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The heart and circulation
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1. The body's transport system
Blood travels around the body in over 75,000 miles of arteries,
veins and capillaries. Stretched end-to-end, that's three times
around the world! They transport oxygen from the lungs,
remove carbon dioxide from the cells and carry nutrients,
hormones and water to all parts of the body.
Arteries
Carry blood: away from
the heart
Picture 1.2 The structure of
arteries, veins and capillaries
Capillaries
Veins
from arteries towards the
to veins
heart
Pressure:
high
low
very low
Walls are:
thick and
muscular
with elastic
fibres
very thin and thin
leaky - one
cell thick
Blood is:
oxygenated
(except
pulmonary
artery)
exchanging
nutrients and
gases with
cells
deoxygenated
(except
pulmonary
vein)
Pulse:
Strong
none
none
Humans are endothermic and keep a constant body temperature
of 37 °C. The circulatory system plays a big part in regulating
body temperature and it is self-repairing. A blood clot quickly
forms to seal up a cut before new tissue grows to replace the
damaged area.
Layout of the circulation
The circulation in humans,
and other mammals, is a
closed loop of tubes that run
in a continuous figure of "8"
centred on the heart.
The heart is the pump that
keeps the blood flowing.
This is called a "double
circulation" system: one loop
carries blood around the
lungs . The blood is carried
to the lungs in the pulmonary
arteries and returns in the
pulmonary veins.
Picture 1.3a Circulation
system
The other loop supplies
blood at high pressure to the
head and body. The main
artery from the heart is the
aorta. It branches to carry
blood to the head and body.
The blood returns to the
heart in the vena cava.
Picture 1.3b. Figure of 8.
Question 1
Look at each of the descriptions below and
decide whether they relate to veins, arteries or
capillaries. Make your choice using the buttons
then press the 'Show answers' button to see how
you got on.
vein artery capillary
a) Oxygen and
glucose move out
into the tissues
b) The walls are under
a lot of pressure
c) Carbon dioxide is
picked up and
dissolves in the
plasma
d) contains valves to
stop the backflow
of blood
e) The blood flows
very quickly
f) There is one
specific vessel that
carries oxygenated
blood at a low
pressure. Type your
answer in the box
(make sure you
spell it correctly).