The normal venous pressure in the feet is $3.3\,\text{kPa}$. If a person stands very still, venous blood pressure in the feet increases to $5.0\,\text{kPa}$. What causes this high pressure?
- AMuscles in the walls of the veins contract, reducing the diameter of the veins.
- BSkeletal muscles in the legs are not squeezing blood upward in the veins.
- CSystolic blood pressure increases.
- DThe valves in the veins of the legs allow blood to flow to the feet.