The cecum is the blind-ended sac at the beginning of the large intestine (Figure 10-1A and B). The cecum is inferior to the ileocecal valve and is located in the right lower quadrant of the abdomen, within the iliac fossa. Attached to the cecum is the vermiform appendix (unknown function in humans). The taenia coli (longitudinal smooth muscle bands) of the ascending colon lead directly to the base of the appendix.
VBy identifying the taenia coli during surgery, surgeons locate the origin of the appendix on the cecum. The position of the remainder of the appendix varies because it is intraperitoneal (mobile). The surface projection of the appendix (McBurney's point) is most often located one-third of the distance between the right anterior superior iliac spine and the umbilicus. ▼
The ileocolic artery, a branch of the superior mesenteric artery, supplies the cecum. In addition, a small branch of the ileocolic artery, the appendicular artery, supplies the appendix (Figure 10-1B).
VThe appendix may become inflamed, resulting in appendicitis. Sensory neurons from the visceral peritoneum of the appendix signal the central nervous system that the appendix is inflamed. These signals are transmitted via visceral sensory neurons in the lesser splanchnic nerve, which enters the T10 vertebral level of the spinal cord. However, somatic sensory neurons from the skin around the umbilicus also enter at the T10 vertebral level of the spinal cord. Because both visceral and somatic neurons enter the spinal cord at the same level and synapse in the same region, the brain interprets the inflammation from the appendix as if the pain originated in the region of the umbilicus. This phenomenon is known as referred pain. ▼
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