Chapter 62: Peritoneum, Mesentery & Peritoneal Cavity

Peritoneum, Mesentery & Peritoneal Cavity explores the peritoneum, the body's largest serous membrane, detailing its anatomy, specialized structures, and profound clinical importance, forming the foundation of abdominal surgery and diagnostics. The peritoneum is a closed sac in males but is open in females at the uterine tubes. It is composed of a single layer of mesothelium overlying a rich lymphatic plexus. Anatomical features like microscopic peritoneal stomata and lymphoid aggregates known as ‘milky spots’ are critical for the absorption of peritoneal fluid. This fluid, usually less than 5 ml in healthy males but up to 25 ml in healthy young females, lubricates the viscera, allowing them to glide freely. Fluid circulation is predominantly clockwise, influenced by respiration and peristalsis, guiding fluid and potential pathology (like malignant cells or infection leading to ascites) toward dependent sites such as the right paracolic gutter and subphrenic spaces. The mesentery is emphasized as a continuous structure spanning from the esophagus to the rectum, containing essential neurovascular bundles and lymphatic vessels supplying the digestive organs. The chapter defines various peritoneal reflections and attachments, distinguishing between the larger greater omentum and the smaller lesser omentum. The greater omentum, characterized by its mobility and vascularity, serves significant defensive roles, absorbing fluid, promoting hemostasis, and walling off infection, making it useful in reconstructive surgery. The peritoneal cavity is anatomically subdivided into the greater sac and the omental bursa (lesser sac), which communicate through the omental foramen (Foramen of Winslow). The omental foramen's anterior boundary is the hepatoduodenal ligament, which strategically contains the hepatic portal vein, bile duct, and proper hepatic artery. For clinical assessment, the cavity is often conceptually divided into supramesocolic (supracolic) and inframesocolic regions, containing clinically significant areas like the hepatorenal recess (a common site for fluid collection). Differential innervation is key to understanding pain presentation: the parietal peritoneum receives somatic innervation, resulting in well-localized pain, while the visceral peritoneum receives autonomic innervation, resulting in poorly localized, referred pain (e.g., foregut pain in the epigastric region). Peritoneal recesses, particularly duodenal, caecal, and intersigmoid, are rare but recognized sites for internal herniation. Finally, the absorptive and permeable nature of the peritoneum is exploited clinically in procedures such as peritoneal dialysis for renal failure and ventriculoperitoneal shunts for draining cerebrospinal fluid.