Page 125 - Biology Form Two

Biology for Secondary Schools
The pressure developed during these 2.
actions can be felt in the arteries. Blood
pressure is measured by considering
the systolic pressure and the diastolic
pressure. It is measured in millimeters
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of mercury (mmHg). For example, if 3.
the pressure during systole phase is
120 mmHg and the pressure during
diastole phase is 80 mmHg, the blood
pressure is 120/80 mmHg. This is the
average blood pressure in a normal
human being. The instrument used
to measure blood pressure is called a
sphygmomanometer.
Activity 5.4: Measure blood pressure
Materials
Sphygmomanometer and a note book
Procedure
1. Watch closely as your teacher or the
health officer demonstrates how
to use the sphygmomanometer to
measure blood pressure, as shown
in Figure 5.17.
Figure 5.17: Measuring blood pressure
Student’s Book - Form Two
BIOLOGY FORM 2 NEW.indd 119
BIOLOGY FORM 2 NEW.indd 119
Under the guidance of your teacher,
measure the blood pressure of
your fellow student. Your fellow
student should also measure your
blood pressure.
Compare your results with those
from the rest of the class members.
Diseases and disorders of the human
circulatory system
Diseases and disorders of the human
circulatory system affect blood, blood
vessels, and the heart. Diseases and
disorders may be caused by genetic
factors, unhealthy eating habits, and other
lifestyles. Eating food with high levels
of cholesterol and fat causes narrowing
of blood vessels due to their deposition
in blood vessels. Stress and lifestyles
such as smoking, lack of exercise, and
alcohol consumption cause a great risk
of developing heart diseases, including
coronary heart disease and high blood
pressure.
Arteriosclerosis
Arteriosclerosis is the hardening of
arteries. It happens when there are fat
depositions on the wall of the artery
or when fibrous tissues form in the
artery wall causing the narrowing of
the lumen of the artery (Figure 5.18).
It can also occur when the artery wall
degenerates. This hinders the normal
working of the artery, affecting the
efficiency of blood flow.
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