Chickens have two well-developed ceca, with an epithelium that is histologically and functionally heterogeneous. The proximal region, close to the ileorectal junction, has well-developed villi and microvilli and is able to transport sugars and amino acids against a concentration gradient, by mechanisms virtually identical to those described for the small intestine. The medial-distal region does not have true villi but has mounds and ridges, and it cannot transport either sugars or amino acids in the adult bird. In newborn chicks, the whole cecum can accumulate and transport sugars, but this property is soon restricted to the proximal region. The medial cecum, however, retains some transport capacity until the 8th week after the hatch. Ceca are thus well suited for sugar and amino acid absorption. Their contribution to the overall nutrient absorption is, however, limited, because the absorbing epithelium is exposed to the intestinal contents only during the filling and emptying of the cecal segments.