3. (Aeronautics) any structure corresponding to or resembling the keel of a ship, such as the central member along the bottom of an aircraft fuselage. 4. (Biology) biology a ridgelike part; carina. 5. a poetic word for ship.
Transverse colon and sigmoid colon. The transverse colon and the sigmoid colon have a mesentery (ie, transverse mesocolon and sigmoid mesocolon, respectively), but the ascending colon and descending colon are retroperitoneal, while the cecum is intraperitoneal but uses the mesentery of the ileum.
As the narrowest segment of the large intestine, and the segment closest to the rectum (the part of the intestine that stores feces until a bowel movement occurs), the sigmoid colon is often subject to the straining and pressure increases that can weaken the colonic muscles over time.