Content Reviewers:Scott Caterine, BSc (Hons.), MSc, MB, BCh, BAO (Hons.), Viviana Popa, MD
The large intestine is a part of the digestive tract specialized in absorbing water from the residual digested food coming from the small intestines, while forming and storing feces until defecation occurs.
Second, there are the teniae coli, which are three strips of smooth muscle that run lengthwise from the base of the appendix through the colon and merge at the rectosigmoid junction to form a longitudinal layer around the rectum.
The cecum is the first part of the large intestine and it receives the terminal ileum, which invaginates into the medial side of the cecum. The cecum lies in the right iliac fossa in the right lower quadrant of the abdomen, and it looks a bit like an intestinal pouch.
It is intraperitoneal, mobile, and doesn’t have its own mesentery. On its posteromedial wall, inferior to the ileocecal junction, the cecum has a blind-ended organ called the appendix, which can vary in length up to and over 10cm.
The appendix is usually retrocecal, meaning behind the cecum, but its position can vary a bit as well. It’s full of lymphoid tissue and its proximal part has attachment to the cecum by a small mesentery called the mesoappendix.
The orifice is usually closed due to tonic contraction, and the lips of the ileal papilla serve as passive flaps to prevent regurgitation of fecal matter from the cecum into the ileum. Just inferior to the ileal orifice, there’s the opening to the appendix.
Then, the cecum continues as the second part of the large intestine, or the ascending colon. The ascending colon extends superiorly from the cecum along the right side of the abdominal cavity towards the right lobe of the liver.
Inferior to the liver and below the ninth and tenth ribs, the colon turns to the left, forming the right colic flexure, also called the hepatic flexure. The ascending colon is positioned retroperitoneally, therefore just behind the peritoneum.
Laterally, between the ascending colon and the lateral abdominal wall is a shallow trench covered by parietal peritoneum called the right paracolic gutter. Medial to the ascending colon is the small intestine, while anteriorly is the greater omentum.
Once at the spleen, it turns downwards in front of the lower portion of the left kidney to become the descending colon, and this gives us the left colic flexure - or splenic flexure - which is more superior than the hepatic flexure and has a more acute angle.
The transverse colon is intraperitoneal and therefore mobile, and can hang down to the level of the umbilicus.
As it descends towards the third sacral vertebra, the sigmoid colon makes an S shape as it connects and continues as the rectum. The sigmoid colon is intraperitoneal, very mobile, and has a mesentery called the sigmoid mesocolon.
The cecum is supplied by the superior mesenteric artery through its terminal branch called the ileocolic artery, and the appendix is supplied by the appendicular artery, which, in turn, is a branch of the ileocolic artery.
The transverse colon is supplied by a branch of the SMA called the middle colic artery. The middle colic artery anastomoses with the right colic artery and they together supply the right colic flexure.
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