This review will cover the layers of the heart.
Surrounding your heart is a sac called the pericardium, which acts as a protective and supportive covering. It helps prevent overstretching of the heart, keeps out invaders that could cause infection, and holds your heart in place, preventing it from moving excessively within your chest, especially during activities.
Fibrous Pericardium
The pericardium is composed of two layers. The first, or outer layer, is known as the fibrous pericardium. This layer consists of tough connective tissue, hence its name, fibrous, indicating its strength. Due to its composition, it provides anchorage to nearby structures like the great vessels and the diaphragm, keeping the heart in place within the mediastinum. Furthermore, the fibrous pericardium plays a significant role in preventing the heart from overstretching during increased blood volume.
Serous Pericardium
The second layer is known as the serous pericardium, which produces serous fluid that helps lubricate the heart, preventing friction between layers as the heart beats. This layer itself is made up of two continuous layers, forming the pericardial space, which stores the serous fluid.
Parietal and Visceral Layers of the Serous Pericardium
The first layer is the parietal layer of the serous pericardium, which contacts the fibrous pericardium. Next, you will find the pericardial space. Adjacent to this is the second layer of the serous pericardium, the visceral layer, also called the epicardium. This is the outermost layer of the heart wall and adheres directly to the heart itself.
Remembering Visceral vs. Parietal Layers
To help you remember the difference between visceral and parietal layers, think of visceral layers as surrounding the vital organ itself. “Visceral” and “vital” both start with “vi,” which can help you recall their function.
Pericardial Space
These connected layers fold in a manner that creates the pericardial space, which contains serous fluid to allow the heart to beat without friction or resistance. It acts as a protective barrier against infection or trauma.
Nursing Considerations to Remember about these Layers
From a nursing perspective, understanding the pericardium is crucial due to various diseases that can affect these layers and their space. For example, pericardial effusion occurs when there is an excessive accumulation of fluid in the pericardial space.
Inflammation of these layers, known as pericarditis, can lead to a pericardial friction rub, a distinctive grating sound caused by the unlubricated layers rubbing against each other. This sound is best heard at the left sternal border when the patient is sitting up, leaning forward, and during the end of expiration.
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Now, circling back to the heart wall layers, we just discussed the visceral layer of the serous pericardium, or the epicardium. This is the outermost layer.
Myocardium
Beneath the epicardium lies the myocardium, the second layer and the thickest of the heart wall. The myocardium consists of myocytes, which form a specialized network of cardiac muscle bundles. These bundles are responsible for the involuntary, rhythmic, and continuous contractions of the heart, functioning within the heart’s electrical conduction system. This layer also contains and supports the heart’s electrical structures and is supplied by the coronary arteries.
Nursing Considerations for Myocardium
As a nurse, you must be familiar with the myocardium, as it is essential for the heart’s pumping function. Diseases affecting this layer, such as myocardial infarction (heart attack) and myocarditis, are common. Myocardial infarction occurs when blood flow through the coronary arteries is restricted, leading to the death of myocytes and impairing the heart’s ability to function. Myocarditis can result from toxins or infection affecting this layer.
Endocardium
The third and innermost layer is the endocardium. The term “endo” means inner, referring to this layer’s position inside the heart. It consists of an endothelium that covers the heart’s internal structures, such as the atria, ventricles, and valves. The smoothness of this layer facilitates smooth blood flow, preventing clot formation.
Nursing Considerations for Endocardium
Unfortunately, problems can arise with the endocardium, particularly with conditions like endocarditis, an inflammation of this layer. Invaders may enter the bloodstream through infection or IV drug use, sticking to the endocardium and causing infection, often affecting the heart valves like the tricuspid or aortic valves.
That wraps up this review on the layers of the heart. You may also be interested in more layers of the heart quiz.
References:
Amerman, E. C., & Irintcheva, V. (2016). Chapter 17 The Cardiovascular System I: The Heart. In Human Anatomy and Physiology (p. 636).
How the Heart Works | NHLBI, NIH. Retrieved 2 September 2022, from https://www.nhlbi.nih.gov/health-topics/how-heart-works
Marieb, E. N., & Mallatt, J. (2001). Chapter 18 The Heart. In Human Anatomy (Third, pp. 534–535).
Ogobuiro I, Wehrle CJ, Tuma F. Anatomy, Thorax, Heart Coronary Arteries. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK534790/