Download THE FUNCTION OF CIRCULATION

THE FUNCTION OF
CIRCULATION
IMPORTANT TERMS
 Pulmonary artery
 Pulmonary vein
 Atrioventricular valve
 Semilunar valve
 Pulmonary circulation
 Systemic circulation
 Cardiac circulation
 Plasma
 Erythrocytes
leukocytes
platelets
vasoconstriction
vasodilation
Understanding
 Arteries convey blood at high pressure from the
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ventricles to the tissues of the body
Arteries have muscles and elastic fibres in their walls
The muscle and elastic fibres assist in maintaining blood
pressure between pump cycles
Blood flows through tissues in capillaries with
permeable walls that allow exchange of materials
between cells in the tissue and the blood in the capillary
Veins collect blood at low pressure from the tissues of the
body and return it to the atria of the heart
Valves in veins and the heart ensure circulation of blood
by preventing backflow
There is a separate circulation for the lungs
Understanding (continued)
 The heartbeat is initiated by a group of specialized
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muscle cells in the right atrium called the sinoatrial node
The sinoatrial node acts as a pacemaker
The sinoatrial node sends out an electrical signal that
stimulates contraction as it is propagated through the
walls of the atria and then the walls of the ventricles
The heart rate can be increased or decreased by impulses
brought to the heart through two nerves from the
medulla of the brain
Epinephrine increases the heart rate to prepare for
vigorous physical activity
Skills
 Identification of blood vessels as arteries, capillaries
or veins from the structure of their walls
 Recognition of the chambers and valves of the heart
and the blood vessels connected to it in dissected
hearts or in diagrams of heart structure
Applications
 William Harvey’s discovery of the circulation of the
blood with the heart acting as the pump
 Causes and consequences of occlusion of the
coronary arteries
 Pressure changes in the left atrium, left ventricle and
aorta during the cardiac cycle
MAIN FUNCTION
 The main function of the circulatory system
is to deliver oxygen and nutrients to all the
body’s cells
Other important functions include:
Regulating internal temperature
 Protects the body against invading microbes
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COMPONENTS
Main components of the circulatory system
include:
The
heart
Blood
Blood
vessels (arteries and veins)
THE HEART
 Your heart is tucked in behind your left lung slightly
to the left of your sternum (central rib bone)
 Humans have a four chambered heart that includes
the:
 Right
atrium
 Left atrium
 Right ventricle
 Left ventricle
THE HEART
 The atria are small chambers at the top of the heart.
They receive blood from veins
 The ventricles are larger chambers at the bottom of
the heart. They pump blood out
THE CARDIAC CYCLE
 Blood takes a very specific path through the body
and this path repeats over and over again. It is called
the cardiac cycle
 It starts at the right atrium.
THE RIGHT ATRIUM
 Blood from here has just
come from the body.
Oxygen has been
removed from this blood
and it contains CO2
 It is dark maroon blue
colour
 Blood gets pumped from
here through a valve
called the tricuspid valve
into the right ventricle
RIGHT VENTRICLE
 Blood here is still
deoxygenated (has no
oxygen). It gets pumped
out of the heart into the
pulmonary artery.
 It then travels to the
lungs to pick up oxygen
LEFT ATRIUM
 Blood has just returned
from the lungs where it
has picked up oxygen
 It is fully oxygenated and
has a bright red colour
 It is pumped through the
bicuspid valve into the
left ventricle
LEFT VENTRICLE
 This is the strongest,
most muscular chamber
of the heart
 Blood from here is
pumped out of the heart
into the aorta where it
will travel throughout the
body. As the blood
travels through the body
it drops of oxygen and
nutrients at all the cells
Heart Diagram
Heart Diagram
CARDIAC CYCLE
Controlling the Heart
 The heart is a unique organ. It is mostly made of
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muscle cells. While other muscles are contracted
because of impulses from nerves, the heart has the
ability to contract itself without the help of nerves
In fact, hearts can continue to pump
for a while even after they have been
removed from the body.
This property is known as myogenic
pacemaker potential
The Sinoatrial Node
 The Sinoatrial, or SA, node is the place in the heart
where contraction is initiated.
 It is located at the top of the right atrium and
consists of specialized muscle cells. It is able to
change the concentration of certain ions in the cells
which causes contraction to occur
 When it contracts, adjacent cells
will contract as well.
The Atrioventricular Node
 The signal from the SA
node spreads quickly
throughout the ventricles
 It reaches another centre
for specialized cells, the
atrioventricular, or AV
node.
 The AV node transmits the
electrical signal to the
ventricles after a slight
delay so the ventricles can
fill with blood
Bundle of His/Bundle Branches/Purkinje Fibers
 From the AV node, the
signal travels down
through more specialized
muscle cells including the
bundle of His and bundle
branches that are located in
the septum between the
ventricles.
 The signal travels down to
the bottom of the ventricles
and contraction starts there
and works its way up both
sides of the ventricles
(purkinje fibers). This leads
to a more efficient heart
beat
Controlling the Heart Rate
 The SA node sets the initial heart rate
 It varies from person to person but is usually between 60
and 100 beats per minute
 The pressure and content of the blood is constantly
monitored by special receptors; baroreceptors monitor
pressure and chemoreceptors monitor levels of oxygen,
CO2 and other substances
Controlling the Heart
 https://www.youtube.com/watch?v=RYZ4daFwMa8
Control of the Heart
 These receptors are connected to nerves that can
cause the heart to speed up or slow down depending
on the need. The following are all indicators that the
heart needs to speed up
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Low oxygen levels
Low pH
Low blood pressure
Conversely, the opposite readings will signal the
heart to slow down.
Nerves That Affect Heart Rate
 The autonomic nervous system (the part of the
nervous system that we can’t control) is divided into
two parts:
The sympathetic system &
 The parasympathetic system
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Generally speaking, the sympathetic system
increases metabolism while the parasympathetic
system slows it down.
Nerves Affecting the Heart
The heart has two major nerves connected to it:
1.
The acclerator nerve (sympathetic
speeds it up)
2.
The vagus nerve (parasympathetic
slows it down)
Hormones
 Hormones are chemical messengers that are released into the blood
and affect a target organ. Some hormones target the heart
 Most notably, epinephrine and norepinephrine (also called adrenaline
and noradrenaline) are released from the adrenal glands during times
of stress and cause the heart rate to increase
The Cardiac Cycle
 Go through the phases of the cardiac cycle described
on page 300. Compare the time intervals to the chart
below
 https://www.youtube.com/watch?v=jLTdgrhpDCg
Cardiac Cycle
 Confusing but important!!!
BLOOD VESSELS
 Blood vessels take blood throughout the body. If
your body were a city, blood vessels would be the
roads and highways
 There are two types of blood vessels; arteries and
veins
BLOOD VESSELS
ARTERIES
VIENS
 Carries blood away
 Brings blood back to
from the heart
 Thicker and more
muscular
 More elastic
the heart
 Thinner
 Less elastic, more
compliant (stretchy)
 Have valves that keep
blood moving in the
right direction
BLOOD VESSELS
ARTERIES
VEINS
MORE TYPES OF BLOOD VESSELS
 Blood leaves the heart through large arteries (aorta and
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pulmonary)
Large arteries branch off to smaller arteries
Smaller arteries branch into smaller arterioles
Arterioles continue to branch until they form tiny vessels
called capillaries
Blood flows through capillaries which merge together to
form venules
Venules merge to form veins
Veins come together to form larger veins (vena cava and
pulmonary vein) which deliver blood back to the heart
BLOOD VESSELS
BLOOD VESSELS
BLOOD
 If you take a test tube of blood and spin it in a
centrifuge it will quickly divide into two parts. They
are:
 Cells
and
 Plasma
BLOOD
HEMATOCRIT
PLASMA
 Approximately 45% of
 Approximately 55% of
your blood
 Contains mostly red
blood cells or
erythrocytes and
some white blood cells
or leukocytes
your blood
 Contains mostly water
but also has dissolved
gases, proteins, salts
and other nutrients
TYPES OF BLOOD CELLS
RED CELLS
(ERYTHROCYTES)
WHITE CELLS
(LEUKOCYTES)
 Shaped like a donuts
 Different shapes
without a hole
 Make up over 99% of
blood cells
 Made in bone marrow
 Contain hemoglobin
which carries oxygen
 Make up less than 1% of
blood cells
 Purpose is to attack
foreign microbes
 Two main types:
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Granulocytes – engulf
invaders
Agranulocytes – involved in
the formation of antibodies
TYPE OF BLOOD CELLS
RED
WHITE
PLATELETS
 Prevent excessive blood loss by causing blood to clot
or coagulate
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Broken blood vessels release chemicals that attract platelets
Platelets rupture which releases substances which react with
certain plasma proteins to form thromboplastin which gets
converted to thrombin (an enzyme)
Thrombin converts fibrinogen (a plasma protein) to fibrin
Fibrin forms a mesh like substance (a scab) that stops blood
from escaping
BLOOD CLOTTING
CONTROL OF BLOOD FLOW
 One of the really amazing things about the
circulatory system is that it has the ability to control
where the blood goes.
 Remember, arteries have a layer of muscle cells
called smooth muscle. Smooth muscle is not a
voluntary muscle. It is controlled by the brain.
 When it contracts, called vasoconstriction, the
arteries narrow and decrease the blood supply.
 When smooth muscle relaxes, it is called
vasodilation. This makes the artery wider and
increases the amount of blood that flows through it
Blood flow is
controlled for two
main reasons:
1.
To allow more
active parts of the
body to receive
more blood than
inactive parts.
2. To maintain body
temperature in the
most important
parts of the body
CONTROL OF BLOOD FLOW