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The Cardiac cycle text p.90

Pressure and volume changes and associated valve

movements during the cardiac cycle.

How does the heart pump blood? Imagine the force needed to squeeze a tennis ball.

That’s how much force the heart uses to pump blood around the body!

How does the heart produce enough force to keep doing this 24 hours a day?

The heart can pump blood because it is made of muscle. Muscle tissue works by contracting (squeezing) and relaxing.

How does the heart pump blood? All the parts of the heart on either side, work togetherin a repeated sequence.

The two atria contract and relax; then the two ventricles contract and relax. This is called ISOMETRIC CONTRACTION

This is how blood moves through the heart and is pumped to the lungs and the body.

One complete sequence of contraction and relaxation is called a heartbeat.

Stages of a heartbeat Stage 1 relaxation of heart (diastole): A heartbeat begins with the heart muscle relaxed and semilunar valves closed.

Blood flows into the two atria and both sides fill up with blood.

This blood has to be pushed through the valves to get into the ventricles. How does this happen?

Stages of a heartbeatStage 2 contraction of the atria (atrial systole): The atria contract and the blood is squeezed which causes the valves leading to the ventricles to open.

Blood then flows from the atria into the ventricles.

What happens to the open valves when the atria are empty?Why are atria walls thin?

Stages of a heartbeat Stage 3 contraction of the ventricles (ventricular systole): the ventricles contract and the blood is squeezed. The valves between the atria and the ventricles close.

This prevents any backflow

The pressure of the blood forces open the valves leading out of the heart.

Blood is pumped outof the heart.

What happens to the open valves when the ventricles are empty?

Stages of a heartbeat

Stage 3 (continued): When the ventricles are empty, the valves leading out of the heart close and the heart muscle relaxes.

This completes the sequence of contraction and relaxation in one heartbeat.

What will happen next?

Stages of a heartbeat Stage 1 (again): The atria fill up with blood as the heartbeat sequence begins again.

Why are the walls of the atria thinner than the walls of the ventricles?

Why is the wall of the left ventricle thicker than the right ventricle?

What does a doctor hear when they listen to a patients’ heart?

Listening to a beating heart: lub-dub

The “lub” is caused bythe closing of the valves leading to the ventricles.

The “dub” is caused by the closing of the valvesleading out of the heart.

lub-dub,

The sound of a heartbeat is the sound of the heart valves.

lub-dub, lub-dub, lub-dub, lub-dub, lub-dub…

What are the stages in the cardiac cycle?

The cardiac cycle• Stick diagram in centre of page• Use text p. 90 to add labels to each stage• Example;

• Atria contract• Blood pressure is higher in the

atria than the ventricles• Atrioventricular valves open• Blood flows into the ventricles

• Ventricles contract• Blood pressure is higher

in the ventricles than the atria

• Atrioventricular valve closes causing lub heart sound

• Blood pressure is higher in ventricles than in arteries

• Semi lunar valves open• Blood surges into the

arteries under high pressure

• Atria and ventricles relax• Blood pressure is higher in

the arteries than the ventricles

• Semi lunar valves close causing dub heart sound

• Blood runs into the heart from the veins

Cardiac output

• p.91

Homework ?complete in class

• Worksheet heart function• Cardiac cycle graph questions• Text p.93 q.1,4,5• Text p.98 q.1

Silent movie technique