<P> The three sections of the small intestine look similar to each other at a microscopic level, but there are some important differences . The parts of the intestine are as follows: </P> <Table> <Tr> <Th> Layer </Th> <Th> Duodenum </Th> <Th> Jejunum </Th> <Th> Ileum </Th> </Tr> <Tr> <Td> Serosa </Td> <Td> 1st part serosa, 2nd--4th adventitia </Td> <Td> Normal </Td> <Td> Normal </Td> </Tr> <Tr> <Td> Muscularis externa </Td> <Td> Longitudinal and circular layers, with Auerbach's (myenteric) plexus in between </Td> <Td> Same as duodenum </Td> <Td> Same as duodenum </Td> </Tr> <Tr> <Td> Submucosa </Td> <Td> Brunner's glands and Meissner's (submucosal) plexus </Td> <Td> No BG </Td> <Td> No BG </Td> </Tr> <Tr> <Td> Mucosa: muscularis mucosae </Td> <Td> Normal </Td> <Td> Normal </Td> <Td> Normal </Td> </Tr> <Tr> <Td> Mucosa: lamina propria </Td> <Td> No PP </Td> <Td> No PP </Td> <Td> Peyer's patches </Td> </Tr> <Tr> <Td> Mucosa: intestinal epithelium </Td> <Td> Simple columnar . Contains goblet cells, Paneth cells </Td> <Td> Similar to duodenum </Td> <Td>? </Td> </Tr> </Table> <Tr> <Th> Layer </Th> <Th> Duodenum </Th> <Th> Jejunum </Th> <Th> Ileum </Th> </Tr> <Tr> <Td> Serosa </Td> <Td> 1st part serosa, 2nd--4th adventitia </Td> <Td> Normal </Td> <Td> Normal </Td> </Tr>

Absorbed following digestion of carbohydrates in the small intestine