Orientation to the Body - Cavities & Linings

Open Visceral Cavities

Open visceral cavities are largely tubular passageways (tracts) of visceral organs that open to the outside of the body, and include 1) the respiratory tract, which open at the nose and mouth, 2) the digestive tract that opens at both the mouth and the anus, 3) the urinary tract that opens in the perineum at the urethral orifices, 4) the male genital tract opens into the lower urinary tract, and 5) the female genital tract opens into the perineum by way of the vagina. These cavities are lined with a mucus-secreting layer (mucosa) that is the working tissue of open cavities (providing secretion, absorption, and protection). The mucosa is lined with epithelial cells, and supported by a vascular connective tissue layer and a smooth muscle layer. Both reproductive tracts are lined with mucosa.

Abdominopelvic Cavity or Abdominal and Pelvic Cavities

The abdominopelvic cavity, containing the gastrointestinal tract and related glands, the urinary tract, and great numbers of vessels and nerves, has muscular walls anterolaterally, the lower rubs and muscle laterally, and the lumbar and sacral vertebrae and muscles posteriorly. The roof of the abdominal cavity is the thoracic diaphragm. The internal surface of the abdominal wall is lined by a serous membrane, the peritoneum, that is continuous with the outer membrane of the abdominal viscera. The serous secretions enable the mobile abdominal viscera to slip and slide frictionlessly during movement. The abdominal and pelvic cavities are closed body cavities that are continuous with one another. The pelvic cavity contains the urinary bladder, rectum, reproductive organs, and lower gastrointestinal tract, has muscular walls anteriorly, bony walls laterals, and the sacrum posteriorly.

Cranial Cavity

The cranial cavity is a closed body cavity that is occupied by the brain and its coverings, cranial nerves, and blood vessels. It is lined by dura mater, a tough fibrous membrane.

Thoracic Cavity

The thoracic cavity is also a closed body cavity that contains the lungs, heart, and neighboring structures in the chest. Its skeletal walls are the thoracic vertebrae and ribs posteriorly, the ribs anterolaterally, and the sternum and costal cartilages anteriorly. The root of the cavity is membranous; the floor is the muscular thoracic diaphragm. The middle of the thoracic cavity, called the mediastinum, is a partition packed with structures (e.g., heart). It separates the thoracic cavity into discrete left and right parts that are lined with pleura and contain the lungs.

Vertebral Cavity

The vertebral cavity houses the spinal cord, its coverings, related vessels, and nerve roots. Like the cranial cavity, it too is lined by dura mater, and the dura mater of the vertebral column is continuous with the cranial dura at the foramen magnum. The vertebral cavity is a closed body cavity.