Which of the following is not true about a heart chamber or valve? 

• A. Endocardium lines the inner walls of heart chambers and reduces friction as blood flows through the chambers. 
• B. Heart valves are situated at the entrances & exits of the ventricle and ensure that blood flows in one direction only. 
• C. Atria are the upper chambers that receive blood while the ventricles pump out blood when they contract. 
• D. Tricuspid valve is an atrioventricular valve and allows blood from the ventricles to enter the atria. 

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the function of the endocardium. The endocardium is the inner lining of the heart chambers, and its role is to reduce friction as blood flows through the chambers, which helps maintain smooth blood flow.
2. Step 2: Review the location and function of heart valves. Heart valves are located at the entrances and exits of the ventricles, and their primary function is to ensure unidirectional blood flow, preventing backflow.
3. Step 3: Recall the roles of the atria and ventricles. The atria are the upper chambers of the heart that receive blood returning to the heart, while the ventricles are the lower chambers that pump blood out to the lungs or the rest of the body.
4. Step 4: Analyze the statement about the tricuspid valve. The tricuspid valve is an atrioventricular valve, meaning it is located between an atrium and a ventricle. It allows blood to flow from the right atrium to the right ventricle, not the other way around.
5. Step 5: Identify the incorrect statement. Since the tricuspid valve allows blood to flow from the atria to the ventricles, the statement that it allows blood from the ventricles to enter the atria is false.