abdomen
Meaning of abdomen: Clinicians divide it into four quadrants or nine regions, because where pain sits narrows down which organ is speaking.
Definition of abdomen
The abdomen is the part of the body between the chest and the pelvis. Muscular walls enclose it at the front and sides, the spine and its muscles form the back, and the diaphragm, a dome of muscle used in breathing, separates it from the chest above. It holds most of the digestive organs along with the spleen and kidneys.
What is inside it?
| Quadrant | Main contents |
|---|---|
| Right upper | Liver, gallbladder, part of the colon, head of the pancreas |
| Left upper | Stomach, spleen, tail of the pancreas, part of the colon |
| Right lower | Appendix, end of the small intestine, right ovary or spermatic cord |
| Left lower | Sigmoid colon, left ovary or spermatic cord |
The kidneys and the aorta sit toward the back on both sides. A finer nine region grid is also used, giving names such as epigastric for the area just below the breastbone and umbilical for the area around the navel.
What is the peritoneum, and why does it matter?
A thin double layered membrane called the peritoneum lines the cavity and folds over most of the organs, leaving a slippery film of fluid between the layers so loops of bowel glide past one another. Some structures lie behind that lining rather than within it, including the kidneys, the pancreas, most of the duodenum and the large vessels. The distinction is practical. The outer layer of the peritoneum carries nerves that localize pain precisely, so once inflammation reaches it, pain that began as a vague central ache moves to sit exactly over the offending organ and worsens with movement or coughing.
Why does abdominal pain need so much interpretation?
Organs from the digestive, urinary, reproductive and vascular systems are packed into one space, and pain from a hollow organ is felt in the midline according to its embryonic origin rather than its adult position. That is why appendicitis so often starts around the navel before settling in the right lower quadrant. Pain can also be referred from outside the region entirely, with a heart attack felt in the upper abdominal area and pneumonia at the lung base felt below the diaphragm.
Used in a sentence
Physical examination of the abdomen revealed tenderness in the lower right quadrant.
Good to know
The location of abdominal pain, whether central, upper or in a specific quadrant, narrows the range of likely causes, but pain from a hollow organ is often felt in the midline before it settles over the organ involved.