Download Pluck Dissection

Technicians as demonstrators
Demonstration: Pluck
The organs (offal) of the thoracic cavity of livestock are known collectively as the
pluck.
Plucks are available from abattoirs, butchers and suppliers such as
http://www.samples-for-schools.co.uk/
They can be any animal that has come through these suppliers but you may want
to take cultural differences into account with certain animals.
Health and safety
In terms of Health & Safety and disposal refer to CLEAPSS handbook or SSERC,
good general hygiene is needed. Wash hands thoroughly after touching dissection
material; gloves and safety specs can be worn (especially when cutting bone or
cartridge etc).
Equipment
Have a selection of scalpels/blades, scissors, plastic or wooden dowel, tweezers,
a board, Virkon or other disinfectant and a guide. Make sure you count all
dissection tools used at the end of the lesson.
The Pluck
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What side of the heart is which?
The right side should feel a lot more flexible
than the left (due to the relative thicknesses
in the ventricles walls on either side) the
ventricles are the bottom chambers; the
atria are the top.
Incisions
Cut along the dotted lines this should allow
you to see structure in left and right
ventricles/atria.
(Taken from Practical Biology for Advanced
Level, Michael Roberts, 1994)
The lungs
The lungs can be inflated using a rubber
tube slotted into the trachea and firmly held
in place. The lungs should be inflated by a
hand or foot pump (doing it yourself can
result in any content of the lungs being
blown back when they deflate). The lungs
may be damaged by cuts from the abattoirs
if so place them in a plastic bag, over cover
with cling film to eliminate spraying.
2
Comparing the structure of the lung
Together, the lungs contain approximately
the same length as 1500 miles (2,400 km)
of airways and 300 to 500 million alveoli,
having a total surface area of about 70 m2 in
adults — roughly the same area as one side
of a tennis court. With the passageways
and alveoli the lungs are very spongy and
light, you can compare the lung to the liver
by trying to float them in water, the lung
should float and the liver should sink.
Help learners make the journey from macroto micro-.
Use evidence to imagine what the structure
of lung must be like, and think about why.
Cover a small sliver with water and use a
hand lens to see bubbles on the surface.
Compare to another tissue (why?).
Look at a prepared (or downloaded) thin
section of lung, and compare again.
3
The Structure of the Heart
Things to look out for in a heart dissection
include the difference in size between the
right and left ventricles. This size difference
is due to the right only having to pump
blood to the lungs via the pulmonary artery
and the left size needs to pump to the rest
of the body via the aorta. Inside the atria
and the ventricles you will see various
valves and the “heartstrings”, which stop the
valve flaps everting.
Using a plastic or wooden rod you can
follow the blood vessels that connect to the
heart. From the right atria you should be
able to follow the vena cava (vein) back out
(the vena cava supplies deoxygenated
blood to the heart for it to be sent to the
lungs). The rod should pop out of the pluck
at some point (this allows you to
differentiate between the vena cava and the
pulmonary artery) you can cut sections of it
to compare with the structure of the aorta.
4
Using the rod, follow the pulmonary artery
into the lungs from the right ventricle. This
artery transports deoxygenated blood to the
lungs (they are the only arteries that carry
deoxygenated blood, with the exception of
umbilical arteries). All blood vessels leading
away from the heart are arteries; all vessels
leading to the heart are veins regardless
whether or not they contain oxygenated or
deoxygenated blood. Veins are lowpressure vessels; & vice versa.
From the left atria you can follow the
pulmonary vein in reverse, back to the
lungs; this is transporting oxygenated blood
to the heart to be pumped round the body.
From the left ventricle you can follow the
aorta out of the dissection (this allows you
to differentiate between this and the
pulmonary vein). The aorta is a very thick
walled blood vessel as it has to cope with
blood under enormous pressure being
pumped from the left ventricle. You can
follow it along and using scissors cut
lengths of it to compare it with the vena
cava which is a lot thinner walled as it’s
under low pressure.
5
Blood vessel comparisons
Aorta (the thickest-walled artery, bang in the
middle when you look at a heart from
“above”)
Vena cava
Cut rings from each and do Hook’s Law
comparisons!
Coronary artery
The coronary arteries supply blood to the
heart muscle itself and are found on and
below the surface of the heart. When
dissecting the heart on the left ventricle just
below the aorta you should cut though the
coronary artery and with care you can use a
mounted needle to follow its path. This is a
nice learning point as the artery is very
small and if blocked causes angina, heart
attacks or full scale cardiac infarction (death
of zones of muscle).
Simon Quinnell & Jeremy Airey
STEM Learning
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