Transcript H5 THE TRANSPORT SYSTEM

H5.1 Explain the events of the cardiac cycle
including atrial and ventricular systole and
diastole, and heart sounds
The heart undergoes dramatic movements as it alternately
contracts (systole), forcing blood out of its chambers, and
then relaxes (diastole), allowing its chambers to refill with
blood.
The cardiac cycle includes all events associated with the
flow of blood through the heart during one complete
heartbeat, that is, atrial systole and diastole followed by
ventricular systole and diastole
The cardiac cycle is marked by pressure and volume
changes within the heart with pressure changes being 5
times greater in the left side of the heart
Each ventricle pumps the same volume of blood per beat
and the overall relationships are the same for both chambers
One cardiac cycle involves the following phases:
• Blood enters the atria; the bicuspid and tricuspid valves open
when atrial pressure exceeds ventricular pressure. This resting
period is called diastole (atrial filling)
• Then the 2 atria contract simultaneously (atrial systole)
causing the blood to be pushed into the ventricles
• Almost immediately the ventricles contract (ventricular
systole); this increases the pressure in the ventricle which
closes the tricuspid and bicuspid valves and opens the
semilunar valves, pushing the blood into the aorta and
pulmonary artery. The atria relax.
• When the ventricles relax (ventricular diastole), some of the
blood in the aorta and pulmonary artery will try to flow back
and will close the semilunar valves
The sound that the heart makes is usually considered to be a
“lub-dup” sound.
 The “lub” is caused by the closing of the bicuspid and
tricuspid valves
 The “dup” is caused by the closing of the semilunar
valves in the arteries
Therefore:
Ventricular systole = “lub”
Ventricular diastole = “dup”
Systole: Contraction of the heart muscle
Diastole: Relaxation of heart muscle
A). First the atria go through systole and diastole
together
B). Then the ventricles go through systole and
diastole together
H5.2 Analyze data showing pressure and volume
changes in the left atrium, left ventricle and the
aorta, during the cardiac cycle
In the data below, you can see that
the volume and pressure inside the
chambers of the heart changes as it
goes through the cardiac cycle
 The atria fill up with blood during ventricular systole and
diastole. As they fill up, both volume and pressure
increase. When atrial systole starts, the volume of the
atria decreases and the pressure goes up. After the blood
flows into the ventricle, the atria relax and the volume
increases while the pressure decreases. All these changes
are small compared to the changes which occur in the
ventricles and the changes in the left ventricle are much
greater than in the right ventricle
 The left ventricle quickly fills with blood and then
ventricular systole starts. The pressure in the ventricle
increases in 0.1s. The pressure remains high for the
next 0.2s and the volume of the ventricle goes from
100% to almost 0%. During diastole, the ventricle
also fills up with blood so its volume increases. The
pressure remains low until atrial systole forces blood
into the ventricle which also sharply increases the
volume of the ventricles
H5.3 Outline the mechanisms that control the
heartbeat including the SA (sinoatrial) node, AV
(atrioventricular) node and conducting fibers in the
ventricular walls
• The ability of the heart muscle to depolarize and
contract is not dependent on the nervous system
• The heart contains specialized autogenic (selfdepolarizing) cells which can begin depolarization
without neural activation
 The SA node is a group of autogenic cells located in the
wall of the right atrium just below the entrance of the
superior vena cava
 The SA node acts as the pacemaker of the heart by
producing spontaneous depolarization at a faster rate than
other autogenic cardiac cells (generates impulses about
75-100 times/minute)
 Its characteristic rhythm, called sinus rhythm, determines
heart rate
 From the SA node, the depolarization wave spreads by
way of gap junctions throughout the atria via the
internodal pathway to the AV node
 The AV node is located in the inferior portion of the right
atrium just above the tricuspid valve
 The AV node conducts impulses more slowly because the
fibers are of a smaller diameter and there are fewer gap
junctions here thus allowing the atria to respond and
contract fully before the ventricles contract
 From the AV node the impulse sweeps to the bundle of
His (also referred to the AV bundle) in the inferior part of
the interatrial septum
 The bundle of His splits into two pathways, the right
and left bundle branches which run along the
interventricular septum toward the apex of the heart
 The Purkinje fibers complete the pathway through
the interventricular septum and penetrate into the apex
of the heart and turn superiorly to stimulate the
myocardial cells of the left and right ventricles,
causing their almost simultaneous contraction
H5.4 Outline atherosclerosis and the causes of
coronary thrombosis
Atherosclerosis is the result of an accumulation of fatty
materials within the walls of the arteries causing blood
flow to be reduced
The lumen of the artery may be further reduced in size
by a clot (thrombus) that forms as a result of the
atherosclerosis; in severe cases, the artery may become
completely blocked
The most serious consequences to the heart are hypertensive
heart disease and coronary artery occlusion which in turn,
increase the risk of heart attack (coronary thrombosis) and
stroke
H5.5 Discuss factors which affect the occurrence of
coronary heart disease
Atherosclerosis, as well as other conditions, can lead to coronary
heart disease.
The following risk factors can lead to coronary heart disease:
 Genetic predisposition (having parents who have experienced
a heart attack)
 Smoking
 Hypertension
 High blood cholesterol levels
 Aging; 10% of individuals with CHD are over 65
 Diets high in saturated fat
Being male (higher risk than being female)
Lack of exercise
Obesity
Race – seen in more ethnic groups than others
Stress and diabetes