Lesson 1, Topic 1
In Progress

06-Body Cavities

March 28, 2021

Body cavities
Contrary to its external appearance, the body is not a solid structure. It is made up of open spaces or cavities that in turn contain compact, well-ordered arrangements of internal organs. The major body cavities are categorized as the dorsal body cavities and ventral body cavities. The location and outlines of the major body cavities are illustrated in Figure 1-5.

Dorsal cavities
The dorsal cavities shown in Figure 1-5 include the space inside the skull that contains the brain. It is called the cranial cavity. The space inside the spinal column is called the spinal cavity. It contains the spinal cord. The cranial and spinal cavities are dorsal cavities because they are located in a dorsal position in the body.

Ventral cavities
The ventral cavities are located in a ventral position in the body.

Thoracic and abdominopelvic cavities
The upper ventral cavities include the thoracic cavity, a space that you may think of as your chest cavity. Its midportion is a subdivision of the thoracic cavity, called the mediastinum. The lateral subdivisions of the thoracic cavity are called the right and left pleural cavities.

The lower ventral cavities in Figure 1-5 include an abdominal cavity and a pelvic cavity. Actually, they form only one cavity, the abdominopelvic cavity, because no physical partition separates them. In Figure 1-5 a faint line shows the approximate point of separation between the abdominal and pelvic subdivisions. Notice, however, that an actual physical partition separates the thoracic cavity above from the abdominopelvic cavity below. This muscular sheet is the diaphragm. It is dome-shaped and is the most important muscle for breathing.

Abdominopelvic quadrants and regions

Abdominopelvic quadrants
To make it easier to locate organs in the large abdominopelvic cavity, anatomists have divided the abdominopelvic cavity into four abdominopelvic quadrants:

1. Right upper quadrant or RUQ (right superior quadrant)
2. Right lower quadrant or RLQ (right inferior quadrant)
3. Left upper quadrant or LUQ (left superior quadrant)
4. Left lower quadrant or LLQ (left inferior quadrant)

As you can see in Figure 1-6, the midsagittal and transverse planes, which were described in the previous section, pass through the navel (umbilicus) and divide the abdominopelvic region into the four quadrants. This method of subdividing the abdominopelvic cavity is frequently used by health professionals and is useful for locating the origin of pain or describing the location of a tumor or other abnormality.