Transcript St. Francis Xavier University Circulatory Systems

Biology 201
Dr. Edwin DeMont
Circulation
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Circulation
The evolution of multicellularity required
the development of fluid transport systems.
Why?
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Circulation
An internal transport system is useful because it
reduces the distances over which substances must
diffuse—substances can be brought close to a target
point via the blood and then diffuse outward from
that point
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Circulatory Systems
Internal transport systems of invertebrates range
from simple fluid filled cavities to open systems and
some even have closed systems, analogous to
vertebrate systems.
Open circulatory system: the heart pumps fluid out
into the body cavity or at least to parts of the body
cavity, and bathes the cells, tissues and organs.
Closed circulatory system: fluid circulates in the
confines of tubular vessels.
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Transport Systems
St. Francis Xavier University
Transport Systems
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Circulatory Systems
Fluid: Hemolymph
High volume and slow circulation
Cells: Hemocytes
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Circulatory Systems
Blood is always in arteries, arterioles, capillaries, venules, veins, or within
the chambers of the heart.
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Fluid flow
Blood moves at
high velocity.
Heart generates
high pressure.
Total cross-sectional area
of capillaries is large and
velocity of flow is very
small.
Diffusion occurs here
so need low velocity.
Best to move blood
over large distances in
large vessels.
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Vertebrates
The disadvantage of this
system is the low
pressure flow through
the gills supports only a
low metabolic rate.
Energy is lost as
the blood flows
through the
capillaries – why?
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Vertebrates
A double circuit occurs
when blood from the lungs
is sent directly to the heart,
and blood from the tissues
also goes to the heart—
these systems are the
pulmonary and systemic
circulations, respectively
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Blood vessels
Arteries are characterized as elastic vessels that carry
blood away from the heart (high pressure).
Veins are larger, less elastic vessels that carry blood
to the heart (low pressure).
Capillaries are
one cell layer
thick – to allow
diffusion.
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Blood
Blood contains a fluid matrix called plasma and cellular
elements called formed elements.
Plasma is primarily composed of water, and also
contains proteins, ions, hormones, nutrients, and
wastes.
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Blood: Formed elements
Erythrocytes (red blood cells) contain hemoglobin, which
binds to oxygen for transport from lungs to other tissues.
Leukocytes (white blood cells). These cells function
in immunity.
Thrombocytes (platelets). They function in
clotting of the blood in response to injury.
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Red Blood Cells
Each cell has about 280 million molecules of hemoglobin.
The biconcave shape of RBCs is adaptive, as it gives
30% more surface area than a sphere.
RBCs are slightly larger
than capillaries and have
to squeeze through the
tiny capillaries.
This is adaptive. Why?
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