Closed Body Cavity
The thoracic, cranial, vertebral and abdominopelvic cavities are what we call as the closed body cavities. They are termed as closed in the sense that they do not open to the outside of the body. Organs may be in them or may pass through them but the organs’ cavities do not necessarily open into these cavities. Hard, rigid and solidly built, these cavities are primed with one task in hand, and that is to protect the contents inside the cavity. Although these cavities are hard as a rock, the inner lining is lined with a membrane and the lining differs on what closed cavity is serves together with. A thick dura mater lines the cranium and the vertebral cavity, the watery membrane or serous membranes in the thoracic and abdominopelvic cavities.
The Cranial Cavity
The main processor of the body, the brain, is housed by the cranial cavity. This daunting task of protecting one of the most vital organs of the body, together with the cranial nerves and the blood vessels is well taken care of by the skull thanks to the tough dura mater lining that envelops the brain. As the dura mater envelops the brain, it forms a meningeal that cradles the brain inside the cranial cavity. The dura mater covering continues down to the vertebral cavity as it also protects the spinal cord and its coverings, the nerve roots and the vessels. This is all possible due to the opening at the base of the skull known as the foramen magnum. The dura mater exiting through the foramen magnum forms a sac that terminates at the second sacral vertebra.
The Thoracic Cavity
The cardiovascular system’s main proponent, the heart and the lungs are all housed by the thoracic cavity. Aside from these key players, the blood vessels, the tubular airways, nerves etc are also under the protection of the thoracic cavity or as the lay man understand it, the chest. The thoracic cavity employs the thoracic vertebrae protecting the back, with the ribs extending the protection from the back to the sides and the sternum at the front together with the costal cartilages. The floor of the thoracic cavity is the main respiratory muscle of our body, the diaphragm and the ceiling is membranous. The mediastinum exists in the middle of the thoracic cavity, a partition that separates the cavity into the left and the right parts. On either side, the structures are lined with a membrane called the pleura. This thin, vascular layer permits the lungs to rub against the thoracic wall without worrying about injury or friction.
The Abdominal Cavity
The abdominal cavity is a unique cavity since unlike other cavities, it does not employ the help of the tough bones but instead it utilizes the strength of the muscles in protecting its precious contents. The lower rib, supported by the muscles offers protection laterally, and posteriorly protection is given by the lumbar vertebrae. The gastrointestinal tract is the primary system that needs protection, together with the related glands and urinary tract, the vast number of blood vessels and the nerves. The diaphragm, which was the floor of the thoracic cavity, is now the roof of the abdominal cavity. The abdominal cavity and the pelvic cavity is an inseparable pair, evidenced by the continuity of the two cavities. The pelvic cavity houses the rectum, the urinary bladder and the reproductive organs. In addition to the muscles that protect this cavity, the sacrum also lends a helping hand in protecting the back portion. A unique feature of the pelvic cavity is largely associated with a serous membrane, the peritoneum. It allows for the contents of the abdominal viscera to slide and slip frictionlessly during movement.
If you invest time and have interest in learning more about our body, you will not run out of moments where you will be amazed on how delicate and intricate the body processes are and the installed fail-safe mechanisms it has. It gives justification to a song, your body is a wonderland and it truly is.