Resistance is a force that Select one: A. is always higher than blood pressure. B. acts with pressure to move blood along a vessel. C. never changes in a blood vessel. D. decreases blood flow. E. increases blood flow.
The correct answer and explanation is:
The correct answer is D. decreases blood flow.
Explanation:
In the context of the cardiovascular system, resistance refers to the force that opposes the flow of blood through blood vessels. Blood flow is influenced by several factors, including the pressure within the vessels, the diameter of the vessels, and the overall resistance to flow.
Resistance to blood flow is mainly determined by the following factors:
- Vessel Diameter: The smaller the diameter of a blood vessel, the greater the resistance to flow. This is because blood encounters more friction along the walls of the vessel as the space for flow narrows.
- Blood Viscosity: The thicker the blood (i.e., higher viscosity), the higher the resistance. For example, in conditions like polycythemia, where there is an increase in red blood cells, the blood becomes more viscous, increasing resistance.
- Vessel Length: The longer the vessel, the greater the resistance. For example, the resistance to blood flow is greater in the smaller arteries and capillaries compared to larger vessels like veins or the aorta.
As blood flows through the circulatory system, it moves from areas of high pressure (the heart) to areas of low pressure (the veins). The blood flow rate decreases as resistance increases, which is described by Poiseuille’s Law. This law shows that blood flow is inversely proportional to the resistance within a vessel. In other words, higher resistance means less blood can flow through a vessel, which can have a direct impact on blood pressure and overall circulation.
If the resistance is high, it makes it harder for blood to flow through the vessels, thereby decreasing the overall blood flow to organs and tissues. Conversely, if resistance is low, blood flow increases. Thus, changes in resistance, such as narrowing or widening of blood vessels (vasoconstriction or vasodilation), have a direct effect on the amount of blood that reaches different parts of the body.