Final answer:
The S-shaped portion of the large intestine in the lower left quadrant is the sigmoid colon. It's the part of the colon that extends medially to the midline before connecting to the rectum.
Step-by-step explanation:
The S-shaped portion of the large intestine, located in the lower left quadrant, is the sigmoid colon. The large intestine can be divided into several parts: the cecum, ascending colon, transverse colon, descending colon, and sigmoid colon. The cecum, where the appendix attaches, is the first part of the large intestine and it leads upwards into the ascending colon. The food residue then enters the transverse colon which goes across the upper abdomen, and then it descends down the left side of the abdomen as the descending colon. After this, it moves into the sigmoid colon, which extends medially to the midline before connecting to the rectum.