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Exchange of materials with the environment
• Overview: Trading with the Environment
• Every organism must exchange materials with
its environment and this exchange ultimately
occurs at the cellular level
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• In unicellular organisms the exchange of
materials occurs directly with the environment
• However, for most of the cells making up
multicellular organisms direct exchange with
the environment is not possible as they are not
in direct contact with the environment.
• Multicellular animals thus need structures
specialized for exchange with the outside and a
means of transporting materials from these
structures to all of the body’s cells.
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Salmon gills
• The feathery gills projecting from a salmon are
an example of a specialized exchange system
found in animals.
Figure 42.1
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Internal transport systems
• 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 substances with the outside
environment.
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Invertebrate Circulation
• The wide range of invertebrate body size and
form is paralleled by a great diversity in
circulatory systems.
• Simple animals, such as cnidarians (corals and
jellyfish) 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.
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Cnidarian gastrovascular cavity
• Some cnidarians, such as jellyfish have elaborate
gastrovascular cavities that funnel substances
throughout the body.
Circular
canal
Mouth
Radial canal
5 cm
Figure 42.2
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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)
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Open circulatory system
• 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
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Closed circulatory system
• In a closed circulatory system blood is confined
to vessels and is distinct from the interstitial
fluid (the fluid that surrounds the cells).
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
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Survey of Vertebrate Circulation
• Closed systems are more efficient at
transporting circulatory fluids to tissues and
cells because pressure can be maintained
more easily.
• 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 fourchambered heart.
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• Arteries carry blood to capillaries the sites of
chemical exchange between the blood and
interstitial fluid.
• Capillaries are extremely thin-walled blood
vessels.
• Veins return blood from capillaries to the heart.
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Fishes
• A fish heart has two main chambers
– One ventricle (the chamber from which blood
flows out of the heart) and one atrium (the
chamber in the heart blood enters into)
• Blood pumped from the ventricle travels to the
gills, where it picks up O2 and disposes of CO2
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Amphibians
• Frogs and other amphibians have a threechambered heart, with two atria and one
ventricle
• The ventricle pumps blood into a forked artery
that splits the ventricle’s output into the
pulmocutaneous (lung and skin) circuit and the
systemic (rest of the body) circuit.
• Because there is only one ventricle a mix of
oxygenated and deoxygenated blood is
pumped to the tissues.
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• Vertebrate circulatory systems
AMPHIBIANS
REPTILES (EXCEPT BIRDS)
MAMMALS AND BIRDS
Lung and skin capillaries
Lung capillaries
Lung capillaries
FISHES
Gill capillaries
Artery
Pulmocutaneous
circuit
Gill
circulation
Heart:
ventricle (V)
A
Atrium (A)
Systemic
Vein circulation
Systemic capillaries
Right
systemic
aorta
Pulmonary
circuit
A
A
V
Right
V
Left
Right
Systemic
circuit
Systemic capillaries
Figure 42.4
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Pulmonary
circuit
Left
Systemic
V aorta
Left
A
Systemic capillaries
A
V
Right
A
V
Left
Systemic
circuit
Systemic capillaries
Reptiles (Except Birds)
• Reptiles have double circulation with a
pulmonary circuit (lungs) and a systemic circuit,
but there is still only a single ventricle although
it is partially divided reducing mixing of
oxygenated and deoxygenated blood.
• Turtles, snakes, and lizards have a threechambered heart.
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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
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Four-chambered heart
• A powerful four-chambered heart was an
essential adaptation of the endothermic way of
life characteristic of mammals and birds.
• Keeping oxygen rich and oxygen depleted
blood separated enables oxygen to be
delivered to the tissues more efficiently.
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• Vertebrate circulatory systems
AMPHIBIANS
REPTILES (EXCEPT BIRDS)
MAMMALS AND BIRDS
Lung and skin capillaries
Lung capillaries
Lung capillaries
FISHES
Gill capillaries
Artery
Pulmocutaneous
circuit
Gill
circulation
Heart:
ventricle (V)
A
Atrium (A)
Systemic
Vein circulation
Systemic capillaries
Right
systemic
aorta
Pulmonary
circuit
A
A
V
Right
V
Left
Right
Systemic
circuit
Systemic capillaries
Figure 42.4
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Pulmonary
circuit
Left
Systemic
V aorta
Left
A
Systemic capillaries
A
V
Right
A
V
Left
Systemic
circuit
Systemic capillaries
Mammalian Circulation: The Pathway
• Heart valves dictate a one-way flow of blood
through the heart by preventing blood flowing
backwards.
• Blood begins its flow with the right ventricle
pumping blood to the lungs via the pulmonary
artery.
• In the lungs the blood loads O2 and unloads
CO2
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Mammalian Circulation: The Pathway
• Oxygen-rich blood from the lungs travels
through through the pulmonary vein and enters
the heart at the left atrium. It then is pumped
by the left ventricle via the aorta to the body
tissues.
• Blood returns to the heart from the body via the
anterior and posterior venae cavae (singular
vena cava) through the right atrium.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
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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 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
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Left ventricle
Cardiac Cycle
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cardiac Cycle
• Two sets of valves in the heart are important in
controlling blood flow within the heart.
• The semilunar valves control the flow of blood
from the ventricles into the aorta and the
pulmonary arteries.
• The atrioventricular (or AV) valves control the
flow of blood from the atria to the ventricles.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• During the cardiac cycle first both atria and
ventricles relax and blood flows into the atria and
from the atria into the ventricles. The AV valves
are open and semilunar valves are closed.
• Then the atria contract and the ventricles remain
relaxed so the blood from the atria flows into the
ventricles.
• Finally, the semilunar valves open and the AV
valves close. The atria relax and the ventricles
contract forcing blood out of the ventricles into the
arteries.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
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AV valves
closed
3 Ventricular systole;
atrial diastole
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
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• The impulses that travel during the cardiac
cycle can be recorded as an electrocardiogram
(ECG or EKG).
• The pacemaker is influenced by nerves,
hormones, body temperature, and exercise
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• 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.
to heart apex.
4 Signals spread
Throughout
ventricles.
Bundle
branches
AV node
Heart
apex
ECG
Figure 42.8
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Purkinje
fibers
Blood Vessel Structure and Function
• The “infrastructure” of the circulatory system is
its network of blood vessels: arteries,
capillaries and veins.
• Structural differences in arteries, veins, and
capillaries are related to their different
functions.
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• Arteries have thick muscular walls because they
must withstand the high pressure of blood pumped
from the heart.
• Veins have thinner walls that can be squeezed by
surrounding muscles and also valves that prevent
blood flowing backwards.
• Capillaries have extremely thin walls to facilitate
the transfer of materials across them.
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• In the thinly 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
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• The velocity of blood flow varies in the circulatory
system. It is slowest in the capillary beds as a
result of the high resistance and large total crosssectional area
• The critical exchange of substances is between
the blood and interstitial fluid. It takes place
across the thin endothelial walls of the
capillaries.
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Blood Composition and Function
• Blood is a connective tissue with several kinds
of cells suspended in a liquid matrix called
plasma
• The cellular elements occupy about 45% of the
volume of blood.
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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 and
• Plasma proteins which influence blood pH,
osmotic pressure, and viscosity.
• Various types of plasma proteins also function
in lipid transport, immunity, and blood clotting.
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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
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• 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
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250,000
400,000
Blood clotting
Cellular elements of blood
• Red blood cells, or erythrocytes are by far the
most numerous blood cells and transport oxygen
throughout the body.
• White blood cells, or leukocytes function in
defense by phagocytizing bacteria and debris or
by producing antibodies
• Platelets function in blood clotting
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Stem Cells and the Replacement of Cellular Elements
• The cellular elements of blood wear out and
are replaced constantly throughout a person’s
life.
• The spleen is the organ that scrutinizes blood
cells and destroys those that have become old
and inflexible (and less able to squeeze
through capillaries).
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• 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
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Platelets
Monocytes
Blood Clotting
• When the endothelium of a blood vessel is
damaged the clotting mechanism begins.
• Platelets adhere to collagen fibers in the
connective tissue and release a substance that
makes nearby platelets sticky.
• Platelets form a plug in the opening. In
addition, a cascade of complex reactions
converts fibrinogen to fibrin. Threads of fibrin
form a mesh patch that seals the opening
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Respiratory structures
• Animals require large, moist respiratory
surfaces for the adequate diffusion of
respiratory gases between their cells and the
respiratory medium, either air or water.
• Gas exchange can occur across the skin, but
specialized structures (lungs and gills) and
common.
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Gills in Aquatic Animals
• Gills are outfoldings of the body surface specialized for gas
exchange.
• 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
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• 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
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Blood flow
through capillaries
in lamellae
showing % O2
Countercurrent exchange
Lungs
• Spiders, land snails, and most terrestrial
vertebrates including mammals have internal
lungs.
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Mammalian Respiratory Systems: A Closer Look
• 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
50 µm
Larynx
Esophagus
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
SEM
Heart
Figure 42.23
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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
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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.
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
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EXHALATION
Diaphragm relaxes
(moves up)
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
EXHALATION
Air sacs empty; lungs fill
INHALATION
Air sacs fill
Figure 42.25
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1 mm
• In birds air passes through the lungs in one
direction only
• Every exhalation completely renews the air in
the lungs. Air flows in only one direction and a
countercurrent blood flow system maximizes
oxygen extraction.
• As a result, bird lungs are more efficient than
mammalian lungs.
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Control of breathing in humans
• The main breathing control centers are located
in two regions of the brain, the medulla
oblongata and the pons.
• 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.
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Control of Breathing in Humans
The
1 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.
Nerve
impulses trigger
2
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
Cerebrospinal
The medulla’s control center
fluid
also helps regulate blood CO2 level.
Sensors in the medulla detect changes
in the pH (reflecting CO2 concentration)
4
of the blood and cerebrospinal fluid
bathing the surface of the brain.
Nerve impulses relay changes in
5
CO2 and O2 concentrations. Other
sensors in the walls of the aorta
Pons
and carotid arteries in the neck
detect changes in blood pH and
send nerve impulses to the medulla.
Medulla
In response, the medulla’s breathing
oblongata
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
Figure
In a person at rest, these
nerve impulses
result in
3
about 10 to 14 inhalations
per minute. Between
inhalations, the muscles
42.26relax and the person exhales.
Aorta
Diaphragm
Rib muscles
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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.
Control of breathing in humans
• Sensors in the aorta and carotid arteries
monitor O2 and CO2 concentrations in the
blood and exert secondary control over
breathing.
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O2 and CO2 transport
• The metabolic demands of many organisms
require that the blood transport large quantities
of O2 and CO2
• 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
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Respiratory Pigments
• Respiratory pigments are proteins that
transport oxygen and they greatly increase the
amount of oxygen that blood can carry.
• The respiratory pigment of almost all
vertebrates is the protein hemoglobin,
contained in the erythrocytes.
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Hemoglobin structure
• 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
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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
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• Cooperative O2 binding and release is evident
in the dissociation curve for hemoglobin
• A drop in pH occurs when CO2 reacts with
water in red blood cells and forms carbonic
acid. The reduced pH lowers the affinity of
hemoglobin for O2
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O2 saturation of hemoglobin (%)
(a) PO2 and Hemoglobin Dissociation at 37°C and pH 7.4
O2 unloaded from
hemoglobin
during normal
80 metabolism
O2 reserve that can
be unloaded from
60
hemoglobin to
tissues with high
40
metabolism
100
20
0
0
20
40
60
80
Tissues duringTissues
at rest
exercise
100
Lungs
(b) pH and Hemoglobin Dissociation
Figure 42.29a, b
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O2 saturation of hemoglobin (%)
PO2 (mm Hg)
100
pH 7.4
80
Bohr shift:
Additional O2
released from
pH 7.2 hemoglobin at
lower pH
(higher CO2
concentration)
60
40
20
0
0
20
60 80
40
PO2 (mm Hg)
100
Carbon Dioxide Transport
• Hemoglobin also helps transport CO2 and
assists in buffering.
• Most CO2 diffuses into the blood plasma and
then into erythrocytes and is ultimately
released in the lungs
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