Human Anatomy Health Article

Cavities of the body

Within the axial portion of the body lie two major cavities: the dorsal and ventral body cavities. The dorsal body cavity lies posterior to the ventral body cavity and protects the organs of the central nervous system. It is composed of the cranial cavity (enclosing the brain) and the vertebral cavity (containing the spinal cord).

The ventral body cavity is the larger of the two and encloses the viscera or visceral organs (internal organs). It also has two major subdivisions: the thoracic cavity and the abdominopelvic cavity. The thoracic cavity is surrounded anteriorly by the ribs and chest muscles. It encloses two pleural cavities, each encasing a lung, and the mediastinum. The pericardial cavity is located inside of the mediastinum and encloses the heart. The mediastinum also surrounds the esophagus, trachea, and other thoracic organs. The abdominopelvic cavity is separated from the thoracic cavity by the diaphragm, a thin muscle below the lungs and heart that is important for breathing. The abdominopelvic cavity contains the abdominal cavity (enclosing the stomach, liver, spleen, intestines, and other digestive organs) and the pelvic cavity (containing the bladder, reproductive organs, and rectum).

There are also smaller body cavities that exist throughout the axial portion of the body. The oral cavity (mouth) contains the teeth and tongue. The digestive cavity includes the oral cavity and extends down to the anus, including all digestive organs. The nasal cavity is found posterior to the nose and is part of the respiratory system.

The middle ear cavity is medial to the external ear and contains three small bones (the malleus, the incus, and the stapes) that are essential to normal hearing. The orbital cavities are found in the skull and contain the eyes, as well as skeletal muscles and nerves. The freely movable joints of bones are found in synovial cavities, where synovial fluid is secreted that helps lubricate joints and reduce friction between bones.

VENTRAL BODY CAVITY MEMBRANES. The ventral body cavity is lined with a thin membrane called the parietal serosa; internal organs are covered with a similar membrane called the visceral serosa. These membranes secrete a small amount of fluid called serous fluid that separates and lubricates them. Different parietal and visceral membranes have different names for the cavities and organs that they protect. The parietal pericardium lines the cavity that contains the heart and the visceral pericardium covers the surface of the heart. Likewise, the parietal pleura lines the thoracic cavity and the visceral pleura covers the surface of the lungs.

Regions and quadrants

The abdominopelvic region is often further divided into regions or quadrants for reference in study or clinical examination. The abdomen may be partitioned into nine regions, with two transverse planes and two parasagittal planes positioned in a grid. The central grid surrounds the umbilicus (navel) and is subsequently called the umbilical region; the left and right lumbar regions are found lateral to the umbilical region. The epigastric region is located superior to the umbilical region and includes the area of the stomach; the left and right hypochondriac regions are found to each side. Inferior to the umbilical region is the hypogastric or pubic region in which the urinary bladder is found; to each side are the left and right iliac or inguinal regions.

The quadrant system is often used by health care workers during examinations to localize pain, tumors, or abdominal structures. The median sagittal plane marks the vertical division while a transverse plane across the umbilicus marks the horizontal division. The subsequent four divisions are named the left upper quadrant (LUQ), right upper quadrant (RUQ), left lower quadrant (LLQ), and right lower quadrant (RLQ).

Different regional terms exist that help to specifically identify different regions or parts of the body. The following are some of the more common regional terms: nasal (nose), oral (mouth), otic (ear), cervical (neck), sternal (sternum or breastbone), axillary (armpit), thoracic (chest), mammary (breast), brachial (arm), abdominal (abdomen), olecranal (elbow), carpal (wrist), digital (fingers and toes), manus (hand), pubic (genitals), patellar (kneecap), crural (leg), femoral (thigh), tarsal (ankle), pedal (foot), vertebral (spinal column), dorsal (back), and gluteal (buttock). If an individual broke a bone in or near the elbow, for example, he or she would experience pain in the olecranal region.