Download Blood Flow - JEMasters

The cardiac
cycle
Candidates should know and understand:
Pressure and volume changes and associated valve
movements during the cardiac cycle.
Cardiac output as the product of heart rate and stroke
volume.
Blood Flow
Artery
Ventricle
Vein
Atrium
Blood Flow
Vein
Atrium
Walls of atrium contract
(systole)
Ventricle
Artery
Walls of ventricles contract
(systole), and atria relax
(diastole)
How is heart beat controlled?
• Automatic (Myogenic)
• Heart has its own inbuilt
pacemaker – sino-atrial
node (SAN)
• Group of cells in wall of right
atrium that produce their
own nerve impulses at
regular intervals
• Cause atria, then ventricles
to contract as the impulses
spread out – domino effect
• Blood at a low pressure in the veins flows into the atria. This increases
the pressure inside the empty atria as they fill. Some of the blood trickles
through the open atrioventricular valves into the relaxed ventricles
below.
• When the atria are full, they go into atrial systole (contraction), and blood
is pushed through the valves into the ventricles. The pressure in the atria
is increased due to the contractions and the pressure is increasing in the
ventricles as they fill with blood.
• When the atria contract, blood cannot flow back into the veins because
the pressure of the blood pushes on the valves in the veins to shut them.
• After a short delay the ventricles contract from the base upwards. The
pressure inside the ventricles increases due to the ventricular systole. As
the pressure increases to a higher level than the pressure in the atria,
blood pushes against the atrioventricular valves, shutting them (the first
heart sound) and preventing backflow.
• The semilunar valves open under the pressure and blood leaves the
heart through the artery.
• The ventricles relax - ventricular diastole - and the semilunar valves
snap shut behind the blood (the second heart sound).
Which side of the heart is the graph showing? How can you tell? What
would the difference be if it was the other side? How long is one heart
beat?
Cardiac Output
• Definition: the volume of blood pumped by
one ventricle in one minute.
• Units: dm3min-1
• Depends on: Heart rate and stroke
volume (volume of blood pumped per
beat)
Cardiac output = heart rate x stroke volume