Body Cavities Overview

Overview

This lecture introduces the major body cavities, their subdivisions, associated membranes, and the organs they contain.

Body cavities are internal spaces within the body that house organs.
Posterior (dorsal) cavities include the cranial cavity (contains the brain) and vertebral canal/spinal cavity (contains the spinal cord).
The vertebral canal is formed by the vertebrae and contains the spinal cord, which passes through the vertebral foramen.
Minor cavities include the orbital cavity (eye), oral cavity (mouth), nasal cavity (nose), and middle ear cavity (tympanic cavity with auditory ossicles).

Ventral (anterior) cavities include the thoracic cavity (chest) and abdominopelvic cavity (abdomen and pelvis).
The thoracic cavity is surrounded by the rib cage and separated from the abdominopelvic cavity by the diaphragm (a muscle for breathing).
The abdominopelvic cavity extends from below the diaphragm to the pelvic floor and is divided into the abdominal cavity (digestive organs) and pelvic cavity (reproductive organs, rectum, bladder).

The thoracic cavity contains the mediastinum (central compartment with heart, esophagus, thymus), the pericardial cavity around the heart, and two pleural cavities around each lung.
Serous membranes (two-layered) cover organs: inner visceral layer (touches organ) and outer parietal layer (lines cavity), with serous fluid between to reduce friction.
The pericardium is the serous membrane around the heart; the pleura surrounds the lungs.
Inflammation of serous membranes: pericarditis (heart), pleurisy (lungs).

The peritoneum is the serous membrane lining most abdominal organs.
Organs fully surrounded by peritoneum are intraperitoneal; those only partially covered (e.g., pancreas, kidneys) are retroperitoneal.
The pelvic cavity contains infra-peritoneal organs (rectum, bladder, reproductive organs) which are covered only superiorly by peritoneum.

Cranial cavity — cavity within the skull containing the brain.
Vertebral canal (spinal cavity) — cavity within vertebrae containing the spinal cord.
Thoracic cavity — chest cavity containing heart and lungs.
Diaphragm — muscle separating thoracic and abdominal cavities.
Abdominopelvic cavity — combined abdominal and pelvic cavities.
Serous membrane — double-layered membrane with serous fluid, reduces friction.
Visceral layer — inner serous membrane layer touching organs.
Parietal layer — outer serous membrane lining the cavity.
Pericardium — serous membrane around the heart.
Pleura — serous membrane around the lungs.
Peritoneum — serous membrane around abdominal organs.
Retroperitoneal — organs behind the peritoneum.
Intraperitoneal — organs fully enclosed by the peritoneum.