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Layers of the Heart

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The heart is a large muscular organ that is comprised of four different layers known as the pericardium, the epicardium, the myocardium and the endocardium, from the outside to the inside. Each layer has a different function, which primarily aids the pumping action of the heart which allows the blood to flow around the body. This article presents a brief overview of each cardiac layer, as well as potential pathological developments.

Posteroinferior view of the Heart
Recommended video: Posteroinferior view of the Heart
Structures seen on the posteroinferior view of the heart.

Pericardium

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. Read more about the Pericardium here.

Epicardium

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.

Myocardium

The myocardium is the middle muscular layer of the heart's walls and it functions by providing a scaffolding for the heart chambers, assisting 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.

Endocardium

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 is 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.

Pathology

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 which 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.

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Show references

References:

  • Frank H. Netter, MD, Atlas of Human Anatomy, Fifth Edition, Saunders - Elsevier, Chapter 3 Thorax, Subchapter 22 Heart, Guide Thorax: Heart Page 111 to 114.
  • Michael Schuenke et al., Atlas of Anatomy: Neck and Internal Organs, First Edition, Thieme, Thorax Chapter 2 Organs, 2.14 to 2.22 Heart, Page 96 to 112.
  • Neil S. Norton, Ph.D. and Frank H. Netter, MD, Netter’s Head and Neck Anatomy for Dentistry, 2nd Edition, Elsevier Saunders, Chapter 22 Introduction to the Upper Limb, Back, Thorax and Abdomen, Page 586 to 588.

Author:

  • Dr. Alexandra Sieroslawska

Illustrators:

  • Heart anterior view - myocardium - Yousun Koh 
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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