Anatomy and Physiology II Practice Test

What occurs to the interstitial fluid when blood pressure is high?

1. It moves into the plasma

2. It remains the same

3. It moves out into the interstitial fluid

4. It is absorbed by tissues

The correct answer is: It moves into the plasma

When blood pressure is high, the force exerted by the blood on the vessel walls increases. This elevated pressure causes fluid to be pushed from the capillaries into the interstitial space surrounding the cells. This fluid that leaves the blood vessels is called interstitial fluid. However, if blood pressure remains high, it can lead to a situation where the movement of fluid into the interstitial space continues, resulting in an increased amount of interstitial fluid. Eventually, the interstitial fluid can equilibrate with the lymphatic system, and some of it is reabsorbed back into the bloodstream, maintaining fluid homeostasis. However, the immediate response includes a shift of fluid from the interstitial space back into the plasma, as the body works to counteract the effects of high blood pressure. This homeostatic mechanism ensures that the volume of fluid in the blood vessels does not become excessively low, which is essential for maintaining circulatory efficiency and preventing complications such as edema. Understanding this process highlights the dynamic nature of fluid movement in the body, especially in response to changes in blood pressure, and emphasizes the importance of the balance between blood plasma and interstitial fluid.