Download BL 1021 * Unit 1

BL 1021 – Unit 4.6 – 4.8
The Circulatory System
4.6 Circulatory Systems
• As animals get larger and more complex, the need
for a system to more nutrients and wastes from
place to place develops.
• There are three elements common to all circulatory
systems:
• A liquid carrier substance (blood)
• Vessels to carry the liquid (may not carry the liquid
all the time however)
• A pump to move the liquid (heart)
4.7 Open and Closed
Circulatory Systems
• The Open Circulatory
system is the more
primitive circulatory
system in which a heart is
present and the fluid
being pumped is a
combination of blood
and body cavity fluid.
• As the fluid does not stay
in the vessels the whole
time, it mixes with fluids
throughout the body to
form hemolymph.
• This type of system is
found in Phylum
Arthropoda.
4.7 Open and Closed
Circulatory Systems
• This open system has
one major
disadvantage – the
organism must keep
moving to assure that
the hemolymph bathes
all the cells of the
body.
4.7 Open and Closed
Circulatory Systems
• A closed circulatory
system is a more recent
and more complex
development. In a
closed system, the
blood never leaves the
vessels and does not
mix directly with the
various intercellular
fluids.
4.7 Open and Closed
Circulatory Systems
• By having vessels
reaching to every
corner of the creature,
blood can reach all
cells of the body
without needing the
body to move.
• In this type of system,
blood flows in a direct
loop or circuit.
4.7 Open and Closed
Circulatory Systems
• Closed systems have
three types of vessels to
carry blood:
• Arteries deliver blood
from the heart. They
have thick and strong
wall to handle the highpressure blood that
comes directly from the
heart.
4.7 Open and Closed
Circulatory Systems
• Veins return blood to
the heart. They are
thinner than arteries as
the blood has dropped
in pressure by the time
it reaches them.
• Veins have one-way
valves to prevent
blood from flowing
backwards and
pooling up.
4.7 Open and Closed
Circulatory Systems
• Capillaries are the
middle-section of the
system. These are very
small and very thin
vessels that can reach
all the parts of the
body. Their thin walls
allows them to easily
diffuse nutrients and
wastes between the
tissues and the blood.
4.8 Human Circulatory System
• The human cardiovascular system is composed of a
powerful four chamber heart (two atria which
receive blood and two ventricles which send
blood), a multitude of veins, arteries and network of
capillaries, and blood.
• The circuit of blood is known as double circulation
because blood will make its way through the heart
twice (through the right side then the left side)
before completing its circuit through the body. In a
very simplified description, the flow of blood is as
follows
4.8 Human Circulatory System
• On this diagram, the
left of the diagram
shows the right side of
the body.
• The path of blood
through the body:
• 1) Blood enters the right
ventricle. This
compartment seals off
and compresses to
release high-pressure
blood.
4.8 Human Circulatory System
• 2) Blood leaves the
heart and travels to the
lungs via the
pulmonary artery.
• 3) In the lungs, the
blood takes up oxygen
and releases carbon
dioxide.
• 4) Blood returns to the
heart through the
pulmonary vein.
4.8 Human Circulatory System
• The path so far is known
as the pulmonary
circuit. This pathway
gets fresh oxygen that
will be delivered to the
rest of the body in the
next step, the systemic
circuit.
• That circuit will carry
nutrients to the body’s
tissues and remove
wastes.
4.8 Human Circulatory System
• 5) Once blood returns
from the pulmonary
vein, it collects in the
left atrium.
• 6) The blood then
pumps into the left
ventricle.
• 7) The ventricles
contract, pumping out
the blood at max
pressure into the aorta.
4.8 Human Circulatory System
• 8) Blood heads to the
various parts of the
body from the aorta
through a number of
smaller arteries.
• Arteries connect to
capillary beds which
exchange substances
with the body’s tissues.
4.8 Human Circulatory System
• 9) After exchanging
substances with the
body, the blood
collects in a series of
veins that ultimately
combine into the vena
cava.
• 10) The blood collects
into the right atrium.
4.8 Human Circulatory System
• From the right atrium
blood returns to the
right ventricle to
complete the cycle.
• Both atria contract at
the same time and
both ventricles
contract at once.