Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 83

The heart is surrounded, protected and anchored in position by a compound membrane called the pericardium which consists of two major layers. The first of these is the fibrous pericardium, which forms an outer protective sheath and is composed of collagenous connective tissue. It anchors the heart in position within the thoracic cavity; anteriorly it is attached to the inner surface of the sternum and inferiorly to the diaphragm, the dome-shaped breathing muscle that separates the thoracic cavity from the abdominal cavity.

Figure 3.1 Overview of the cardiovascular system

Since the heart is continually beating, the fibrous pericardium is essential to stop excessive movement and drifting of the heart within the thorax. The serous pericardium is the inner portion of the pericardium and is itself composed of two distinct layers of tissue: the parietal pericardium, a fluid-producing membrane that is attached to the inner portion of the fibrous pericardium, and the visceral pericardium, which is actually the outer layer of the heart and is also known as the epicardium (see below).

Table 3.1

The two layers of the serous pericardium secrete a watery fluid termed pericardial fluid which fills the narrow pericardial space between the visceral and parietal pericardium. In health around 10–20 ml of this slippery pericardial fluid surrounds the heart, acting as a lubricant to prevent abrasion and damage to the beating heart and the surrounding tissues. This fluid also functions as an effective shock absorber, cushioning the heart against any knocks and bumps.