22.7
De hartcyclus
Het hart klopt ritmisch in een reeks die de hartcyclus wordt genoemd—een snelle coördinatie van contractie (systole) en ontspanning (diastole).
Het pr…
- [Instructeur] Het hart klopt ritmisch in een sequentie die de hartcyclus wordt genoemd. Een snelle coördinatie van samentrekking, systole, en ontspanning, diastole. Een elektrisch signaal van de sinusknoop in de buurt van de rechter atriumwand zorgt ervoor dat beide atria tegelijkertijd samentrekken en bloed in de hartkamers duwen.
Wanneer de hartslag de atrioventriculaire knoop tussen de rechterboezem en de rechterhartkamer bereikt, pauzeert het ongeveer een tiende van een seconde, waardoor het bloed volledig uit de atria kan wegvloeien. De lading verspreidt zich vervolgens door de bundel van His langs de interventriculaire septum door middel van de rechter en linker bundeltakken en vervolgens door de wanden van de Purkinje vezels van de ventrikel, waardoor ventriculaire samentrekking wordt veroorzaakt en bloed uit het hart en in de longslagader en de aorta gepompt wordt. Nadat de hartspier ontspant, vullen de atria zich met bloed en wordt de cyclus herhaald.
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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.