Abstract
The small intestine is of essential significance for assimilation,plays a role as the main mechanical and immunological barrier separating the external and internal environment, and of equal significance is its endocrine,exocrine and paracrine humoral activity.Developmentally,it arises from the ectoderm,the same germ layer as the brain; that is why substances identical in their composition and function are produced in both organs,which often have an important regulatory effect, virtually from birth. The large intestine is not only an organ of water and electrolyte absorption and the site of evacuation of indigestible food consumed but its functions are wider.From birth and throughout life,there occurs fermentation of food fibre due to microbial colonization in the large intestine.
Mucosal microbial flora,intestinal epithelium,and mucosal immune system make up the gastrointestinal ecosystem that is formed from birth and modified throughout life.