The document discusses blood pressure and the factors that affect it. It explains that blood pressure is highest during systole when the heart ventricles contract and pump blood, and lowest during diastole when the ventricles relax. It also notes that elastic blood vessels help regulate blood pressure by stretching during systole to absorb some pumping force and gradually returning to normal size during diastole to maintain low pressure. Finally, it lists the main factors that can influence blood pressure: cardiac output, blood volume, resistance in blood vessels, and blood viscosity.