Overview
The pericardium is a conical, flask-like, fibroserous sac that encases the heart with 20 to 25 mL of serous fluid and roots of the great vessels. It defines the middle mediastinum and acts as the medial border of the pleural space on either side of the heart.
Layers
- Fibrous pericardium – the outer layer of dense irregular connective tissue
- Serous pericardium – the inner layer of mesothelium, consists of two layers:
- parietal layer (lays under the fibrous pericardium)
- visceral layer (epicardium) (lays over the heart)
Fibrous Pericardium
Outermost layer made of tough, relatively non-distensible connective tissue
- At its base, it is continuous and inseparable from the central tendon of the diaphragm
- Superiorly, it blends with the tunica adventitia of the great vessels
- It is continuous with the pre-tracheal layer of deep cervical fascia
- Anteriorly it is attached to the posterior surface of the sternum by sternopericardial ligaments
- Phrenic nerve (C3-5) and pericardiacophrenic vessels travel within its substance, supplying it
Serous pericardium
- As with all serous membranes, the serous pericardium consists of two layers:
- Parietal layer – outer layer which lines the inner surface of the fibrous pericardium
- Visceral layer – inner layer, also known as the epicardium, incompletely surrounds the heart
- The parietal and visceral layers enclose the pericardial cavity, containing a thin film of serous fluid secreted by pericardial cells.
- Visceral and parietal layers continuous around the roots of great vessels reflected about two points:
- Superiorly around the arteries (aorta and pulmonary trunk)
- Posteriorly around the veins (superior (SVC) and inferior vena cava (IVC), and four pulmonary veins)
Sinuses
- Oblique pericardial sinus: cul-de-sac formed around the posterior reflection that is J-shaped and located behind the left atrium
- Transverse pericardial sinus: the passage between the anterior and posterior reflections which lies superior to the left atrium
Blood Supply
- Main: Pericardiophrenic branches of the internal thoracic vessels – runs between the pericardium and the pleura alongside the phrenic nerve.
- Other arteries: Musclophrenic, bronchial, oesophageal, superior phrenic
- Coronary arteries contribute to supply, only to the visceral layer of the pericardium
Venous Drainage
- Azygous system
- Pericardiacophrenic veins – tributaries of the brachiocephalic vein
Innervation
- Phrenic nerves (C3 – C5) (sensory) – pain, temperature, sensory
- Sympathetic trunk (vasomotor) – postganglionic vasomotor fibres
- Vagus nerve – uncertain involvement
Lymphatic
Lymphatic drainage of the visceral pericardium utilizes the tracheal and bronchial lymph chain while the parietal pericardium drains similarly to the sternum and diaphragm.
Relations
- Anteriorly: posterior surface of the body of sternum, costocartilage of left 3-7th ribs, thymus, pleura and lungs
- Posterior: contents of the posterior mediastinum
- Descending thoracic aorta
- Oesophagus
- Azygos system
- Thoracic duct
- Sympathathetic trunk
- Lateral: mediastinal pleura, lungs and phrenic nerves and pericardiacophrenic vessels
- Superior: continuous with the tunica adventitia of the great vessels of the heart
- Inferior: central tendon of the diaphragm
Development
- Develops simultaneously with the heart
- As the heart tubes fuse and attach to anterior and posterior walls, the left and right intraembryonic coelomic cavities approach each other.
- The cavities then fuse and form the pericardial cavity, enveloping the heart tube within its dorsal wall. –