Which of the following does not directly drain into right atrium-
**Core Concept**
The heart's venous system is responsible for returning deoxygenated blood to the right atrium. The superior and inferior vena cava are the primary vessels that directly drain into the right atrium.
**Why the Correct Answer is Right**
The correct answer is related to the anatomy of the venous system. The superior and inferior vena cava, coronary sinus, and hepatic veins directly drain into the right atrium. However, the left atrium receives oxygenated blood from the pulmonary veins.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the superior vena cava directly drains into the right atrium.
**Option B:** This option is incorrect as the inferior vena cava directly drains into the right atrium.
**Option C:** This option is incorrect as the coronary sinus directly drains into the right atrium.
**Option D:** This option is correct because the left atrium receives oxygenated blood from the pulmonary veins, not directly draining into the right atrium.
**Clinical Pearl / High-Yield Fact**
Remember that the pulmonary veins are the only veins that carry oxygenated blood from the lungs to the heart, specifically to the left atrium. This is a key distinction in understanding the anatomy of the venous system.
**Correct Answer: D. Left atrium receives oxygenated blood from the pulmonary veins, not directly draining into the right atrium.**