The Thorax

Thoracic Cage: Sternum

The sternum or breastbone is a long, flat, bony plate connected to the rib bones via cartilage that forms the anterior section of the rib cage.

Learning Objectives

Describe the structure and function of the sternum

Key Takeaways

Key Points

  • The sternum, or breastbone, is a long, flat, bony plate that forms the most anterior section of the rib cage.
  • The primary function of the sternum is the protection of the heart, lungs, and blood vessels from physical damage.
  • The sternum is made of the manubrium, the gladiolus, and the xiphoid process.

Key Terms

  • xiphoid process: The most inferior region of the thorax.
  • gladiolus: The body of the thorax.
  • manubrium: The most superior region of the thorax.

The sternum, or breastbone, is a long, flat, bony plate that forms the most anterior section of the ribcage. The sternum is highly vascular in nature and covered with a thin layer of compact bone providing a degree of flexibility.

Function of the Sternum

This is a drawing of the sternum with its three regions labeled. From top to bottom, they are the manubrium, the gladiolus, and the xiphoid process regions.

Sternum: This image shows the parts of the sternum.

Together with the anterior ribs, the sternum helps to protect the heart and lungs from damage, as well as facilitates the expansion and contraction of the thoracic cavity during respiration. During development the sternum is comprised of four individual sections called sternebrae, which fuse to form the sternum in adulthood.

Structure of the Sternum

The sternum is divided into three regions:

  1. The manubrium.
  2. The gladiolus.
  3. The xiphoid process.

The manubrium is the most superior region of the sternum and articulates with the clavicles or collarbones and the first pair of ribs. The manubrium is the thickest portion of the sternum as it carries the greatest physical load.

Located below the manubrium, the gladiolus is the longest portion of the sternum and articulates with the ribs, either directly or indirectly, through the costal cartilage

The thin, pointed xiphoid process forms the most inferior region of the sternum to which the costal cartilage and cartilage of the celiac, or solar, plexus attaches.

Thoracic Cage: Ribs

The ribs are long, curved bones that protect the lungs, heart, and other organs of the thoracic cavity.

Learning Objectives

Describe the ribs of the thoracic cage

Key Takeaways

Key Points

  • Ribs are long, curved bones that form the rib cage surrounding the thorax.
  • Articulating from the spine, the majority attach to the sternum either directly or indirectly.
  • Humans have 24 ribs split into pairs. Pairs 1–5 attach directly to the sternum through the costal cartilage, 6–10 attach indirectly though the costal cartilage, and 11–12 are termed floating ribs and do not attach.

Key Terms

  • rib: A long, curved bone that forms the rib cage surrounding the thorax.
  • costal: Pertaining to a rib.

Ribs are long, curved bones that form the rib cage surrounding the thorax. The thoracic cage can expand and contract to facilitate breathing in association with the diaphragm; it also protects the lungs, heart, and other organs of the thoracic cavity.

Structure of a Rib

This is a drawing of a rib cage that shows its connections to vertebrae. In particular, the first thoracic vertebra is labeled to display how a rib attached to it curves across and attaches to the sternum.

Ribs: Lateral view of rib cage showing its connections to vertebrae. The first thoracic vertebra has a rib attached to it that curves across to the sternum.

A rib consists of a head, neck, and shaft. The head of the rib is the most posterior region of the rib and articulates with the vertebral column. The flattened neck region provides an attachment point for numerous muscles located within the back. Finally, the shaft forms the majority of the length of the rib as it curves around the thoracic cavity forming the rib cage.

Organization of the Ribs

Humans have 24 ribs split into pairs that are named numerically passing inferiorly from the neck. The first five ribs are termed true ribs because they attach directly to the sternum through the costal cartilage.

The next five ribs are termed false ribs because they attach to the sternum indirectly through the costal cartilage.

Finally, the last two ribs are termed floating ribs because they do not attach to the sternum at all.

Rib 1 is the shortest and most curved of the ribs. Descending from rib 1, the ribs increase in size up until rib 7 before decreasing in length again.