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.
Numerous conditions can cause pain in the right upper abdomen. According to the Merck Manuals Online Medical Library, pain that manifests in the abdomen, including the right upper abdominal quadrant, can be caused by the viscera or abdominal organs, structures outside the abdomen or the parietal peritoneum -- the membrane that lines the abdominal wall.