Abdomen

The abdomen is commonly called the stomach and occupies the lower part of the trunk beneath the thorax from which it is separated by the diaphragm muscle, and above the pelvis which contains the bladder and the genital organs.

It is a cavity internally lined by a membrane, the peritoneum, which covers the different viscera lying to the front and leaves a retro-peritoneal region behind it.

The retro-peritoneal region primarly contains the kidneys and urinary tract, lymph nodes, and connective tissue and through which the major vessels (aorta, inferior vena cava) and the nerves pass.