The human torso, or trunk, is the central mass of the body that serves as the foundation for the head, neck, and limbs. This anatomical region contains the body’s primary organ systems and acts as the structural axis. The upper torso is defined as the thorax, or chest, a cone-shaped compartment situated between the neck and the abdomen. This region provides maximum protection and necessary flexibility for movement and respiration. Understanding the thorax involves mapping its physical limits, bony framework, and the organs it encloses.
Defining the Boundaries
The upper torso is delineated superiorly by the thoracic inlet. This inlet forms the boundary with the neck, defined by the first pair of ribs, the top edge of the sternum (manubrium), and the first thoracic vertebra (T1). These superior boundaries are relatively narrow, allowing passage for the trachea, esophagus, and major blood vessels to and from the head and upper limbs.
Inferiorly, the lower boundary is the thoracic outlet, which is significantly wider than the inlet. This lower limit is formed by the muscular dome of the diaphragm, which separates the thoracic cavity from the abdominal cavity below. Externally, this boundary is traced by the costal margin, the collective lower edge of the rib cage.
The posterior border is established by the twelve thoracic vertebrae (T1 to T12). These vertebrae form the vertebral column’s thoracic segment, providing a strong, flexible anchor for the ribs. The entire space enclosed by these borders is called the thoracic cavity, a region that changes volume dynamically during breathing. This enclosure ensures that vital contents are protected while allowing for necessary physiological movements.
Skeletal Framework
The protective architecture of the upper torso is the thoracic cage, a bony and cartilaginous structure resembling a truncated cone. This cage is composed of the sternum, twelve pairs of ribs, and twelve thoracic vertebrae. Anteriorly, the sternum (or breastbone) consists of three fused parts: the manubrium, the body, and the xiphoid process.
Twelve pairs of ribs articulate posteriorly with the thoracic vertebrae. The first seven pairs are “true ribs” because they connect directly to the sternum via their own costal cartilage. The next three pairs, “false ribs,” attach indirectly by connecting to the cartilage of the rib above them. The final two pairs are “floating ribs” because they do not connect to the sternum or costal cartilage, ending instead in the back musculature.
This skeletal framework offers mechanical protection for internal organs and provides attachment sites for respiratory and upper limb muscles. The mobility between the ribs, sternum, and vertebrae allows the cage to expand and contract, which is fundamental to breathing.
Major Internal Structures
The thoracic cavity contains structures important for circulation and respiration. The central compartment is the mediastinum, which houses the heart, the muscular pump driving blood throughout the body. The heart is slightly positioned left of the midline and is enclosed within the protective pericardium sac.
The mediastinum is also the pathway for several major vessels, including the aorta, which arches over the heart before descending. The superior and inferior vena cava return deoxygenated blood to the heart. The trachea (windpipe) and the esophagus (the tube for food transport) also pass vertically through this central space.
Flanking the mediastinum are the two pleural cavities, each containing a lung. These organs are the site of gas exchange, taking in oxygen and expelling carbon dioxide. The lungs are enveloped by the pleura, a double-layered membrane that reduces friction as the lungs inflate and deflate.