The piping system consists of several components. The first part of the piping system is the sinus node. Without neuronal stimulation, the sinus node rhythmically initiates impulses 70 to 80 times per minute. Because it determines the basic rhythm of the heart rate, it is called the pacemaker of the heart. Other parts of the conduction system include the atrioventricular node, atrioventricular bundle, beam branches, and conduction myofibers. All these components coordinate the contraction and relaxation of the heart chambers. The sounds associated with heartbeat are due to vibrations in tissues and blood caused by valve closure. Abnormal heart murmurs are called marbles. Peripheral factors such as emotions, ion concentrations, and body temperature can affect heart rate.
These are usually mediated by the heart center. The sinus node acting alone produces a constant rhythmic heart rate. Regulatory factors depend on the atrioventricular node to increase or decrease heart rate in order to adjust cardiac output to changing body needs. Most changes in heart rate are mediated by the heart center in the elongated marrow of the brain. The center has both sympathetic and parasympathetic components that adjust the heart rate to the changing needs of the body. .