Download Blood Pressure Handout File

Blood Pressure
1. Blood pressure is caused by the
a. beating of the heart
b. recoil of the elastic arteries
c. peripheral resistance caused by the narrow capillaries
2. When the ventricles contract pressure is applied to the
blood in them forcing it out of the major arteries. This
pressure is called the SYSTOLIC PRESSURE and is
normally 100 – 140 mm/Hg
3. When the ventricles relax the stretched arteries recoil onto
the blood applying pressure known as the DIASTOLIC
PRESSURE.
This is normally 60 – 90 mm/Hg.
4. Blood pressure is measured using a SPHYGMO-MANOMETER and is recorded this way:
120
80
systolic
diastolic
5. Some factors affecting blood pressure:
a. elasticity of the vessel walls - this decreases with age
due to atherosclerosis.
b. rate and force of heart beat
CARDIAC OUTPUT = STROKE VOLUME X STROKE RATE
c. blood volume – increased by contraction of the spleen
Falls in haemorrhage or severe shock
d. peripheral resistance – narrow arteries caused by
adrenalin
e. pain can cause widening of the arteries, loss of BP
leading to fainting.
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Blood pressure in parts of the circulatory system
160
140
Systolic pressure
120
100
80
Diastolic pressure
60
40
20
0
Aorta
Arteries
Flow rate
200 mm/s
Arterioles
Capillaries
Flow rate
0.5 mm/s
Veins
Flow rate
133 mm/s
166 000 mm2
Total cross sectional area
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