Diaphragm Anatomy: Location, Function & System Classification

The diaphragm is a dome‑shaped skeletal muscle separating the thoracic and abdominal cavities. It is the primary muscle of inspiration.

Anatomic Location

• Attaches to: xiphoid process (sternum), costal margin (ribs 6–12), lumbar vertebrae (L1–L3) via crura.
• Central tendon: aponeurotic insertion point for muscle fibers.
• Openings: Caval foramen (T8, IVC), Esophageal hiatus (T10, esophagus + vagal trunks), Aortic hiatus (T12, aorta + thoracic duct + azygos).

System Classification

• Muscular system: Skeletal muscle (voluntary control possible, but autonomic drive dominates).
• Respiratory system: Essential for ventilation.
• NOT cardiovascular: The heart sits atop the diaphragm (pericardium fused to central tendon), but the diaphragm is not a cardiovascular organ.

Physiology

1. Phrenic nerves (C3–C5) fire → diaphragm contracts → flattens.
2. Thoracic volume ↑ → intrapleural pressure ↓ → alveolar pressure ↓ → air flows in.
3. Relaxation → elastic recoil → expiration (passive at rest).

Clinical Notes

• Phrenic nerve injury → hemidiaphragm paralysis → dyspnea, orthopnea.
• Hiatal hernia: stomach protrudes through esophageal hiatus.
• Diaphragmatic breathing (slow, deep) activates vagal tone → stress reduction.