The Anatomy of the Sternum and Thoracic Cavity
Your sternum, or breastbone, is a long, flat bone located in the central part of your chest. It serves as a protective shield for many of the organs that reside within your thoracic cavity. The thoracic cavity is the space enclosed by your ribs, spine, and diaphragm, and it is further divided into two pleural cavities (containing the lungs) and a central area known as the mediastinum.
The mediastinum is the key region for answering the question of what organ is under your sternum. This central space is where you find the heart, the thymus gland, the esophagus, the trachea, and major blood vessels. Understanding this anatomical layout helps clarify how different organs are positioned in relation to your breastbone and the potential sources of pain or discomfort.
Major Organs Protected by the Sternum
While the sternum and ribcage provide a bony framework, they specifically protect several crucial, soft organs that are fundamental to bodily function.
The Heart
The heart is one of the most prominent organs located partially behind and slightly to the left of your sternum. Positioned in the middle mediastinum, this muscular organ acts as the body's pump, circulating blood throughout the body. Its vital function and central location make the sternum a critical part of its protection. A common misconception is that the heart is exclusively on the left side of the chest, but it is actually centered in the middle, behind the sternum, with a portion extending to the left.
The Thymus Gland
The thymus gland is another important organ situated directly behind the upper part of the sternum. Part of the immune system, the thymus is most active during childhood and puberty. It is responsible for producing T-lymphocytes, or T-cells, which are a type of white blood cell essential for fighting infection. After puberty, the thymus gradually shrinks and is replaced by fatty tissue, though it remains an important part of the body's immune memory.
The Lungs and Esophagus
The inner parts of both lungs are also housed within the thoracic cavity, protected by the sternum and ribcage. The sternum helps shield the mediastinum and the vital connection points of the respiratory system. Posterior to the trachea (windpipe) and heart lies the esophagus, a muscular tube that transports food and liquids from the pharynx to the stomach. The sternum indirectly provides protection for this vital part of the digestive tract as well.
Understanding Pain in the Sternum Area
Because so many organs are located near the sternum, many people experience chest discomfort that they attribute to their heart. However, pain in this area can have numerous causes, not all of which are related to the heart. It is crucial to understand the different possibilities and when to seek medical attention.
Common causes of substernal (behind the sternum) pain include:
- Gastroesophageal Reflux Disease (GERD): Often called heartburn, this occurs when stomach acid flows back into the esophagus, causing a burning sensation behind the breastbone.
- Costochondritis: An inflammation of the cartilage that connects your ribs to your sternum, which can cause sharp, localized pain.
- Anxiety: High levels of stress or anxiety can trigger symptoms that mimic a heart attack, including chest tightness and shortness of breath.
- Muscular Strain: Overexertion from lifting heavy objects or vigorous exercise can strain the muscles in the chest wall.
- Cardiac Issues: More serious conditions, such as angina or a heart attack, can also cause pain behind the sternum, but these are often accompanied by other symptoms like shortness of breath, sweating, or pain radiating to the arm.
Heartburn vs. Heart Attack: A Comparison
| Feature | Heartburn (GERD) | Heart Attack (Angina) |
|---|---|---|
| Sensation | Burning sensation | Pressure, tightness, squeezing, or aching |
| Location | Behind the sternum, sometimes rising to throat | Center of chest, possibly radiating to arms, back, neck, or jaw |
| Timing | Often occurs after eating, when lying down, or bending over | Can occur at rest or with physical exertion |
| Duration | Can last minutes to hours | Can last for several minutes |
| Triggers | Specific foods, large meals, stress | Physical activity, emotional stress |
| Relief | Antacids or sitting upright | Rest and medication like nitroglycerin (for angina) |
The Function and Importance of Your Breastbone
The sternum's main function is to protect the delicate, vital organs that are housed behind it. It acts as a shield, capable of absorbing impact from external forces and preventing damage to the heart, great vessels, and parts of the lungs. The sternum also serves as an anchor point for the ribcage, creating the robust thoracic cage that is essential for breathing and overall chest stability.
To ensure your chest and its internal organs remain healthy, it is important to lead a healthy lifestyle. This includes eating a balanced diet, exercising regularly, and managing stress. For issues related to your immune system, the thymus plays a critical role, and you can learn more about it from reputable sources like the National Cancer Institute (NCI).
Conclusion
While a variety of organs and structures are located under your sternum, the most significant are the heart and the thymus gland. These, along with the lungs and esophagus, are all contained within the protective bony structure of the chest. The sternum is an essential part of our anatomy, and understanding its function and the organs it protects is key to understanding your overall health. If you ever experience persistent or severe chest pain, it is always wise to consult a healthcare professional to rule out serious conditions.
