Figure 8.21: Heart attack: the blood clot blocks the coronary arteries and cardiac muscle dies from
lack of oxygen.
Hypertension
As previously mentioned blood pressure is the pressure exerted by the blood against the walls
of the blood vessels, especially the arteries. Normal blood pressure at rest is within the range
of 100–140 mm Hg systolic (top reading) and 60–90 mm Hg (bottom reading). High blood
pressure (hypertension) is said to be present if it is persistently at or above 140/90 mm Hg.
Hypertension is a major risk factor for strokes, heart attacks and bursting of blood vessels
(aneurysms). Hypertension is essentially caused by a resistance to blood flow in blood
vessels.
Figure 8.22: The instrument used to measure blood pressure is asphygmomanometer. This figure
shows an automated arm blood pressure meter showing arterial hypertension. From the top reading
systolic pressure is 158 mm Hg and diastolic reading is 99 mm Hg and the heart rate is 80 beats per
minute.
Hypotension
Hypotension refers to abnormallylowblood pressure, especially in the arteries of the sys-
temic circulation. A patient is considered hypotensive if he/she has a systolic blood pressure
Chapter 8. Transport systems in animals 245