Although the small intestine is only 3 to 4 cm in diameter and approximately 7 metres in length, it has been estim.... cell surfac

Although the small intestine is only 3 to 4 cm in diameter and approximately 7 metres in length, it has been estimated that its total absorptive surface area is approximately 4,500 square metres (5,400 square yards). It has been estimated that the small intestine contains approximately 800 plicae circulares and that they increase the surface area of the lining of the small bowel by five to eight times the outer surface area. Goblet cells are found scattered among the surface epithelial cells covering the villi and are a source of mucin, the chief constituent of mucus. The cells that line these glands continue up and over the surface of the villi. In the bottom of the glands, epithelial cells called are filled with alpha granules, or eosinophilic granules, so called because they take up the rose-coloured stain eosin. There are three other cell types in the Lieberkhn's glands: undifferentiated cells, which have the potential to undergo changes for the purpose of replacing loss! es of any cell type; the goblet cells mentioned above; and endocrine cells, which are described below. The main functions of the undifferentiated cells in these glands are cell renewal and secretion. A remarkable feature of the mucosa villi is the rough, specialized surface of the epithelial cells. The microvilli play an important role in the digestion and absorption of intestinal contents by enlarging the absorbing surface approximately 25 times. Molecular receptors for specific substances are found on the microvilli surfaces at different levels in the small intestine. cell surfac