Final answer:
In an AP Upper rib study, the ribs that should be visible are the first through the seventh, known as the true ribs, due to their direct attachment to the sternum. The sternal angle, marked by the attachment of the second rib, serves as a landmark for the identification of the lower ribs.
Step-by-step explanation:
In an AP Upper rib study, the range of ribs that should be visible include the first through the seventh ribs. These ribs are known as the true ribs, and they attach directly to the sternum via their costal cartilage. The sternal angle is a key anatomical landmark, located at the junction between the manubrium and the body of the sternum, where the second rib attaches. Since the first rib is obscured by the clavicle, the second rib is used as a landmark for identifying and counting ribs in radiographic studies. The true ribs are considered the most crucial for assessment in this type of study. Furthermore, the visibility of the 8th to 10th ribs, which are referred to as the vertebrochondral ribs, may vary as their costal cartilages attach indirectly to the sternum. However, an AP Upper rib study intends to visualize and diagnose conditions affecting the true ribs and their attachments to the spine and sternum.