with diarrhea stools usually are looser whether or not the frequency of bowel movements is increased. this looseness of stool -- which can vary all the way from slightly soft to watery -- is caused by increased water in the stool. during normal digestion food is kept liquid by the secretion of large amounts of water by the stomach upper small intestine pancreas and gallbladder. food that is not digested reaches the lower small intestine and colon in liquid form. the lower small intestine and particularly the colon absorb the water turning the undigested food into a more-or-less solid stool with form. increased amounts of water in stool can occur if the stomach and/or small intestine secretes too much fluid the distal small intestine and colon do not absorb enough water or the undigested liquid food passes too quickly through the small intestine and colon for enough water to be removed. of course more than one of these abnormal processes may occur at the same time. for example some viruses bacteria and parasites cause increased secretion of fluid either by invading and inflaming the lining of the small intestine (inflammation stimulates the lining to secrete fluid) or by producing toxins (chemicals) that also stimulate the lining to secrete fluid but without causing inflammation. inflammation of the small intestine and/or colon from bacteria or from ileitis/colitis can increase the rapidity with which food passes through the intestines reducing the time that is available for absorbing water. conditions of the colon such as collagenous colitis can block the ability of the colon to absorb water. diarrhea generally is divided into two types acute and chronic. acute diarrhea lasts from a few days up to a week. chronic diarrhea can be defined in several ways but almost always lasts more than three weeks. it is important to distinguish between acute and chronic diarrhea because they usually have different causes require different diagnostic tests and require different treatment.
why does diarrhea develop?