A body cavity is a closed, internal space within the body that serves to house, protect, and separate internal organs. These spaces are typically filled with fluid and lined with membranes, providing an organized environment for complex structures. This arrangement ensures that delicate organs are cushioned from external forces and allows internal organs to change size and shape without disrupting nearby tissues.
The Primary Divisions: Dorsal and Ventral
The body’s internal spaces are organized into two major divisions based on their location and the systems they contain. The Dorsal cavity is situated along the posterior side of the body, encompassing the head and back of the trunk. This division is dedicated to protecting the central nervous system.
In contrast, the Ventral cavity is the much larger division, located on the anterior side of the trunk. It houses the viscera, which are the organs involved in the respiratory, cardiovascular, digestive, urinary, and reproductive systems. The segregation of the central nervous system from the major visceral organs provides a distinct, protective environment for each.
Contents of the Dorsal Cavities
The Dorsal division is composed of two continuous cavities that function as a singular protective unit for the body’s control center. The Cranial Cavity is the superior component, formed by the bones of the skull, which surrounds the brain.
The second component is the Vertebral Cavity, also known as the Spinal Cavity, which is an elongated space running down the vertebral column. This cavity encloses the delicate spinal cord, which extends directly from the brainstem. Because the brain and spinal cord form one continuous structure, their protective bony cavities are also continuous with each other.
Contents of the Ventral Cavities
The Ventral cavity contains the majority of the body’s large organs and is separated into two main compartments by the diaphragm, a dome-shaped sheet of muscle. This muscular partition divides the superior Thoracic Cavity from the inferior Abdominopelvic Cavity. The separation ensures that the pressure changes necessary for lung function do not interfere with the organs in the lower abdominal region.
The Thoracic Cavity, located in the chest, is further subdivided into three distinct spaces. The two Pleural cavities house the lungs and are situated on either side of the central partition. This central region is called the Mediastinum, which contains the heart, the major blood vessels, the trachea, and the esophagus.
Within the Mediastinum lies the Pericardial cavity, the specific space that directly surrounds the heart. The inferior compartment, the Abdominopelvic Cavity, is not separated by a physical wall but is defined by an imaginary line at the level of the pelvic bone.
The superior portion is the Abdominal Cavity, which holds the stomach, liver, spleen, intestines, and kidneys. This is the largest of the ventral subdivisions and houses the majority of the digestive and associated organs. The inferior portion is the Pelvic Cavity, bounded by the bones of the pelvis, containing the urinary bladder, portions of the large intestine, and the internal reproductive organs.
Protective Linings of the Ventral Cavities
The organs within the Ventral cavities are enveloped in thin, double-layered Serous Membranes, or serosa. These membranes are named according to their location and function to reduce friction during organ movement. Each serous membrane consists of two distinct layers: the parietal layer and the visceral layer.
The parietal layer is the outer membrane, adhering closely to the wall of the cavity itself. The visceral layer is the inner membrane that directly covers the surface of the internal organ. The small space between these two layers is called the serous cavity, which is filled with a thin film of serous fluid.
This fluid acts as a natural lubricant, allowing the two layers of the membrane to slide smoothly against one another. This lubrication is particularly important for organs that constantly move, such as the lungs expanding and contracting within the Pleura, or the heart beating within the Pericardium. The serous membrane lining the abdominal and pelvic cavities and covering the digestive organs is known as the Peritoneum.