The sternum, or breastbone, is a flat, T-shaped bone located centrally in the front of the chest. It forms part of the thoracic cage, the bony framework enclosing the chest cavity. This structure anchors various bones and muscles, contributing to upper body stability. Its midline location makes it easily palpable.
The Heart
The heart is located directly beneath the sternum. Positioned between the lungs, it sits slightly behind and to the left of the breastbone. Roughly the size of a clenched fist, it typically measures about 13 by 9 by 6 centimeters. Its conical shape has a broader upper part, the base, directed upward and to the right, while the lower, pointed tip, or apex, points downward and to the left.
A double-layered membrane, the pericardium, surrounds the heart, separating it from other chest structures. The heart’s anterior surface lies deep to the sternum and the costal cartilages, which connect the ribs to the sternum. As the central pump of the circulatory system, the heart moves blood throughout the body. This action ensures oxygenated blood reaches all tissues, while deoxygenated blood returns to the heart for re-oxygenation in the lungs.
Other Organs and Structures
Other anatomical structures are found near the sternum. The lungs, situated on either side of the heart, are protected by the rib cage, which articulates with the sternum. These organs facilitate gas exchange, bringing oxygen into the body and releasing carbon dioxide. The thymus gland, part of the lymphatic system, is located behind the upper sternum and in front of the heart.
The thymus is prominent during childhood, playing a role in the immune system by producing and training specialized white blood cells called T-cells. These T-cells defend the body against infections. The esophagus, a muscular tube transporting food from the throat to the stomach, passes behind the sternum. Major blood vessels, such as the aorta and vena cavae, also traverse this region. The aorta carries oxygen-rich blood away from the heart, while the superior and inferior vena cavae return deoxygenated blood to the heart from the body.
Protective Function of the Sternum
The sternum’s primary function is to protect chest organs. Along with the ribs and spine, it forms the thoracic cage, a bony barrier for internal structures. This framework safeguards the heart, major blood vessels, and lungs from external impacts and injury. The sternum also supports the rib cage, maintaining the chest cavity’s structural integrity. This support allows for the expansion and contraction necessary for effective respiration.