This document defines and describes several common medical terms and tests related to the digestive system. It explains that a nasogastric tube is inserted through the nose into the stomach to pump food in or suck fluids out. It also describes how a fecal occult blood test checks for hidden blood in stool, which can indicate various conditions. Additionally, it defines aspartate transaminase as a liver enzyme and explains how its levels indicate liver disease or damage. Finally, it provides details on gastroesophageal reflux disease, including that it occurs when stomach acid rises into the esophagus due to a faulty lower esophageal sphincter.