Physical pain is the awareness of an unpleasant and uncomfortable physical sensory stimulus. The human body experiences three types of physical pain, which are called somatic, neuropathic, and visceral. Of these, visceral pain is the most common type. Viscera refer to internal parts of the body that are enclosed in a cavity, so visceral pain is the pain felt when internal organs and body tissues are injured or inflamed. This includes the heart and lungs which are located in the chest cavity; the reproductive organs and bladder found in the pelvic cavity; and the digestive organs, the spleen, and the kidneys that are found in the abdominal cavity.
Unlike neuropathic pain, which is usually a stabbing pain, or somatic pain, which is usually aching pain in a specific area of the musculoskeletal system, the location of visceral pain is more ambiguous. It is a dull internal pain caused by infiltration, expansion, perforation, blockage, stretching or irritation of the internal organs. Visceral pain is often described as pressure or a feeling of pressure that radiates throughout the cavity. However, the level of intensity can range from mild to excruciating, depending on the disease causing pain receptors to alert the brain that there is a problem. Although pain is unpleasant, it is a necessary element in the diagnosis and treatment of diseases and disorders.
Some organs are more sensitive to visceral pain than others. Any injury or problem with the stomach or bladder is likely to cause a considerable amount of pain, but the lungs and kidneys can take a lot of damage with little indication of the pain receptors located in those organs. It depends entirely on the number of sensory neurons, called nociceptors, found within each organ. Therefore, the level of pain is not always indicative of the true amount of damage experienced by a particular organ. Some common examples of visceral pain are indigestion, menstrual cramps, constipation, cancer pain, gallstones, and appendicitis.
Visceral pain is referred or non-referred. Non-referred visceral pain is pain felt in the area or organ actually affected by the irritant or damage. Referred visceral pain is pain that is felt in areas other than those where the damage has occurred. Referred pain is a phenomenon that is not fully understood and is still being investigated. This is especially important as it relates to visceral pain, as it is sometimes difficult to pinpoint the location of damage, and patterns of referred pain have provided clinicians with an additional diagnostic tool.