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Transcript of 2 SAN sets heart rate at beats per minute Nerves act as Vagus nerve Sympathetic nerve about 120...
REGULATION OF HEART BEAT
2
CHANGING HEART RATE SAN sets heart rate at
beats per minute Nerves act as Vagus nerve Sympathetic nerve
about 120
brake and acceleratorslows heart rate
speeds up heart rate
The intrinsic impulses of the SAN set the heart beat
These timings can be altered through the neural control & hormones.
Central to the regulation of heart rate is the Cardiac Control Centre in the medulla- made up of 2 components.
Autonomic Nervous System
ParasympatheticSympathetic
SLOWER FASTER
Via Vegus Nerve adrenaline/noradrenaline
Acetylcholine These both act on the SA node to change HR
ON YER BIKE! Think of a cyclist going down hill. Speed of the bike is like the speed of
your heart Brakes- vagus nerve Pedals- sympathetic nerve To reduce the speed you use the brakes To speed up you pedal faster To go fast downhill you take the brakes off completely (vegus nerve) and pedal faster (sympathetic nerve)
5
INCREASING HEART RATE
Exercise - blood CO2 levels rise
Detected by chemoreceptorsMedulla
Decreased vagus impulses to SAN - lets
heart beat faster
Increased sympathetic impulses to SAN - lets heart beat even faster
6
REDUCING HEART RATE
Stop exercise – blood pressure falls
Detected by baroreceptors
Medulla
Increased vagus impulses to SAN - lets heart beat slower
Decreased sympathetic impulses to SAN - allows
heart rate to slow
LETS SUMMARISE...
Sympathetic system Parasympathetic system
DESCRIBE HOW THE PARASYMPATHETIC AND SYMPATHETIC NERVOUS PATHWAYS
CONTROL HEART RATE DURING A GAME (5)
A.Controlled by medulla/cardiac centre B. Sympathetic pathway increases heart
rate C. By release of
adrenaline/noradrenaline D. Increase stroke volume/ejection
fraction E. Parasympathetic decreases HR F. By vagus nerve G. Production of Acetylcholine H. (Both) act on sino atrial node/SAN
EXPLAIN HOW LEVELS OF CO2 IN BLOOD CAUSE HEART RATE TO
INCREASE
Increase in C02 Causes increase in blood acidity,
decrease in pH. Detected by Chemorecepetors Sends impulse to medulla – Cardiac
control centre Decreases Vegus simulation Increase sympathetic pulses Heart rate increases!*Breathing rate= respiratory control centre
NEURAL CONTROL OF THE HEART
The CCC receives information from lots of different sources in the body.
Mechanoreceptors & Proprioceptors-Extent of movement taking place in the
muscles. In movement = in HR.
Chemoreceptors -Detect changes in pH.
Baroreceptors-stretch receptor based in arteries and vena
cava. Detect increases in blood flow and pressure
WHAT DO THEY DO? CCC responds to information from these
sensory receptors during exercise. Stimulate the SA Node via sympathetic
nerve. This causes heart rate and stroke
volume to increase. Once exercise stops- stimulation of
sympathetic nerve decreases and allows parasympathetic vagus nerve to take over and slow heart rate down.
HORMONES! Adrenaline and noradrenaline are
released during times of stress- ‘butterflies’
Prepares body for impending exercise by increasing heart rate and strength of ventricular contraction.
Mimicking the action of the sympathetic system
Anticipatory Rise
ANTICIPATORY RISE
HORMONES.. Action of another hormone
Acetylcholine released by Parasympathetic system that slow the heart rate down
HOW DOES THE CARDIAC CONTROL CENTRE REGULATE
HEART RATE? (5 MARKS)
Neural Factors; Proprioceptors & mechanoreceptors in
muscles relay info to the brain that amount of movement has increased and muscles will need more blood.
Chemoreceptors in aorta and carotid arteries detect changes in composition of the blood- C02
Baroreceptors respond to changes in blood pressure
HOW DOES THE CARDIAC CONTROL CENTRE REGULATE
HEART RATE?
Hormonal factors;Release of adrenaline and noradrenaline
increase heart rate and strength of contraction
Release of Acetylcholine following exercise to reduce the heart rate
Intrinsic factorsIncrease in temperature- blood flows
better less viscous
QUESTIONS Describe how the parasympathetic
and sympathetic nervous pathways control heart rate during a game.
Explain how levels of CO2 in blood cause heart rate to increase
How does the cardiac control centre regulate heart rate?
DEFINITIONS! Stroke Volume- blood ejected per beatNot all blood in ventricle is ejected.. Ejection Fraction- amount of blood that
leaves the ventricle Cardiac Output – amount of blood
pumped out of a ventricle per minute Heart rate x stroke volume 5 litres resting male
EXAM QUESTION Explain the terms stroke volume and
cardiac output and the relationship between them
(3 marks)
ANSWER Amount of blood ejected form the
ventricle per beat Amount of blood ejected from the
ventricle per minute Relationship- SV x HR = Cardiac output
WORK OUT THE CARDIAC OUTPUT
Subject A heart rate= 80bpm; stroke volume
=90mls
Subject B- heart rate=110bpm; stroke volume =
100mls
Subject C- heart rate160bpm; stroke
volume=120mls
STROKE VOLUME When we exercise this will change...1) More blood enters the ventricle during
diastole (venous return) as it is flowing faster round the body
2) Walls of the ventricle stretch and contract more forcibly.
Starlings law of the heart
STARLINGS LAW
The greater the venous return, the greater the strength of contraction.
???
How does stroke volume increase during exercise?
HOW DOES STROKE VOLUME INCREASE DURING EXERCISE?
Increased venous return Greater diastolic filling Cardiac muscle stretched Greater strength/ force of contraction
Increased ejection fraction
EFFECTS OF EXERCISE Increased exercising heart rate and
increased stroke volume have a huge impact on Cardiac Output
Heart rate 200bpm Stroke volumes 180mls 36 litres per minute Increase in Cardiac Output (Q) is to
supply working muscles with oxygen
???What are the effects of exercise on the heart?
EFFECTS OF EXERCISE ON THE HEART (4-5 MARKS)
heart rate increases
stroke volume increases
due to Starlings Law
cardiac output increase
because cardiac output= SV x HR