The Heart Wall

The heart wall consists of three layers—the epicardium, myocardium, and endocardium (fig. 19.5). The epi-cardium3 (= visceral pericardium) is a serous membrane

2 peri = around

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

19. The Circulatory System: The Heart

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Chapter 19 The Circulatory System: The Heart 719

Pericardium Epicardium MyocardiumMcgraw Hill Anatomy Review Heart
Figure 19.4 External Anatomy of the Heart. (a) Anterior aspect; (b) posterior aspect. The coronary blood vessels on the heart surface are identified in figure 19.10.

Saladin: Anatomy & I 19. The Circulatory System: I Text I I © The McGraw-Hill

Physiology: The Unity of The Heart Companies, 2003 Form and Function, Third Edition

720 Part Four Regulation and Maintenance

Pericardium Epicardium

Fibrous layer

/- Serous layer

Myocardium

Endocardium Visceral pericardium (epicardium)

Parietal pericardium

Figure 19.5 The Pericardium and Heart Wall. The inset shows the layers of the heart wall In relationship to the pericardium.

-Pericardial cavity

Fibrous layer

/- Serous layer

Parietal pericardium

- Visceral pericardium

- Myocardium

- Endocardium

Myocardium

Endocardium Visceral pericardium (epicardium)

Parietal pericardium

Figure 19.5 The Pericardium and Heart Wall. The inset shows the layers of the heart wall In relationship to the pericardium.

composed of a simple squamous epithelium overlying a thin layer of areolar tissue. Over much of the heart, it has thick deposits of fat that fill grooves in the heart surface and protect the coronary blood vessels. In nonfatty areas, the epicardium is thin and translucent, allowing the myocardium to show through.

The myocardium,4 by far the thickest layer, is composed of cardiac muscle and performs the work of the heart. Its muscle cells spiral around the heart and are bound together by a meshwork of collagenous and elastic fibers that make up the fibrous skeleton. The fibrous skeleton has at least three functions: to provide structural support for the heart, especially around the valves and the openings of the great vessels; to give the muscle something to pull against; and, as a nonconductor of electricity, to limit the routes by which electrical excitation travels through the heart. This insulation prevents the atria from stimulating the ventricles directly and is important in the timing and coordination of electrical and contractile activity. Elastic recoil of the fibrous skeleton may also aid in

4myo = muscle refilling the heart with blood after each beat, but physiologists are not in complete agreement about this.

The endocardium5 consists of a simple squamous endothelium overlying a thin areolar tissue layer. It forms the smooth inner lining of the chambers and valves and is continuous with the endothelium of the blood vessels.

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Responses

  • lalia
    Where is the anterial apical wall of the heart?
    7 years ago
  • genet
    Where is posterior wall of the heart?
    7 years ago
  • Alem
    Where is the lateral wall of the heart?
    1 year ago

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