Let’s take a closer look at the operation of this amaz-
ing pump.
The Heart Is Located in the
Thoracic Cavity
For all its might, the heart is relatively small, roughly the
same size (but not the same shape) as your closed fist. It
is about 12 cm (5 in.) long, 9 cm (3.5 in.) wide at its wid-
est point, and 6 cm (2.5 in.) thick, with an average mass
of 250 g (8 oz.) in adult females and 300 g (10 oz.) in adult
males. The heart rests on the diaphragm, near the midline
of the thoracic cavity. It lies in the mediastinum (
me-de-a-
STl-num
), an anatomical region that extends from the ster-
num to the vertebral column, the first rib to the diaphragm,
and between the lungs. About two-thirds of the mass of the
heart lies to the left of the body’s midline (Figure 11.2).
You can visualize the heart as a cone lying on its side. Its
pointed apex rests on the diaphragm and is directed toward
the left hip. The base of the heart is its posterior surface,
formed by the upper chambers of the heart.
T he location o f th e h e a rt • Figure 11.2
The heart is located in the thoracic cavity, with two-thirds of its mass to the left
of the midline
Anterior
Posterior
a.
Inferior
view
of transverse section of thoracic cavity
showing
heart
in mediastinum (dashed outline)
Heart
Diaphragm
Apex of heart
Right lung
Left lung
Heart
Left lung
b. Anterior
view
of
heart
in thoracic cavity
The Heart Pumps Blood Through Blood Vessels to All Tissues
311
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