Fibrous pericardium, parietal serous layer, pericardial cavity, visceral serous layer
Mnemonic
“Fibrous outside, then two serous layers”:
- Fibrous pericardium - tough, inelastic, fused to the central tendon of the diaphragm below and continuous with the great vessel adventitia above
- Parietal serous pericardium, lining the fibrous layer
- Visceral serous pericardium (epicardium), on the heart itself
- Between them, the pericardial cavity, containing about 50 ml of fluid
“The fibrous layer is why tamponade happens.” Because it cannot stretch acutely, a rapidly accumulating 150 ml can tamponade, while a slowly accumulating litre may not.
Innervation is the phrenic nerve (C3, 4, 5), which is why pericarditis refers pain to the shoulder tip and why it is relieved by sitting forward.
Two sinuses form where the serous layer reflects around the great vessels: the transverse sinus, behind the aorta and pulmonary trunk and in front of the atria, used to pass a ligature around the outflow vessels in cardiac surgery; and the oblique sinus, behind the left atrium.
Expansion
From the outside inwards:
- Fibrous pericardium - tough outer sac, fused to the central tendon of the diaphragm below and continuous with the adventitia of the great vessels above
- Parietal serous pericardium - lines the fibrous layer
- Pericardial cavity - a potential space with a few millilitres of serous fluid
- Visceral serous pericardium (epicardium) - on the heart surface
Sensory innervation of the fibrous and parietal layers comes from the phrenic nerve (C3, C4, C5), which is why pericarditis refers pain to the shoulder tip. The visceral layer has no somatic sensory supply.