Stressful events might cause immune dysfunction and trigger various disorders. Adverse effects of acute or chronic stress exposure on the gastrointestinal system have been shown previously in several studies. In this experimental study, we used chronic unpredictable stress (CUS) paradigm to better mimic effects of the intermittent exposure to daily life stress and investigated the morphometric alterations occurring in the small intestines of rats. Methods: Male Wistar rats were randomly divided into stress and control groups (n=8, each). While stress group was subjected to chronic unpredictable stress protocol for 21 days, control group remained undisturbed. Intestinal tissue samples were obtained from two different regions; one was 3-6 cm away from the pylorus and the other one 3-6 cm prior to the ileocaecal valve. Tissue sections were obtained from paraffin blocks at the thickness of 3 micrometers and stained with hematoxylin-eosin (HE) or periodic acid-Shiff (PAS). The lengths of villi were measured from the basal membrane to the top of the villus. The ratio of degranulating and non-degranulating mast cells per unit area were estimated by point counting method. Results: The mean villi length in the stress group were significantly higher (p
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