Left ventricular systole corresponds
**Core Concept**
Left ventricular systole refers to the contraction phase of the left ventricle during the cardiac cycle. This phase is characterized by the shortening of the ventricular muscle fibers, resulting in the ejection of blood into the aorta. The contraction is triggered by the depolarization of the ventricular muscle fibers, which is initiated by the electrical impulse from the sinoatrial node.
**Why the Correct Answer is Right**
During left ventricular systole, the ventricular muscle fibers contract due to the sliding filament theory. The troponin-tropomyosin complex is activated, allowing the actin and myosin filaments to slide past each other, resulting in muscle contraction. The contraction is also facilitated by the increased intracellular calcium concentration, which is released from the sarcoplasmic reticulum. The increased contractility of the left ventricle is essential for maintaining adequate blood pressure and perfusion of vital organs.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not accurately describe the phase of left ventricular contraction.
* **Option B:** This option is incorrect as it refers to the filling phase of the left ventricle, not contraction.
* **Option C:** This option is incorrect as it refers to the relaxation phase of the left ventricle, not contraction.
**Clinical Pearl / High-Yield Fact**
The left ventricular systolic ejection time is an important parameter in assessing cardiac function. A prolonged systolic ejection time can indicate left ventricular hypertrophy or aortic stenosis.
**Correct Answer:** D.