H 5 - The transport system - IBDPBiology-Dnl

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Assessment Statements
 H.5.1
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Explain the events of the cardiac cycle, including
atrial and ventricular systole and diastole, and heart
sounds.
H.5.2 Analyse data showing pressure and volume
changes in the left atrium, left ventricle and the aorta,
during the cardiac cycle.
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.
H.5.4 Outline atherosclerosis and the causes of coronary
thrombosis.
H.5.5 Discuss factors that affect the incidence of
coronary heart disease.
Events of the cardiac cycle
 Sinoatrial (SA) node fires electrical signal
throughout walls of atria to begin the cardiac
cycle
 the SA signal causes atria to undergo systole atria contract & blood flows to the ventricles
 SA signal reaches atrioventricular (AV) node,
which spreads signal throughout the Purkinje
fibres
 causing ventricles to undergo systole,
 when ventricular pressure rise above atrial
pressure, atrioventricular valves slap shut,
causing “lub” sound
 semi-lunar valves open, blood is pumped into
arteries
 as ventricles relax, ventricular pressure falls,
pressure in artery exceeds pressure in
ventricle, semilunar valves close, causing
“dub” sound
 atrioventricular valves open, ventricles begin
diastole and start filling with blood
 all four chambers are in diastole and filling
with blood
 when atria are completely filled with blood
and ventricles are 70 % full, the cycle ends &
the cycle repeats
Higher human biology animation: Cardiac cycle
Pressure & volume changes in the left atrium, left
ventricle & the aorta, during the cardiac cycle
Pressure & volume changes in the left atrium, left
ventricle & the aorta, during the cardiac cycle
Mechanisms that control the
heartbeat
 heartbeat is myogenic i.e.
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initiated in heart muscle
itself
SA node (pacemaker) sends
waves of excitation to atria
stimulus is then passed to the
AV node
conducting fibres (Purkinje
fibres) conducts impulses to
lower ventricles
heartbeat is moderated by
ANS i.e. parasympathetic
nervous system
Control of the heartbeat
Role of the (SA) sinoatrial node in the cardiac cycle
 SA node is located in the wall of
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right atrium of heart muscle
SA has characteristics of both
nerve and muscle tissue
SA node initiates each impulse &
acts as pacemaker of the heart
no nerve impulses needed for
contraction i.e. SA is myogenic
SA is connected to nerves which
slow or accelerate heart rate;
impulses spread out in all
directions through walls of atria
stimulating atrial systole
(contraction)
fibres in walls of atria prevent
impulses from reaching
ventricles
impulses only reach AV node
after atrial contraction
Role of the AV (atrioventricular) in the cardiac cycle
 AV node situated at the
base of the right atrium, it
receives impulse (wave of
excitation) from atrial
walls
 AV node causes time delay
before the impulse is
passed to the ventricular
tissue
 AV node then passes the
impulse to modified
muscle fibres called
Purkinje fibres (bundle of
His) in the ventricular wall
Role of conducting fibres in the cardiac cycle
 AV bundles (bundle of His)
originates from AV node, run along
interventricular septum & branch
into Purkinje fibres
 AV bundles conducts nerve impulse
from AV node to Purkinje fibres
 Purkinje fibres are specialized
muscle fibres found in ventricular
muscles
 Purkinje fibres are insulated from
the muscle and do not cause
contraction
 their function is to relay impulses
from the AV bundle to the ventricle
muscles causing a contraction
 the impulse emerges into the
muscle at the apex of the heart so
that the ventricular contraction
begins at the apex spreading
upwards
Atherosclerosis and coronary thrombosis
 Atherosclerosis –is a progressive
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degeneration of artery walls
lipids (cholesterol) are deposited on
endothelium narrowing the artery
lumen
fibrous tissue may also be laid down
impeding blood flow, causing
platelets to stick together
clotting factors may then be
released, a blood clot within the
vessel or thrombus may then form
if atherosclerosis occurs in coronary
artery, coronary thrombosis, flow
of blood to part of heart muscle is
reduced or stopped leading to lack
of glucose & oxygen
myocardial infarction, heart attack,
cardiac arrest, heart failure may
result
Causes of coronary thrombosis
 atheroma, fatty deposits
in arteries occurs
 atheroma causes
hardening of arteries i.e.
atherosclerosis
(arteriosclerosis)
 rough surface in artery
lumen causes rupture of
platelets
 blood clots form in
coronary artery coronary thrombosis
Incidences of coronary heart disease events
 Incidences of coronary heart disease events was significantly
associated with: with age; gender (men); diabetes & hyperlipidemia
i.e. high lipid levels usually cholesterol
 Is there significant difference between events of gender (men),
diabetes & hyperlipidemia?
 Support your answer.
 * BNP = brain natriuretic peptide
Factors that affect the incidence of
coronary heart disease
 genetic factors – some people
are predisposed for high
cholesterol levels & high blood
pressure
 age – older people are at greater
risk due to less elasticity in
arteries
 sex – males are at greater risk of
heart disease than premenopausal women because
they have less estrogen, as
estrogen protects against heart
disease
 smoking – nicotine causes
vasoconstriction of blood
vessels, increases blood
pressure, heart-rate & decreases
oxygenation of heart muscle
 diet – eating too much
saturated fat, high cholesterol &
LDL in blood leads to plaque
formation in arteries - coronary
thrombosis
 exercise – helps reduce high
blood pressure, reduces the rate
of fatty deposits building up in
the inner lining of arteries &
thickens the heart muscle walls
so they pump blood more
efficiently
 obesity – lead to increase in
blood pressure & leads to plaque
formation in arteries
 high salt diet , excessive
amounts of alcohol & stress
can also affect the incidences of
coronary heart disease
Revision Questions
 Explain the events of the
cardiac cycle.
[7]
 Describe the mechanisms
that control the heartbeat.
[4]
 Outline how the
contraction of the atria
and the ventricles is
controlled.
[4]
 Explain the role of the SA
(sinoatrial) node in the
cardiac cycle.
[6]
 Explain the role of the AV
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(atriolventricular) node in
the cardiac cycle.
[4]
Explain the role of the
conducting fibres in the
cardiac cycle.
[4]
Outline the condition
atherosclerosis and how it
may cause coronary
thrombosis.
[5]
Outline how coronary
thrombosis can be caused.[3]
Discuss the factors which
that affect the incidence of
coronary heart disease. [7]
 The graph above shows pressure changes in the left
atrium, left ventricle and the aorta, during the cardiac
cycle. Explain the changes in pressure.
 The graph above shows volume changes in the left
ventricle during the cardiac cycle. Explain the changes
in volume.

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