Topic 7: Run for your Life
Exercise
Effect of exercise on heart rate and breathing rate
When you exercise, your skeletal muscle is contracting quickly and frequently. This requires energy
from respiration. To ensure that muscle cells have plenty of oxygen and glucose for respiration, heart
rate increases to pump these substances around the body quicker. An increased heart rate also
ensures the faster removal of the waste products of respiration (carbon dioxide). During exercise, our
breathing rate also increases and we take deeper breaths. This results in getting a larger amount of
oxygen into our body, as well as getting rid of the increased amount of carbon dioxide being
produced.
Control of heart rate
The medulla oblongata is a brain region found at the
bottom of the brain, in the brain stem. It is involved in
unconscious processes, such as controlling heart rate
and breathing rate. A part of the medulla oblongata
called the cardiovascular control centre is responsible
for changing heart rate according to our body’s needs. It
works by sending impulses along sympathetic or
parasympathetic neurones which release different
neurotransmitters onto the SAN - the SAN then modifies
its rate of firing to slow down or speed up the heart rate.
Two types of receptors, baroreceptors (pressure receptors) and chemoreceptors (chemical
receptors) are responsible for detecting stimuli in the blood and signalling to the medulla oblongata to
modify our heart rate. Baroreceptors detect changes in blood pressure and are found in the aortic
and carotid bodies. Chemoreceptors detect the concentration of oxygen in the blood. They are
also sensitive to changes in pH resulting from the carbon dioxide dissolved in the blood (its reacts
with the water to form carbonic acid), which is an indication of oxygen availability. Chemoreceptors
are also located in the aortic and carotid bodies.
When the medulla oblongata receives signals from baroreceptors and chemoreceptors, it changes
the rate at which the sino-atrial node (SAN) fires. If blood pressure or oxygen concentration is low,
the cardiovascular control centre increases the rate of SAN firing through activation of the
sympathetic nervous system. The sympathetic nervous system is involved in the ‘fight and flight’
, response and increases heart rate through the release of a neurotransmitter called noradrenaline,
which binds to receptors on the SAN. On the other hand, high blood pressure and high oxygen
concentration causes the cardiovascular control centre to reduce the rate of SAN firing by activating
the parasympathetic nervous system. This is involved in the ‘rest and digest’ response and
decreases heart rate through the release of another neurotransmitter called acetylcholine.
Acetylcholine binds to receptors on the SAN to slow down its rate of firing.
Cardiac Output
Cardiac output is the total volume of blood pumped by a ventricle every minute. The larger the
heart, and the more forceful the contractions, the larger the cardiac output. Cardiac output depends
on stroke volume, which is the volume of blood pumped by one ventricle each time it contracts. You
can calculate cardiac output by multiplying heart rate with stroke volume:
Exercise
Effect of exercise on heart rate and breathing rate
When you exercise, your skeletal muscle is contracting quickly and frequently. This requires energy
from respiration. To ensure that muscle cells have plenty of oxygen and glucose for respiration, heart
rate increases to pump these substances around the body quicker. An increased heart rate also
ensures the faster removal of the waste products of respiration (carbon dioxide). During exercise, our
breathing rate also increases and we take deeper breaths. This results in getting a larger amount of
oxygen into our body, as well as getting rid of the increased amount of carbon dioxide being
produced.
Control of heart rate
The medulla oblongata is a brain region found at the
bottom of the brain, in the brain stem. It is involved in
unconscious processes, such as controlling heart rate
and breathing rate. A part of the medulla oblongata
called the cardiovascular control centre is responsible
for changing heart rate according to our body’s needs. It
works by sending impulses along sympathetic or
parasympathetic neurones which release different
neurotransmitters onto the SAN - the SAN then modifies
its rate of firing to slow down or speed up the heart rate.
Two types of receptors, baroreceptors (pressure receptors) and chemoreceptors (chemical
receptors) are responsible for detecting stimuli in the blood and signalling to the medulla oblongata to
modify our heart rate. Baroreceptors detect changes in blood pressure and are found in the aortic
and carotid bodies. Chemoreceptors detect the concentration of oxygen in the blood. They are
also sensitive to changes in pH resulting from the carbon dioxide dissolved in the blood (its reacts
with the water to form carbonic acid), which is an indication of oxygen availability. Chemoreceptors
are also located in the aortic and carotid bodies.
When the medulla oblongata receives signals from baroreceptors and chemoreceptors, it changes
the rate at which the sino-atrial node (SAN) fires. If blood pressure or oxygen concentration is low,
the cardiovascular control centre increases the rate of SAN firing through activation of the
sympathetic nervous system. The sympathetic nervous system is involved in the ‘fight and flight’
, response and increases heart rate through the release of a neurotransmitter called noradrenaline,
which binds to receptors on the SAN. On the other hand, high blood pressure and high oxygen
concentration causes the cardiovascular control centre to reduce the rate of SAN firing by activating
the parasympathetic nervous system. This is involved in the ‘rest and digest’ response and
decreases heart rate through the release of another neurotransmitter called acetylcholine.
Acetylcholine binds to receptors on the SAN to slow down its rate of firing.
Cardiac Output
Cardiac output is the total volume of blood pumped by a ventricle every minute. The larger the
heart, and the more forceful the contractions, the larger the cardiac output. Cardiac output depends
on stroke volume, which is the volume of blood pumped by one ventricle each time it contracts. You
can calculate cardiac output by multiplying heart rate with stroke volume:
