Posterior to sternum is ?
**Core Concept**
The question is testing the student's knowledge of the anatomical location of various structures in relation to the sternum, specifically the posterior aspect. The sternum is a long, flat bone that forms the anterior (front) part of the thoracic cage, and it is surrounded by various organs and tissues.
**Why the Correct Answer is Right**
The correct answer refers to the location of the pericardium, which is a fibroserous sac that encloses the heart and the roots of the great vessels. The pericardium is situated posterior to the sternum, specifically between the sternum and the spine, and it plays a crucial role in protecting the heart and maintaining its position within the thoracic cavity. The pericardium consists of two layers: the fibrous pericardium, which is a tough, fibrous layer that attaches the pericardium to the surrounding tissues, and the serous pericardium, which is a thin, smooth layer that produces a small amount of fluid that helps to reduce friction between the heart and the pericardium.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the mediastinum is a region of the thoracic cavity that contains the heart, great vessels, trachea, esophagus, and other structures, but it is not specifically located posterior to the sternum.
* **Option B:** This option is incorrect because the diaphragm is a dome-shaped muscle that separates the chest cavity from the abdominal cavity, but it is not located posterior to the sternum.
* **Option C:** This option is incorrect because the lungs are a pair of spongy organs that are located within the thoracic cavity, but they are not specifically located posterior to the sternum.
**Clinical Pearl / High-Yield Fact**
The pericardium is a crucial structure that plays a vital role in maintaining the heart's position and function, and any damage to the pericardium can lead to pericardial tamponade, a life-threatening condition that requires immediate medical attention.
**Correct Answer:** C. The diaphragm is posterior to the sternum.