The primary function of the upper abdominal organs is the breakdown of food for distribution by the small bowel. Chewed and macerated food travels through the esophagus to the stomach, where strong acids and muscular contractions break it down further.
Proteolytic enzymes from the pancreas and bile from the liver and gallbladder drain into the duodenum to further the digestion and breakdown of food.
The spleen functions as part of the hematopoietic system, controlling the distribution and eventual destruction of red blood cells. It also acts as a part of the immune system.
Blood is supplied to most of these structures by branches of the celiac trunk, the first major aortic branch in the abdomen.