Final answer:
The myocardium is the thickest layer of the heart, with the left ventricle having the thickest myocardial wall to pump blood through the systemic circuit. Structures like the pericardial cavity and epicardium protect the heart, while muscle fiber arrangements enhance pump efficiency.
Step-by-step explanation:
The myocardium is the thickest layer of the heart and is composed predominantly of cardiac muscle cells. It is designed to support the heart's continuous pumping action, playing a crucial role in maintaining blood circulation throughout the body. Within the myocardium, it is the left ventricle that has the thickest muscular wall due to its responsibility for pumping blood through the much larger systemic circuit, having to generate higher pressures to overcome greater resistance. The presence of myocardial contractile cells and specialized pacemaker cells, which conduct electrical impulses, contributes to the myocardium's ability to regulate heartbeats and ensure efficient blood flow.
Meanwhile, structures such as the pericardial cavity and the epicardium serve to protect and lubricate the heart, while the complex arrangement of muscle fibers allows for a more effective pumping motion.