The

Show

The Heart

• The heart is a bag of cardiac muscle filled with blood

• Has 4 chambers: 2 atria & 2 ventricles

• Right side contains oxygenated blood

• Left side contains deoxygenated blood

• Mass – 300g• Size – of Your fist• Beats – 70 times

per minute• Cardiac muscle –

contracts and relaxes naturally

Cross section of the HeartCarries

deoxygenated blood away from

the heart

Upper left chamber

Oxygenated blood leaves the left

ventricle to circulate through the body

Receives blood from the venae

cavae

Deoxygenated blood flows

into the pulmonary arteries

Oxygenated blood flows

into the aorta.

Receives blood from the

pulmonary veins

Lower right chamber

Upper right chamber

Lower left chamber

vena cava from lower body

Control the flow &

backflow of blood

vena cava from the

head

Control the flow &

backflow of blood

But how does it work?

1. Atrial systole stage: The heart fills with blood > the atrial wall muscle contracts

2. The pressure forces the blood in the atria down into the ventricles

3. Semilunar valves prevent blood backflow

4. Ventricular systole stage: the ventricle thick muscular wall squeezes inwards > increasing pressure pushes the blood out of the heart

5. Backflow is prevented by the pressure difference that pushes the atrio-ventricular valves shut

But how does it work?

Blood moves downwards into ventricles through the atrio-ventricular valves > the atrial muscle contracts to push the blood forcefully down into the ventricles >

8. The cycle begins again

6. The blood rushes upwards into the aorta & the pulmonary artery pushing open the semilunar valves

7. Ventricular diastole stage: all the heart muscles relax > low pressure blood from the veins flows into the 2 atria >

How is it controlled?

• The cardiac cycle –sinoatrial node (SAN) or the pacemaker

• SAN contracts > a wave of electrical activity spreads out quickly over the atrial walls > the cardiac muscle in the atrial wall responds by contracting at the same rhythm as the SAN

• SAN can’t pass into the ventricle walls

• Atrio-ventricular node (AVN) fibres pick up the wave > pass it on to conducting fibres called Purkyne tissue > which then transmit the wave quickly through the ventricle walls

Bibliography• Biology 1 – pgs 120-127• http://www.patient.co.uk/showdoc/21692435/