| MadSci Network: Anatomy |
Hi Breanna,
You've asked a very interesting question - one I pose to my students when they study the Digestive System during our Human Body Unit. At first the thought of swallowing while upside down seems impossible - many people think that food just sort of 'drops' down from our throats into our stomachs. In reality, 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 ("pear-ih-stall-sis"). Once food or water reaches the end of the esophagus, a valve called a sphincter ("sfink-tur") 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!
Hope that answers your question, Breanna. The following sites may also be helpful:
Good luck on your Science project!
-Jen Baucom, MAD Scientist
References: Biology, 5th Edition, Helena Curtis & N. Sue Barnes, 1989.
Try the links in the MadSci Library for more information on Anatomy.