The last 12cm (4.7 in) length of large intestine covered in smooth muscle emptying into the anal canal.
The final section of digestive tract, from 2.5 to 4 cm (1 to 1.6 inches) in length, emptying through the anus.
A swelling of the veins around your rectum and anus!
Prevention: When you gotta go, GO! The more you hold it, the more prone you are to hemoroids!
See also User's Manual: Large Intestine
Glands involved in digestion