Anatomy of the Diaphragm
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🫁 Anatomy of the Diaphragm
The diaphragm is a dome-shaped, musculotendinous structure that separates the thoracic cavity from the abdominal cavity.
It is the primary muscle of respiration and also plays roles in pressure regulation and reflux prevention.
1️⃣ Structure
- 🛑 Dome Shape: Convex superior surface (thoracic) & concave inferior surface (abdominal).
- ⭐ Central Tendon: Non-contractile anchor where muscle fibres converge; fused with fibrous pericardium (explains hiccups sometimes felt in the chest).
- 💪 Muscle Portions:
- Sternal Part: From xiphoid process.
- Costal Part: From inner surfaces of ribs 7–12 & costal cartilages.
- Lumbar Part: Anchored by right & left crura (important in oesophageal function).
– Right crus surrounds oesophageal hiatus → contributes to anti-reflux barrier.
- 🚪 Major Openings (Hiatuses):
- 🧃 Caval Opening (T8): Inferior vena cava + right phrenic nerve branches.
👉 “Vena cava at 8”.
- 🥤 Oesophageal Hiatus (T10): Oesophagus + vagus nerves.
👉 “Eggs (Oesophagus) at 10”.
- 🅰️ Aortic Hiatus (T12): Aorta + thoracic duct + azygos vein.
👉 “Aorta at 12”.
- Mnemonic: “I 8 10 Eggs At 12” 🥚.
2️⃣ Innervation
- 💡 Phrenic nerves (C3–C5): “C3, 4, 5 keep the diaphragm alive” → motor supply + central sensory.
- 🌐 Additional sensory: lower intercostal nerves supply peripheral parts of the diaphragm.
3️⃣ Blood Supply
- Arterial:
– Superior phrenic arteries (thoracic aorta)
– Pericardiophrenic & musculophrenic arteries (branches of internal thoracic artery)
– Inferior phrenic arteries (from abdominal aorta).
- Venous drainage:
– Via brachiocephalic, azygos, and inferior vena cava.
⚙️ Physiology of the Diaphragm
🌬️ 1. Role in Respiration
- Primary muscle of breathing (in quiet respiration, contributes ~75% of air movement).
- Inhalation: Contracts & flattens → ↑ thoracic volume, ↓ intrathoracic pressure → air flows in.
- Exhalation: Relaxes → dome rises → ↓ thoracic volume → air expelled.
💡 2. Other Functions
- Pressure regulation: Contributes to intra-abdominal pressure for 💩 defecation, 🚻 urination, and 🤰 childbirth.
- Anti-reflux role: Right crus fibres + oesophageal hiatus act as functional lower oesophageal sphincter (prevents GERD).
- Venous return: Inspiration increases negative intrathoracic pressure → assists venous return to heart (respiratory pump).
📊 Clinical Pearls
- 📌 Hernias: Weakness → hiatal hernia (sliding/rolling).
- 📌 Referred pain: Irritation of diaphragm → shoulder tip pain (via phrenic nerve → C3–C5 dermatomes).
- 📌 Injury: Phrenic nerve palsy → raised hemidiaphragm on chest X-ray.
- 📌 Hiccups: Due to phrenic nerve irritation or gastric distension.
