What is the resistance that blood must overcome to move within the blood vessels?

The correct choice is systemic vascular resistance (SVR) because this term specifically refers to the resistance that blood encounters as it flows through the blood vessels in the circulatory system. SVR is primarily influenced by the diameter of the blood vessels; when the blood vessels constrict, the resistance increases, making it harder for blood to flow. Conversely, when the vessels dilate, resistance decreases, facilitating easier blood flow.

Understanding SVR is crucial for comprehending how blood pressure is regulated and how efficient circulation is maintained. It is also essential in various clinical scenarios, particularly in managing conditions related to cardiovascular health.

The other choices, while related to the circulatory system, describe different concepts. Cardiac output refers to the volume of blood the heart pumps per minute, which is important for understanding heart function but does not define resistance. Blood pressure is the force exerted by circulating blood on the walls of blood vessels, and while it is influenced by resistance, it is a separate measure. Vascular permeability relates to how easily substances pass through blood vessel walls, which is important for fluid exchange but does not directly describe the resistance to blood flow.