The main organ found underneath the left lung is the heart. The heart sits in the middle of the chest, tilted slightly to the left side. This means the bottom portion of the left lung covers a part of the heart.
Anatomy of the Lungs and Heart
To understand what sits underneath the lungs, it’s helpful to review the basic anatomy of the chest cavity. The chest contains the lungs, heart, major blood vessels, and other structures.
The lungs are a pair of spongy, air-filled organs used for respiration. The right lung has three sections, called lobes. The left lung is slightly smaller as it has just two lobes to make room for the heart.
The heart sits between the lungs, behind the sternum and above the diaphragm. It tilts to the left side of the chest. The heart is a muscular organ that pumps blood throughout the body. It is surrounded by a fluid-filled sac called the pericardium.
The major blood vessels connected to the heart run through the mediastinum, the space between the lungs. These include the aorta, pulmonary arteries, and pulmonary veins.
Left Lung Covers the Heart
When you take a deep breath, the lungs expand and fill up the chest cavity. The left lung is adjacent to the heart, covering the lower portion. However, the heart does not sit directly underneath the full span of the left lung.
Approximately 2/3 of the heart sits under the left lung. This includes the left ventricle, left atrium, and part of the right atrium and ventricle. The superior vena cava, a large vein carrying blood to the heart, also passes under the middle of the left lung.
The left lung covers these vital structures and organs to protect them. Having the lung adjacent to the heart also allows for important physiological interactions. For example, changes in lung volume can impact heart function and vice versa.
Other Structures Under the Left Lung
In addition to the heart, several other structures lie underneath the left lung:
- Diaphragm – The diaphragm is a dome-shaped muscle located at the base of the lungs. The left diaphragm sits directly below the left lung.
- Stomach – The top portion of the stomach and the spleen sit just below the lower tip of the left lung in the upper left quadrant of the abdomen.
- Left adrenal gland – This small triangular gland rests on top of the left kidney under the lower end of the lung.
- Pancreas tail – The tail end of the pancreas tucks under the lower left lung above the spleen.
- Left kidney – The upper half of the left kidney sits below the left lung adjacent to the adrenal gland.
Protection for the Heart and Other Organs
The lower portion of left lung covers sensitive vascular structures like the heart while also concealing abdominal organs. This positioning helps protect these critical organs from exterior trauma or damage.
Additionally, the lung filters blood and regulates pressures on the heart. The close proximity allows the lung to perform these protective functions. Problems with the left lung can sometimes directly impact underlying organs.
Importance of Left Lung Anatomy
Understanding what anatomical structures lie below the lungs is important for accurately diagnosing and treating health conditions. For example:
- Heart sounds can be heard with a stethoscope placed under the left lung. Abnormal heart sounds may indicate problems like murmurs or arrhythmias.
- Cancers or lesions on the left lung can sometimes invade the heart tissue below.
- A perforated stomach ulcer can cause inflammation under the left lung called subphrenic abscess.
- Pancreatitis or splenic rupture may cause pain under the left lung.
- Pneumonia in the lower left lung can affect movement of the diaphragm muscle.
Knowing the structures that lie deep to the lungs allows for a better understanding of how organs interact in health and disease. The heart’s intimate relationship with the adjacent left lung highlights the importance of this anatomy.
Conclusion
The main organ that sits underneath the lower portion of the left lung is the heart. While the heart tilts leftward, it doesn’t fully extend under the entire left lung. Only about the inferior 2/3 of the heart rests under the lung’s coverage. This positioning allows the lung to protect the heart while also permitting physiological interactions between the two organs.
Several other abdominal organs also lie below the lower tip of the left lung, including the stomach, spleen, adrenal gland, pancreas tail, and left kidney. Understanding the anatomical relationships between the lungs and adjacent structures is clinically important when diagnosing and treating health conditions affecting the chest and upper abdomen.