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.
Pain in the right upper abdomen Pain and discomfort may be felt in the upper right side of the abdomen where the liver is located. Pain may be caused by the liver growing in size due to the accumulation of fat, acute inflammation or any injury that can expand and stretch the sensitive membrane covering the liver.