Transcript Lecture #11 – Animal Circulation and Gas Exchange Systems

Lecture #10 – Animal Circulation
and Gas Exchange Systems
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Key Concepts:
•
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•
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Circulation and gas exchange – why?
Circulation – spanning diversity
Hearts – the evolution of double circulation
Blood circulation and capillary exchange
Blood structure and function
Gas exchange – spanning diversity
Breathing – spanning diversity
Respiratory pigments
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Animals use O2 and produce CO2
• All animals are aerobic
Lots of oxygen is required to support active
mobility
Some animals use lots of oxygen to maintain
body temperature
• All animals produce CO2 as a byproduct of
aerobic respiration
• Gasses must be exchanged
Oxygen must be acquired from the environment
Carbon dioxide must be released to the
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environment
Animals use O2 and produce CO2
• Circulation systems move gasses (and other
essential resources such as nutrients,
hormones, etc) throughout the animal’s
body
• Respiratory systems exchange gasses with
the environment
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Circulation systems have evolved
over time
• The most primitive animals exchange
gasses and circulate resources entirely by
diffusion
Process is slow and cannot support 3-D large
bodies
• Sponges, jellies and flatworms use diffusion
alone
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Critical Thinking
• Why isn’t diffusion adequate for exchange
in a 3D large animal???
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Critical Thinking
• Why isn’t diffusion adequate for exchange
in a 3D large animal???
• Surface area / volume ratio becomes too
small
• Remember, area is a square function;
volume is a cubic function
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Critical Thinking
• But…..plants rely on
diffusion for gas
exchange…..how do
they get so big???
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Critical Thinking
• But…..plants rely on
diffusion for gas
exchange…..how do
they get so big???
• Their living tissue is
close to the surface
and exposed to air –
either in the open
atmosphere or in the
soil atmosphere
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Circulation systems have evolved
over time
• The most primitive animals exchange
gasses and circulate resources entirely by
diffusion
Process is slow and cannot support 3-D large
bodies
Surface area / volume ratio becomes too small
• Sponges, jellies and flatworms use diffusion
alone
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Virtually every cell in a sponge is in direct
contact with the water – little circulation is
required
Diagram of sponge structure
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• Jellies and flatworms have thin bodies and
elaborately branched gastrovascular cavities
Again, all cells are very close to the external
environment
This facilitates diffusion
Some contractions help circulate (contractile
fibers in jellies, muscles in flatworms)
Diagram of jellyfish structure, and photos
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Circulation systems have evolved
over time
• Most invertebrates (esp. insects) have an
open circulatory system
 Metabolic energy is
used to pump
hemolymph through
blood vessels into the
body cavity
 Hemolymph is returned
to vessels via ostia –
pores that draw in the
fluid as the heart
relaxes
Diagram of open
circulatory system in a
grasshopper
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Circulation systems have evolved
over time
• Closed circulatory systems separate blood
from interstitial fluid
 Metabolic energy is
used to pump blood
through blood vessels
 Blood is contained
within the vessels
 Exchange occurs by
diffusion in capillary
beds
Diagram of a closed
circulatory system, plus
a diagram showing an
earthworm circulatory
system
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Open vs. Closed…both systems
are common
Open systems….
• Use less metabolic
energy to run
• Use less metabolic
energy to build
• Can function as a
hydrostatic skeleton
• Most invertebrates
(except earthworms
and larger mollusks)
have open systems
Closed systems….
• Maintain higher
pressure
• Are more effective at
transport
• Supply more oxygen
to support larger and
more active animals
• All vertebrates have
closed systems
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All vertebrates have a closed
circulatory system
• Chambered heart pumps blood
Atria receive blood
Ventricles pump blood
• Vessels contain the blood
Veins carry blood to atria
Arteries carry blood from ventricles
• Capillary beds facilitate exchange
Capillary beds separate arteries from veins
Highly branched and very tiny
We’ll go over these
Infiltrate all tissues in the body
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step by step
Chambered heart pumps blood
• Atria receive blood
• Ventricles pump
blood
Diagram of a chambered heart
• One-way valves
direct blood flow
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Critical Thinking
• Atria receive blood; ventricles pump
• Given that function, what structure would
you predict???
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Critical Thinking
• Atria receive blood; ventricles pump
• Given that function, what structure would
you predict???
• Atria are soft, flexible chambers
• Ventricles have much more muscular walls
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Chambered heart pumps blood
• Atria receive blood
Soft walled, flexible
• Ventricles pump
blood
Thick, muscular
walls
Diagram of a chambered heart
• One-way valves
direct blood flow
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Vessels contain the blood
• Arteries carry blood
from ventricles
Always under pressure
• Veins carry blood to
atria
One-way valves
prevent back flow
Body movements
increase circulation
Pressure is always low
Diagram showing
artery, vein and
capillary bed
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Note that blood vessel names reflect the
direction of flow, NOT the amount of
oxygen in the blood
• Arteries carry blood
AWAY from the heart
Arterial blood is always
under pressure
It is NOT always
oxygenated
Diagram of blood
circulation pattern
in humans
• Veins carry blood TO
the heart
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Capillary beds facilitate exchange
•
•
•
•
Capillary beds separate arteries from veins
Highly branched and very tiny
Infiltrate all tissues in the body
More later
Diagram showing
artery, vein and
capillary bed
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All vertebrates have a closed
circulatory system – REVIEW
• Chambered heart pumps blood
Atria receive blood
Ventricles pump blood
• Vessels contain the blood
Veins carry blood to atria
Arteries carry blood from ventricles
• Capillary beds facilitate exchange
Capillary beds separate arteries from veins
Highly branched and very tiny
Infiltrate all tissues in the body
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Key Concepts:
•
•
•
•
•
•
•
•
Circulation and gas exchange – why?
Circulation – spanning diversity
Hearts – the evolution of double circulation
Blood circulation and capillary exchange
Blood structure and function
Gas exchange – spanning diversity
Breathing – spanning diversity
Respiratory pigments
25
Evolution of double circulation –
not all animals have a 4-chambered heart
Diagram showing progression from a 1chambered heart to a 4-chambered heart.
This diagram is used in the next 12 slides.
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Fishes have a 2-chambered heart
• One atrium, one ventricle
• A single pump of the heart
circulates blood through 2
capillary beds in a single circuit
Blood pressure drops as blood
enters the capillaries (increase in
cross-sectional area of vessels)
Blood flow to systemic capillaries
and back to the heart is very slow
Flow is increased by swimming
movements
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Two circuits increases the efficiency of
gas exchange = double circulation
• One circuit goes to exchange surface
• One circuit goes to body systems
• Both under high pressure – increases flow rate
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Amphibians have a 3-chambered heart
• Two atria, one ventricle
• Ventricle pumps to 2 circuits
One circuit goes to lungs and skin
to release CO2 and acquire O2
The other circulates through body
tissues
• Oxygen rich and oxygen poor
blood mix in the ventricle
A ridge helps to direct flow
• Second pump increases the
speed of O2 delivery to the body
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Most reptiles also have a 3-chambered
heart
• A partial septum further
separates the blood flow and
decreases mixing
Crocodilians have a complete
septum
• Point of interest: reptiles have
two arteries that lead to the
systemic circuits
Arterial valves help direct blood
flow away from pulmonary circuit
when animal is submerged
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Critical Thinking
• What is a disadvantage of a 3 chambered
heart???
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Critical Thinking
• What is a disadvantage of a 3 chambered
heart???
• Oxygen rich and oxygen poor blood mix in
the ventricle
• Less than maximum efficiency
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Mammals and birds have
4-chambered hearts
• Two atria and two ventricles
• Oxygen rich blood is completely
separated from oxygen poor blood
No mixing  much more efficient
gas transport
Efficient gas transport is essential
for both movement and support of
endothermy
Endotherms use 10-30x more
energy to maintain body
temperatures
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Mammals and birds have
4-chambered hearts
• Mammals and birds are NOT
monophyletic
• What does this mean???
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Mammals and birds have
4-chambered hearts
• Mammals and birds are NOT monophyletic
• Mammals and birds evolved from separate
reptilian ancestors
Phylogenetic tree showing
the diversification of
vertebrates
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Mammals and birds have
4-chambered hearts
• Mammals and birds are NOT
monophyletic
• Four-chambered hearts evolved
independently
• What’s this called???
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Mammals and birds have
4-chambered hearts
• Mammals and birds are NOT
monophyletic
• Four-chambered hearts evolved
independently
• Convergent evolution
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Review: evolution of double circulation
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Key Concepts:
•
•
•
•
•
•
•
•
Circulation and gas exchange – why?
Circulation – spanning diversity
Hearts – the evolution of double circulation
Blood circulation and capillary exchange
Blood structure and function
Gas exchange – spanning diversity
Breathing – spanning diversity
Respiratory pigments
39
Blood Circulation
• Blood vessels are organs
Outer layer is elastic connective tissue
Middle layer is smooth muscle and elastic
fibers
Inner layer is endothelial tissue
• Arteries have thicker walls
• Capillaries have only an endothelium and
basement membrane
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Critical Thinking
• Arteries have thicker walls than veins
• Capillaries have only an endothelium and
basement membrane
• What is the functional significance of this
structural difference???
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Critical Thinking
• Arteries have thicker walls than veins
• Capillaries have only an endothelium and
basement membrane
• What is the functional significance of this
structural difference???
• Arteries are under more pressure than
veins
• Capillaries are the exchange surface
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Form reflects function…
• Arteries are
under more
pressure than
veins
• Capillaries are
the exchange
surface
Diagram showing
artery, vein and
capillary bed
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Blood
pressure
and velocity
drop as
blood moves
through
capillaries
Graph showing relationships
between blood pressure,
blood velocity, and the crosssectional area of different
kinds of blood vessels –
arteries to capillaries to
veins. This same graph is
on the next 3 slides.
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Total crosssectional area
in capillary
beds is much
higher than in
arteries or
veins; slows
flow
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Velocity
increases as
blood passes
into veins
(smaller crosssectional
area);
pressure
remains
dissipated
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One-way
valves and
body
movements
force blood
back to right
heart atrium
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Critical Thinking
• What makes rivers curl on the Coastal
Plain???
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Critical Thinking
• What makes rivers curl on the Coastal
Plain???
• Velocity is controlled by gravity in rivers
• The Coastal Plain is just a few meters
above sea level – little gravity to force
forward momentum
• The water slows; the rivers meander
• The functional equivalent to blood
meandering through a capillary bed
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Capillary Exchange
• Gas exchange and other transfers occur in
the capillary beds
• Muscle contractions determine which beds
are “open”
Brain, heart, kidneys and liver are generally
always fully open
Digestive system capillaries open after a meal
Skeletal muscle capillaries open during
exercise
etc…
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Bed fully open
Bed closed, throughflow only
Diagram showing
sphincter muscle
control over
capillary flow.
Micrograph of a
capillary bed.
Note scale – capillaries
are very tiny!!
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Capillary Transport Processes:
• Endocytosis  exocytosis across membrane
• Diffusion based on electrochemical gradients
• Bulk flow between endothelial cells
Water potential gradient forces solution out at
arterial end
Reduction in pressure draws most (85%) fluid
back in at venous end
Remaining fluid is absorbed into lymph, returned
at shoulder ducts
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Capillary Transport Processes:
• Endocytosis  exocytosis across membrane
• Diffusion based on concentration gradients
• Bulk flow between endothelial cells
Water potential gradient forces solution out at
arterial end
Reduction in pressure draws most (85%) fluid
back in at venous end
Remaining fluid is absorbed into lymph, returned
at shoulder ducts
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Bulk Flow in Capillary Beds
• Remember water potential: Ψ = P – s
• Remember that in bulk flow P is dominant
No membrane
Plus, in the capillaries, s is ~stable (blood
proteins too big to pass)
• P changes due to the interaction between
arterial pressure and the increase in crosssectional area
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Bulk Flow in Capillary Beds
Remember: Ψ = P – s
Diagram showing osmotic changes across a capillary bed
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Capillary Transport Processes:
• Endocytosis  exocytosis across membrane
• Diffusion based on concentration gradients
• Bulk flow between endothelial cells
Water potential gradient forces solution out at
arterial end
Reduction in pressure draws most (85%) fluid
back in at venous end
Remaining fluid is absorbed into lymph, returned
at shoulder ducts
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