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 may accompany other symptoms, which vary depending on the underlying disease, disorder or condition. Upper abdominal pain is often related to the digestive tract, and may accompany other digestive tract symptoms.Symptoms related to other body systems may also occur and sometimes upper abdominal pain is not related to a condition of the digestive tract.pper abdominal pain is often related to the digestive tract, and may accompany other digestive tract symptoms. Symptoms related to other body systems may also occur and sometimes upper abdominal pain is not related to a condition of the digestive tract.