All veins opens into coronary sinus, EXCEPT?
**Core Concept**
The coronary sinus is a vital structure responsible for collecting deoxygenated blood from the myocardium and returning it to the right atrium. It serves as the primary venous drainage pathway for the heart.
**Why the Correct Answer is Right**
The coronary sinus collects blood from the heart's venous system, specifically from the great, small, and middle cardiac veins, as well as the oblique vein of the left atrium. These veins drain deoxygenated blood from the myocardium into the coronary sinus, which then empties into the right atrium. The mechanism of blood flow into the coronary sinus is facilitated by the absence of valves, allowing for a one-way flow of blood towards the right atrium.
**Why Each Wrong Option is Incorrect**
* **Option A:** The great cardiac vein is one of the primary contributors to the coronary sinus, making this statement incorrect.
* **Option B:** The middle cardiac vein also drains into the coronary sinus, making this statement incorrect.
* **Option C:** The superior vena cava is a major vein that returns deoxygenated blood from the upper body to the right atrium, but it does not drain directly into the coronary sinus, making this statement correct.
**Clinical Pearl / High-Yield Fact**
The coronary sinus is an important landmark for cardiac surgeons and electrophysiologists, as it is often targeted for procedures such as cardiac ablation and pacemaker lead placement.
**Correct Answer:** C. The superior vena cava is the correct exception to the statement that all veins open into the coronary sinus.