AS OCR Biology: Control of Heart Rate in Humans

AS OCR Biology: Control of Heart Rate in Humans

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  • Created on: 25-05-11 00:11
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Control of heart rate in Humans
The human heart:
Pumps blood around the circulatory system
Blood supplies tissues with oxygen and nutrients such as glucose, fatty acids and
amino acids
It also removes waste products, such as carbon dioxide and urea, from tissues so that
they don't accumulate and inhibit cell metabolism
How the heart adapts to supply more oxygen and glucose:
Increase in heart rate
Increase in volume of blood pumped per beat (stroke volume)
Increased strength of contractions of heart
Control of heart rate:
The heart muscle is myogenic
The heart contains a pacemaker (sinoatrial node) - This initiates a random impulse that
travels down to the atrioventricular node and finally to the Purkyne tissue, causing the
contraction of the heart ventricles.
The heart is supplied by nerves from the medulla oblongata that connect to the SA
node. The medulla oblongata can affect the frequency of contractions.
The heart muscle responds to adrenaline in the blood by increasing stroke volume and
heart rate.
Interaction between control mechanisms:
Under resting conditions, the heart is controlled by the SA node. This has a set frequency at
which it initiates waves of excitation, typically being 60-80 waves per minute. However the
frequency of waves can be altered and controlled by the cardiovascular centre in the medulla
oblongata.
Factors that affect heart rate:
Movement of limbs detected by stretch receptors in the muscles. These send
impulses to the cardiovascular centre informing it that extra oxygen may be needed.
This then increases the heart rate.
In exercise, muscles produce CO2 and some reacts with the water in the blood plasma,
reducing pH. This change in pH is detected by chemoreceptors in the carotid arteries.
They then send impulses to the cardiovascular centre, which increases heart rate.

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When exercising ceases, concentration of CO2 in the blood falls, this reduces the activity
of the accelerator pathway and so the heart rate declines.
Adrenaline is secreted in response to stress, excitement, shock or anticipation. The
presence of adrenaline increases heart rate.
Blood pressure is monitored by stretch receptors in the walls of the carotid sinus. If
blood pressure is too high, stretch receptors send impulses to the cardiovascular
centre, responding by reducing heart rate.…read more

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