Cross section of Thorax at the level of 4th Thoracic vertebra
This specimen shows Cross section of Thorax at the level of fourth Thoracic vertebra.
In this specimen we can see the, sternum anteriorly; the vertebrae and spinal cord posteriorly. The lungs can be seen on both sides of the mediastinum. The Structures which can be seen in the mediastinum are the arch of aorta, superior vena cava, trachea dividing into right and left bronchi, esophagus, and the azygos vein.
It is also called the breast bone and forms the anterior median part of the thoracic skeleton. It is a flat bone and is made up of three parts: the manubrium (head), body and xiphoid process/xiphisternum (tail). The angle between the manubrium and the body is called the sternal angle/ angle of Louis and is represented by the manubriosternal joint. It is an important landmark and corresponds to the level of the second costal cartilage and the fourth thoracic vertebra.
Vertebrae are the 33 individual, interlocking bones that form the vertebral column. Each vertebra has three main functional components: the vertebral body for load-bearing, the vertebral arch to protect the spinal cord, and transverse processes for the attachment of ligaments.
The spinal cord is the lower elongated part of the central nervous system. It extends as a downward continuation of the medulla oblongata in the vertebral column. It measures about 45 cm long and contains ascending and descending tracts that serve as conduits for nervous information. It is composed of outer white matter and inner grey matter. The inner grey matter encloses the central canal which contains cerebrospinal fluid. It also provides attachment to 31 pairs of spinal nerves.
The main functions of the spinal cord are: - Execution of simple reflexes - Transmission of impulses to and from the brain
The lungs are the paired respiratory organs situated in the pleural cavity. They aid in the oxygenation of the blood. Each lung is conical in shape with a rounded apex, a broad base or diaphragmatic surface, costal surface and medial surface separated by three borders. The right lung is divided into three lobes (upper, middle and lower) by two fissures (oblique and horizontal). The left lung is divided into two lobes (upper and lower) by an oblique fissure.
Arch of aorta:
The arch of aorta is the part of the aorta that distributes blood to the head and neck and upper extremities of the body via the brachiocephalic trunk, the left common carotid, and the left subclavian arteries.
Superior vena cava:
A large vein draining the upper part of the body. It is formed by the union of the right and left brachiocephalic veins.
The trachea (Latin, air vessel; also called the wind-pipe) is a 10-15 cm long tube situated in the lower part of the neck and superior mediastinum. Its upper under is continuous with the larynx at the level of C6 vertebra. It is made up of C-shaped cartilaginous rings (hyaline in nature and 16-20 in number) anteriorly. Posteriorly the gap is closed by a fibro-elastic membrane and contains trachealis muscle. At the level of the sternal angle (i,e, lower border of T4 vertebra) the trachea bifurcates into two principal bronchi.
The esophagus is a muscular tube which begins as a continuation of the pharynx at the level of C6 vertebra. Its course is divisible into three parts: cervical, thoracic and abdominal. It enters the abdominal cavity by passing through the esophageal opening of the diaphragm at the level of T8 vertebra and opens into the stomach. The esophagus presents a series of constrictions along its course. The constrictions are formed by the following structures: cricopharyngeus muscle (part of inferior constrictor of pharynx), arch of aorta, left bronchus, espophageal opening of the diaphragm.
The azygos vein is a single vein (unpaired) present in the posterior mediastinum on the right side. It is formed by the union of the right ascending lumbar and right subcostal veins. It terminates by arching over the root of the right lung and finally drains into the superior vena cava. Its main tributaries are the right superior intercostal, posterior intercostal (5-11), hemiazygos and accessory hemiazygos veins.