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The thorax is the area of the body situated between the neck and the abdomen. The thorax itself can be split up into various areas that contain important structures.
The thorax or chest is a part of the anatomy of humans, mammals, other tetrapod animals located between the neck and the abdomen.[rx][rx] In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the creature’s body, each of which is in turn composed of multiple segments.
The thorax is bound by bony structures including the 12 pairs of ribs and thoracic vertebrae, whilst also being supported by many ligaments and muscles. The muscles of the thorax are also important for the vital actions of breathing and muscles that attach to the thoracic wall may also contribute to the general movement of the trunk, upper limbs and the neck.
The thoracic cavity is home to many vital organs, notably the lungs/pleurae and the heart, but also includes the thymus gland and the breasts. As the heart is found here, the great vessels associated with it are also found – including the pulmonary arteries/veins, the superior vena cava and the aorta (as well as some of its proximal branches).
In this section, learn more about the areas of the thorax, bones of the thorax, muscles of the thorax, organs of the thorax and the vasculature of 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.
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.
The function of the Sternum
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:
- The manubrium.
- The gladiolus.
- 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.
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
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.
Contents
The contents of the thorax include the heart and lungs (and the thymus gland); the (major and minor pectoral muscles, trapezius muscles, and neck muscle); and internal structures such as the diaphragm, the esophagus, the trachea, and a part of the sternum known as the xiphoid process). Arteries and veins are also contained – (aorta, superior vena cava, inferior vena cava and the pulmonary artery); bones (the shoulder socket containing the upper part of the humerus, the scapula, sternum, thoracic portion of the spine, collarbone, and the rib cage and floating ribs). External structures are the skin and nipples.
The chest
In the human body, the region of the thorax between the neck and diaphragm in the front of the body is called the chest. The corresponding area in an animal can also be referred to as the chest.
The shape of the chest does not correspond to that part of the thoracic skeleton that encloses the heart and lungs. All the breadth of the shoulders is due to the shoulder girdle and contains the axillae and the heads of the humeri. In the middle line, the suprasternal notch is seen above, while about three fingers’ breadth below it a transverse ridge can be felt, which is known as the sternal angle and this marks the junction between the manubrium and body of the sternum. Level with this line the second ribs join the sternum, and when these are found the lower ribs can often be counted. At the lower part of the sternum, where the seventh or last true ribs join it, the ensiform cartilage begins, and above this, there is often a depression known as the pit of the stomach.
