Which of the following statements about veins in the human circulatory system is true?

Introduction / Context:
Arteries and veins are the two major types of blood vessels in the human circulatory system. They differ in structure, function, and the direction in which they carry blood relative to the heart. Recognizing these differences is essential for understanding blood flow, blood pressure, and common medical conditions such as varicose veins. This question asks which statement accurately describes a true feature of veins.

Given Data / Assumptions:

Arteries and veins both carry blood but in different directions relative to the heart.
Their walls and internal structures differ due to pressure differences.
We consider typical systemic circulation in humans.

Concept / Approach:
Arteries carry blood away from the heart and usually experience higher pressure, so they have thicker muscular and elastic walls. Veins carry blood back toward the heart at lower pressure, often against gravity, especially in the legs. Because venous pressure is lower, veins rely on valves and surrounding muscle contractions to keep blood moving in the correct direction and to prevent backflow. Arteries generally lack such valves, except near the heart where semilunar valves exist at the exits of the ventricles. Consequently, the presence of valves within many veins is a key distinguishing feature.

Step-by-Step Solution:
Step 1: Recall that in systemic circulation, arteries carry blood away from the heart and veins return blood to the heart. Step 2: Remember that arterial walls are usually thicker and more muscular than venous walls because they must withstand higher pressure. Step 3: Recognize that veins contain internal valves to prevent backflow, especially in the limbs, while arteries generally do not have such valves along their length. Step 4: Choose the option that correctly states the presence of valves in veins and their absence in most arteries.

Verification / Alternative check:
Clinical examples such as varicose veins result partly from failure of venous valves, which allows blood to pool and veins to become distended. No similar valve failure occurs in arteries along their length because they do not normally have these segmental valves. Additionally, anatomical diagrams consistently show venous valves but not arterial valves except at the heart, confirming the accuracy of the correct option.

Why Other Options Are Wrong:
Veins carry blood away from the heart: This reverses the true direction; veins carry blood back to the heart.
Veins have thicker muscular walls than arteries: The opposite is true; arteries have thicker walls to handle higher pressure.
Veins have a smaller lumen: Veins often have a larger, more collapsible lumen than corresponding arteries.

Common Pitfalls:
Some students equate oxygen content with arteries and veins, thinking arteries always carry oxygen rich blood and veins always carry oxygen poor blood. The more accurate way to distinguish them is by direction of blood flow and structural features such as wall thickness and valves. Keeping these features in mind helps avoid confusion, especially when learning about pulmonary circulation where oxygenation patterns are reversed.

Final Answer:
The true statement is that veins contain valves to prevent backflow of blood, whereas arteries generally do not.