Learning Objective
At the end of this session, the learner should be able to describe the anatomy of the diaphragm, including its attachments, openings, innervation, actions, and clinical significance.
The diaphragm is a double-domed musculotendinous sheet forming the floor of the thoracic cavity and the roof of the abdominal cavity. It serves two key functions:
- Partition: Separates the thoracic and abdominal cavities.
- Respiration: Contracts and relaxes to change thoracic volume, allowing inspiration and expiration.
The term “diaphragm” derives from the Greek diáphragma, meaning partition.
Anatomical Position and Attachments
The diaphragm fills the inferior thoracic aperture and attaches both peripherally and centrally.
Peripheral Attachments
- Lumbar vertebrae and arcuate ligaments
- Costal cartilages of ribs 7–10 (and directly to ribs 11–12)
- Xiphoid process of the sternum
Crura (Tendinous Attachments)
- Right crus: Arises from L1–L3 and surrounds the oesophageal hiatus, acting as a physiological sphincter.
- Left crus: Arises from L1–L2.
Central Tendon
All muscle fibres converge into a central tendon, which fuses with the fibrous pericardium. At rest, the right dome lies higher than the left, due to the underlying liver.
Activity
Openings in the Diaphragm
Structures passing between the thoracic and abdominal cavities traverse three main openings:
| Opening | Vertebral Level | Structures Passing Through |
|---|---|---|
| Caval hiatus | T8 | Inferior vena cava, terminal branches of the right phrenic nerve |
| Oesophageal hiatus | T10 | Oesophagus, vagus nerves, oesophageal branches of left gastric artery/vein |
| Aortic hiatus | T12 | Aorta, thoracic duct, azygos vein |
Mnemonic: “I 8 10 Eggs At 12” I (IVC) – T8 – 10 (Oesophagus) – T10 12 (Aorta) – T12
Activity
Actions
- Inspiration: Contraction flattens the diaphragm → increases thoracic volume → air is drawn into lungs.
- Expiration: Relaxation restores dome shape → decreases thoracic volume → air expelled.
Thus, the diaphragm is the primary muscle of respiration.
Innervation
- Motor: Phrenic nerve (C3–C5) — “C3, 4, 5 keep the diaphragm alive”
- Sensory:
- Central part: Phrenic nerve
- Peripheral part: Intercostal nerves
Blood Supply
- Inferior phrenic arteries (from abdominal aorta) — main supply
- Superior phrenic, pericardiacophrenic, and musculophrenic arteries — supplementary supply
- Venous drainage mirrors arterial supply.
Clinical Relevance: Diaphragmatic Paralysis
Paralysis results from interruption of the phrenic nerve supply, due to:
- Surgical trauma
- Tumour compression
- Myasthenia gravis or diabetic neuropathy
Clinical signs:
- Paradoxical movement — the affected dome moves up during inspiration.
- Unilateral paralysis — often asymptomatic.
- Bilateral paralysis causes orthopnoea, fatigue, and restrictive lung function.
Management:
- Treat the underlying cause.
- Supportive therapy (e.g., CPAP or non-invasive ventilation).
