The human rib cage is a skeletal structure that forms the chest, or thorax, in the upper torso. This bony enclosure protects the organs housed within the chest cavity. Understanding the ribs involves knowing their location, number, and connection points to the rest of the skeleton.
The Framework of the Rib Cage
The ribs are located within the thoracic cavity, extending from the back toward the front. Humans typically have 12 pairs of ribs, totaling 24 individual bones, with an equal number on the left and right sides. Males and females possess the same number of ribs.
Each of the 12 pairs of ribs forms a joint with a corresponding thoracic vertebra in the spine at the back. Moving toward the front, the ribs terminate in flexible costal cartilage. This cartilage connects the ribs to the sternum, or breastbone, which runs down the center of the chest. This framework of ribs, cartilage, vertebrae, and sternum is also known as the thoracic cage.
Differentiating Rib Types
The 12 pairs of ribs are categorized into three groups based on how they connect to the sternum: true, false, and floating ribs. The first seven pairs (Pairs 1–7) are designated as true ribs because their costal cartilage connects directly to the sternum. Each of these upper ribs has its own separate strip of cartilage that attaches independently to the breastbone.
The next three pairs (Ribs 8, 9, and 10) are called false ribs because their connection to the sternum is indirect. Instead of having their own sternal attachment, their costal cartilage connects to the cartilage of the rib immediately above them. This means the cartilage of the 8th, 9th, and 10th ribs ultimately joins the cartilage of the 7th rib before attaching to the sternum.
The lowest two pairs (Pairs 11 and 12) are classified as floating ribs. These ribs are shorter and do not connect to the sternum or the cartilage of any other rib. They only attach to the vertebrae in the back, with their front ends embedded in the muscle and tissue of the body wall. This lack of a forward connection provides flexibility to the lower rib cage and torso.
Primary Functions of the Ribs
The primary purpose of the rib cage is to provide a protective shield for the organs within the chest cavity. The bony structure offers defense against external forces that could harm the heart and lungs. The ribs also protect organs sitting just below the diaphragm, such as the upper parts of the kidneys and the liver.
The ribs also play a significant role in the mechanics of respiration (breathing). The flexible costal cartilage permits movement of the rib cage. During inhalation, muscles attached to the ribs, such as the intercostal muscles, contract and lift the rib cage up and out. This movement increases the internal volume of the chest cavity, allowing the lungs to expand and draw in air.