The most obvious function of the GI tract is digestion and absorption of food for continued growth and survival of the organism. Which of the following statement(s) is/are true concerning small bowel absorption?

b. Eighty percent of water presented to the gastrointestinal system is reabsorbed by the small bowel

c. The absorption of carbohydrates requires digestion of large starch molecules by salivary and pancreatic amylase, therefore presenting smaller oligosaccharides to the brush border of the jejunum to complete the digestion and absorptive process

d. Dietary fiber represents poorly digestible carbohydrates which can absorb organic materials such as bile salts and lipids

The jejunum is the site of maximum absorption of all ingested materials expect for vitamin B12. Although its mucosa contains numerous specific transport processes, the presence of large intercellular pores produces a permeable membrane and allows for rapid passive transfer or solutes and water. The ileum is less permeable and makes greater use of activetransport mechanisms. Normally about 1 to 1.5 liters of water is ingested each day with another 5 to 10 liters secreted by the GI tract in some form. About 80% of this fluid is absorbed by the small bowel. Because of this large bidirectional movement of water, a small alteration in bowel permeability or transport can rapidly result in net secretion and diarrheal disease states. A major source of caloric nutrition comes in the form of carbohydrate. In the Western diet, this is made up primarily of starch (about 60%), sucrose (30%), and lactose (10%). The digestive process for starch begins with digestion of the polysaccharide first by salivary amylase and continues with pancreatic amylase yielding smaller oligosaccharides which along with sucrose and lactose are then presented to the brush border of the jejunum to complete the digestion and absorptive processes. Dietary fiber consists of nondigestible carbohydrate, such as cellulose. Fiber is found commonly in all-bran cereals, beans, partially cooked vegetables, and raw pulpy fruits. High fiber diets retain water within the bowel lumen and significantly shorten bowel transit time. Dietary fiber can absorb organic materials such as bile salts and lipids and inorganic materials such as zinc, calcium, magnesium and iron.