Makindo Medical Notes

Related Subjects: |Anatomy of the Ear |Anatomy of the Oesophagus |Anatomy of the Diaphragm |Anatomy of Large Bowel |Anatomy of Small Bowel |Anatomy of the Biliary system |Anatomy of the Eye |Anatomy of the Larynx |Anatomy of the Ear

🫁 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.