1 Red blood cells (RBCs) are also called erythrocytes. They make up almost half of blood. Red blood cells are filled with hemoglobin. That's a protein that picks up oxygen in the lungs and brings it to cells all around the body.  White blood cells (WBCs) are also called leukocytes.
Pain originating in the stomach or esophagus is often felt in the upper abdomen and can be due to heartburn, gastroesophageal reflux disease (GERD), or hiatal hernia (weakening in the diaphragm that allows the stomach to protrude into the chest). You may also have gastritis (inflammation of the stomach lining) or ulcers.
Upper abdominal pain: Introduction. Upper abdominal pain: The occurrence of abdominal pain which occurs in the upper abdoment. See detailed information below for a list of 47 causes of Upper abdominal pain, Symptom Checker, including diseases and drug side effect causes. Causes of Upper abdominal pain: Introduction.  The occurrence of abdominal pain which occurs in the upper abdoment. See detailed information below for a list of 47 causes of Upper abdominal pain, Symptom Checker, including diseases and drug side effect causes. Â» Review Causes of  Causes | Symptom Checker Â».