The Circulatory System
The function of your circulatory system is to carry
your blood to and from all of the organs in your
body. It consists of your heart, blood vessels and
all of the blood in your body (around 5 litres). By
transporting the blood around your body, it is
ensuring that oxygen, nutrients, hormones and
waste products are transported throughout the
body to the correct places. The circulatory system
is powered by your body’s hardest working organ
– your heart – this is your body’s engine.
Blood Vessels
Blood vessels are your body's transport systems
– they allow blood to flow quickly from the heart
to every area of your body and back again. The
amount of blood flow that passes through the
vessel will determine the size of the blood vessel.
All blood vessels contain a hollow area through
the middle where the blood is able to flow – this
is called the lumen. Surrounding the lumen is
the wall of the vessel, which can be thin or thick,
depending on the function of the vessel.
The Heart
The muscula
r pumping o
rgan, located
between you
r lungs in the
middle of yo
chest is your
ur
heart. The ve
ry bottom tip
of your heart
is called its a
pex, and this
turned to th
is
e left, meanin
g that about
thirds of you
two
r heart is loca
ted on your
side, with th
left
e other third
on your righ
heart has fo
t. Your
ur main cham
bers – the le
right atriums,
ft and
which are on
the top half
your heart, a
of
nd the left a
nd right ven
which are on
tricles,
the bottom h
alf of your h
eart.
TO YOUR BO
DY
right atrium
NGS
left atrium
FROM LUNG
S
FROM YOUR
There are three main types
of blood vessel:
TO YOUR LU
BODY
right ventricle
the septum
left ventricle
ARTERIES AND ARTERIOLES
Arteries are muscular elastic blood vessels that
bring oxygenated blood from the heart to all of
the cells of the body. The blood is usually highly
oxygenated. Blood is pushed into the arteries
with great force, and arteries need to be able
to withstand this. Therefore, artery walls are
much thicker, more elastic and more muscular
than other vessels. There are smaller arteries
that are more muscular in their walls as they
contract and expand in order to regulate blood
flow to different parts of the body depending on
circumstances.
Arterioles are even narrower arteries that
branch off from arteries and carry the blood into
capillaries. The blood pressure in arterioles is
lower than in arteries, as there are more of them,
less blood flowing through them, and they are
further from the heart. These arterioles are also
capable of controlling the blood flow through
them, regulating blood flow and pressure.
10 IGNIS
VEINS AND VENULES
Veins are the conduits that transport
deoxygenated blood back to the heart after it
has travelled to different areas of the body. They
are the blood counterparts of arteries. Because
it is the arteries, then the arterioles, then the
capillaries that absorb the force of the heart's
contractions, by the time blood gets to veins
and venules, there is very little blood pressure.
This means veins can have thinner walls with
less elasticity. Some veins have one-way valves
which prevent blood from flowing back away
from the heart, forcing the blood to travel in only
one direction. As skeletal muscles in your body
contract and move, they squeeze veins and help
push the blood through those valves and back
to your heart. Venules are similar to arterioles
in that they are small vessels, but instead of
connecting to arteries they connect to veins.
CAPILLARIES
These are the branchin
are the smallest and th
and also the most comm
in your body has capilla
it. Capillaries connect to
and venules on the oth
crucial to the exchange
waste and so they mus
to the cells of the tissue
exchange.