h5 the transport system
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H5 The transport system. Assessment Statements. H.5.1 Explain the events of the cardiac cycle, including atrial and ventricular systole and diastole, and heart sounds . - PowerPoint PPT PresentationTRANSCRIPT
H5 The transport system
Assessment StatementsH.5.1 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 heartbeatheartbeat is myogenic i.e.
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 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 �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 thrombosisatheroma, 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 pre-menopausal 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 (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.