**Core Concept**
Normal portal venous pressure is a critical parameter in assessing liver function and portal hypertension. It is influenced by the resistance in the hepatic sinusoids, the liver's vascular tone, and the pressure in the hepatic veins. The normal portal venous pressure is essential for maintaining the proper blood flow through the liver.

**Why the Correct Answer is Right**
The normal portal venous pressure is approximately 5-10 mmHg. This pressure is crucial for maintaining the proper blood flow through the liver, allowing for the efficient exchange of nutrients, hormones, and waste products. The hepatic sinusoids are the primary site of resistance in the portal circulation, and any increase in resistance can lead to portal hypertension. The liver's vascular tone is also regulated by various vasoactive substances, such as nitric oxide and endothelin, which can affect portal pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it is too high, and elevated portal pressure is a hallmark of portal hypertension.
**Option B:** This option is also incorrect as it is too low, and portal pressure below 5 mmHg may indicate liver dysfunction.
**Option C:** This option is incorrect as it is not a valid measurement unit for portal pressure.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that portal hypertension is defined as a portal pressure above 10 mmHg, which can lead to complications such as varices, ascites, and splenomegaly.

**Correct Answer: C. 5-10 mmHg**