled
air
2
3
4
5
6
7
(b) Partial pressure of O2 and CO2 at different points in the
circulatory system numbered in (a)
8
Figure 42.30a
1 Inhaled air
8 Exhaled air
Alveolar
epithelial
cells
2 Alveolar
spaces
CO2
O2
Alveolar
capillaries
7 Pulmonary
arteries
3 Pulmonary
veins
6 Systemic
veins
4 Systemic
arteries
Heart
CO2
O2
Systemic
capillaries
5 Body tissue
(a) The path of respiratory gases in the circulatory
system
Partial pressure (mm Hg)
Figure 42.30b
160
PO
2
PCO
Inhaled
air
2
Exhaled
air
120
80
40
0
1
2
3
4
5
6
7
8
(b) Partial pressure of O2 and CO2 at different points in the
circulatory system numbered in (a)
Respiratory Pigments
• Respiratory pigments, proteins that
transport oxygen, greatly increase the
amount of oxygen that blood can carry
• Arthropods and many molluscs have
hemocyanin with copper as the oxygenbinding component
• Most vertebrates and some invertebrates
use hemoglobin
• In vertebrates, hemoglobin is contained
within erythrocytes
Hemoglobin
• A single hemoglobin molecule can carry four
molecules of O2, one molecule for each iron
containing heme group
• The hemoglobin dissociation curve shows that
a small change in the partial pressure of
oxygen can result in a large change in delivery
of O2
• CO2 produced during cellular respiration
lowers blood pH and decreases the affinity of
hemoglobin for O2; this is called the Bohr
shift
Figure 42.UN01
Iron
Heme
Hemoglobin
O2 saturation of hemoglobin (%)
Figure 42.31a
100
O2 unloaded
to tissues
at rest
80
O2 unloaded
to tissues
during exercise
60
40
20
0
0
20
40
60
Tissues during Tissues
at rest
exercise
PO2 (mm Hg)
80
100
Lungs
(a) PO2 and hemoglobin dissociation at pH 7.4
O2 saturation of hemoglobin (%)
Figure 42.31b
100
pH 7.4
80
pH 7.2
Hemoglobin
retains less
O2 at lower pH
(higher CO2
concentration)
60
40
20
0
0
20
40
60
80
PO2 (mm Hg)
(b) pH and hemoglobin dissociation
100
Carbon Dioxide Transport
• Hemoglobin also helps transport CO2 and assists
in buffering the blood
• CO2 from respiring cells diffuses into the blood
and is transported either in blood plasma, bound
to hemoglobin, or as bicarbonate ions (HCO3–)
Animation: O2 from Blood to Tissues
Animation: CO2 from Tissues to Blood
Animation: CO2 from Blood to Lungs
Animation: O2 from Lungs to Blood
Animation: O2 from Blood to Tissues
Right-click slide / select “Play”
Animation: CO2 from Tissues to Blood
Right-click slide / select “Play”
Animation: CO2 from Blood to Lungs
Right-click slide / select “Play”
Animation: O2 from Lungs to Blood
Right-click slide / select “Play”
Figure 42.32
Body tissue
CO2 produced
CO2 transport
from tissues
Interstitial
CO2
fluid
Plasma
within capillary CO2
H2O
Red
blood
cell
Capillary
wall
CO2
H2CO3
Hb
Carbonic
acid
HCO3 
Bicarbonate
HCO3
H+
To lungs
CO2 transport
to lungs
HCO3
HCO3 
H2CO3
Hemoglobin (Hb)
picks up
CO2 and H+.
H+
Hb
Hemoglobin
releases
CO2 and H+.
H2O
CO2
CO2
CO2
CO2
Alveolar space in lung
Figure 42.32a
Body tissue
CO2 produced
CO2 transport
from tissues
Interstitial
CO2
fluid
Plasma
CO2
within capillary
Capillary
wall
CO2
H2O
Red
blood
cell
H2CO3
Hb
Carbonic
acid
HCO3 
Bicarbonate
Hemoglobin (Hb)
picks up
CO2 and H+.
H+
HCO3
To lungs
Figure 42.32b
To lungs
CO2 transport
to lungs
HCO3
HCO3 
H2CO3
H+
Hb
Hemoglobin
releases
CO2 and H+.
H2O
CO2
CO2
CO2
CO2
Alveolar space in lung
Respiratory Adaptations of Diving Mammals
• Diving mammals have evolutionary
adaptations that allow them to perform
extraordinary feats
– For example, Weddell seals in Antarctica can
remain underwater for 20 minutes to an hour
– For example, elephant seals can dive to 1,500
m and remain underwater for 2 hours
• These animals have a high blood to body
volume ratio
• Deep-diving air breathers stockpile O2
and deplete it slowly
• Diving mammals can store oxygen in
their muscles in myoglobin proteins
• Diving mammals also conserve oxygen
by
– Changing their buoyancy to glide
passively
– Decreasing blood supply to muscles
– Deriving ATP in muscles from
fermentation once oxygen is depleted
Figure 42.UN02
Inhaled air
Exhaled air
Alveolar
epithelial
cells
Alveolar
spaces
CO2
O2
Alveolar
capillaries
Pulmonary
arteries
Pulmonary
veins
Systemic
veins
Systemic
arteries
Heart
CO2
O2
Systemic
capillaries
Body tissue
O2 saturation of
hemoglobin (%)
Figure 42.UN03
100
80
60
Fetus
Mother
40
20
0
0 20 40 60 80 100
PO2 (mm Hg)
Figure 42.UN04