Final answer:
The assertion regarding the pericardium is true; it secures the heart in the mediastinum, prevents excessive movement and overdistension, and provides a lubricated environment to lessen friction during heartbeats. Valves in the cardiovascular system are essential for preventing blood backflow and maintaining circulatory efficiency. Pacemaker cells in the heart create and regulate the heart rate, with additional modulation by the nervous system.
Step-by-step explanation:
The statement that the pericardium helps prevent overfilling of the heart and that it lessens the friction of movements during heartbeats is true. The pericardium is a double-walled sac containing the heart and the roots of the great vessels. Its two main layers are the fibrous pericardium and the serous pericardium, with the latter split into parietal and visceral layers. The pericardial cavity, which is the space between these layers, is filled with serous fluid that lubricates the heart and prevents friction as the heart beats.
The importance of the pericardium is multifaceted: it fixes the heart within the mediastinum and thus limits its motion; it prevents over distension of the heart when blood volume increases, which could impair the heart's function and it creates a near frictionless environment. If an excessive amount of fluid accumulates rapidly in the pericardial cavity, like after trauma, this can lead to a condition known as cardiac tamponade, where the pressure on the heart can prevent it from effectively pumping blood, potentially leading to death if untreated.
In the cardiovascular system, valves such as the tricuspid and mitral valves, prevent the backflow of blood. This is crucial as it ensures unidirectional blood flow and maintains the efficiency of the circulatory system. If valves did not function properly, blood could flow backward, making circulation inefficient and possibly leading to heart failure.
Pacemaker cells located within the sinoatrial (SA) node of the heart are responsible for establishing the heart rate. These cells generate electrical impulses that spread throughout the heart muscle to signal it to contract. The rhythm of these contractions can be modulated by the nervous system, to accommodate for varying demands for oxygen and nutrients from the body.