Thoracic Cavity and its Structure

The thoracic cavity is the region between the root of neck and diaphragm, which separate it from the abdominal cavity. It is also known as chest cavity and thorax. It contains large nimber of body organs and its associated structures, which leads into the cavity through the oblique opening, situated anterior to the body of 1st thoracic vertebra and leaves by a large opening, which is situated inferior to the xiphoid process and anterior to the body of the 12th thoracic vertebra.

The Structure of Thoracic Wall

 Wall of the thoracic cavity, externally covered with skin and muscles which connect shoulder girdle to the trunk. The thoracic wall is formed posteriorly by the thoracic part of the vertebral column, anteriorly by the sternum and costal cartilages, laterally by the ribs and intercostal spaces, superiorly by the supra-pleural membrane and inferiorly by the diaphragm, which separates it from the abdominal cavity. In addition to these following are some of the main structures of the rib cage.

Sternum

It is a flat bone, situated in the midline of the anterior chest wall. In addition to supporting rib cage, it has a dominant role in the formation of red blood cells ( hematopoiesis ). Sternum has three main structures, which are given below.

• Manubrium

It is the superior structure of the sternum, which articulate with the body of sternum and forms manubriosternal joint with it, which lies anterior to the body of the 3rd thoracic vertebra. Manubrium provides a site for articulation to the clavicles, first rib and an upper portion of the 2nd rib.

• Body of the sternum

The body of the sternum articulates above with manubrium and below with xiphoid process, giving rise to the xiphisternal joint. It also provides a site for articulation to the ribs ranging from 2nd to 7th.

• Xiphoid Process

It is the inferior structure of the sternum, it articulates above with the body of sternum and forms xiphisternal joint ( cartilaginous joint ), which lies anterior to the body of the 12th thoracic vertebra.

Ribs

 In humans, chest cavity has 12 pairs of ribs, which articulates anteriorly with the lateral body of the sternum and posteriorly with the numerically corresponding vertebra of the thoracic part of the vertebral column. Ribs are of three types, true ribs, false ribs and floating ribs.

Sternum and Bone marrow Biopsy

Sternum provides support and protection to the internal organs, situated in the chest cavity. Since it contains red hemopoietic marrow throughout life, it is the common site for marrow biopsy. During red bone marrow biopsy, a wide, bore needle is introduced into the cavity through the anterior surface of the bone.

Thoracic Outlet

In humans, chest cavity communicates with the root of the neck through a small opening called thoracic outlet. This is the region through which most parts of the body organs and the other structures ( blood vessels and nerves ) leads to or away from thorax cavity, therefore it's named as an outlet. 

The upper opening is bounded posteriorly by the first thoracic vertebra, laterally by the medial parts of the first ribs and their costal cartilages. It is an anteriorly bounded with superior part of the sternum (manubrium). The opening is obliquely placed forward and upward. Because of the obliquity of the opening, the apices of the lung and pleurae project upward into the neck.

It communicates with the abdomen through the large opening, which is posteriorly bounded with the 12th thoracic vertebra, laterally by curving costal margins, and anteriorly by the xiphisternal joint.

Sternal angle

It is also known as the angle of Louis. Sternal angle is formed by the articulation between the manubrium and the body of the sternum. It lies at a level to the 2nd costal cartilage and anterior to the midsection between 3rd and 4th vertebra of the thoracic vertebral column. It is recognized by the presence of transverse ridge on the anterior surface of the sternum,