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The Three Layers of the Heart Wall

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  • 0:03 What Are the Layers of…
  • 0:53 Epicardium - a Layer…
  • 2:12 Myocardium
  • 3:08 Endocardium
  • 3:36 Lesson Summary
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Lesson Transcript
Instructor: Sarah Phenix
In this lesson, you will learn about the three layers of the heart: the epicardium, myocardium, and the endocardium. Explore how they function to create the amazing pumping machine that is your heart.

What Are the Layers of the Heart Wall?

Your heart is one of the most important muscles in your body. Each day, your heart beats about 100,000 times and, over your life span, about 2.5 billion times!

The fibrous pericardium encases, protects and secures the heart. Inside the pericardium is the heart wall, and this is organized into three main layers. The outermost layer of the heart wall is the epicardium, which is also the innermost layer of the pericardium. The middle layer of the heart wall is the myocardium; this is the actual muscular layer of the heart responsible for contracting and pumping blood throughout your body. The endocardium is the thin innermost layer of tissue that makes direct contact with the blood pumping through the heart chambers. Now, let's explore each layer in more detail.

Epicardium - A Layer of the Pericardium

The pericardium is composed of three membranous layers that encircle the exterior of the heart: the outer fibrous pericardium, the middle parietal pericardium, and the inner epicardium (also referred to as the visceral pericardium). Together, these layers fuse to form a space around the heart called the pericardial cavity.

The thick, fibrous pericardium anchors your heart in place so that when you run, jump, and skip, your heart sits securely in your chest. Just like a boat anchor keeps a ship from drifting, this layer anchors the heart to the front of your chest, at your sternum, (the long bone connecting your ribs), as well as to your diaphragm (the muscle below your heart that divides your chest cavity from your abdomen).

The parietal pericardium lies just underneath the fibrous pericardium, and is one of two layers responsible for producing serous fluid, which helps lubricate your heart and decrease friction against other organs as it pumps. The epicardium, also known as the visceral pericardium, is a layer of the parietal pericardium that reflects down and directly adheres to the heart tissue. This means that both the visceral pericardium and the parietal pericardium are serous-producing tissues that form the inner and outer membranes of the pericardial cavity.

Myocardium

When you talk about the heart muscle, you are specifically referring to the myocardium of the heart. This tissue contracts and relaxes to pump blood to your lungs for oxygenation and then sends it to the tissues of your body. The myocardium varies in thickness, based on how much force that particular chamber of your heart needs to pump blood to the desired location.

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