Transcript chapter42_circulation and gas exchange

Circulation and Gas Exchange
Overview: Trading with the Environment
 Every organism must exchange materials with
its environment

 And this exchange ultimately occurs at the cellular
level

In unicellular organisms
 These exchanges occur directly with the
environment

For most of the cells making up multicellular
organisms
 Direct exchange with the environment is not
possible

The feathery gills projecting from a salmon
 Are an example of a specialized exchange system
found in animals
Figure 42.1
Concept 42.1: Circulatory systems reflect
phylogeny
 Transport systems

 Functionally connect the organs of exchange with
the body cells

Most complex animals have internal transport
systems
 That circulate fluid, providing a lifeline between
the aqueous environment of living cells and the
exchange organs, such as lungs, that exchange
chemicals with the outside environment
Invertebrate Circulation

The wide range of invertebrate body size and
form
 Is paralleled by a great diversity in circulatory
systems
Gastrovascular Cavities

Simple animals, such as cnidarians
 Have a body wall only two cells thick that encloses
a gastrovascular cavity

The gastrovascular cavity
 Functions in both digestion and distribution of
substances throughout the body

Some cnidarians, such as jellies
 Have elaborate gastrovascular cavities
Circular
canal
Mouth
Radial canal
5 cm
Figure 42.2
Open and Closed Circulatory
Systems

More complex animals
 Have one of two types of circulatory systems: open
or closed

Both of these types of systems have three
basic components
 A circulatory fluid (blood)
 A set of tubes (blood vessels)
 A muscular pump (the heart)

In insects, other arthropods, and most
molluscs
 Blood bathes the organs directly in an open
circulatory system
Heart
Hemolymph in sinuses
surrounding ograns
Anterior
vessel
Figure 42.3a
Lateral
vessels
Ostia
Tubular heart
(a) An open circulatory system

In a closed circulatory system
 Blood is confined to vessels and is distinct from the
interstitial fluid
Heart
Interstitial
fluid
Small branch vessels
in each organ
Dorsal vessel
(main heart)
Auxiliary hearts
Figure 42.3b
Ventral vessels
(b) A closed circulatory system

Closed systems
 Are more efficient at transporting circulatory fluids to
tissues and cells
Survey of Vertebrate Circulation

Humans and other vertebrates have a closed
circulatory system
 Often called the cardiovascular system

Blood flows in a closed cardiovascular system
 Consisting of blood vessels and a two- to four-
chambered heart

Arteries carry blood to capillaries
 The sites of chemical exchange between the blood
and interstitial fluid

Veins
 Return blood from capillaries to the heart
Fishes

A fish heart has two main chambers
 One ventricle and one atrium

Blood pumped from the ventricle
 Travels to the gills, where it picks up O2 and
disposes of CO2
Amphibians

Frogs and other amphibians
 Have a three-chambered heart, with 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
Reptiles (Except Birds)

Reptiles have double circulation
 With a pulmonary circuit (lungs) and a systemic
circuit

Turtles, snakes, and lizards
 Have a three-chambered heart
Mammals and Birds

In all mammals and birds
 The ventricle is completely divided into separate
right and left chambers

The left side of the heart pumps and receives
only oxygen-rich blood
 While the right side receives and pumps only
oxygen-poor blood

A powerful four-chambered heart
 Was an essential adaptation of the endothermic
way of life characteristic of mammals and birds

Vertebrate circulatory systems
AMPHIBIANS
REPTILES (EXCEPT BIRDS)
MAMMALS AND BIRDS
Lung and skin capillaries
Lung capillaries
Lung capillaries
FISHES
Gill capillaries
Artery
Right
systemic
aorta
Pulmocutaneous
circuit
Gill
circulation
Heart:
ventricle (V)
A
Atrium (A)
Systemic
Vein circulation
Systemic capillaries
Pulmonary
circuit
A
A
V
Right
V
Left
Right
Systemic
circuit
Systemic capillaries
Figure 42.4
Pulmonary
circuit
Left
Systemic
V aorta
Left
A
Systemic capillaries
A
V
Right
A
V
Left
Systemic
circuit
Systemic capillaries
Concept 42.2: Double circulation in mammals
depends on the anatomy and pumping cycle of
the heart
 The structure and function of the human
circulatory system

 Can serve as a model for exploring mammalian
circulation in general
Mammalian Circulation: The
Pathway

Heart valves
 Dictate a one-way flow of blood through the heart

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 to
the body tissues by the left ventricle

Blood returns to the heart
 Through the right atrium

The mammalian cardiovascular system
7
Capillaries of
head and
forelimbs
Anterior
vena cava
Pulmonary
artery
Aorta
Pulmonary
artery
9
6
Capillaries
of right lung
Capillaries
of left lung
2
4
3
Pulmonary
vein
5
1
Right atrium
3
11
Left atrium
Pulmonary
vein
10
Left ventricle
Right ventricle
Aorta
Posterior
vena cava
8
Figure 42.5
Capillaries of
abdominal organs
and hind limbs
The Mammalian Heart:

how double circulation works
Pulmonary artery
Aorta
Pulmonary
artery
Anterior vena cava
Left
atrium
Right atrium
Pulmonary
veins
Pulmonary
veins
Semilunar
valve
Semilunar
valve
Atrioventricular
valve
Atrioventricular
valve
Posterior
vena cava
Figure 42.6
Right ventricle
Left ventricle

The heart contracts and relaxes
 In a rhythmic cycle called the cardiac cycle

The contraction, or pumping, phase of the
cycle
 Is called systole

The relaxation, or filling, phase of the cycle
 Is called diastole

The cardiac cycle
2 Atrial systole;
ventricular
diastole
Semilunar
valves
closed
0.1 sec
Semilunar
valves
open
0.3 sec
0.4 sec
AV valves
open
1 Atrial and
ventricular
diastole
Figure 42.7
AV valves
closed
3 Ventricular systole;
atrial diastole

The heart rate, also called the pulse
 Is the number of beats per minute

The cardiac output
 Is the volume of blood pumped into the systemic
circulation per minute
Maintaining the Heart’s Rhythmic
Beat

Some cardiac muscle cells are self-excitable
 Meaning they contract without any signal from the
nervous system

A region of the heart called the sinoatrial (SA)
node, or pacemaker
 Sets the rate and timing at which all cardiac muscle
cells contract

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 impulses that travel during the cardiac
cycle
 Can be recorded as an electrocardiogram (ECG or
EKG)

The control of heart rhythm
1 Pacemaker generates
wave of signals
to contract.
SA node
(pacemaker)
2 Signals are delayed
3 Signals pass
at AV node.
AV node
to heart apex.
4 Signals spread
Throughout
ventricles.
Bundle
branches
Heart
apex
ECG
Figure 42.8
Purkinje
fibers

The pacemaker is influenced by
 Nerves, hormones, body temperature, and exercise
Concept 42.3: Physical principles govern blood
circulation
 The same physical principles that govern the
movement of water in plumbing systems

 Also influence the functioning of animal circulatory
systems
Blood Vessel Structure and
Function

The “infrastructure” of the circulatory system
 Is its network of blood vessels

All blood vessels
 Are built of similar tissues
 Have three similar layers
Artery
Vein
Basement
membrane
Endothelium
100 µm
Valve
Endothelium
Smooth
muscle
Connective
tissue
Endothelium
Capillary
Smooth
muscle
Connective
tissue
Artery
Vein
Venule
Figure 42.9
Arteriole

Structural differences in arteries, veins, and
capillaries
 Correlate with their different functions

Arteries have thicker walls
 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
Direction of blood flow
in vein (toward heart)
Valve (open)
Skeletal muscle
Valve (closed)
Figure 42.10
Blood Flow Velocity

Physical laws governing the movement of
fluids through pipes
 Influence blood flow and blood pressure
The velocity of blood flow varies in the
circulatory system
 And is slowest in the capillary beds as a result of the
Systolic
pressure
Veins
Venules
Arterioles
Capillaries
Diastolic
pressure
Arteries
120
100
80
60
40
20
0
Aorta
Area (cm2)
50
40
30
20
10
0
Venae cavae
Figure 42.11
5,000
4,000
3,000
2,000
1,000
0
Velocity (cm/sec)
high resistance and large total cross-sectional area
Pressure (mm Hg)

Blood Pressure

Blood pressure
 Is the hydrostatic pressure that blood exerts against
the wall of a vessel

Systolic pressure
 Is the pressure in the arteries during ventricular
systole
 Is the highest pressure in the arteries

Diastolic pressure
 Is the pressure in the arteries during diastole
 Is lower than systolic pressure

Blood pressure
 Can be easily measured in humans
1 A typical blood pressure reading for a 20-year-old
is 120/70. The units for these numbers are mm of
mercury (Hg); a blood pressure of 120 is a force that
can support a column of mercury 120 mm high.
4 The cuff is loosened further until the blood flows freely
through the artery and the sounds below the cuff
disappear. The pressure at this point is the diastolic
pressure remaining in the artery when the heart is relaxed.
Blood pressure
reading: 120/70
Pressure
in cuff
above 120
Rubber cuff
inflated
with air
120
Pressure
in cuff
below 120
Pressure
in cuff
below 70
120
70
Sounds
audible in
stethoscope
Artery
Artery
closed
2 A sphygmomanometer, an inflatable cuff attached to a
pressure gauge, measures blood pressure in an artery.
The cuff is wrapped around the upper arm and inflated
until the pressure closes the artery, so that no blood
flows past the cuff. When this occurs, the pressure
exerted by the cuff exceeds the pressure in the artery.
Figure 42.12
3 A stethoscope is used to listen for sounds of blood flow
below the cuff. If the artery is closed, there is no pulse
below the cuff. The cuff is gradually deflated until blood
begins to flow into the forearm, and sounds from blood
pulsing into the artery below the cuff can be heard with
the stethoscope. This occurs when the blood pressure
is greater than the pressure exerted by the cuff. The
pressure at this point is the systolic pressure.
Sounds
stop

Blood pressure is determined partly by cardiac
output
 And partly by peripheral resistance due to variable
constriction of the arterioles
Capillary Function

Capillaries in major organs are usually filled to
capacity
 But in many other sites, the blood supply varies

Two mechanisms
 Regulate the distribution of blood in capillary beds

In one mechanism
 Contraction of the smooth muscle layer in the wall
of an arteriole constricts the vessel

In a second mechanism
 Precapillary sphincters control the flow of blood
between arterioles and venules
Precapillary sphincters
Thoroughfare
channel
(a) Sphincters relaxed
Arteriole
Venule
Capillaries
Arteriole
Venule
(b) Sphincters contracted
(c) Capillaries and larger vessels (SEM)
Figure 42.13 a–c
20 m

The critical 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
Tissue cell
Capillary
Capillary
Red
blood
cell
INTERSTITIAL FLUID
Net fluid
movement out
Net fluid
movement in
15 m
At the arterial end of a
capillary, blood pressure is
greater than osmotic pressure,
and fluid flows out of the
capillary into the interstitial fluid.
At the venule end of a capillary,
blood pressure is less than
osmotic pressure, and fluid flows
from the interstitial fluid into the
capillary.
Direction of
blood flow
Pressure

Blood pressure
Osmotic pressure
Inward flow
Outward flow
Figure 42.14
Arterial end of capillary
Venule end
Fluid Return by the Lymphatic
System

The lymphatic system
 Returns fluid to the body from the capillary beds
 Aids in body defense

Fluid reenters the circulation
 Directly at the venous end of the capillary bed and
indirectly through the lymphatic system
Concept 42.4: Blood is a connective tissue
with cells suspended in plasma
 Blood in the circulatory systems of vertebrates

 Is 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
Plasma
Blood plasma is about 90% water
 Among its many solutes are

 Inorganic salts in the form of dissolved ions,
sometimes referred to as electrolytes

The composition of mammalian plasma
Plasma 55%
Constituent
Major functions
Water
Solvent for
carrying other
substances
Icons (blood electrolytes
Sodium
Potassium
Calcium
Magnesium
Chloride
Bicarbonate
Osmotic balance
pH buffering, and
regulation of
membrane
permeability
Plasma proteins
Albumin
Osmotic balance,
pH buffering
Fibringen
Clotting
Immunoglobulins
(antibodies)
Defense
Substances transported by blood
Nutrients (such as glucose, fatty acids, vitamins)
Waste products of metabolism
Respiratory gases (O2 and CO2)
Hormones
Separated
blood
elements

Another important class of solutes is the
plasma proteins
 Which influence blood pH, osmotic pressure, and
viscosity

Various types of plasma proteins
 Function in lipid transport, immunity, and blood
clotting
Cellular Elements

Suspended in blood plasma are two classes of
cells
 Red blood cells, which transport oxygen
 White blood cells, which function in defense

A third cellular element, platelets
 Are fragments of cells that are involved in clotting

The cellular elements of mammalian blood
Cellular elements 45%
Cell type
Separated
blood
elements
Number
per L (mm3) of blood
Functions
Erythrocytes
(red blood cells)
5–6 million
Transport oxygen
and help transport
carbon dioxide
Leukocytes
(white blood cells)
5,000–10,000
Defense and
immunity
Lymphocyte
Basophil
Eosinophil
Neutrophil
Monocyte
Platelets
Figure 42.15
250,000
400,000
Blood clotting
Erythrocytes

Red blood cells, or erythrocytes
 Are by far the most numerous blood cells
 Transport oxygen throughout the body
Leukocytes

The blood contains five major types of white
blood cells, or leukocytes
 Monocytes, neutrophils, basophils, eosinophils, and
lymphocytes, which function in defense by
phagocytizing bacteria and debris or by producing
antibodies
Platelets

Platelets function in blood clotting
Stem Cells and the Replacement of Cellular Elements

The cellular elements of blood wear out
 And are replaced constantly throughout a person’s
life

Erythrocytes, leukocytes, and platelets all
develop from a common source
 A single population of cells called pluripotent stem
cells in the red marrow of bones
Pluripotent stem cells
(in bone marrow)
Lymphoid
stem cells
Myeloid
stem cells
Basophils
B cells
T cells
Lymphocytes
Eosinophils
Neutrophils
Erythrocytes
Figure 42.16
Platelets
Monocytes
Blood Clotting

When the endothelium of a blood vessel is
damaged
 The clotting mechanism begins

A cascade of complex reactions
 Converts fibrinogen to fibrin, forming a clot
1 The clotting process begins
when the endothelium of a
vessel is damaged, exposing
connective tissue in the
vessel wall to blood. Platelets
adhere to collagen fibers in
the connective tissue and
release a substance that
makes nearby platelets sticky.
2 The platelets form a
plug that provides
emergency protection
against blood loss.
3 This seal is reinforced by a clot of fibrin when
vessel damage is severe. Fibrin is formed via a
multistep process: Clotting factors released from
the clumped platelets or damaged cells mix with
clotting factors in the plasma, forming an
activation cascade that converts a plasma protein
called prothrombin to its active form, thrombin.
Thrombin itself is an enzyme that catalyzes the
final step of the clotting process, the conversion of
fibrinogen to fibrin. The threads of fibrin become
interwoven into a patch (see colorized SEM).
Collagen fibers
Platelet
plug
Platelet releases chemicals
that make nearby platelets sticky
Fibrin clot
Clotting factors from:
Platelets
Damaged cells
Plasma (factors include calcium, vitamin K)
Prothrombin
Figure 42.17
Thrombin
Fibrinogen
Fibrin
5 µm
Red blood cell
Cardiovascular Disease

Cardiovascular diseases
 Are disorders of the heart and the blood vessels
 Account for more than half the deaths in the United
States

One type of cardiovascular disease,
atherosclerosis
 Is caused by the buildup of cholesterol within arteries
Connective
tissue
Smooth muscle
Plaque
Endothelium
(a) Normal artery
50 µm
(b) Partly clogged artery
Figure 42.18a, b
250 µm

Hypertension, or high blood pressure
 Promotes atherosclerosis and increases the risk of
heart attack and stroke

A heart attack
 Is the death of cardiac muscle tissue resulting from
blockage of one or more coronary arteries

A stroke
 Is the death of nervous tissue in the brain, usually
resulting from rupture or blockage of arteries in the
head
Concept 42.5: Gas exchange occurs across
specialized respiratory surfaces
 Gas exchange

 Supplies oxygen for cellular respiration and
disposes of carbon dioxide
Respiratory
medium
(air of water)
O2
CO2
Respiratory
surface
Organismal
level
Circulatory system
Cellular level
Energy-rich
molecules
from food
Figure 42.19
Cellular respiration
ATP

Animals require large, moist respiratory
surfaces for the adequate diffusion of
respiratory gases
 Between their cells and the respiratory medium,
either air or water
Gills in Aquatic Animals

Gills are outfoldings of the body surface
 Specialized for gas exchange

In some invertebrates
 The gills have a simple shape and are distributed
over much of the body
(a) Sea star. The gills of a sea
star are simple tubular
projections of the skin.
The hollow core of each gill
is an extension of the coelom
(body cavity). Gas exchange
occurs by diffusion across the
gill surfaces, and fluid in the
coelom circulates in and out of
the gills, aiding gas transport.
The surfaces of a sea star’s
tube feet also function in
gas exchange.
Gills
Coelom
Figure 42.20a
Tube foot

Many segmented worms have flaplike gills
 That extend from each segment of their body
(b) Marine worm. Many
polychaetes (marine
worms of the phylum
Annelida) have a pair
of flattened appendages
called parapodia on
each body segment. The
parapodia serve as gills
and also function in
crawling and swimming.
Parapodia
Figure 42.20b
Gill

The gills of clams, crayfish, and many other
animals
 Are restricted to a local body region
(c) Scallop. The gills of a
scallop are long,
flattened plates
that project from the
main body mass
inside the hard shell.
Cilia on the gills
circulate water around
the gill surfaces.
(d) Crayfish. Crayfish and
other crustaceans
have long, feathery
gills covered by the
exoskeleton. Specialized
body appendages
drive water over
the gill surfaces.
Gills
Gills
Figure 42.20c, d

The effectiveness of gas exchange in some
gills, including those of fishes
 Is increased by ventilation and countercurrent flow
of blood and water
Oxygen-poor
blood
Gill arch
Gill
arch
Water
flow
Blood
vessel
Oxygen-rich
blood
Lamella
Operculum
O2
Figure 42.21
Water flow
over lamellae
showing % O2
Gill
filaments
Blood flow
through capillaries
in lamellae
showing % O2
Countercurrent exchange
Tracheal Systems in Insects
 Consists of tiny branching tubes that penetrate the
body
Air sacs
Tracheae
Spiracle
(a) The respiratory system of an insect consists of branched internal
tubes that deliver air directly to body cells. Rings of chitin reinforce
the largest tubes, called tracheae, keeping them from collapsing.
Enlarged portions of tracheae form air sacs near organs that require
a large supply of oxygen. Air enters the tracheae through openings
called spiracles on the insect’s body surface and passes into smaller
tubes called tracheoles. The tracheoles are closed and contain fluid
(blue-gray). When the animal is active and is using more O2, most of
the fluid is withdrawn into the body. This increases the surface area
of air in contact with cells.
Figure 42.22a

The tracheal tubes
 Supply O2 directly to body cells
Body
cell
Air
sac
Tracheole
Trachea
Air
Tracheoles
Mitochondria
Body wall
Myofibrils
(b) This micrograph shows cross
sections of tracheoles in a tiny
piece of insect flight muscle (TEM).
Each of the numerous mitochondria
in the muscle cells lies within about
5 µm of a tracheole.
Figure 42.22b
2.5 µm
Lungs

Spiders, land snails, and most terrestrial
vertebrates
 Have internal lungs
Mammalian Respiratory Systems:
A system of branching ducts
 Conveys air to the lungs
Branch
from the
pulmonary
artery
(oxygen-poor
blood)
Branch
from the
pulmonary
vein
(oxygen-rich
blood)
Terminal
bronchiole
Nasal
cavity
Pharynx
Left
lung
Alveoli
50 µm
Larynx
Esophagus
Trachea
50 µm

Right lung
Bronchus
Bronchiole
Diaphragm
Heart
SEM
Figure 42.23
Colorized SEM

In mammals, air inhaled through the nostrils
 Passes through the pharynx into the trachea,
bronchi, bronchioles, and dead-end alveoli, where
gas exchange occurs
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 Mammal Breathes

Mammals ventilate their lungs
 By negative pressure breathing, which pulls air into
the lungs
Rib cage
expands as
rib muscles
contract
Air inhaled
Rib cage gets
smaller as
rib muscles
relax
Air exhaled
Lung
Diaphragm
INHALATION
Diaphragm contracts
(moves down)
Figure 42.24
EXHALATION
Diaphragm relaxes
(moves up)

Lung volume increases
 As the rib muscles and diaphragm contract
How a Bird Breathes

Besides lungs, bird have eight or nine air sacs
 That function as bellows that keep air flowing
through the lungs
Air
Air
Anterior
air sacs
Trachea
Posterior
air sacs
Lungs
Lungs
Air tubes
(parabronchi)
in lung
INHALATION
Air sacs fill
EXHALATION
Air sacs empty; lungs fill
Figure 42.25
1 mm

Air passes through the lungs
 In one direction only

Every exhalation
 Completely renews the air in the lungs
Control of Breathing in Humans

The main breathing control centers
 Are located in two regions of the brain, the
medulla oblongata and the pons
Cerebrospinal
fluid
1 The control center in the
medulla sets the basic
rhythm, and a control center
in the pons moderates it,
smoothing out the
transitions between
inhalations and exhalations.
Pons
2 Nerve impulses trigger
muscle contraction. Nerves
from a breathing control center
in the medulla oblongata of the
brain send impulses to the
diaphragm and rib muscles,
stimulating them to contract
and causing inhalation.
Breathing
control
centers
Medulla
oblongata
4 The medulla’s control center
also helps regulate blood CO2 level.
Sensors in the medulla detect changes
in the pH (reflecting CO2 concentration)
of the blood and cerebrospinal fluid
bathing the surface of the brain.
5 Nerve impulses relay changes in
CO2 and O2 concentrations. Other
sensors in the walls of the aorta
and carotid arteries in the neck
detect changes in blood pH and
send nerve impulses to the medulla.
In response, the medulla’s breathing
control center alters the rate and
depth of breathing, increasing both
to dispose of excess CO2 or decreasing
both if CO2 levels are depressed.
Carotid
arteries
Aorta
Figure 42.26
3 In a person at rest, these
nerve impulses result in
about 10 to 14 inhalations
per minute. Between
inhalations, the muscles
relax and the person exhales.
Diaphragm
Rib muscles
6 The sensors in the aorta and
carotid arteries also detect changes
in O2 levels in the blood and signal
the medulla to increase the breathing
rate when levels become very low.

The centers in the medulla
 Regulate 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

Sensors in the aorta and carotid arteries
 Monitor O2 and CO2 concentrations in the blood
 Exert secondary control over breathing
Concept 42.7: Respiratory pigments bind and
transport gases
 The metabolic demands of many organisms

 Require that the blood transport large quantities of
O2 and CO2
The Role of Partial Pressure
Gradients

Gases diffuse down pressure gradients
 In the lungs and other organs

Diffusion of a gas
 Depends on differences in a quantity called partial
pressure

A gas always diffuses from a region of higher
partial pressure
 To a region of lower partial pressure

In the lungs and in the tissues
 O2 and CO2 diffuse from where their partial
pressures are higher to where they are lower
Inhaled air
Exhaled air
160 0.2
O2 CO2
120 27
Alveolar spaces
O2 CO2
104
Alveolar
epithelial
cells
40
O2 CO2
Blood
entering
alveolar
capillaries
40
O2
CO2
2
1
O2
Alveolar
capillaries
of lung
45
O2 CO2
104
Pulmonary
veins
Systemic
arteries
Systemic
veins
CO2
40
45
Heart
Tissue
capillaries
O2
3
4
O2
CO2
Blood
entering
tissue
capillaries
100
40
O2 CO2
O2 CO2
Tissue
cells
Figure 42.27
40
O2 CO2
Pulmonary
arteries
Blood
leaving
tissue
capillaries
Blood
leaving
alveolar
capillaries
<40 >45
O2 CO2
Respiratory Pigments

Respiratory pigments
 Are proteins that transport oxygen
 Greatly increase the amount of oxygen that blood
can carry
Oxygen Transport

The respiratory pigment of almost all
vertebrates
 Is the protein hemoglobin, contained in the
erythrocytes

Like all respiratory pigments
 Hemoglobin must reversibly bind O2, loading O2 in
the lungs and unloading it in other parts of the body
Heme group
Iron atom
O2 loaded
in lungs
O2 unloaded
In tissues
Figure 42.28
Polypeptide chain
O2
O2

Loading and unloading of O2
 Depend on cooperation between the subunits of the
hemoglobin molecule

The binding of O2 to one subunit induces the
other subunits to bind O2 with more affinity

Cooperative O2 binding and release
 Is evident in the dissociation curve for hemoglobin

A drop in pH
 Lowers the affinity of hemoglobin for O2
O2 saturation of hemoglobin (%)
(a) PO2 and Hemoglobin Dissociation at 37°C and pH 7.4
O2 unloaded from
hemoglobin
during normal
metabolism
100
80
O2 reserve that can
be unloaded from
hemoglobin to
tissues with high
metabolism
60
40
20
0
0
20
40
60
Tissues during Tissues
at rest
exercise
80 100
Lungs
(b) pH and Hemoglobin Dissociation
Figure 42.29a, b
O2 saturation of hemoglobin (%)
PO2 (mm Hg)
100
pH 7.4
80
60
pH 7.2
40
20
0
0
20
40
Bohr shift:
Additional O2
released from
hemoglobin at
lower pH
(higher CO2
concentration)
60
PO2 (mm Hg)
80 100
Carbon Dioxide Transport

Hemoglobin also helps transport CO2
 And assists in buffering

Carbon from respiring cells
 Diffuses into the blood plasma and then into
erythrocytes and is ultimately released in the lungs
1
2
Carbon dioxide produced by
body tissues diffuses into the
interstitial fluid and the plasma.
Over 90% of the CO2 diffuses
into red blood cells, leaving only 7%
in the plasma as dissolved CO2.
Tissue cell
Some CO2 is picked up and
transported by hemoglobin.
1
Blood plasma CO2
within capillary
Capillary
wall
2
CO2
Carbonic acid dissociates into a
biocarbonate ion (HCO3–) and a
hydrogen ion (H+).
HCO3–
7
Hemoglobin binds most of the
H+ from H2CO3 preventing the H+
from acidifying the blood and thus
preventing the Bohr shift.
Figure 42.30
9
Carbonic acid is converted back
into CO2 and water.
10
CO2 formed from H2CO3 is unloaded
from hemoglobin and diffuses into the
interstitial fluid.
To lungs
CO2 transport
to lungs
HCO3–
8
H2CO3
Hb
9
11 CO2
Hemoglobin
releases
CO2 and H+
H2O
CO2
6
In the HCO3– diffuse
from the plasma red blood cells,
combining with H+ released from
hemoglobin and forming H2CO3.
6
HCO3– + H+
5
8
Red
Hemoglobin
H2CO3
blood Carbonic acid Hb
picks up
cell
CO2 and H+
5
+ H+
Bicarbonate
However, most CO2 reacts with water
in red blood cells, forming carbonic
acid (H2CO3), a reaction catalyzed by
carbonic anhydrase contained. Within
red blood cells.
Most of the HCO3– diffuse
into the plasma where it is
carried in the bloodstream to
the lungs.
3
4
HCO3–
4
7
Interstitial CO
2
fluid
H2O
3
CO2 transport
from tissues
CO2 produced
CO2
CO2 10
CO2 11
Alveolar space in lung
diffuses into the alveolar
space, from which it is expelled
during exhalation. The reduction
of CO2 concentration in the plasma
drives the breakdown of H2CO3
Into CO2 and water in the red blood
cells (see step 9), a reversal of the
reaction that occurs in the tissues
(see step 4).
Elite Animal Athletes

Migratory and diving mammals
 Have evolutionary adaptations that allow them to
perform extraordinary feats
The Ultimate Endurance Runner

The extreme O2 consumption of the antelopelike pronghorn
 Underlies its ability to run at high speed over long
distances
Figure 42.31
Diving Mammals

Deep-diving air breathers
 Stockpile O2 and deplete it slowly