During the operation on the small intestine the surgeon revealed an area of the mucous membrane with a single longitudinal fold among the circular folds. Which portion of the small intestine is this structure typical for?

Answer options

1. jejunum
2. Pars descendens duodeni
3. Distal ileum
4. Pars horizontalis duodeni
5. Pars ascendens duodeni

Explanation

The longitudinal fold occurs as a result of the invagination of the bile duct running along the wall of the descending part of the duodenum.