📝 STANDARD DESCRIPTION:
High-Yield Points:
• Dome-shaped musculotendinous partition between thorax and abdomen.
• Origin: Sternal part (xiphoid), Costal part (last ribs), Lumbar part (crura — attach to the ventral lumbar vertebral bodies, with attachment length differing between right and left crura).
• Insertion: Central tendon (no bone — like a trampoline).
• 3 Hiatuses: Aortic (aorta + azygous v. + thoracic duct, between crura), Oesophageal (oesophagus + vagal trunks), Caval (caudal vena cava — through central tendon).
• Innervation: Phrenic nerve (C5, C6, C7).
• Chief muscle of inspiration; its exact contribution to tidal volume varies with posture and breathing conditions.
📚 DETAILED DESCRIPTION:
DIAPHRAGM — THE BORDER & THE ENGINE
The diaphragm is the chief inspiratory muscle AND the cranial wall of the abdomen. It is dome-shaped (convex toward thorax) and consists of muscular periphery + central tendon.
PARTS:
• Sternal part — short, from xiphoid cartilage.
• Costal part — long, from medial face of caudal ribs (8-13).
• Lumbar part — two crura (right + left) attached asymmetrically to the ventral bodies of the cranial lumbar vertebrae. Right crus is larger and longer than left.
• Central tendon (tendinous centre); the cupula is the cranially convex dome of the diaphragm — heart-shaped fibrous central area; the converging insertion of all muscle fibres.
HIATUSES (3 OPENINGS):
• Aortic hiatus — between right & left crura; bony floor (vertebral bodies). Transmits: aorta, azygos vein, thoracic duct.
• Oesophageal hiatus — through right crus muscular fibres. Transmits: oesophagus, dorsal & ventral vagal trunks.
• Caval foramen — through central tendon. Transmits: caudal vena cava (largest opening).
INNERVATION: Phrenic nerves (paired), each from C5, C6, C7 ventral rami; descend through neck and thorax to reach diaphragm. Mnemonic: 'C3-4-5 keeps the diaphragm alive' (humans) — but in ox it's C5-6-7.
BLOOD SUPPLY: Phrenicoabdominal, internal thoracic, dorsal intercostal arteries.
RELATIONS:
• Thoracic surface: covered by parietal pleura; lungs and heart sit on it.
• Abdominal surface: covered by parietal peritoneum; LIVER lies right side, RUMEN/RETICULUM on left, RETICULUM presses against it directly — the basis of 'hardware disease'.
// COMPARATIVE ANALYSIS
| OX |
Reticulum sits directly behind diaphragm — major site of hardware disease (foreign metal pierces diaphragm → pericardium). |
| HORSE |
Sturdy diaphragm — diaphragmatic hernia rare but devastating (intestinal strangulation when it occurs). |
| DOG/CAT |
Diaphragmatic hernia common after road traffic accidents — abdominal viscera enter thorax causing dyspnea. |
CLINICAL RELEVANCE
Traumatic Reticulopericarditis (Hardware Disease): Wire from reticulum penetrates diaphragm → pericardium → septic pericarditis. Phrenic Nerve Paralysis: Cervical trauma → paradoxical breathing (diaphragm sucked up during inspiration). Diaphragmatic Hernia: Common in dogs/cats after blunt trauma — radiographic loss of diaphragmatic line.
