Final answer:
Stroke volume is affected by three primary factors: preload, contractility, and afterload. Preload is related to ventricular filling, contractility to the strength of heart contractions, and afterload to the resistance faced by the ventricles. These factors jointly influence cardiac output and the body's blood flow and pressure.
Step-by-step explanation:
Three primary factors impact stroke volume (SV): preload, afterload, and contractility. Preload refers to the stretch on the ventricles prior to contraction, which is influenced by the volume of blood returning to the heart (end-diastolic volume or EDV). Contractility is the forcefulness of contraction of the heart muscle itself, influenced by factors like calcium levels and sympathetic stimulation. Afterload is the resistance the left ventricle must overcome to circulate blood, largely dictated by arterial pressure and vascular resistance.
Stroke volume is ultimately dependent upon the difference between EDV and end-systolic volume (ESV), with anything that increases EDV or contractility generally increasing SV, while increases in afterload generally decrease SV. Positive factors affecting heart contractility include sympathetic stimulation and increased calcium levels, and negative factors include parasympathetic stimulation and decreased calcium levels.
Changes in stroke volume, alongside heart rate, determine cardiac output, which is critical for maintaining adequate blood flow and pressure throughout the body. Understanding these factors assists in grasping the cardiac response to variations in blood flow and pressure.