Physical pain is the awareness of a displeasing 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 refers to internal parts of the body that are enclosed in a cavity, so pain in the viscera is that which is felt when internal organs and body tissues are injured or inflamed. This includes the heart and lungs found in the thoracic cavity; the reproductive organs and bladder found in the pelvic cavity; and the digestive organs, spleen, and kidneys found in the abdominal cavity.
Unlike neuropathic pain which is typically a stabbing pain, or somatic pain which is usually an aching pain in a specific area of the musculoskeletal system, visceral pain location is more ambiguous. It is a dull pain from within caused by infiltration, expansion, perforation, blockage, stretching, or irritation of internal organs. It is often described as pressure or a squeezing sensation which radiates throughout a cavity. The level of intensity can vary from mild to excruciating, however, depending on the malady causing the pain receptors to alert the brain that an issue exists. Though pain is unpleasant, it is a necessary element in the diagnosis and treatment of disease and disorders.
Some organs are more sensitive to visceral pain than others. Any injury or issue with the stomach or bladder is likely to cause a considerable amount of pain, but the lungs and kidneys may sustain much damage with little indication by the pain receptors located in those organs. It is entirely dependent on the quantity of sensory neurons, called nociceptors, found within each organ. So, 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, pain caused by cancer, gall stones, and appendicitis.
This type of pain is either referred or unreferred. Unreferred visceral pain is pain felt in the area or organ actually affected by the irritant or damage. Referred visceral pain is pain felt in areas other than those where the damage has occurred. Referred pain is a phenomena that is not fully understood and is still being investigated. This is especially important as it relates to visceral pain, as it is sometimes hard to pinpoint the location of damage, and patterns of referred pain have given physicians an additional diagnostic tool.