question: Which cavity, filled with lubricating serous fluid, lies between the epicardium and the pericardium?
distractor3: thoracic cavity
distractor1: cranial cavity
distractor2: oral cavity
correct_answer: pericardial cavity
support: and is part of the heart wall. The pericardial cavity, filled with lubricating serous fluid, lies between the epicardium and the pericardium. In most organs within the body, visceral serous membranes such as the epicardium are microscopic. However, in the case of the heart, it is not a microscopic layer but rather a macroscopic layer, consisting of a simple squamous epithelium called a mesothelium, reinforced with loose, irregular, or areolar connective tissue that attaches to the pericardium. This mesothelium secretes the lubricating serous fluid that fills the pericardial cavity and reduces friction as the heart contracts. Figure 19.5 illustrates the pericardial membrane and the layers of the heart.