Circulation & Gas Exchange
Chapter 42, Campbell, 6th edition
Nancy G. Morris
Volunteer State Community College
Exchange of materials
between organism and environment:
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always occurs across a moist
membrane
nutrients, gases, and wastes
diffuse across membrane
molecules must be dissolved in
water in order to diffuse
across
Exchange of materials…
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In protozoans, the entire surface is
used for exchange.
Simple animals like sponges and
cnidarians are constructed so that
each cell is exposed to the
surrounding water. (What pattern
of construction permits this?)
What about triploblastic animals?
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some cells are isolated from the
surrounding environment
they require specialized organs for
exchange with the environment
AND special systems for internal
transport through body fluids to the
cells
What are the advantages of specialized
organs with an internal transport system?
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1) reduces distance over which
molecules must diffuse to enter
& leave a cell AND
2) permits regulation of internal
body fluids
Circulation in Animals
Transport systems functionally connect body
cells with the organs of exchange.
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Diffusion alone is too slow for complex
multicellular animals.
The time of diffusion is proportional to
the square of the distance the chemical
must travel:
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if a glucose molecule takes 1 second
to diffuse 100µm, it will take 100
seconds to diffuse 1 mm.
The presence of a circulatory system
reduces the distance a substance must
diffuse…
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because it connects the aqueous
environment of the cell with organs
specialized for exchange.
For example,
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O2 diffuses from air across thin epithelium
in the lung into the blood.
Oxygenated blood is carried via the
circulatory system to all parts of the body.
As blood passes through capillaries in the
tissues, O2 diffuses from the blood into the
cells across the plasma membrane.
CO2 is produced by the cells and moves in
the opposite direction.
The circulatory system…
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not only moves gases, but is a
critical component in maintaining
homeostasis of the body.
Blood passes from cells through
organs (liver, kidneys) that
regulate the nutrient and waste
content of the blood.
Circulation in Animals
Invertebrates have either a
gastrovascular cavity or a
circulatory system for
internal transport.
GASTROVASCULAR CAVITIES
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In sponges & cnidarians, nutrients have
only a short distance to diffuse to the
outer cell layer.
(Figure 42.1)
In flatworms & other platyhelminthes, no
cell is more than a few mm away from the
body surface.
Complex multicellular animals require some
type of circulatory system.
OPEN CIRCULATORY SYSTEMS
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Hemolymph bathes the internal organs directly
while moving through sinuses (Figure 42.2a)
Hemolymph acts as both blood and interstitial
fluid
Relaxation of the heart draws hemolymph
through the ostia into the vessel.
Insects, arthropods, mollusks
CLOSED CIRCULATORY SYSTEMS
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Blood is confined to vessels and interstitial
fluid is present
Heart (or hearts) pumps blood into large
vessels
Major vessels branch into smaller ones which
supply blood to organs (Figure 42.2b)
In the organs, materials are exchanged
between the blood and the interstitial fluid
bathing the cells.
Annelids and vertebrates
CARDIOVASCULAR SYSTEM
A closed circulatory system
consists of
1) a heart
2) blood vessels
3) blood
Closed cardiovascular systems
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A heart has one atrium or two atria, chambers
that receive blood, and one or two ventricles,
chambers that pump blood out.
Arteries carry blood away from the heart to
organs where they branch into smaller arterioles
that give rise to microscopic capillaries.
Capillaries rejoin to form venules, which converge
to form veins that return blood to the heart.
Capillaries
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Capillaries have thin, porous walls and
are arranged into networks called
capillary beds that infiltrate each
tissue.
The capillary wall is a single cell
thick.
This is the site of chemical exchange
between blood & interstitial fluid.
Fish: 2-chambered heart
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one atrium & one ventricle. (Fig 42.3a)
Blood pumped from the ventricle goes to the
gills. O2 diffuses into the gill capillaries and
CO2 diffuses out.
Gill capillaries converge into arteries that
carry blood to capillary beds in other organs.
Blood from the organs travels through veins to
the atrium, then into the ventricle.
Fish: 2-chambered heart
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Blood flows through two capillary beds during
each complete circuit: one in the gills and the
second in the organ systems (systemic
capillaries).
As blood flows through a capillary bed, blood
pressure drops substantially (due to the
resistance of the numerous small vessels).
Blood flow to the tissues and back to the
heart is aided by swimming motions.
2-chambered heart
1 atrium & 1 ventricle
in fish
Amphibians: 3-chambered heart
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two atria and one ventricle (Fig. 42.3b)
Blood flows in a double circulation scheme
through:
1) pulmocutaneous circuit (to lungs and skin)
2) systemic circuit (to all other organs)
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Blood flow pattern: ventricle -> lungs &
skin-> left atrium -> ventricle -> all other
organs -> right atrium
3-chambered
heart
• 2 atria & 1 ventricle of amphibian
Amphibians: 3-chambered heart
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There is some mixing of oxygen-rich
and oxygen-poor blood in the single
ventricle.
A ridge present in the ventricle
diverts most of the oxygenated blood
to the systemic circuit and most of
the deoxygenated blood to the
pulmonary circuit.
Reptiles: 3-chambered heart
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most reptiles (except crocodilians)
ventricle is partially divided
providing for double circulation:
1) a systemic circuit
2) a pulmonary circuit
partial division of ventricle reduces mixing of
oxygenated and deoxygenated blood
Birds & mammals: 4 chambers
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Double circulation:
1) systemic
2) pulmonary
complete septum eliminates mixing of
oxygenated and deoxygenated blood
separation greatly increases the efficiency
of O2 delivery to the cells
4-chambered heart
• 2 atria & 2 ventricles
• complete seperation of oxygenated
and deoxygenated blood
• right heart drives pulmonary
circulation
• left heart dives systemic
circulation
• complete separation of oxygenation
& deoxygenated blood
Human heart:
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located beneath the sternum
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cone-shaped about size of fist
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surrounded by pericardium (2 layers)
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cardiac muscle tissue
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atria collect blood returning to heart
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ventricles are powerful pumps
Four valves of human heart.
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Valves are flaps of connective tissue.
Atrioventricular valves –
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found between atria & ventricles
prevent backflow of blood
Semilunar valves
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located where aorta leaves left ventricle
located where pulmonary arteries leave
the right ventricle
A heart murmur
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is a defect in one or
more of the valves that
allows backflow of blood.
Heart’s rhythmic beat:
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Cardiac muscle is myogenic
(self-excitable).
contracts without input from the
nervous system
tempo is controlled by the sinoatrial
node (SA) sometimes called the
pacemaker.
SA node
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located in right atrium near the entrance
of the superior vena cava
composed of specialized muscle tissue
with characteristics of both muscle and
nervous tissue
contraction of SA causes a wave of
excitation to spread rapidly from the
node causing the two atria to contract in
unison
AV node
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second mass of specialized tissue
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receives the wave of excitation from SA
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impulse is delayed at the AV node for 0.1
second to ensure that the atria are
completely empty before the ventricles
contract
impulse is then carried by a mass of
specialized fibers, Bundle of His,
throughout the ventricle walls
Heart rate
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controlled by SA
influenced by:
1) two antagonistic sets of nerves– one
speeds contractions and the other slows
contractions
2) hormones influence the SA node –
epinephrine increases heart rate
3) other factors: body temperature &
exercise influence heart rate