22.7
心拍数の推移
心臓は、収縮（収縮期）と弛緩（拡張期）を繰り返す「心周期」と呼ばれる一連の流れの中で、リズミカルに拍動しています。
プロセス
右心房壁にある中房（SA）結節から、右心房と右心室の間にある房室（AV）結節に電気信号が送られ、両心房が同時に収縮します。信号が房室結節に到達すると、信号は約10分の1秒ほど…
心臓は心周期と呼ばれる シーケンスで律動的に拍動します。収縮をする収縮期と弛緩する弛緩期が 素早く協調します。右心房壁近くの洞房結節から 電気信号が送られると 両心房が同時に収縮し 心室に血液が送り込まれます。脈拍が右心房と右心室の間にある 房室結節に到達すると 約0.1秒停止して 心房からすべての血液を出しきります。その後、電荷がヒス束を通り 右脚と左脚を経由して心室中隔へと流れ 壁に沿ったプルキンエ線維を通って 心室収縮を誘発し 心臓から血液を肺動脈と大動脈に送り込みます。心筋が弛緩したら心房に血液が満たされ 再びサイクルを繰り返します。
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Q1: What is the cardiac cycle and how does it work?
The cardiac cycle is a rhythmic sequence of heart contractions and relaxations that pumps blood throughout the body. It consists of systole, when the heart muscle contracts, and diastole, when it relaxes and refills. This coordinated process ensures blood continuously circulates through the circulatory system heart and blood vessels.
Q2: Where does the electrical signal that starts the cardiac cycle originate?
The sinoatrial node, located near the right atrial wall, generates the electrical signal that initiates the cardiac cycle. This signal causes both atria to contract simultaneously, pushing blood into the ventricles. The signal then travels to the atrioventricular node, where it pauses briefly to allow complete blood emptying.
Q3: What is the purpose of the pause at the atrioventricular node?
The atrioventricular node pauses the electrical signal for approximately one-tenth of a second, allowing the atria to fully contract and empty all blood into the ventricles before ventricular contraction begins. This timing ensures efficient blood flow and prevents backflow, optimizing the heart's pumping efficiency.
Q4: How does the electrical impulse travel through the ventricles?
After passing through the atrioventricular node, the electrical signal travels through the Bundle of His and splits into right and left bundle branches along the intraventricular septum. The signal then spreads through Purkinje fibers in the ventricular walls, triggering coordinated ventricular contraction that pumps blood into the pulmonary artery and aorta.
Q5: What happens during diastole in the cardiac cycle?
During diastole, the ventricles relax and the atria continue filling with blood returning from the body and lungs. As ventricular pressure drops, blood flows passively into the ventricles from the atria. This relaxation phase prepares the heart for the next contraction cycle.
Q6: Why is the coordination between atrial and ventricular contractions important?
Coordinated atrial and ventricular contractions ensure blood moves efficiently through the heart chambers in one direction. The brief delay at the atrioventricular node allows atria to empty completely before ventricles contract, maximizing blood volume pumped with each heartbeat and maintaining consistent circulation throughout the body.
Q7: What role do Purkinje fibers play in the cardiac cycle?
Purkinje fibers are specialized conduction pathways in the ventricular walls that rapidly spread the electrical signal throughout both ventricles. This ensures synchronized ventricular contraction, allowing the ventricles to contract as a unified unit and effectively pump blood out of the heart with maximum force.