The torso, also known as the trunk, is the central section of the human body. It serves as the primary structural unit, anchoring the head, neck, and all four limbs. This structure protects and contains almost all of the body’s major organ systems. The torso maintains stability and provides the flexibility necessary for movement.
Defining the Torso and Its Boundaries
The torso is defined anatomically as the body’s central mass, distinct from the appendages that extend from it. Its upper boundary is generally considered the base of the neck, marked by the clavicles, or collarbones. The lower boundary is defined by the pelvis and the groin area, which serves as the attachment point for the lower limbs.
This central region explicitly excludes the head, neck, and all four limbs. The torso is composed of several distinct external regions, including the chest (thorax), the abdomen, the pelvis, and the back.
Essential Internal Divisions
The main function of the torso is to protect and separate the internal organs, which it achieves through several body cavities. The largest is the ventral cavity, located at the front of the trunk and subdivided into two main sections. This organization allows organs to expand and contract without interfering with neighboring tissues.
The superior section is the thoracic cavity, which fills the chest and is enclosed by the rib cage. This cavity is divided into two pleural cavities (housing the lungs) and the pericardial cavity (containing the heart). The dome-shaped diaphragm, a sheet of muscle that plays a major role in respiration, separates the thoracic cavity from the lower section.
Below the diaphragm is the abdominopelvic cavity, the largest single compartment in the torso. This area is divided into the abdominal cavity and the pelvic cavity. The abdominal section contains most digestive organs, such as the stomach, liver, gallbladder, intestines, and kidneys. The pelvic cavity, situated lower down and enclosed by the pelvic bones, houses the organs of excretion and reproduction, including the bladder and internal reproductive organs.
Skeletal and Muscular Framework
The structural integrity of the torso is provided by the axial skeleton, which includes the bones that form the central axis of the body. The vertebral column, or spine, runs the length of the back, acting as the central support and protecting the spinal cord. This flexible column allows for a wide range of movements, including bending, twisting, and side-to-side motion.
The rib cage shields the thoracic cavity, protecting the heart and lungs. It consists of the sternum (breastbone) at the front, the ribs, and the thoracic vertebrae in the back. At the base of the torso, the pelvic girdle provides a solid ring of bone that connects the spine to the lower limbs and supports the weight of the upper body.
A complex network of skeletal muscles attaches to this bony framework, providing both movement and stability. Major muscle groups, such as the abdominals (rectus abdominis) and the deep back muscles (erector spinae), stabilize the trunk and maintain posture. These muscles also form a protective wall around the abdominal contents and assist with the mechanics of breathing.