The diaphragm is a dome-shaped muscle at the base of the chest, separating the thoracic and abdominal cavities. It is the primary muscle for breathing, allowing for the expansion and contraction of the lungs. A specific component, the crural diaphragm, plays a distinct and important role in various bodily processes, extending beyond general respiratory function to contribute to digestive health.
Anatomy and Location
The crural diaphragm is a muscular segment of the larger diaphragm, characterized by two tendinous structures called crura. These crura originate from the front surfaces of the lumbar vertebrae: the right crus from L1-L3, and the left crus from L1-L2 and their intervertebral discs. Initially tendinous, these structures become fleshy as they extend upwards to merge with the main diaphragm.
The crural diaphragm forms an opening within the diaphragm called the esophageal hiatus, allowing the esophagus and vagus nerve to pass through. The right crus primarily contributes to forming this hiatus, with its fibers looping around the esophagus in a sling-like manner. This opening is located at the level of the tenth thoracic vertebra (T10).
Key Physiological Roles
The crural diaphragm contributes to breathing by contracting and flattening during inspiration, increasing thoracic cavity volume. While the costal diaphragm is primarily responsible for most respiratory force, the crural diaphragm participates in this process, with its rhythm coordinated with the costal diaphragm’s actions.
Beyond its respiratory contribution, the crural diaphragm has an important role in digestive function, particularly in preventing gastroesophageal reflux. It acts as an extrinsic sphincter, creating pressure around the lower esophagus where it meets the stomach, working with the lower esophageal sphincter (LES). This combined mechanism forms a barrier that helps keep stomach contents from flowing back into the esophagus, especially when abdominal pressure increases. During swallowing, the crural diaphragm briefly relaxes, allowing food to pass into the stomach.
When Function is Compromised
When the crural diaphragm does not function optimally, a common condition is a hiatal hernia. This occurs when a portion of the stomach protrudes upwards into the chest cavity through an enlarged or weakened esophageal hiatus. Factors contributing to hiatal hernias include increased abdominal pressure from obesity, chronic coughing, or heavy lifting, and age-related weakening of diaphragmatic muscles.
Dysfunction of the crural diaphragm is also linked to Gastroesophageal Reflux Disease (GERD). Reduced ability to augment pressure during inspiration can lead to a less effective anti-reflux barrier. A hiatal hernia disrupts the normal anatomical relationship, further compromising this barrier and making it easier for stomach acid to reflux into the esophagus, causing symptoms like heartburn and regurgitation. The crural diaphragm contributes significantly to contractility at the esophagogastric junction, underscoring its role in preventing reflux.