Download video slide

Circulation and gas exchange
• Overview
• Circulation
• Gas exchange
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview
• 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
– These exchanges occur directly with the
environment
• For most of the cells making up multicellular
organisms
– Direct exchange with the environment is not
possible
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The feathery gills projecting from a salmon
– Are an example of a specialized exchange
system found in animals
Figure 42.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Circulation
• Overview
• Circulatory systems
– Open and closed
– Circulation in invertebrates
– Circulation in vertebrates
• Mammalian circulation system
–
The Pathway
–
The Pumping
–
The Movement
–
The Exchange
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Circulation
• Diffusion alone is not adequate for transporting
substances over long distances in animals
– Time for a substance to diffuse is proportional
to the square of the distance
• Transport systems
– Functionally connect the organs of exchange
with the body cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Some cnidarians, such as jellies
– Have elaborate gastrovascular cavities
Circular
canal
Mouth
Radial canal
5 cm
Figure 42.2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Open systems
– Less energetically costly
– Can function as a hydrostatic skeleton
• Closed systems
– Are more efficient at transporting circulatory
fluids to tissues and cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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 fourchambered heart
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Arteries carry blood to capillaries
– The sites of chemical exchange between the
blood and interstitial fluid
• Veins
– Return blood from capillaries to the heart
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Pulmonary
circuit
Left
Systemic
V aorta
Left
A
Systemic capillaries
A
V
Right
A
V
Left
Systemic
circuit
Systemic capillaries
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A powerful four-chambered heart
– Was an essential adaptation of the
endothermic way of life characteristic of
mammals and birds
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mammalian Circulation: The Pathway
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Capillaries of
abdominal organs
and hind limbs
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mammalian Circulation: The Pumping
• 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
• 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
• It depends on the heart rate and stroke
volume
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The SA node generates electrical impulses that
spread rapidly through the wall of the atria
• Purkinje fibers conduct the signals to the apex
of the heart and throughout ventricular walls
• This stimulates the ventricles to contract from
the apex toward the atria, driving blood to the
arteries
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The pacemaker is influenced by
– Nerves, hormones, body temperature, and
exercise
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mammalian Circulation: The Movement
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The “infrastructure” of the circulatory system
– Is its network of blood vessels
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Structural differences in arteries, veins, and
capillaries
– Correlate with their different functions
• Capillaries have very thin walls
– To enhance exchange
• Arteries have thicker walls
– To accommodate the high pressure of blood
pumped from the heart
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Blood Flow Velocity
• Physical laws governing the movement of fluids
through pipes
– Influence blood flow and blood pressure
• Blood travels over a thousand times faster
in the aorta than in capillaries
• Law of continuity
– Fluid flows through narrower segments of
the pipe faster than it flows through wider
segments
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The velocity of blood flow varies in the
circulatory system
Systolic
pressure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Veins
Venules
Venae cavae
Figure 42.11
Arterioles
Diastolic
pressure
Capillaries
120
100
80
60
40
20
0
Arteries
Velocity (cm/sec)
50
40
30
20
10
0
Aorta
Area (cm2)
5,000
4,000
3,000
2,000
1,000
0
Pressure (mm Hg)
– And is slowest in the capillary beds as a result of the
large total cross-sectional area
Blood Pressure
• Fluids exert a force called hydrostatic pressure
– Fluids flow from areas of high to low pressure
• Blood pressure
– Is the hydrostatic pressure that blood exerts
against the wall of a vessel; it is much greater
in the arteries when the heart contracts during
systole
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Surge of pressure felt during pulse is due to
narrow openings of arterioles impeding the exit
of blood from arteries, the peripheral resistance
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Blood pressure is determined partly by cardiac
output
– And partly by peripheral resistance due to
variable constriction of the arterioles
• Nerve impulses, hormones and other
signals control the arteriole wall muscles
– Stress, both physical and emotional can
raise blood pressure by triggering nervous
and hormonal responses that will constrict
blood vessels
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Cardiac output is adjusted in concert with
changes in peripheral resistance
– During heavy exercise, arterioles in working
muscles dilate admitting greater flow of oxygen
and decreasing peripheral resistance
– At the same time cardiac output increases
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Capillary Function
• Capillaries in major organs are usually filled to
capacity
– But in many other sites, the blood supply
varies
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
20 m
Mammalian Circulation: The Exchange
• The critical exchange of substances between
the blood and interstitial fluid
– Takes place across the thin endothelial walls of
the capillaries
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Direction of
blood flow
Blood pressure
Osmotic pressure
Inward flow
Pressure
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.
Outward flow
Figure 42.14
Arterial end of capillary
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Venule end
Fluid Return by the Lymphatic System
• The lymphatic system
– Returns fluid to the body from the capillary
beds
– Aids in body defense
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Fluid reenters the circulation
– Directly at the venous end of the capillary bed
and indirectly through the lymphatic system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Gas exchange
• Respiratory surfaces
• Respiratory adaptations for aquatic animals
• Respiratory adaptations for terrestrial animals
• Breathing across vertebrates
• Diffusion of gases
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Cellular respiration
Figure 42.19
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• For simple animals, plasma membrane of
every cell is close enough to outside
environment for gases to diffuse in and out
• Most animals, the bulk of the body lacks direct
access to the respiratory medium
– Some animals like earthworms and
amphibians use entire outer skin as a
respiratory organ, how?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Gills in Aquatic Animals
• Gills are outfoldings of the body surface
– Specialized for gas exchange
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Blood flow
through capillaries
in lamellae
showing % O2
Countercurrent exchange
Tracheal Systems in Insects
• The tracheal system of 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.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2.5 µm
Lungs
• Spiders, land snails, and most terrestrial
vertebrates
– Have internal lungs
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Colorized SEM
• Breathing ventilates the lungs
• The process that ventilates the lungs is
breathing
– The alternate inhalation and exhalation of air
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
How an Amphibian Breathes
• An amphibian such as a frog
– Ventilates its lungs by positive pressure
breathing, which forces air down the trachea
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
EXHALATION
Diaphragm relaxes
(moves up)
• Lung volume increases
– As the rib muscles and diaphragm contract
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1 mm
• Air passes through the lungs
– In one direction only
• Every exhalation
– Completely renews the air in the lungs
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A gas always diffuses from a region of higher
partial pressure
– To a region of lower partial pressure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• In the lungs and in the tissues
– O2 and CO2 diffuse from where their partial
pressures are higher to where they are lower
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
40
O2 CO2
Pulmonary
arteries
Blood
leaving
tissue
capillaries
Blood
leaving
alveolar
capillaries
Heart
Tissue
capillaries
O2
3
4
45
O2
CO2
Tissue
cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
100
40
O2 CO2
O2 CO2
Figure 42.27
Blood
entering
tissue
capillaries
<40 >45
O2 CO2