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.
Constant dull upper abdominal pain that worsens during or after the meal is the main symptom. Diagnosis is made by the ultrasound, CT or MRI. 13. Heart Attack. Heart attack may appear with upper middle or left upper abdominal pain and is rare before 40 years of age. Smoking and high blood cholesterol are two important risk factors.