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Hind Leys Biology
F211
Transport in animals 5.2
The mammalian heart
Objectives
 Describe the external and internal structure of the mammalian heart.
 Explain the differences in thickness of the walls of the different chambers of
the heart in terms of their functions.
The heart
The mammalian heart is a muscular double pump, It is divided into two sides; the right
pumps deoxygenated blood to the lungs, and the left pumps oxygenated blood to the
rest of the body. Both sides of the heart contract putting the blood under pressure to
Aorta
force it along arteries.
Pulmonary
artery
Vena
cava
Left
atrium
Left
ventricle
Pulmonary
vein
Figure 1
External features
of the heart
Right
atrium
Coronary
artery
Right
ventricle
Vena
cava
The heart sits slightly off-centre to the left of the chest cavity, with the atria in the
middle of the cavity. The lower, main part of the heart is the firm muscle of the
ventricles. Above the ventricles are two thin-walled atria.
Coronary arteries lie over the surface of the heart, carrying oxygenated blood to the
heart muscle itself. Constriction of these can have severe consequences, restricting the
delivery of oxygen and nutrients to the heart muscle. This may cause angina or a heart
attack, a myocardial infarction.
Examiner tip
An easy way to
remember which
Inside the heart
chamber is attached to
The heart is divided into four chambers; two upper
which vessel is to
atria which receive blood from the major veins. Deoxygenated
remember that A and V
blood flows into the right atrium via the vena cava.
always go together.
Oxygenated blood flows via the pulmonary vein into the left atrium.
Atria link to Veins, and
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Ventricles link to Arteries.
Hind Leys Biology
F211
Transport in animals 5.2
Tendinous
cords
Septum
Figure 2 The internal structure of the heart
http://www.kscience.co.uk/animations/heart_labelling.htm
There are atrioventricular valves between each
atrium and its ventricle. These are thin flaps of
tissue arranged in a cup shape. As the venticles
contract the valves fill with blood and close,
preventing blood flowing back into the atria. The
valves are attached to the inside of the ventricles
by tendinous cords which prevent them from turning
inside out.
At the base of the major arteries, where they exit
the heart, are valves called semi-lunar valves. These
prevent blood returning to the heart as the
ventricles relax.
Examiner tip
When trying to label a diagram
of the heart, remember that right
is longer than left! Every
structure on the right side of the
heart is a longer word than its
corresponding feature on the left
side of the heart.
This also includes the colours
used to indicate oxygenated and
deoxygenated blood. And
indeed the words oxygenated
and deoxygenated.
http://www.youtube.com/watch?v=H04d3rJCLCE&feature=related
Structure related to function
Each chamber of the heart contracts to increase the pressure of the blood. The higher
the pressure, the further the blood will be pushed. Each chamber has a structure which
is adapted to its function in circulating the blood.
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Hind Leys Biology
Chamber
Atria
Structure
Thin walled
F211
Transport in animals 5.2
Function
To push blood into the ventricles. No
need to create much pressure
Right
ventricle
Left
ventricle
Thicker than atria, but
Pumps blood to lungs, short distance. Also
not as thick as those of
risk of damage to lung capillaries if
left ventricle.
pressure too high.
2-3x thicker than right
Blood needs to be pumped at high
ventricle.
pressure out of heart into aorta and
around rest of body, avoiding resistance
of systemic circulation.
Table 1 Comparison of structure and function of heart chambers
1. What is the name of the blood vessel which supplies the heart muscle with
oxygenated blood?
2. State whether the blood in each of the following structures is oxygenated or
deoxygenated;
a) vena cava b) pulmonary artery
c) left atrium
3. List the correct sequence of four main blood vessels and four heart chambers
that a red blood cell passes through on its journey from the lungs, through the
heart and body and back to the lungs.
4. Suggest why it is important to prevent mixing of the blood in the two sides of the
heart, and name a condition in new-borns which enables this to occur.
5. Describe the function of the atrioventricular valves.
6. Describe the role of the tendinous cords, or ’heart strings’.
7. Explain why the wall of the left ventricle needs to be much thicker than that of
the right ventricle.
8. Explain the danger of the pressure created by the right ventricle being too high.
This work can be reinforced using pages 65-66 of your textbook.
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