Anatomy and Physiology II Practice Test

Blood plasma proteins primarily play a crucial role in maintaining the osmotic balance between blood plasma and interstitial fluid. They exert colloid osmotic pressure, which helps retain water in the bloodstream. This function is vital for regulating the volume of blood and ensuring that interstitial fluid does not excessively enter plasma or leak out of capillaries into surrounding tissues.

In essence, the presence of proteins in the plasma draws interstitial fluid back into the blood vessels, preventing excessive loss of fluids from the capillaries. By doing so, they contribute to maintaining proper fluid levels in both the plasma and interstitial spaces, which is essential for homeostasis and proper cellular function.

The other choices do not accurately reflect the primary function of plasma proteins. For example, moving plasma into interstitial fluid would counteract this function and could lead to fluid overload within tissues. Additionally, moving extracellular fluid into intracellular fluid is a process predominantly governed by cell membrane permeability and not directly related to blood plasma proteins. Similarly, moving interstitial fluid into the extracellular fluid does not accurately capture the dynamic relationship facilitated by plasma proteins.