This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
Hematocrit increases in venous blood due to 
Select and explain. 
A. Increased sodium, B. Increased chloride, C. Increased potassium, D. Increased calcium
B: Increased chloride
Answer: B: Increased chloride 
Explanation: CHLORIDE SHFTFor each CO2 molecule added to a red cell, there is an increase of one osmotically active paicle in the cell-- either an HCO3- or a Cl- in the red cell (Figure 36-6). Consequently, the red cells take up water and increase in size. For this reason, plus the fact that a small amount of fluid in the aerial blood returns the lymphatics rather than the veinsThe hematocrit of venous blood is normally 3% greater than that of the aerial blood. In the lungs, the Cl- moves out of the cells and they shrink.Thus increased Cl- in venous blood cause increased hematocrit