Most nutrients are normally digested, enzymatically split into small basic components, and absorbed in the proximal part of the small intestine. Absorption may be passive or active. The villous structure of the small intestine significantly increases the absorptive area. This area is further increased by the microvilli at the luminal end of the enterocytes. The enterocytes are formed by mitotic active cells at the bottom of the crypts and then move up to the tip of the villus before they are lost. The lifespan of a small intestinal enterocyte is 2 to 3 days.

In addition to adequate intestinal blood flow, the absorptive process depends on reasonably well maintained secretion of bile and pancreatic juice, as well as on secretion of fluids and enzymes by the gastrointestinal tract mucosa itself. The mucosa produces enzymes (e.g. proteases and disaccharidases) necessary for the final breakdown of proteins and carbohydrates to small peptides, amino acids, and monosaccharides. Long-chain fatty acids, bile acids, and vitamin B 12 are examples of substances absorbed mainly or exclusively in the distal part of the small intestine (the distal ileum), while most molecules are absorbed in the jejunum. The function of the proximal part of the small intestine (jejunum) can easily be taken over by the distal part, but the reverse does not hold true. Absorption of fluid and basic nutrients, such as those used in various nutritional formulas, are maintained during critical illness and recover rapidly following intra-abdominal operations. Pathologically prolonged postoperative paralysis, which might be caused by an intraperitoneal postoperative abscess, may impair the absorptive capacity of the small intestine; more clinically evident is the prolonged inhibition of the motor function of the stomach and colon in these situations.

Good Carb Diet

Good Carb Diet

WHAT IT IS A three-phase plan that has been likened to the low-carbohydrate Atkins program because during the first two weeks, South Beach eliminates most carbs, including bread, pasta, potatoes, fruit and most dairy products. In PHASE 2, healthy carbs, including most fruits, whole grains and dairy products are gradually reintroduced, but processed carbs such as bagels, cookies, cornflakes, regular pasta and rice cakes remain on the list of foods to avoid or eat rarely.

Get My Free Ebook

Post a comment