The circular folds slow the passage of the partly digested food along the intestines, and afford an increased surface for absorption. They are covered with small finger-like projections called villi (singular, villus). Each villus, in turn, is covered with microvilli.
While rugae is only evident when an organ or tissue deflares or relaxes. The rugae unfolds for increase in volume . Plicae remains folded in the intestinal walls.
Rugae is not associated with the large absorptive surfaces in the small intestine.
