FACT
Cardiac outputis
the volume of blood
that is pumped by
the heart in
one-minute.
Cardiac output is
equal to the stroke
volume (SV)
multiplied by the
heart rate (HR).FACT
Laughing is good
exercise for your
heart. Whenever
you laugh, the
blood vessels dilate
(open up), causing
the blood flow to
increase, thus
keeping your heart
healthy.- Write down TWO ways in which the accuracy of this investigation can be improved.
- What conclusions can be made about your cardiovascular fitness?
- Explain why the heart rate increases during exercise?
Stroke Volume
The stroke volume is the amount of blood pumped through the heart during each cardiac
cycle. The stroke volume can change depending on the needs of the body. During exercise,
muscles need more oxygen and glucose in order to produce energy in the form of ATP.
Therefore the heart increases its stroke volume and stroke rate to meet this demand. This
is a temporary change to maintain homeostasis, and after exercise the heart rate and stroke
volume return to normal.
When a person exercises regularly, and is fit, the heart undergoes certain long-term adapta-
tions. The heart muscle gets stronger, and expels more blood with each contraction. There
is therefore a greater stroke volume with each heartbeat. Since the heart expels more blood
with each stroke, the heart has to beat less often in order to maintain the same volume of
blood flow. Therefore, fit people often have lower resting heart rates.
Blood Pressure
Blood pressure refers to the force that the blood exerts on the blood vessel walls. Blood
pressure is determined by the size of the blood vessels and ensures that blood flows to all
the parts of the body. Normal blood pressure is 120/80 (120 over 80) measured in units of
mercury. The 120 represents the systolic pressure, which is when the ventricles contract.
The 80 represents the diastolic pressure, which is when general diastole occurs.
Blood pressure can be increased by smoking, stress, adrenalin surges, water retention, high
cholesterol, obesity and lack of exercise. High blood pressure(hypertension)is dangerous
and increases the risk of an aneurysm, stroke or heart attack. Low blood pressure(hypoten-
sion)can lead to light-headedness and fainting because of insufficient blood supply to the
brain.
Blood vessels DUMMY
Structure and functioning of arteries, capillaries, veins and valves
Arteries
Arteries carry bloodAway from the heart. The pressure created by the pumping heart forces
blood down the arteries. Arteries have three layers. They have an outside layer made up
of connective tissue, a middle layer made up of smooth muscle to allow contraction of the
arteries and regulate the pressure of blood flow and an inside layer of tightly connected
simple squamous endothelial cells. The large arteries close to the heart branch into smaller
arterioles (smaller arteries) and eventually branch into capillaries.
Chapter 8. Transport systems in animals 235