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M01.05.009 Diaphragm
The diaphragm is a double-domed musculotendinous structure forming the boundary between the thoracic and abdominal cavities. It plays a crucial role in respiration and is a key anatomical structure in the human body.
Functions of the Diaphragm
- Partitioning Role
- Separates the thoracic cavity from the abdominal cavity.
- The term “diaphragm” is derived from the Greek word diáphragma, meaning partition.
- Respiratory Role
- Inspiration: Contraction increases the thoracic cavity volume, enabling lung expansion.
- Expiration: Relaxation decreases thoracic cavity volume, assisting in air expulsion.
Anatomy of the Diaphragm
Position and Attachments
- Location: Inferior-most aspect of the rib cage, filling the inferior thoracic aperture.
- Attachments: Divided into peripheral and central components.
| Attachment Type | Structures |
|---|---|
| Peripheral | 1. Lumbar vertebrae and arcuate ligaments. |
| 2. Costal cartilages of ribs 7-10 and ribs 11-12. | |
| 3. Xiphoid process of the sternum. | |
| Central | The central tendon, which fuses with the fibrous pericardium and forms left and right domes. |
Right and Left Crura
- Right Crus: Arises from L1-L3 vertebrae; encircles the oesophageal opening, acting as a physiological sphincter.
- Left Crus: Arises from L1-L2 vertebrae.
Pathways through the Diaphragm
The diaphragm has three openings for structures passing between the thoracic and abdominal cavities:
| Opening | Vertebral Level | Structures Passing Through |
|---|---|---|
| Caval Hiatus | T8 | Inferior vena cava, terminal branches of right phrenic nerve. |
| Oesophageal Hiatus | T10 | Oesophagus, right and left vagus nerves, oesophageal branches of left gastric artery/vein. |
| Aortic Hiatus | T12 | Aorta, thoracic duct, Azygos vein. |
Mnemonic:
- “Vena cava” has 8 letters (T8).
- “Oesophagus” has 10 letters (T10).
- “Aortic hiatus” has 12 letters (T12).
Actions of the Diaphragm
- Primary Muscle of Respiration:
- Inspiration: Contracts and flattens, increasing thoracic cavity volume.
- Expiration: Passively relaxes, returning to a dome shape, reducing thoracic cavity volume.
Innervation and Blood Supply
| Aspect | Details |
|---|---|
| Innervation | Phrenic nerve (C3-C5). Each phrenic nerve innervates its respective hemidiaphragm. |
| Arterial Supply | Inferior phrenic arteries (primary), superior phrenic, pericardiacophrenic, and musculophrenic arteries. |
| Venous Drainage | Follows the corresponding arterial supply. |
Clinical Relevance: Diaphragmatic Paralysis
Causes
- Mechanical Trauma: Nerve damage during surgery.
- Compression: Tumors in the chest cavity.
- Myopathies: Conditions like myasthenia gravis.
- Neuropathies: Examples include diabetic neuropathy.
Clinical Presentation
- Paradoxical Movement:
- Affected side moves upward during inspiration and downward during expiration.
- Symptoms:
- Unilateral paralysis: Often asymptomatic and detected on X-rays.
- Bilateral paralysis: Leads to orthopnoea, fatigue, and reduced exercise tolerance.
Management
- Identify and treat the underlying cause.
- Provide symptomatic relief using non-invasive ventilation (e.g., CPAP).
Points to Remember
- The diaphragm’s function extends beyond respiration, impacting gastrointestinal reflux via its crural structures.
- Paralysis often results in paradoxical movements, best observed during respiratory cycles.
- Mnemonics aid in remembering diaphragmatic apertures and their vertebral levels.
References
- Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 7th ed. Lippincott Williams & Wilkins.
- Gray H. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Churchill Livingstone.
- Netter FH. Atlas of Human Anatomy. 6th ed. Elsevier.