why does food goes into our stomach even by eating in upside down position?
Food is actually pushed toward the stomach through the esophagus, an approximately 10 inch long and 1 inch in diameter (in adults) muscular tube leading to the stomach. The esophagus is lined with smooth muscle, a type of muscle that contracts involuntarily (without us making it contract). Food and water entering the esophagus does not drop down and fall into the stomach; instead it is pushed through by waves of contractions (squeezes) from the bands of muscles that encircle the esophagus (of course, gravity does help a little bit). These contractions are known as peristalsis. Once food or water reaches the end of the esophagus, a valve called a sphincter closes so it can't come back up. Peristalsis is so strong that it can actually enable a person to swallow food or water while upside down.