Sitting to supine posture leads to what change in plasma concentration?

• A. Hemoconcentration
• B. Hemodilution
• C. No change
• D. Dehydration

Answer: (A)

When you move from sitting to lying down, gravity’s pull that normally pools blood in the legs is reduced. This increases venous return to the heart and expands central blood volume. As more fluid shifts into the intravascular space, the plasma volume increases and the concentration of plasma components becomes diluted. In other words, plasma concentration decreases because of hemodilution.

This is in contrast to standing, where gravity promotes fluid leakage into the interstitial space in the legs, reducing central blood volume and causing hemoconcentration (higher plasma concentration). Dehydration is a broader fluid-deficit condition, not a direct result of a posture change.