use case sequence class activity diagram

During systole, the blood vessels are distended by the heart forcing blood from the ventricles into the systemic (or pulmonic) system. The energy propelling the blood into the ventricle during diastole is derived from the potential energy from the elasticity of the blood vessels. The aortic valve closure is the source of the second heart sound (in concert with the pulmonic valve) denoted as S2. A healthy ventricle will eject more than 60% of its volume, and after the aortic valve closes, the cycle begins again. Eventually, the pressure within the ventricle exceeds the pressure in the arteries, and the aortic valve opens, marking the beginning of rapid ventricular ejection. This is where pressure builds, yet the blood does not leave the ventricle.

The time between this closing of the mitral valve and the opening of the aortic valve is the isovolumic contraction period. This gradient closes the mitral valve, which marks the beginning of systole and causes the first heart sound (in concert with the tricuspid valve), denoted as S1. After the ventricle fills and transitions to contracting, the pressure eventually exceeds that of the blood vessels. This period represents a time of very low pressure in the ventricle, which helps create the gradient, which opens the mitral valve. The mitral valve opens, signifying the beginning of ventricular filling where the high pressure from the blood vessels forces blood into the expanding ventricle. Isovolumic relaxation is the period immediately after ventricular contraction when the aortic valve has closed, but the mitral valve has not yet opened. The ventricular function can be divided into four phases: isovolumic relaxation, ventricular filling, isovolumic contraction, and rapid ventricular ejection. Frequently, this only represents the left ventricle, but an analogous process occurs in the right ventricle, albeit at much lower pressures. Ī detailed look at the ventricular filling and contraction can be visualized on a pressure-volume curve with the pressure on the Y-axis and the volume on the X-axis. When a ventricle contracts, the pressure within the ventricles will (barring pathology) become greater than adjacent blood vessels, and the valves will allow the blood out. This stage of the cardiac cycle represents ventricular contraction, forcing blood into the arteries. Systole begins when the mitral valve (or tricuspid) closes and concludes with the closure of the aortic valve (or pulmonic). Diastole represents when the blood vessels return blood to the heart in preparation for the next ventricular contraction. This period encompasses the ventricular relaxation and filling. Systole and diastole occur in both the right and left heart, though with very different pressures (see hemodynamics below).ĭiastole begins with the closing of the aortic valve (or pulmonic) and ends with the closing of the mitral valve (or tricuspid). Diastole represents ventricular filling, and systole represents ventricular contraction/ejection. Due to this functional similarity between the right and left side, this article will often only comment on the left ventricle, with it known that a similar sequence of events is taking place in the right heart as well.Ĭardiac cycle events can be divided into diastole and systole. This contraction sequence allows the separation of the right and left heart, at least functionally, as two separate circuits.

The contraction of the atria (both the right and left) physiologically precede that of the ventricles (both right and left). Ĭoncerning the events of the cardiac cycle, it is important to compartmentalize their sequence. In other words, though the depolarization has gone through the myocardium (the ECG tracing), there is little or no contraction because the depolarization read as the electrical signal is the very beginning of the muscle’s movement. This is well-illustrated on a Wiggers diagram where the QRS complex on the ECG directly precedes ventricular systole (represented on the diagram by increased ventricular pressure). These contractions come after a slight “lag” concerning the electrical conduction that makes them possible. This lag is due to a time gap between the electrical conduction and the actual application of the myocardial force. Due to this conduction originating at the sinoatrial (SA) node, the atria contract together and then, after a short pause at the atrioventricular (AV) node, the two ventricles contract together. The pressure and volume changes are directly related to Ca++ ions entering the myocytes perpetuating conduction. Cardiac excitation and contraction directly result in the changes in pressure and volume.

Use case sequence class activity diagram