Layers of the Heart
The heart is a large muscular organ that is comprised of four different layers. From the outside to the inside, the layers are:
- The pericardium
- The epicardium
- The myocardium
- The endocardium
Each layer has a different function, which primarily aids the pumping action of the heart which allows the blood to flow around the body.
|Pericardium||Two layers of connective tissue (visceral and parietal) that enclose the heart and protect it|
|Epicardium||Layer of connective tissue fused with myocardium at one side, and visceral pericardium at the other
Provides that the pericardium encompases the heart contractions
Muscle layer (the thickest of all)
Its contractions define the heart cycle and provide blood pumping
|Endocardium||Covers all appandages of the heart chambers|
This article presents a brief overview of each cardiac layer, as well as clinical cases.
The pericardial sac is a folded fibrous connective tissue layer that encompasses the entire heart and the roots of the great vessels. It has an inner and an outer layer which are continuous and create a fascial space known as the pericardial sac.
Within this sac is a viscous liquid known as the pericardial fluid, which helps lubricate the outer beating surfaces of the heart and prevents friction between the fibrous and serious layers of the pericardium. This layer of the heart functions by stabilizing the heart within the mediastinum, protecting it against infection and preventing cardiac overload.
The epicardium is the layer of muscle found covering the external surfaces of the heart. It is directly fused with the myocardium internally and is in contact with the serous layer of the pericardium. It is sometimes considered as a division of the inner layer of the pericardium. It is comprised mainly of connective tissue and protectively encompasses the heart.
The myocardium is the middle muscular layer of the heart's walls and it functions by providing a scaffolding for the heart chambers. It assists in contraction and relaxation of the cardiac walls so that blood can pass between the chambers and electrostimulation conduction through its own tissues and into the epicardium. It sits between the inner endocardium and the outer epicardium.
The endocardium is the most inner layer of the heart. It forms the inner layer of all four heart chambers and is directly connected to all the inner cardiac appendages, such as the bicuspid valve, the tricuspid valve, the pulmonary valve, the aortic valve, the chordae tendineae and the papillary muscles. Its primary composition consists of endothelial cells and it is thought to control both itself and the myocardium through the spread of action potentials via the purkinje fibers within the cardiac muscle.
Myocardial infarction is the clinical name for the pathological condition known as heart attack. It is caused by a lack of blood flow to an area of the heart which stops it working due to muscular injury. When the cardiac muscle is insufficiently oxygenated and provided with the necessary nutrients, its cells start to die. This stops the action potentials required for cardiac contraction to occur and the heart is weighed with an area which isn’t beating. Beta Blockers, nitroglycerin, oxygen and aspirin are immediately administered to a cardiac patient upon arrest in order to improve their prognosis and combat the attack. This type of pathological change is important because it can affect all the layers of the heart.