Expert: Walter Hintz - 9/25/2005

Question
WHY IS WATER REABSORBED IN THE LG INTESTINE, IS ATP NECCESARY FOR THE WATER TO BE REABSORBED AND WHAT IS IT'S PROCESS. I WAS ASKED THIS BY MY BIOLOGY TEACHER AND HE SAID I COULD USE ANY REFERENCE TO GET THE ANSWER. COULD YOU PLEASE HELP ME, I HAVE LOOKED EVERYWHERE.

Answer
I really do not like "why"  questions carolyn.  Your first question is best answered by stating because that is what the large intestine does.  Water moves out of the a large intestine by osmosis ( energy not needed). Why the large intestine and not the small intestine?  Absorbtion of digested materials occurs in the small intestine and water is still required for this to happen.  By the time the wastes reach the colon excess water has to renter the system and the colon has a larger surface area nedded for osmosis. (osmosis is the process)