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.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter22/animation__the_cardiac_cycle__quiz_2_.html

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.