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H.5 The Transport System
Terms in this set (5)
H.5.1 Explain the events of the cardiac cycle, including atrial and ventricular systole and diastole, and heart sounds.
The pacemaker or sinoatrial node (SA) fires (electrical) signal throughout walls of atria to begin cycle;
causing atria to undergo systole;
SA signal reaches atrioventricular node;
which spreads signal throughout (Purkinje fibres);
causing ventricles to undergo systole;
atrioventricular valves slap shut;
causing "lub" sound;
after ventricles are emptied semilunar valves close;
causing "dub" sound;
atrioventricular valves open;
ventricles begin diastole and start filling;
all four chambers are in diastole and filling;
when atria filled and ventricles 70 % filled cycle has ended;
H.5.2 Analyse data showing pressure and volume changes in the left atrium, left ventricle and the aorta, during the cardiac cycle.
Systole = Contraction; Diastole = relaxation
The cardiac cycle begins with the contraction of the atria
Before that, the ventricles are 70% full.
Contractions of the atria pump more blood in the ventricles, so they are fill to their maximum
Contraction of the ventricles increase the pressure
causing the closure of the atrio-ventricular valves (AVV)
This is the first heart sound
The pressure inside the ventricles rise above the one in the aorta and the pulmonary artery
Causing the semi-lunar valves in the aorta and the pulmonary artery to open
The blood will then move from the ventricles to the arteries, raising the blood pressure and decreasing the volume of blood in the ventricles
During the time the ventricles are contracting, the atria are relaxing and blood enters from the vena cava and the pulmonary veins
The blood pressure in the ventricles falls below the pressure in the aorta and the pulmonary artery
causing the closure of the semi-lunar valves
When the pressure in the ventricles is lower than the pressure in the atria, the atrio-ventricular valves will let the blood from the atria enter the ventricles
The atria and ventricles are now in diastole and the four chambers will be drain until the ventricles are 70% full and the cycle will be repeated.
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.
Heart muscle cells are myogenic;
They are stimulated to contract by electrical impulses.
A network between the heart muscle cells allow impulses to spread through the wall of the heart so the heart can contract.
A small region in the right atrium initiates each impulse. It is the pacemaker or the sinoatrial node (SA)
The impulse from the SA spread out in all directions through the wall of the atria, but not the ventricles;
The impulse will then go through the ventricles via the atrioventricular node (AV)
AV node is lower in the right atrium
There is always a delay in before the impulse from the pacemaker (SA) pass on to the AV node;
That way the atria have time to pump blood in the ventricles before the ventricles contract.
From AV node, the impulse are send along two bundles of fibres (bundle of His) found in the septum between the left and right ventricles.
Smaller fibres called Purkinje fibres branch out from these two bundles of His and carry impulses to all parts of the heart
So the ventricles contract at the same time.
H.5.4 Outline atherosclerosis and the causes of coronary thrombosis.
progressive degeneration of artery walls;
lipids, cholesterol deposited on endothelium (def. is the thin layer of cells that lines the interior surface of blood vessels);
fibrous tissue may also be laid down;
blood flow is impeded (slow the progress) causing platelets to stick;
clotting factors may then be released;
a clot or thrombus may form;
if in coronary artery, flow of blood to part of heart muscle is reduced;
H.5.5 Discuss factors that affect the incidence of coronary heart disease.
hypertension / high blood pressure;
having parents who have experienced heart attacks indicates a genetic precondition;
old age leads to less flexible blood vessels;
risk in females increases post-menopause because of fall in estrogen level;
being male (more risk than being female) because of less estrogen;
smoking raises blood pressure because nicotine causes vasoconstriction;
obesity strains heart;
eating too much saturated fat and cholesterol promotes plaque formation / atherosclerosis;
sedentary life style / lack of exercise;
but excessive exercise can be dangerous;
high salt diet / excessive amounts of alcohol / stress can also affect coronary heart disease.
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