The diaphragm is a muscle that helps you inhale and exhale (breathe in and out). This thin, dome-shaped muscle sits below your lungs and heart. It’s attached to your sternum (a bone in the middle of your chest), the bottom of your rib cage and your spine. Your diaphragm separates your chest from your abdominal cavity (belly).

In addition to helping you breathe, your diaphragm increases pressure inside your abdomen. This helps with other important functions, such as getting rid of your urine (pee) and feces (poop). It helps prevent acid reflux by putting pressure on your esophagus (food tube in your throat). Your esophagus and several nerves and blood vessels run through openings in the diaphragm.

What does the diaphragm do?

The diaphragm plays a critical role in the respiratory system. When you breathe in, your diaphragm contracts (tightens) and flattens, moving down towards your abdomen. This movement creates a vacuum in your chest, allowing your chest to expand (get bigger) and pull in air. When you breathe out, your diaphragm relaxes and curves back up as your lungs push the air out.

Several nerves, soft tissues and blood vessels pass through the diaphragm. These include the:

Aorta, a big artery that carries your blood away from your heart to the rest of your body.
Esophagus, a hollow tube that connects the throat to the stomach. Food and liquids move through the esophagus to the stomach.
Inferior vena cava, a vein that carries blood to your heart.
Phrenic nerve, which controls the diaphragm’s movement.
Thoracic duct, a vessel that carries a fluid called lymph through the body as part of the lymphatic system.
Vagus nerve, which has many important jobs, including helping to control the digestive system.