Page 106 - Biology Form Two

Biology for Secondary Schools

The internal structure of the lungs. The lungs are close to the heart.
mammalian heart Therefore, it does not require much
Internally, the human heart consists pressure to pump blood.
of four chambers, which are the right
auricle, right ventricle, left auricle, The heart has various valves that
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and left ventricle, as shown in Figure control the flow of blood between the
5.2. The auricles are also called atria atria and ventricles. The valves have
(singular, atrium). The walls of the flaps that ensure blood flows in only
ventricles are thicker than those of the one direction. The tricuspid valve is
auricles. This is because the ventricles found between the right auricle and
pump blood to a longer distance than right ventricle. The bicuspid valve is
the auricles. Auricles or atria pump found between the left auricle and left
blood to the ventricles and then ventricle. Semilunar valves are located
ventricles pump blood to all other at the bases of the pulmonary artery and
parts of the body. The walls of the left aorta to prevent blood from flowing
ventricle are thicker than the walls of back into the ventricles. The valves
the right ventricle because they left close when blood tries to flow back.
ventricle pumps oxygenated blood to The left and right sides of the heart are
the rest of the body. Therefore, much separated by the septum, which is a
pressure is required to pump blood. muscular wall that prevents mixing of
The right ventricle pumps blood to the oxygenated and deoxygenated blood.

Aorta

Superior vena cava Pulmonary artery

Pulmonary veins

Semilunar valves Left auricle

Right auricle Bicuspid valve

Tricuspid valve
Left ventricle

Right ventricle

Inferior vena cava Septum

Figure 5.2: Internal structure of the mammalian heart

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