Transcript the cardiovascular system - Teachnet UK-home

THE CARDIOVASCULAR
SYSTEM
LEARNING OBJECTIVES
• Understand the interaction between the cardiovascular and
respiratory systems
• Identify and describe the external and internal structures of the
heart.
• Describe and explain the events of the cardiac cycle and how it is
linked to the conduction system
• Know definitions and resting values for stroke volume, heart rate &
cardiac output.
• Describe and explain changes in heart rate, stroke volume and
cardiac output during sub–maximal and maximal work
• Explain how changes in heart rate are regulated by neural, hormonal
and intrinsic factors.
• Be able to represent graphically heart rate response to varying
intensities of workload and during recovery.
• Describe and explain the distribution of cardiac output at rest and on
exercise via the vascular shunt and vasomotor control centre
• Describe how carbon dioxide and oxygen are carried in the blood
• Describe the mechanisms of venous return
• Describe the effects of a warm up and cool down on the vascular
system.
Cardiovascular and respiratory
systems
• Aerobic exercise uses oxygen to
supply the energy needed
• Three distinct systems work together
to ensure oxygen is supplied to the
working muscles during exercise
• These are the heart, vascular (blood
vessels) and respiratory systems.
The Heart
• The heart is a double pump – two separate
pumps that work side by side
• The right side pumps deoxygenated blood to the
lungs
• The left side pumps oxygenated blood to the rest
of the body
• The heart consists of four chambers –two upper
atria and two lower ventricles
• The atrio-ventricular valves separate the atria
and ventricles
• The semi-lunar valves are found in the
pulmonary artery and aorta.
Exercise 1 Exercise 2 Exercise 3
The cardiac cycle
How blood flows through the heart
• Two phases
systole – contraction phase
(atrial and ventricular) – 0.3
secs
diastole – relaxation phase –
0.5 secs
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DIASTOLE
atria fill with blood
pressure rises
atrioventricular valves open
blood passes by gravity into
ventricles
• semi lunar valves closed
Exercise 4
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SYSTOLE
Atrial systole
Atria contract
Forces remaining blood into
ventricles
Ventricles remain relaxed
Ventricular systole
Ventricles contract at same
time
Blood pressure increases
AV valves forced shut (so no
backflow)
Semi-lunar valves forced open
Blood pushed into aorta and
pulmonary artery
The conduction system of the heart
How the cardiac cycle is controlled
• Initial impulse begins in the right atrium – sinoatrial
node SAN (pace maker)
• Wave of contraction spreads through atria causing them
to contract
• Impulse passed to atrioventricular node AVN (lies
between atria)
• AVN sends impulse along muscle fibres between
ventricles (Bundle of His)
• Impulse conducted down septum to base of ventricles to
Purkinje fibres
• Causes ventricles to contract
Exercise 5
http://www.quia.com/rd/30225.html?AP_rand=604219036
Click here for a summary
sheet (Exercise 7)
Exercise 6
Heart definitions
• STROKE VOLUME- volume of blood ejected
from the heart when the ventricles contract (at
rest = 70 cm3)
• HEART RATE – the number of (ventricle)
contractions in one minute (at rest = 72bpm)
• STROKE VOLUME – (Q) volume of blood
ejected from the heart in one minute (at rest =
5Litres)
• Q = HR X SV
Exercise 8
Responding to exercise
• As exercise begins the following sequence of events
takes place in the heart
• 1. Resting heart rate – about 72 for untrained but for
trained can be as low as 60.
• 2. Anticipatory rise – due to the release of the hormone
adrenalin. This acts on the SA node to increase heart
rate.
• 3. Rapid increase of HR – at start of exercise due to
receptors: proprioreceptors detect increased movement;
chemoreceptors detect increased CO2 and lactic acid
and decreased O2. These stimulate the CCC which
stimulates SA node to increase HR
• 4. Continued but slower increase of HR – due to
continued effect of receptors, increase in blood temp and
increase in venous return.
• 5A Slight fall/ steady plateau – (aerobic sub maximal
work) – due to oxygen supply meeting demand,
baroreceptors slow HR to optimal via stimulation of para
sympathetic nerves.
• 5B Continued rise in heart rate – ( maximal aerobic
work) – due to anaerobic work where supply is below
demand and to increasing lactic acid levels.
• 6 Rapid fall in heart rate – as exercise stops due to
decreased stimulation by receptors.
• 7 Slower fall in heart rate towards resting levels- due to
elevated HR to help repay oxygen debt and to remove
by products of respiration such as lactic acid.
• You should be able to show this information graphically
• Make sure whether the question asks for maximal or sub
maximal exercise – use either 5A or 5B
• NB maximum heart rate is 220 minus age Exercise 9
Control of heart rate
• Heart rate is regulated by the cardiac control
centre found in the medulla oblongata of the
brain.
• The cardiac control centre is controlled by the
autonomic nervous system.
• This system consists of sensory and motor
nerves from either the sympathetic or
parasympathetic nervous system.
• Sympathetic nerves increase heart rate and
parasympathetic nerves decrease heart rate.
• The cardiac control centre initiates either
sympathetic or parasympathetic nerves to
stimulate the sino-atrial node to increase or
decrease heart rate.
There are three main factors which affect the activity of
the cardiac control centre. They are neural, hormonal
and intrinsic.
• Neural control
During exercise sensory receptors stimulate the cardiac
control centre. These receptors include:proprio-receptors which sense that movement has
increased.
chemoreceptors which sense changes in chemicals in
the muscles and blood. These changes include
increased levels of carbon dioxide and lactic acid and
increased acidity in the blood.
baroreceptors which are sensitive to stretch within
within the blood vessel walls. These detect increased
blood pressure.
The cardiac control centre responds to this information
by stimulating the sino-atrial node via the sympathetic
cardiac accelerator nerve to increase heart rate.
• Hormonal control
• Before and during exercise adrenalin is
released in the blood.
• This stimulates the sino-atrial node to increase
heart rate.
• Intrinsic control
• During exercise temperature increases which
increases the speed of nerve impulses which in
turn increases heart rate.
• Venous return increases heart rate which
directly increases EDV and therefore stroke
volume (Starlings Law).
Exercise 10
Blood vessels
• There are three main groups of blood
vessels.
• Arteries and arterioles- transport oxygenated
blood away from the heart.
• Capillaries – bring blood to the tissues where
oxygen and carbon dioxide are exchanged.
• Veins and venules – transport deoxygenated
blood back towards the heart.
Blood vessel structure
• Blood vessels have three layers except capillaries which
are single walled.
• Arteries and arterioles have middle layer of smooth
muscle which allows them to vasodilate (widen) and
vasoconstrict (narrow).
• Arterioles have precapillary sphincters at the entry to the
capillary. These control blood flow.
• Capillaries are one cell thick to allow efficient gaseous
exchange.
• Venules and veins have thinner muscular walls. The can
vasodilate and vasoconstrict. They also have valves to
prevent the backflow of blood.
Venous return
• Starlings Law of the Heart states that
stroke volume is dependent on venous
return.
• At rest the amount of blood returning to
the heart (venous return) is enough to
supply the demands of the body.
• On exercise this is not enough so venous
return must be increased. This happens in
the following ways.
MECHANISM
POCKET VALVES
DESCRIPTION
One way valves
Prevent back flow
Direct blood towards the heart
MUSCLE PUMP
Veins between skeletal muscles
When muscles contract on exercise blood
squeezed along these veins back to heart
RESPIRATORY
PUMP
On exercise breathing deeper & faster
Causes pressure changes in thorax &
abdomen
Increased pressure squeezes large veins
here forcing blood back to heart
SMOOTH MUSCLE
Middle layer of veins are smooth muscle
Contraction & relaxation of this pushes
blood back to heart
GRAVITY
Blood from upper body aided by gravity as
it flows back to heart.
Click on the links to complete the
exercises
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Exercise 11 summary sheet
Exercise 12 matching exercise
Exercise 13 crossword
Exercise 14 cloze exercise
VASCULAR SHUNT
• At rest only a small % of the blood supply is supplied to
the muscles (15%).
• The rest supplies the bodies organs.
• Changes during exercise –
• Increased cardiac output is supplied to the muscles (8085%).
• Less blood is supplied to the body organs.
• Blood supply to the brain is maintained.
• During light exercise increased supply to the skin
reduces temperature.
• The process of redistributing blood supply is called the
vascular shunt mechanism.
• Skeletal muscle arterioles and pre-capillary sphincters
vasodilate increasing blood supply to muscles.
• Organ arterioles and pre-capillary sphincters
vasoconstrict decreasing blood supply to organs.
VASCULAR SHUNT MECHANISMS
ORGANS
INCREASED STIMULATION OF
SYMPATHETIC NERVES
VASOCONSTRICTION OF ARTERIOLES
& PRE CAPILLARY SPHINCTERS
DECREASED BLOOD FLOW (Q) TO
CAPILLARIES OR NON ESSENTIAL
ORGANS
MUSCLES
DECREASED STIMULATION OF
SYMPATHETIC NERVES
VASODILATION OF PRE CAPILLARY
SPHICTERS AND ARTERIOLES
INCREASED BLOOD FLOW (Q) TO
CAPILLARIES OR WORKING MUSCLES
CONTROL OF THE VASCULAR
SHUNT MECHANISM
• This is controlled by the vasomotor control
centre found in the medulla oblongata of
the brain.
• Chemoreceptors and baroreceptors
stimulate the VCC.
• VCC stimulates the sympathetic nervous
system which control blood vessel lumen
diameter of organs and muscles.
Click on the links to complete the
exercises
• Exercise 15 Cloze exercise
• Exercise 16 work sheet
• Exercise 17 Summary sheet
Oxygen and carbon dioxide
transport
Oxygen is transported in two ways:
1. 97% is carried in the red blood cells bound to
haemoglobin as oxyhaemoglobin.
2. 3% is carried dissolved in the plasma.
Carbon dioxide is transported in three ways:
1. 70% combined with water within the red blood
cells as carbonic acid.
2. 23% combined with haemoglobin as
carbaminohaemoglobin.
3. 7% dissolved in the plasma.
Warm up
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Warm up – effects on vascular system
Gradual increase in blood flow brings more
oxygen to working muscles
• An increase in temperature produces
1. An increase in the rate transport of enzymes
needed for the energy systems.
2. A decrease in the viscosity of the blood which
improves blood flow
3. An increase in oxygen dissociating from
oxyhaemoglobin
• A warm up delays the onset of blood lactic acid
Cool down
• An active cool down keeps respiratory and
muscle pumps working which prevents
blood pooling in the veins and maintains
venous return.
• Capillaries remain dilated which means
more oxygenated blood reaches the
muscles which results in more lactic acid
and carbon dioxide being removed.
Exercise 18
Click on the links for some revision
games
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