Aim:
The aim of our study was to perform morphological and morphometric analysis of biopsy specimens of the common and biliopancreatic loops after gastric bypass with a single anastomosis 3, 12, 24 months after surgery, which included measurement of villi length, ratio of villi length to the thickness of the lamina propria layer containing crypts, estimation of the number and distribution of goblet cells, quantification of number crypts and Paneth cells and comparing the changes in the biliopancreatic and common loops.

Material and methods:
This study included 36 patients who underwent bariatric surgery due to morbid obesity. Patients underwent one of the following procedures: long-loop gastric bypass with one anastomosis, distal gastric bypass with one anastomosis, or mini-gastric bypass. Patients underwent EGDS with mucosal biopsy from the common and biliopancreatic loop at 3, 12, 24 months after gastric bypass with one anastomosis, followed by morphologic and morphometric study of biopsy specimens, which was part of our study.

Results:
2 years follow up show statistically significant differences in villus length were observed between the common and biliopancreatic limbs, with the length being greater in the common limb (0.390 ± 0.199 mm) than in the biliopancreatic limb (0.377 ± 0.184 mm) (p < 0.05). These changes may indicate hypertrophy of the villi in the efferent limb to increase the absorptive surface area. The thickness of the basal layer was greater in the biliopancreatic limb than in the common limb, measuring 0.196 ± 0.068 mm versus 0.167 ± 0.043 mm, respectively (p< 0.05). Regulatory functions of Paneth cells were preserved in both groups.

Conclusions:
Adaptation of the small intestinal mucosa occurs after gastric bypass with one anastomosis, and these changes are more pronounced in the common loop of the small intestine. The regulatory functions of Paneth cells and their number involve both the common loop and the biliopancreatic region.