Final answer:
The volume of blood ejected during systole, known as stroke volume (SV), typically ranges from 70–80 mL and is influenced by preload, afterload, and contractility. Preload is related to the end-diastolic volume (EDV), afterload to the resistance in blood vessels, and contractility to the strength of heart muscle contraction.
Step-by-step explanation:
Volume of Blood Ejected During Systole:
The volume of blood ejected by the ventricles per beat during systole is known as the stroke volume (SV). This typically ranges from 70–80 mL. SV is crucial for determining cardiac output (CO), which is the product of heart rate (HR) and SV. SV is affected by three main factors: preload, afterload, and contractility.
Preload:
Preload refers to the stretch of the ventricles before contraction, which is directly proportional to the end-diastolic volume (EDV). A higher EDV results in a greater preload, potentially increasing SV due to the Frank-Starling mechanism. However, a rapid HR can decrease filling time, reducing EDV and preload.
Afterload:
Afterload is the resistance the ventricles must overcome to eject blood during systole. High afterload, often due to high blood pressure or valve disease, can decrease SV by increasing the end-systolic volume (ESV).
Contractility:
Contractility is the strength of ventricular contraction. Positive inotropes increase contractility and SV, whereas negative inotropes have the opposite effect. Factors such as autonomic innervation and hormones can modulate contractility and thereby affect SV.