The heart's intricate cycle of blood pumping is essential for...
Biology66 views·Updated Jun 16, 2026·2 pagesThe Human Circulatory System - A Level Biology Edexcel B Topic 4
Hannah @hannah_studys1012
1
of 2
The Heart's Structure and Blood Flow
Your heart has four chambers working in perfect harmony to move blood through your body. Deoxygenated blood returns from the body through the vena cava into the right atrium, then passes through the tricuspid valve to the right ventricle. From there, it travels to the lungs via the pulmonary artery.
After picking up oxygen, blood returns through the pulmonary vein to the left atrium, passes through the bicuspid valve into the left ventricle, and finally exits through the aorta to the body. Special tendinous cords prevent valve backflow, while semilunar valves ensure blood flows in one direction.
The left ventricle has a thicker muscle wall than the right because it needs to generate higher pressure to pump blood throughout the entire body. The right ventricle only needs to pump blood to the nearby lungs, requiring less pressure. The septum separates the chambers, preventing oxygenated and deoxygenated blood from mixing.
Did you know? The pressure difference between chambers is crucial for proper blood flow. When ventricle pressure exceeds atrial pressure, the atrioventricular valves close, preventing backflow and creating the first heart sound ("lub").
2
of 2
The Cardiac Cycle and Electrical System
The cardiac cycle consists of coordinated contractions (systole) and relaxations (diastole) of the heart chambers. During atrial systole, the atria contract, pushing additional blood into relaxed ventricles through open AV valves. This is followed by ventricular systole, where ventricles contract, closing the AV valves and opening semilunar valves to eject blood.
Blood pressure fluctuates throughout this cycle. When ventricular pressure exceeds aortic pressure , the semilunar valves open. When ventricles relax, pressure drops, closing the semilunar valves and creating the second heart sound ("dub"). Eventually, atrial pressure exceeds ventricular pressure, opening the AV valves for the cycle to repeat.
The heart's electrical system controls these contractions through myogenic stimulation - the heart's ability to contract without external nerve signals. The sinoatrial node (SAN) initiates impulses that spread through the atria. These impulses reach the atrioventricular node (AVN) where they're briefly delayed, allowing atria to fully contract before ventricles.
Remember: The AVN delay is crucial - it ensures atria finish contracting before ventricles begin, optimizing blood flow. Without this delay, the heart's pumping efficiency would be significantly reduced.
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Biology66 views·Updated Jun 16, 2026·2 pagesThe Human Circulatory System - A Level Biology Edexcel B Topic 4
Hannah @hannah_studys1012
The heart's intricate cycle of blood pumping is essential for delivering oxygen throughout the body. Understanding how the chambers, valves and electrical system work together reveals how this remarkable organ functions continuously throughout our lives.
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of 2
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The Heart's Structure and Blood Flow
Your heart has four chambers working in perfect harmony to move blood through your body. Deoxygenated blood returns from the body through the vena cava into the right atrium, then passes through the tricuspid valve to the right ventricle. From there, it travels to the lungs via the pulmonary artery.
After picking up oxygen, blood returns through the pulmonary vein to the left atrium, passes through the bicuspid valve into the left ventricle, and finally exits through the aorta to the body. Special tendinous cords prevent valve backflow, while semilunar valves ensure blood flows in one direction.
The left ventricle has a thicker muscle wall than the right because it needs to generate higher pressure to pump blood throughout the entire body. The right ventricle only needs to pump blood to the nearby lungs, requiring less pressure. The septum separates the chambers, preventing oxygenated and deoxygenated blood from mixing.
Did you know? The pressure difference between chambers is crucial for proper blood flow. When ventricle pressure exceeds atrial pressure, the atrioventricular valves close, preventing backflow and creating the first heart sound ("lub").
2
of 2Sign up to see the content. It's free!
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The Cardiac Cycle and Electrical System
The cardiac cycle consists of coordinated contractions (systole) and relaxations (diastole) of the heart chambers. During atrial systole, the atria contract, pushing additional blood into relaxed ventricles through open AV valves. This is followed by ventricular systole, where ventricles contract, closing the AV valves and opening semilunar valves to eject blood.
Blood pressure fluctuates throughout this cycle. When ventricular pressure exceeds aortic pressure , the semilunar valves open. When ventricles relax, pressure drops, closing the semilunar valves and creating the second heart sound ("dub"). Eventually, atrial pressure exceeds ventricular pressure, opening the AV valves for the cycle to repeat.
The heart's electrical system controls these contractions through myogenic stimulation - the heart's ability to contract without external nerve signals. The sinoatrial node (SAN) initiates impulses that spread through the atria. These impulses reach the atrioventricular node (AVN) where they're briefly delayed, allowing atria to fully contract before ventricles.
Remember: The AVN delay is crucial - it ensures atria finish contracting before ventricles begin, optimizing blood flow. Without this delay, the heart's pumping efficiency would be significantly reduced.
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