The poal venous system contributes approximately 75% of the blood and 72% of the oxygen supplied to the liver. Which of the following is TRUE about valves in poal venous system?
**Core Concept**
The portal venous system is a vital pathway for blood return to the liver, primarily responsible for carrying nutrient-rich, deoxygenated blood from the gastrointestinal tract and spleen.
**Why the Correct Answer is Right**
The absence of valves in the portal venous system is crucial for its function. The lack of valves allows for the unidirectional flow of blood from the capillaries of the gastrointestinal tract and spleen to the liver, enabling the efficient exchange of nutrients and waste products. This unique characteristic of the portal venous system is essential for maintaining the liver's role in detoxification, metabolism, and nutrient processing. The absence of valves also facilitates the regulation of blood flow through the liver, allowing for the adjustment of blood pressure and flow in response to changing demands.
**Why Each Wrong Option is Incorrect**
**Option A:** The statement that the portal venous system contains valves is incorrect because the presence of valves would impede the unidirectional flow of blood necessary for its function.
**Option B:** This option is not provided, so we'll skip it.
**Option C:** The claim that the portal venous system has valves similar to those in the venous system of the lower limbs is incorrect because the portal venous system has a distinct anatomical and physiological structure that precludes the presence of valves.
**Option D:** This option is not provided, so we'll skip it.
**Clinical Pearl / High-Yield Fact**
The absence of valves in the portal venous system is a critical anatomical feature that distinguishes it from other venous systems in the body.
**Correct Answer:** C.