The tricuspid valve is located between the

Analyze the question: You are asked where the tricuspid valve sits in the mammalian heart.

Concept: The heart has four chambers: two upper atria (called auricles in older Nigerian textbooks) and two lower ventricles. Between each atrium and its ventricle is an atrioventricular (AV) valve. These valves stop blood from flowing backward when the ventricles contract.

• Right side: the valve has three flaps (cusps), so it is the tricuspid valve.
• Left side: the valve has two flaps, so it is the bicuspid valve, also called the mitral valve.

Step by step:

1. "Tri" means three, which points to the valve with three cusps.
2. The three-cusped valve is on the right side of the heart.
3. It lies between the right auricle (atrium) and the right ventricle.
4. It lets deoxygenated blood flow from the right auricle into the right ventricle, and closes to stop it flowing back.

Checking the options:

• A. Left auricle and left ventricle: this is the bicuspid (mitral) valve, so it is wrong.
• B. Left and right auricles: these are separated by the septum, not a valve, so it is wrong.
• C. Right and left ventricles: these are also separated by the septum, so it is wrong.
• D. Right auricle and right ventricle: correct.
• E. Right auricle and left ventricle: no valve connects these directly, so it is wrong.

Exam tip: Remember "Tri-Right", since both have the letters "Tri" and "R" and you can think "try the right side". The left side is the bicuspid, and a handy phrase is "Left = Less (two) cusps". Also remember that the semilunar valves guard the exits to the aorta and the pulmonary artery.