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 Stomach Pain. The upper part of the abdomen consists of the oesophagus, stomach, liver, gallbladder, pancreas and the duodenum. An infection, a disorder, or an inflammation in any one of these parts of the abdomen can cause upper stomach pain. Pancreatitis-Pancreatitis can occur due to excessive alcohol use, viral infections, and diseases of the gallbladder. 2  Upper abdominal pain is a main symptom of pancreatitis. 3  In addition, abdominal swelling, back pain, nausea, and vomiting can also occur. 4  Reflux Esophagitis-This is due to inflammation of the oesophagus.