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Transcript
The Structure and Function of
The Cardiovascular System and
How it Responds to Exercise
The heart
The heart
• The cardiovascular system is composed of
three main parts: the heart, the blood vessels
and the blood. Its function is to deliver oxygen
and nutrients and excrete waste products
from all the cells of the body.
The heart
• The heart is about the size of a closed fist, and
shaped like a cone. It is located behind the
sternum and ribs, slightly to the left of the
centre of the chest.
• It is made up of four chambers, two upper
atria and two lower ventricles.
Structure
• The heart is divided into four chambers:
• The two chambers at the top are called atria
• The two lower chambers are called ventricles
• Blood travels from the atria to the ventricles.
They are separated by valves, (atrioventricular
valves), to ensure that blood flows in one
direction only.
Cardiac muscle
• The chambers are surrounded by a wall of muscle,
called the myocardium. This muscle is specific to the
heart and is termed cardiac muscle. Cardiac muscle:
• Is involuntary and contracts automatically
• Has interwoven muscle fibres
• Contains many mitochondria.
• The walls of the ventricles are more muscular than the
atria since more force is required to pump blood out of
the heart to the lungs and body.
Structure
• The heart can also be divided into left and
right halves. Each side has a different role /
function:
• The left side is responsible for circulating
blood (rich in oxygen) around the whole body
• The right side is responsible for pumping
blood (low in oxygen) to the lungs to collect
more oxygen
Blood vessels
• The blood and blood vessels are responsible for
carrying blood and nutrients around the body.
There are 3 types of blood vessels: arteries, veins
and capillaries.
• The arteries carry blood away from the heart to
the working muscles and other parts of the body
where oxygen and nutrients are required. The
arteries branch off and progressively become
smaller vessels known as arterioles.
Blood vessels
• These arterioles then join even smaller vessels
known as capillaries where diffusion takes
place. The capillaries are the essential link
between arteries and veins; they are tiny
vessels with semi permeable membranes
allowing oxygen and nutrients to be delivered
to the tissues and waste products such as
carbon dioxide and water to be removed.
Blood vessels
• Following diffusion the blood moves from the
capillaries into venules (small veins); these
then join together to form larger veins as the
blood is moved back towards the heart.
Because the pressure of the blood in the veins
is low they have valves to prevent back flow
which helps the blood to travel in the right
direction.
Blood Vessels
Arteries
Veins
Capillaries
Vessel wall
Thick & muscular
Thin
Very thin
(one cell thick only)
Diameter
Small
Large
Very small
Valves
No
Yes
No
Pressure
High
Very low
Low
Blood
Oxygenated*
De-oxygenated*
Both
Blood flow
Away from heart
Towards heart
From artery to vein
Function
Carry nutrients and
oxygen to working
tissues
Carry waste products
including carbon
dioxide away from
working tissues
Allow diffusion of
nutrients, oxygen and
carbon dioxide
between blood and
working tissues
Blood Vessels
• The pulmonary artery and vein are the exception.
The pulmonary artery carries deoxygenated
blood away from the heart to the lungs and the
pulmonary vein carries the freshly oxygenated
blood from the lungs back to the heart.
• Arterioles and venules are small extensions of the
arteries and veins which distribute blood from
the arteries to the capillaries and back to the
veins.
The Blood
Functions:
• Transport oxygen from the tissues
• Return carbon dioxide from the tissues to the
lungs
• Carry waste products from the tissues to the
liver and kidneys to be broken down/excreted
• Distribute hormones
• Carry essential nutrients
The blood
•
•
•
•
Characteristics:
Thick and more viscous than water
Temperature 30oc
Volume, 4-6 litres (typical man/woman)
The blood
Component
Description / function
Plasma
Straw coloured liquid, mainly water
Carries nutrients
Known as erythrocytes
Contain haemoglobin which carries
oxygen
Produced in bone marrow
Typically 40-45% of total blood volume
Known as leucocytes
Fight infections
Produced in bone marrow
Fewer in number than red blood cells
Thrombocytes
Control bleeding after injury
Help in process of blood clotting and
repairing damaged tissues
Red blood cells
White blood cells
Platelets
Short term effects of exercise on the
cardiovascular system
• Exercise has the following short term effects on
the cardiovascular system:
• There is an increase in heart rate at the onset of
exercise. This is due to the release of the
hormone adrenalin. Adrenalin prepares the body
for action by stimulating the respiratory and
circulatory systems. It is often associated with
nerves, butterflies, rapid breathing, and sweating
palms
Short term effects of exercise on the
cardiovascular system
• There is an increase in stroke volume (the
amount of blood pumped out of the heart per
beat). Because there is an increase in both
heart rate and stroke volume cardiac output
(the amount of blood pumped by the heart
per minute) also increases. (Cardiac output
(Q) = SV x HR)
Short term effects of exercise on the
cardiovascular system
• The working muscles’ demand for oxygen means that
blood is redirected away from areas which need it less.
For example, when cycling blood may be redirected
from the gut to the legs
• The body's temperature increases as does the
temperature of the blood. To cope with this increase in
temperature more blood is shunted to the skin surface
to help it cool. Sweating cools you by evaporation
• Blood pressure increases at the onset of exercise
Long term effects of exercise on the
cardiovascular system
• Exercise has the following long term on the
cardiovascular system:
• The heart muscle will also increase in size (cardiac
hypertrophy), particularly that of the left ventricle
leading to a more forceful contraction. More blood is
pumped per beat (stroke volume) and therefore per
minute (cardiac output)
• Resting HR decreases (bradycardia), but SV increases so
the same amount of blood is pumped out per beat at
rest
Long term effects of exercise on the
cardiovascular system
• There is an increase in the size and number of blood vessels
feeding the muscles and lungs
• After endurance training (low intensity, long duration) the
quantity and quality of the blood improves. More red blood
cells are produced. This means that more oxygen can be
transported to and used by the muscles
• Blood pressure is decreased in individuals with
hypertension.
• All of these effects only occur if regular exercise is
maintained. If the exercise is stopped for a period of time
then the training effects will be lost.
COMPARISON OF BLOOD VESSELS
Artery
Vein
Explain differences
Structure:
Vessel wall
Thick & muscular
Thin
Valves
None
Yes
The artery wall
allows constriction
when the muscle
contracts, which
increases blood
flow
Veins have little
muscle in the walls
to change shape,
so movement of
blood is supported
by pocket valves
which prevent the
backflow of blood
COMPARISON OF BLOOD VESSELS
Function:
Blood flow
Away from heart,
oxygenated blood
Pressure
High pressure
Transport
Oxygen to working
muscles
The exceptions are the
pulmonary artery,
carrying deoxygenated
blood from the heart to
the lungs, and the
pulmonary vein, carrying
oxygenated blood from
the lungs to the heart
Pressure is highest in the
Low pressure
arteries due to the elastic
nature of the vessel wall,
the movement if blood is
much slower in the veins
Carbon dioxide away from Arteries transport oxygen
working muscles
to the capillaries where
gaseous exchange can
take place, and as a result
carbon dioxide enters
capillaries as oxygen
enters the muscle, this is
then passed on to the
veins where it is
transported back to the
lungs for re-oxygenation
Towards the heart, deoxygenated blood
• Capillary walls are composed of a single cell.
They are very thin and allow oxygen and
carbon dioxide to squeeze through. A
membrane which allows gases to pass through
can be termed semi-permeable. The main
function of capillaries is for gaseous exchange.
This process is efficient owing to a dense
capillary network surrounding the muscle.
Circulation
• The vascular system has two pathways of circulation, the
pulmonary circulation (to the lungs) and the systemic
circulation (to the body).
The Double Circulatory System
• Humans have a double circulatory system
where blood passes through the heart twice.
The route around the body of blood leaving
the left and right sides of the heart are
different. These routes or systems, are
referred to as pulmonary circulation and
systemic circulation.
Pulmonary Circulation
• Transport of blood between heart and lungs
• Blood, low in oxygen, is transported to the
lungs where it becomes oxygen rich, then
returns to the heart
Systemic Circulation
• Transport of blood from the heart to the rest
of the body and vice versa
• Blood rich in oxygen is distributed from the
heart to the rest of the body and working
tissues to deliver oxygen. Blood then returns
to the heart, oxygen poor
Vasodilation & Vasoconstriction
• Vasodilation (definition) = the increase in the
internal diameter of blood vessels that is
caused by relaxation of smooth muscle within
the wall of the vessels, thus causing an
increase in blood flow. The opposite effect is
Vasoconstriction. The opposite effect is
vasoconstriction, when blood vessels dilate,
the blood flow is increased due to a decrease
in vascular resistance.
Venous Return
• Blood returning to the right side of the heart
• The heart can only pump as much blood out as it
receives, so cardiac output is dependent upon venous
return
• The process is aided by a muscle pump, as the muscle
contracts, the veins are compressed slightly and
squeeze blood back towards the heart
Blood flow through the heart and
lungs
• Deoxygenated blood is returned from the
muscles and the rest of the body via the
superior and inferior vena cava into the right
atrium. It then passes into the right ventricle
and from here it is pumped into the
pulmonary artery where it travels to the lungs.
It is in the lungs that pulmonary diffusion
occurs; the blood is removed of its waste
produces and enriched with oxygen.
• The blood is then returned to the heart
via the pulmonary vein into the left
atrium. It is then pumped into the left
ventricle and from here into the aorta
where the oxygenated blood is then
delivered the working muscles.
• Within the heart there are a number of valves
which ensure that the blood can only flow in
one direction. Valves are found between atria
and ventricles (atrio-ventricular valves) and
between ventricles and the main vessels
transporting blood away from the heart (semilunar valves). The blood flow pushes the
valve open and it is then closed by connective
tissue called chordae tendineae.
The Cardiac Cycle
• The heart muscle needs to contract in order to eject blood from the
heart and be transported around the body.
How the heart works.
• Cardiac muscle contractions are initiated by an impulse from a
pacemaker, called the sino-atrial node (SAN) within the right atrium
wall.
• The contraction spreads throughout the walls of the atria and through
branched fibres within the ventricle walls.
• The cardiac cycle refers to the sequence of events occurring as this
impulse spreads through the heart.
• One complete contraction / cycle of the heart is one heartbeat
• The cycle usually lasts for about 0.8 seconds, and occurs about 72
times per minute.
Stages of the cardiac cycle
Stages of the cardiac cycle
• Atrial diastole
• Atria fill with blood
• Atrioventricular valves closed
•
•
•
•
•
Ventricular diastole
Pressure builds in atria
Valves pushed open
Ventricles begin to fill with blood
Semi-lunar valves closed
Stages of the cardiac cycle
•
•
•
•
•
•
•
•
•
•
•
Atrial systole
Atria walls contract
Remaining blood forced into ventricles
Semi-lunar valves closed
Ventricular systole
Ventricle walls contract
Atrio-ventricular valves closed
Blood forced into circulatory system
Semi-lunar valves pushed open
Heart Sounds
The closing of the valves within the heart and the circulatory system
are responsible for the ‘lub-dup’ sounds of the heart.
Heart Rate, Stroke Volume and
Cardiac Output
• Heart rate
• The number of times the heart beats per minute
• Stroke Volume
• The amount of blood ejected from the heart every
time it beats
• Typically about 70-80cm3 at rest
Heart Rate, Stroke Volume and
Cardiac Output
• Cardiac Output
•
• The volume of blood ejected from the left ventricle in one
minute
• Typically about 5000cm3 at rest
•
• Can be determined from knowing an individuals heart rate
and stroke volume:
•
•
• Cardiac Output = Stroke Volume x Heart Rate
•
Q
=
SV
x
HR
• Heart rate is controlled through the nervous system,
originating in the brain.
• Heart rate can speed up or slow down in response to
feedback
• For example, during exercise, the heart rate speeds up to
ensure a greater supply of blood and oxygen to the working
tissues. However, when blood pressure rises, there is a need
to slow down the heart rate (and subsequent blood flow rate).
Blood Pressure
• The force exerted by the blood against the walls of the blood
vessels
• Factors affecting blood pressure:
• Cardiac output
• Resistance
• Measurements of blood pressure are taken as systolic pressure
(when the heart is contracting) over diastolic pressure (when the
heart is relaxing).
• A typical reading for resting blood pressure is 120 / 80 mmHg
Vasomotor Control
• Vessels constrict and dilate in order to control
blood flow around the body
• The vasomotor and venomotor control centre
in the brain sends signals via the nervous
system in response to the body’s demands, for
vessels to either increase or decrease the flow
of blood.
Pulse Rate
• When the heart contracts, a wave of pressure is
generated through the vessels and there is a
slight dilation of the arteries.
• This can be felt at various sites in the body
• Most common sites:
• Carotid artery
• Radial artery
• Brachial artery
Factors affecting blood pressure
•
Blood pressure is taken to give an indication of general health. There are a number
of factors which affect blood pressure:
•
exercise - blood pressure increases when you exercise. This is because the heart is
working harder to supply your muscles with more oxygen. Regular exercise helps
to lower resting blood pressure and prevent cardio-vascualr disease.
•
diet - high levels of fat and salt cause the arteries to stiffen or clog up. This
clogging leads to an incresae in blood pressure.
•
age - blood pressure increases as you grow older. This is because the arteries lose
their elasticity and do not expand so much when blood is pumped through them.
•
stress and tension - increases blood pressure. This is because hormones are
released into the bloodstream when the body becomes stressed or anxious.
• smoking - cigarette smoking increases blood pressure because nicotine
reduces the efficiency of the capillaries.
Structure of the Respiratory System
Structure and route of air to lungs
Nose
Air enters here and is filtered by tiny hairs and warmed
Pharynx
Both food and air pass through the pharynx
Food is then directed into the oesophagus
Larynx
Commonly known as voice box
Opening covered by epiglottis (a flap of cartilage) which
prevents food entering here
Trachea
Windpipe, about 10cm long, supported by rings of cartilage
Contains cells which remove foreign particles from the air
Bronchi
Right and left branches, which further divide into
bronchioles
Bronchioles
Further divide into smaller pathways, leading to alvoli
Alveoli
Small air filled sacs
Large surface are
Thin walls
Surrounded by capillaries
Lungs
The bronchi extend into the lungs
2 cone shaped organs separated by the heart
Surrounded by a protective membrane
Mechanics of breathing
• An average adult will inhale and exhale
approximately 12 to 15 breaths per minute.
For air to be drawn into the lungs, the
pressure of the air within the lungs must be
lower than that in the atmosphere. The
greater the difference in pressure, the faster
air can be drawn into the lungs. The pressure
difference is created by altering the size of the
thoracic cavity.
Inspiration
• When an individual breathes in it is referred to
as inspiration. During inspiration the
intercostal muscles contract pulling the ribs
upwards and outwards at the same time as
the diaphragm contracts and flattens. These
combined actions increase the area inside the
lungs meaning that air is then drawn into the
lungs until the pressure inside the lungs is
equal to the atmospheric pressure.
Expiration
• When an individual breathes out it is known
as expiration. During expiration the
intercostal muscles relax lowering the rib cage
to its resting position. The diaphragm also
relaxes (moving upwards). This causes the
area inside the lungs to decrease, increasing
the pressure inside. This greater pressure
forces the air out of the body until the
pressure is equal to that of the atmosphere.
Mechanics of breathing
Gaseous Exchange
• Oxygen passes into the body and carbon
dioxide leaves the body through the process
of gaseous exchange.
• Movement of oxygen and carbon dioxide
occurs from a high concentration to a low
concentration, known as diffusion.
• The amount of each gas which moves is
controlled through a semi-permeable
membrane
Gas exchange at the lungs
• There is a high concentration of oxygen in the lungs as we
breathe in, and a low concentration in the capillaries
surrounding the alveoli.
• There is a high concentration of carbon dioxide in the blood
and capillaries then in the alveoli air from breathing in
• Two way process
• As oxygen diffuses into the capillaries to be delivered to the
tissues, carbon dioxide diffuses into the alveoli to be
expired
• The capillary wall is thin to allow efficient gaseous exchange
• The alveoli have a large surface are to allow optimal
exchange of gases
Transport of Oxygen and Carbon
Dioxide
• Oxygen combines with haemoglobin in the red blood cells
to form oxy-haemoglobin
• In the lungs, where there is little carbon dioxide
haemoglobin is said to be 100% saturated with oxygen
• When large amounts of carbon dioxide are present, the
saturation of haemoglobin with oxygen is reduced,
enabling oxygen to disassociate (unload) and feed the
working tissues
• At the site of the tissues, most oxygen has been unloaded
• Most carbon dioxide is transported in the form of
bicarbonate ion, and some combines with haemoglobin to
form carbaminohaemoglobin
Gas exchange at the muscles and
tissues
• Oxygen is rich in the capillary blood, and low
in the muscle cell. Oxygen can disassociate
from haemoglobin and pass across the
capillary wall into the muscle cytoplasm
• Oxygen forms with myoglobin
• Carbon dioxide produced in the muscle passes
into the capillary and can be transported to
the lungs in the veins
Respiratory volumes
•
There are a number of measures or capacities that can be taken of the amount of
air moving into and out of the lungs:
Lung volume / capacity
Tidal volume (TV)
Inspiratory reserve volume
(IRV)
Expiratory reserve volume
(ERV)
Residual volume (RV)
Definition
The amount of air inspired /
expired per breath
The amount of air forcibly
inspired above tidal volume
The amount of air forcibly
expired above tidal volume
The lungs never completely
empty, and the air that is left
after a maximum exhalation
is the residual volume.
Approximate normal
values
500ml
3300ml
1000 – 1200ml
1200ml
Vital capacity (VC)
5500ml
Vital capacity is the
maximum amount of air that
you can breathe out after
breathing in as deeply as you
can.
IRV + TV + ERV
Total lung capacity
VC + RV
Up to 8000ml
Minute ventilation
The volume of air inspired /
expired per minute.
Minute volume = TV x RR
How many breaths you take
per minute
7500ml
Respiratory rate (RR)
Average is 12-15
Short term effects
• When you take part in sport or exercise the body places a number
of demands on the oxygen transport systems, these demands are
also referred to as the short term effects of exercise:
• even before you start to exercise your body releases the hormone
adrenalin. It prepares you for action by stimulating the respiratory
and circulatory systems. It is often associated with nerves,
butterflies in your tummy, rapid breathing, a quickened heart rate,
sweating palms and sometimes it even makes people feel sick.
• during exercise the working muscles need more oxygen. This
process is referred to as internal or cell respiration and as a result
the levels of carbon dioxide (CO2) in the blood start to rise.
Short term effects
• increased levels of CO2 in the blood are detected by the
brain. The brain then sends a message to the lungs to
breathe faster and deeper in order to expel the CO2 and so
the respiratory rate increases. Levels of CO2 dictate the rate
of breathing of the body during exercise.
• the process of gas exchange in the lungs speeds up as a
result of the increase in the rate of breathing. More CO2 is
absorbed out of the blood and more oxygen is drawn in.
• in order to cope with the working muscles demand for
more oxygen, the brain sends a message to the heart to
speed up.
Short term effects
• as a response to this message, the heart rate increases. More blood
is pumped with each beat of the heart to provide more oxygen to
the working muscles and so the stroke volume increases. If stroke
volume and heart rate both increase then so too does cardiac
Output.
• increased cardiac output means that more blood and therefore
oxygen is being pumped each minute to the working muscles, and
more carbon dioxide is being carried away.
• the arteries and arterioles dilate in order to accommodate the
increased flow of blood. Dilation of the blood vessels also keeps
blood pressure low.
Short term effects
• muscles can receive up to three times the resting amount of
oxygen. Blood flow can be increased up to 30 times the resting rate.
The working muscles therefore can receive up to 90 times the
resting amount of oxygen.
•
• the working muscles demand for oxygen means that blood is
redirected away from areas which need it less. For example, when
cycling blood may be redirected from the gut to the legs.
•
• the body's temperature increases as does the temperature of the
blood. To cope with this increase in temperature more blood is
shunted to the skin surface where it cools. Sweating cools you be
evaporation.
Short term effects
Heart rate
Stroke volume
Cardiac output
Body temperature
Blood flow
Blood pressure
Breathing rate
Tidal volume
Inspiratory reserve volume
Expiratory reserve volume
Effects / Changes
Increases
Increase
Increases
Increase
Re-distribution to working tissues
Aerobic exercise – increase in systolic pressure
Anaerobic exercise – increase in both systolic and
diastolic pressure
Increase
Increase
Decrease
Slight decrease
Residual volume
Slight increase
Vital capacity
Slight decrease
Short term effects
Effects / Changes
Total lung capacity
Slight decrease
Respiratory muscles
Increased rate of contraction
Oxygen disassociation
Increase
Carbon dioxide production
Increase
Long Term
•
Exercise has the following long term effects on the respiratory system:
•
The intercostal muscles become stronger helping to make the respiratory system more
efficient
•
The lungs get bigger, increasing their capacity to draw in oxygen
•
There is an increase in the rate at which carbon dioxide is drawn out of the lungs and oxygen
is drawn in
•
Vital capacity increases
•
The combined respiratory and circulatory systems become more efficient
•
There is an increase in capillary density surrounding the alveoli thus improving gaseous
exchange
•
All of these effects only occur if regular exercise is maintained. If the exercise is stopped for a
period of time then the training effects will be lost.
BODY SYSTEM
MUSCULAR
LONG TERM EFFECTS OF EXERCISE
1.
2.
3.
RESPIRATORY
1.
2.
3.
CIRCULATORY
1.
2.
3.
4.
CARDIO-VASCULAR
1.
muscles develop a bigger blood vessel network. This
feeds more blood (oxygen and energy) to the muscle
muscles adapt to using more oxygen. They can
therefore work more efficiently and for a longer time
increased muscle tone and maybe a reduction in
body fat
the muscles used for breathing become stronger
the lungs get bigger, increasing their capacity to draw
in oxygen
an increase in the rate at which carbon-dioxide is
drawn out of the lungs and oxygen is drawn in
the heart becomes larger and stronger. More blood is
pumped per beat (stroke volume) and therefore per
minute (cardiac output)
each heartbeat pumps more blood, so your resting
heart rate falls, while the same amount of blood is
pumped
there is an increase in the size and number of blood
vessels feeding the muscles
after endurance training (low intensity, long duration)
the quantity and quality of the blood improves. More
red blood cells are produced. This means that more
oxygen can be transported to and used by the
muscles
the combined respiratory and circulatory systems
become more efficient. They take more oxygen and
carbon dioxide to and fro, and they do it more quickly.
Cardio-Respiratory Function
Adaptations
Heart
Cardiac hypertrophy
Increased size of ventricles & walls
Heart rate
Decreased maximum heart rate
Bradycardia (decreased resting heart rate)
Stroke volume
Increased
Blood pressure
Decreased
Blood
Increased haemoglobin levels
Blood vessels
Increased capillary density surrounding muscles
and lungs
Stronger muscle in vessel walls
Gaseous exchange
Increased alveoli
Increased strength of respiratory muscles
Lung Volumes
Increased tidal volume