Pericardium layers
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Here is a full breakdown of the pericardium layers, sourced from Gray's Anatomy for Students and the Color Atlas of Human Anatomy:
Layers of the Pericardium
The pericardium is a fibroserous sac surrounding the heart and the roots of the great vessels. It has two main components:
1. Fibrous Pericardium (Outer Layer)
- Tough, dense collagenous connective tissue
- Cone-shaped sac with its base on the diaphragm and apex continuous with the adventitia of the great vessels
- Attachments:
- Inferiorly: fused to the central tendon of the diaphragm (and a small left-side muscular area)
- Anteriorly: attached to the posterior sternum via sternopericardial ligaments
- Posteriorly: bands to the trachea and vertebral column
- Functions: anchors the heart in the thorax, limits cardiac distention, and prevents over-dilation
2. Serous Pericardium (Inner Layer)
A thin, double-layered closed sac sitting inside the fibrous pericardium. Like all serous membranes, it has two parts:
| Layer | Location | Also called |
|---|---|---|
| Parietal layer | Lines the inner surface of the fibrous pericardium | - |
| Visceral layer | Adheres directly to the heart surface and roots of great vessels | Epicardium |
The two layers are continuous with each other at the roots of the great vessels (at the sites of reflection).
3. Pericardial Cavity
- The potential space between the parietal and visceral serous layers
- Contains a small amount of serous fluid (normally ~15-50 mL) that acts as a lubricant
- Allows relatively uninhibited movement of the heart during contraction
Pericardial Sinuses (clinically important)
- Transverse pericardial sinus: a groove between the arterial (aorta + pulmonary trunk) and venous (pulmonary veins + venae cavae) reflections; surgeons use it to place clamps on the aorta during cardiac surgery
- Oblique pericardial sinus: a blind recess behind the left atrium, between the inferior pulmonary veins and inferior vena cava; a fluid collection here may not be detected on physical exam
Innervation & Blood Supply
- Innervation: phrenic nerve (C3-C5), vagus nerve, sympathetic trunk - the phrenic nerve travels within the fibrous pericardium
- Arterial supply: pericardiacophrenic artery (from internal thoracic artery)
- Venous drainage: pericardiacophrenic vein → brachiocephalic vein
Clinical Notes
- Pericarditis: inflammation can cause fibrinous adhesions between serous layers
- Pericardial effusion: excess fluid accumulates in the pericardial cavity (e.g., in pericarditis, malignancy, trauma)
- Cardiac tamponade: large effusion compresses the heart, impeding ventricular filling - a medical emergency
Sources: Gray's Anatomy for Students; Color Atlas of Human Anatomy Vol. 2, Internal Organs
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