Body Cavities and Membranes: Structure and Classification

Body Cavities and Membranes

Dorsal Cavity

The dorsal cavity is one of the two major body cavities and is located along the posterior (back) side of the body. It primarily protects the central nervous system.

• Cranial cavity: Houses the brain.

• Vertebral (spinal) cavity: Encloses the spinal cord.

Ventral Cavity

The ventral cavity is situated on the anterior (front) side of the body and contains most of the body's visceral organs.

• Thoracic cavity: Contains the lungs and heart.

• Mediastinum: Central compartment of the thoracic cavity, containing the heart, trachea, esophagus, and major vessels.

• Pericardial cavity: Surrounds the heart within the mediastinum.

• Abdominopelvic cavity: Includes both the abdominal and pelvic cavities, housing organs such as the stomach, intestines, liver, and reproductive organs.

Membranes Associated with Body Cavities

Body cavities are lined and organs are covered by specialized membranes, which are named according to their location and the cavity they are associated with.

• Function: Membranes line cavities and cover the outside of organs, providing protection and reducing friction.

• Naming convention: Membranes are named by combining the lining location with the cavity word.

Membrane	Location	Example
Parietal pleura	Lines thoracic cavity	Thoracic cavity lining
Visceral pleura	Covers lungs	Thoracic organs covering
Parietal peritoneum	Lines abdominopelvic cavity	Abdominopelvic cavity lining
Visceral peritoneum	Covers abdominal organs	Abdominopelvic organs covering
Parietal pericardium	Lines pericardial cavity	Pericardial cavity lining
Visceral pericardium	Covers heart	Pericardial organ covering

Other Body Cavities

In addition to the major dorsal and ventral cavities, the body contains several smaller cavities that serve specialized functions.

• Oral cavity: Mouth

• Digestive cavity: Includes the gastrointestinal tract

• Nasal cavity: Inside the nose

• Orbital cavity: Contains the eyes

• Middle ear cavity: Contains the bones of the middle ear

• Synovial cavity: Found within joints

Abdominal Regions and Quadrants

The abdomen is divided into regions and quadrants to help describe the location of organs and pain.

• 9 regions: Used in anatomical studies for precise localization (e.g., right hypochondriac, epigastric, left lumbar, etc.).

• 4 quadrants: Commonly used in clinical settings (right upper, left upper, right lower, left lower quadrants).

Division Type	Number	Purpose
Regions	9	Specific anatomical areas
Quadrants	4	Common clinical use

Key Terms and Definitions

• Parietal membrane: Lines the cavity wall.

• Visceral membrane: Covers the organ itself.

• Serous membrane: General term for membranes that secrete serous fluid to reduce friction.

Example

• When describing inflammation of the peritoneum, the term peritonitis is used.

• Clinicians use the quadrant system to quickly localize abdominal pain (e.g., appendicitis often presents in the right lower quadrant).