22.7
心脏循环
心脏在一个叫做心动周期的序列中有节奏地跳动 - 收缩（缩紧）和放松（舒张）的快速协调。
过程
从右心房壁窦房结（SA）到右心房和右心室之间的房室结的电信号会导致两个心房同时收缩。当信号到达房室结（AV）时，它暂停约第十秒，允许心房收缩并将血液排入心室，然后收缩。
电脉冲由房室束传导到左右束支。然后，…
心脏有节奏的跳动， 这个序列叫做心动周期， 收缩，即心脏收缩 与舒张，即心脏舒张的快速协作。 电信号从窦房结发出， 位于右心房壁附近，将因此两个心房 同时收缩，并将血液 推入心室。 当脉搏到达 位于右心房和右心室之间的房室结， 它就会暂停大约1/10秒， 允许血液彻底从心房中清空。 然后电荷遍布希氏束， 通过左右束枝 从心室间隔向下， 然后通过心室壁的 浦肯野氏纤维， 诱发心室收缩 将血液从心脏泵出 传送到肺动脉和主动脉。 在心肌放松之后， 心房充满血液，循环再次重复。
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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.