The Heart, blood vessels, Cardiac Cycle and CVD

Key features of the Heart: 

• Valves: atrioventricular and semi lunar 
• Aorta
• Vena Cava (superior and inferior) 
• Pulmonary arteries 
• Pulmonary veins 
• Septum 
• Atria: left and right 
• Ventricles: left and right 

The cardiac cycle: 

1. Atrial Systole 

• The ventricles are relaxed 
• The atria contract, increasing the pressure as the volume decreases
• This causes the atrioventricular valves (AV) to open because there is a difference in pressure between the atria and the ventricles, and the pressure is higher in the atria than in the ventricles. 
• The blood is forced into the ventricals due to the increased pressure caused by the contracting atria. 
• The Semi-lunar (SL) valves are closed because there is no difference in pressure from the ventricles to the pulmonary arteries or aorta. 

2. Ventricular systole 

• The atria are relaxed 
• The ejected blood from the atria is now in the ventricles. 
• The ventricles contract, increasing pressure as the volume decreases 
• As there is a higher pressure in the ventricles than the atria, the AV valves close to prevent the backflow of blood and to ensure the flow of blood is only in one direction. 
• The increased pressure causes the SL valves to open and the blood is forced into the pulmonary arteries and aorta.

3. Cardiac diastole

• The atria and the ventricles are both relaxed 
• Blood passively flows into the atria as the pressure is higher in the pulmonary veins and the vena cava than in the atria 
• This increases the pressure within the atria (not due to contraction but due to the passive filling of the atria) 
• this causes the AV valves to open due to the difference in pressure 

Then the cycle continues onto the atrial systole where the atria…