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APPENDIX Blind tube off cecum No important digestive functions in humans

PERITONEUM (FIGURE 15-14) Definitions—peritoneum, serous membrane lining abdominal cavity and covering abdominal organs; parietal layer of peritoneum lines abdominal cavity; visceral layer of peritoneum covers abdominal organs; peritoneal space lies between parietal and visceral layers Extensions—largest are the mesentery and greater omentum Mesentery is extension of parietal peritoneum, which attaches most of small intestine to posterior abdominal wall Greater omentum, or “lace apron,” hangs down from lower edge of stomach and transverse colon over intestines X-ray studies of the GI tract—radiopaque contrast medium used to help visualize structures in study images

DIGESTION (TABLE 15-2) Definition—transforms foods into substances that can be absorbed and used by cells Mechanical digestion—chewing (mastication), swallowing (deglutition), and peristalsis break food into tiny particles, mix them well with digestive juices, and move them along the digestive tract Chemical digestion—breaks up large food molecules into compounds that have smaller molecules; brought about by digestive enzymes (Figure 15-15) Enzymes and chemical digestion Enzymes are specialized protein molecules that act as catalysts Breakdown process called hydrolysis

DIGESTION Carbohydrate digestion—mainly in small intestine Pancreatic amylase—breaks polysaccharides down to disaccharides Intestinal juice enzymes Maltase—changes maltose to glucose Sucrase—changes sucrose to glucose Lactase—changes lactose to glucose

DIGESTION Protein digestion—starts in stomach; completed in small intestine Gastric juice enzyme pepsin partially digests proteins Pancreatic enzyme, trypsin, continues digestion of proteins Intestinal enzymes, peptidases, complete digestion of partially digested proteins and convert them to amino acids Fat digestion Bile contains no enzymes but emulsifies fats (breaks fat droplets into very small droplets) Pancreatic lipase changes emulsified fats to fatty acids and glycerol in small intestine

ABSORPTION Definition—process by which digested food moves from intestine into blood or lymph Foods and most water minerals and vitamins are absorbed from small intestine; some water and vitamin K also absorbed from large intestine Surface area absorption Structural adaptations increase absorptive surface area Fractal geometry—study of fragmented geometric irregular shapes such as those in lining of intestine