The cecum with the vermiform appendix are the very first portions of the large intestine. Both are positioned in the right iliac fossa.

Cecum

The cecum is a blind pouch-like structure that is situated in the right lower quadrant of the abdomen on the iliacus muscle. It is positioned between the ileum and the ascending colon in the right iliac fossa close to the anterior abdominal wall. The cecum is approximately 1.97 - 2.76 inches (5 - 7 cm) long with a diameter of up to 3.54 inches (9 cm), so it is wider than long.

The cecum starts at the distal end of the ileum as its continuation. Both intestines connect through the ileocecal orifice at the ileocecal junction. This junction marks the transition zone between the small and large intestines.

At the ileocecal junction, the terminal ileum protrudes the posteromedial wall of the cecum, forming a slight mucosal elevation called the ileal papilla. Within the ileal papilla, smooth muscle fibers of the cecum and ileum form the ileocecal valve - a functional valve that ensures the intestinal content passage from the ileum into the cecum and prevents its backflow.

The ileocecal valve is composed of two horizontal flaps or lips that surround the ileocecal orifice. The upper is the superior ileocolic lip, while the lower is the inferior ileocecal lip. At the sides where both lips merge, they form narrow membranous ridges called the frenula (sing. frenulum).

The cecum is an intraperitoneal organ, and the peritoneum covers it from all sides. It has no mesentery, and the cecum is rather mobile than fixed. The cecum usually contains all the characteristic features of the large intestine. However, it may lack the epiploic appendices.

The cecum is related to various structures. Posterior to it are the iliacus muscle and psoas major muscle, lateral femoral cutaneous nerve, femoral nerve, and genitofemoral nerve. The anterior surface of the cecum is related to the anterior abdominal wall, and sometimes it is also covered by the greater omentum and loops of the small intestine. Superiorly, the cecum continues as the ascending colon, while inferiorly is the inguinal ligament. Medial to the cecum are the coils of the ileum.

Overall, the cecum functions as a reservoir for the chyme coming from the small intestine, and it also participates in the absorption of the remaining water and electrolytes. Besides the mentioned functions, the cecum provides lubrication of the feces as it contains mucus-producing cells. Also, it participates in cellulose digestion as it contains bacteria that decompose plant-based food rich in cellulose.

Note: Chyme is a thick, semi-fluid mass of partially digested food mixed with digestive secretions of the stomach and intestines.

Vermiform appendix

The vermiform appendix is a freely mobile, narrow, worm-like structure with a small lumen and blind end that originates from the cecum. The Latin word vermiform means "worm-like in form," and indeed, the shape of the vermiform appendix resembles that of a worm.

The vermiform appendix arises from the posteromedial wall of the cecum, usually 0.39 - 1.18 inches (1 - 3 cm) below the ileocecal junction. Along with the cecum, it is also situated in the right iliac fossa, but its distal tip can extend as far as the liver and its position can be quite variable.

The vermiform appendix is usually 2.36 - 3.94 inches (6 - 10 cm) long. However, its length is also very variable and can range from 0.79 to 7.87 inches (2 - 20 cm). Its diameter is usually around 0.2 to 0.39 inches (0.5 - 1 cm).

The vermiform appendix has one opening called the orifice of vermiform appendix, with which it connects with the cecum. Usually, the anterior surface of the vermiform appendix is covered by the coils of the small intestine. But sometimes, it connects with the anterior abdominal wall.

The vermiform appendix contains massive amounts of lymphoreticular tissue, and therefore, it primarily provides immunological function. It also houses gut microflora.

The appendix is an intraperitoneal organ, and it has a triangular-shaped mesentery called the mesoappendix. It attaches the vermiform appendix to the terminal ileum and is derived from it. In contrast to the cecum, the vermiform appendix lacks all characteristic features of the large intestine, such as the taeniae coli, haustra, and epiploic appendices.

Position variations of vermiform appendix

The position of the vermiform appendix varies considerably among individuals, and here are some of its possible positions:

Position variations of vermiform appendix

Position variations of vermiform appendix

Clinical note: The vermiform appendix can be palpated through the abdominal wall in the lower right quadrant of the abdomen in a site called McBurney’s point. If an imaginary line is drawn from the anterior superior iliac spine to the umbilicus, McBurney’s point is located one-third of the distance laterally. Tenderness or pain localized at this point or near it can signify appendicitis - inflammation of the appendix. It is important to remember that pain related to appendicitis can present in two stages - an early stage of poorly localized pain surrounding the umbilicus followed by sharper, well-localized pain in the right lower abdominal quadrant.

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Cecum and vermiform appendix