Final answer:
The diaphragm part of the stethoscope is used to listen to the apical pulse. It is specifically designed for picking up high-frequency sounds such as heart valve closures, with proper placement of the stethoscope's components being critical for effective auscultation.
Step-by-step explanation:
The part of the stethoscope that is placed on the chest to hear the apical pulse is the diaphragm. When performing an auscultation, which is a key diagnostic technique for assessing heart function, the diaphragm's flat surface allows for the high-frequency sounds of the heart to be heard more clearly. This includes the sounds of the heart valves as blood moves through them. Figure 19.30 in Cardiac Physiology underscores the importance of proper placement of the stethoscope's bell to facilitate auscultation; however, for picking up higher-pitched sounds such as the apical pulse, the diaphragm is the correct choice. Sound transmission through the stethoscope is intensified and more effective by being concentrated on a smaller area such as the eardrum, enhancing the clinician's ability to diagnose potential abnormalities in heart sounds.