Transcript H.5 - HL transport-system

H.5
The Transport System
IB Assessment Statement
• H.5.1 Explain the events of the cardiac cycle,
including atrial and ventricular systole and
diastole, and heart sounds.
The Cardiac Cycle
• The cardiac cycle is the repetitive sequence of events in which
the heart chambers contract and relax in a co-ordinated
manner to send blood continuously around the circulatory
system.
• As with all cycles there is strictly speaking no one point that
can be considered the beginning.
The Cardiac Cycle
Diastole: All heart muscle in state of relaxation.
• Arterial blood pressure is greater than
ventricle pressure.
• The semilunar valves are closed
• Ventricle pressures are still higher than
atrial pressures
• Atrio-ventricular valves closed.
Atrial Distention
• At this point the atria are both filling with
blood from both the pulmonary veins and
the vena cava.
The Cardiac Cycle
Atrial Distention:
• The heart is still in a state of
diastole.
• All the valves are all closed.
• The passive return of blood to the
atria along veins causes the
pressure to rise within the atria
and the walls to distend. (swell)
The Cardiac Cycle
Note that this stage is still diastole:
• The pressure in the atria is greater
than the pressure in the ventricles.
• The pressure difference causes the
atrio-ventricular valve to open.
• The ventricle passively fills with
blood.
• Note the semi-lunar valves are still
closed.
The Cardiac Cycle
Early Atrial Systole
• The atria contract together (see
myogenic contraction).
• The contraction of the atrial muscle
reduces the volume of the atria.
• This volume reduction increases the
pressure on the blood within the atria.
• The pressure increases forces the
additional volume of blood into the
ventricle.
• This stretches the ventricle walls
(Starlings Law).
The Cardiac Cycle
Systole: Contraction of the ventricles.
• The ventricle walls contract on both sides.
• There is a sudden pressure increase within the
ventricles.
• The pressure in the ventricles is greater than the
pressure in the atria
• Atrio-ventricular valves close. (First heart sound
"Lub").
• Ventricle pressure is lower than arterial pressure.
• Semi-lunar valves remain closed.
• graph ref: (2)
• Iso-volumetric contraction, in which the ventricle
contracts increasing the blood pressure but the
blood cannot yet pass out into the artery. This
gives a sudden and large pressure increase.
The Cardiac Cycle
Systole continues
• Ventricle pressure is greater than arterial pressure.
• The semi-lunar valves open.
• Blood ejects into the arteries (a pulse).
• graph ref (4)
• Pressure in the ventricles peaks rapidly as we
come to the end of systole.
• Note the atrio-ventricular valves are still closed
(graph ref (5))
• As pressure falls in the ventricle the arterial blood
will backflow closing the semi-lunar valves and
creating the second heart sound, "dub".
• graph ref: (6)
• We now return to the first diagram in the cycle as
we are back in a relaxed condition called diastole.
IB ASSESSMENT STATEMENT
• H.5.2 Analyse data showing pressure and
volume changes in the left atrium, left
ventricle and the aorta, during the cardiac
cycle.
Top-quality animations
available from
www.medmovie.com :
Heart Pressure & Volume Changes
during the Cardiac Cycle
• a) Diastole (ventricles are relaxed)
(b) Systole (ventricles
contracted)
• (1) Atrial systole
• (2) Ventricular Systole , atrioventricular valves close, first
heart sound.
• (3) Iso-volumetric contraction
• (4) Opening semi-lunar valves
• (5) Peak of systolic pressures
Heart Pressure & Volume Changes
during the Cardiac Cycle
• (6) End of ventricular systole,
closure of the semi-lunar valves,
second heart sound. Beginning of
diastole
• (7) Aorta pressure during
ventricular diastole
• (8) Falling ventricular pressure
(Diastole)
• (9) Passive atrial filling with blood/
compression from systole
• (10) Passive filling blood by venus
return
IB ASSESSMENT STATEMENT
• H.5.3 Outline the mechanisms that control the
heartbeat, including the roles of the SA
(sinoatrial) node, AV (atrioventricular) node
and conducting fibres in the ventricular walls
Control of the Heart
Myogenic Rhythm: The heart beat is initiated
within the heart muscle itself.
• Within the right atrium there are a
specialise group of cells called the Sino
Atrial Node.(SAN).
• These cells can generate an
electrochemical potential across the cell
membrane and once threshold is reached
this can be propagated across the other
cells of both atria.
• The speed of conduction across the two
atria is fast enough that both effectively
contract together.
•
However the cell membrane structure alters across a line rough
consistent with the diagram and effectively prevents the
conduction of the contraction stimuli traveling down into the
ventricles.
Control of the Heart
a) The impulse is picked up by a
specialised group of cells in the
right atrium wall called the
Atrio-Ventricular Node (AVN).
(b) The AVN conducts the
impulse down through the
central septum of the heart
along specialised fibres called
the Purkinje fibers. The fibres
are insulated from the muscle
and do not cause contraction.
Control of the Heart
.
c) The impulse emerges into the
muscle at the apex of the heart so
that the ventricular contraction
begins at the apex.
d) The impulse travels on emerging
into the heart muscle higher up the
ventricle wall in this way the
contraction spreads upwards.
•Note that this direction of contraction pushes the
blood towards the semi-lunar valve and also not that
the transmission time down the Purkinje tissue creates
a delay between atrial and ventricular systole. This
delay maintains the correct directional flow of blood
through the different chambers
Control of the Heart
• Myogenic Rhythm can be modified by the central
nervous system to respond to cardiovascular
demands.
• Within the medulla region of the brain there are
a specialised group of receptors and coordinators called the Cardiac Centre.
• These are connected to the the SAN via the two
sets of nerves.
• a) Accelerator nerve that increases the rate SAN
activity to produce faster heart rate.
• b) Decelerator nerve that decreases the rate SAN
activity to slow heart rate.
• In addition the SAN is sensitive to hormones such
as adrenaline that can directly stimulate heart
rate.
•
The brain is sensitive to a wide range of stimuli including pH and CO2
levels which reflect the demand of the tissues for oxygen. As an
example, exercise produces more CO2 in the plasma. Detected by the
cardiac centre this stimulates the accelerator nerve and therefore the
SAN to increase heart rate. ie your heart beats faster when you
exercise
Electrocardiogram (EKG or
ECG)
• An electrocardiogram (EKG or ECG) is a
measure of the electrical currents from the
heart, measured on the surface of the
body.
EKG
http://library.med.utah.edu/kw/pharm/hyper
_heart1.html)
IB Assessment Statements
• H.5.4 Outline atherosclerosis and the causes
of coronary thrombosis.
Atherosclerosis is a stage of arteriosclerosis involving fatty deposits
(atheroma's) inside the arterial walls
The sequence of events in the build up of the
atheroma: 1) damage to the arterial wall (perhaps due
to high blood pressure) 2) attachment of phagocytes
which secrete growth factors 3) enlargement of the
muscle layer 4) permeability of the endothelium to
low density lipoproteins (LDL) 5) deposition of
cholesterol from LDL 6) crystallisation of
cholesterol 7) reduction of the lumen space of the
artery 8) decreased or interrupted flow 9) turbulence
in blood flow can produce clots (thrombosis) 10)
thrombosis in the coronary artery may block blood
flow to heart muscle (myocardial infarction)resulting in
tissue damage or death
IB Assessment Statements
• H.5.5 Discuss factors that affect the incidence
of coronary heart disease.