The peritoneum CONTENT OUTLINE Introduction Layers of peritoneum Nerve supply to the peritoneum Functions of the peritoneum Peritoneal reflections Subdivisions of the peritoneal cavity Epiploic foramen of Winslow Peritoneal folds Classification of abdominal structures Clinical applications Introduction • Peritoneum is the serous membrane that forms the lining of the abdomino-pelvic cavity • It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mesothelium supported by a thin layer of connective tissue. • Supports the abdominal organs and serves as a conduit for their blood vessels, lymph vessels, and nerves. Layers • Two layers of peritoneum and a potential space between them are referenced: • The outer layer, the parietal peritoneum, is attached to the abdominal wall and the pelvic walls. • The tunica vaginalis the serous membrane covering the male testis is derived from the vaginal process, an outpouching of the parietal peritoneum. The visceral peritoneum, • The inner layer, is wrapped around the visceral organs, located inside the intraperitoneal space for protection . • It is thinner than the parietal peritoneum. • The potential space between the visceral and parietal layers is the peritoneal cavity Peritoneal fluid • A small amount (about 50 mL) of slippery serous fluid that allows the two layers to slide freely over each other. • Physical characteristics – the normal appearance of a sample of peritoneal fluid is usually straw- colored/pale yellow and clear. • Abnormal appearances may give clues to conditions or diseases present and may include: Yellow with liver disease, milky from obstruction of the lymphatic system, and greenish from bile. Nerve Supply of the Peritoneum • The parietal peritoneum is sensitive to pain, temperature, touch, and pressure. • The parietal peritoneum lining the anterior abdominal wall is supplied by the lower six thoracic and first lumbar nerves that is, the same nerves that innervate the overlying muscles and skin. Contd • The central part of the diaphragmatic peritoneum is supplied by the phrenic nerves; • peripherally, the diaphragmatic peritoneum is supplied by the lower six thoracic nerves. • The parietal peritoneum in the pelvis is mainly supplied by the obturator nerve, a branch of the lumbar plexus. Nerve supply to visceral peritoneum • The visceral peritoneum is sensitive only to stretch and tearing and is not sensitive to touch, pressure, or temperature. • It is supplied by autonomic afferent nerves that supply the viscera or are traveling in the mesenteries. • Overdistention of a viscus leads to the sensation of pain. The mesenteries of the small and large intestines are sensitive to mechanical stretching. Functions of the Peritoneum • Movement of particulate matter in the cavity • The peritoneal coverings of the intestine tend to stick together in the presence of infection. The greater omentum, which is kept constantly on the move by the peristalsis of the neighboring intestinal tract, may adhere to other peritoneal surfaces around a focus of infection. In this manner, many of the intraperitoneal infections are sealed off and remain localized (see clinical notes). Contd • The peritoneal folds play an important part in suspending the various organs within the peritoneal cavity and serve as a means of conveying the blood vessels, lymphatics, and nerves to these organs. • Large amounts of fat are stored in the peritoneal ligaments and mesenteries, and especially large amounts can be found in the greater omentum. Peritoneal reflections • See diagrams • Transverse sections show reflections from organs to the sides of the walls • Sagittal section shows reflections on the anterior and posterior walls Subdivisions of the peritoneal cavity • There are two main regions of the peritoneal cavity: • The greater sac (or general cavity of the abdomen), represented in red in the diagrams above. • The lesser sac (or omental bursa), represented in blue. • The two are connected by the epiploic foramen (also known as the omental foramen or foramen of Winslow): Contd • Supracolic and infracolic regions • Boundary : the transverse mesocolon Boundaries of epiploic foramen • Anteriorly: Free border of the lesser omentum, the bile duct, the hepatic artery, and the portal vein • Posteriorly: Inferior vena cava • Superiorly: Caudate process of the caudate lobe of the liver • Inferiorly: First part of the duodenum Peritoneal folds • Are omenta, mesenteries and ligaments • They connect organs to each other or to the abdominal wall. • The mesentery is the part of the peritoneum through which most abdominal organs are attached to the abdominal wall and supplied with blood and lymph vessels and nerves. Greater and lesser omentum • The lesser omentum (or gastrohepatic) is attached to the lesser curvature of the stomach and the liver. • The greater omentum (or gastrocolic) hangs from the greater curve of the stomach and loops down in front of the intestines before curving back upwards to attach to the transverse colon. • In effect the greater omentum is draped in front of the intestines like an apron and may serve as an insulating or protective layer- “Policeman of the abdomen”. Greater omentum The omenta Sources Structure From To Contains Greater right and left Dorsal Greater curvature of Transverse gastroepiploic mesentery omentum stomach (and colon vessels and fat spleen) Short gastric Gastrosplenic artery, Left Stomach Spleen ligament gastroepiploic artery Gastrophrenic Left inferior Stomach Diaphragm ligament phrenic artery Right Gastrocolic Transverse Stomach gastroepiploic ligament colon artery – Splenorenal Splenic artery, Spleen Kidney ligament Tail of pancreas The right free Contd margin-hepatic artery, portal vein, and bile duct,lymph Lesser nodes and the Ventral curvature of the Lesser omentum Liver lymph mesentery stomach (and vessels,hepatic duodenum) plexus of nerve,all enclosed in perivascular fibrous sheath. Hepatogastric Right and left Stomach Liver ligament gastric artery Hepatic artery proper, hepatic Hepatoduodenal Duodenum Liver portal vein, bile ligament duct, autonomic nerves Mesenteries Sources Structure From To Contains Superior mesenteric artery, accompanying Small intestine veins, autonomic Posterior Dorsal mesentery Mesentery proper (jejunum and nerve plexuses, abdominal wall ileum) lymphatics, 100– 200 lymph nodes and connective tissue with fat Transverse Posterior Transverse colon Middle colic mesocolon abdominal wall Sigmoid arteries Sigmoid Sigmoid colon Pelvic wall and superior mesocolon rectal artery Mesentery of Appendicular Mesoappendix Appendix ileum artery Other ligaments and folds Sources Structure From To Contains Round Thoracic ligament of Ventral Falciform diaphragm, Liver liver, mesentery ligament anterior paraumbilical abdominal wall veins Round Left umbilical ligament of Liver Umbilicus vein liver Ventral Coronary Thoracic Liver mesentery ligament diaphragm Ligamentum Ductus venosus Liver Liver venosum Phrenicocolic Left colic Thoracic ligament flexure diaphragm Contd Left triangular Ventral ligament, right Liver mesentery triangular ligament Umbilical folds Urinary bladder Ileocecal fold Ileum Cecum Mesovarium, Broad ligament Uterus Pelvic wall mesosalpinx, of the uterus mesometrium Ovarian Uterus Inguinal canal ligament Suspensory ligament of the Ovary Pelvic wall Ovarian artery ovary Pouches Sexes possessing Name Location structure Between rectum and Rectovesical pouch Male only urinary bladder Between rectum and Rectouterine pouch Female only uterus Between urinary Vesicouterine pouch Female only bladder and uterus Pararectal fossa Surrounding rectum Male and female Surrounding urinary Paravesical fossa Male and female bladder Peritoneal Recesses, Spaces, and Gutters Duodenal Recesses: • these are close to the duodenojejunal junction • small pocketlike pouches of peritoneum • Named the – superior duodenal – inferior duodenal – paraduodenal, and – retroduodenal recesses. Cecal Recesses • These are close to the cecum • three peritoneal recesses called the superior ileocecal, the inferior ileocecal, and the retrocecal recesses The intersigmoid recess • is situated at the apex of the inverted, V- shaped root of the sigmoid mesocolon • its mouth opens downward. Subphrenic Spaces • The right and left anterior subphrenic spaces lie between the diaphragm and the liver, on each side of the falciform ligament • The right posterior subphrenic space lies between the right lobe of the liver, the right kidney, and the right colic flexure • The right extraperitoneal space lies between the layers of the coronary ligament and is therefore situated between the liver and the diaphragm Paracolic Gutters • The paracolic gutters lie on the lateral and medial sides of the ascending and descending colons • The subphrenic spaces and the paracolic gutters are clinically important because they may be sites for the collection and movement of infected peritoneal fluid (see clinical notes) Classification of abdominal structures • The structures in the abdomen are classified as: – intraperitoneal, – retroperitoneal or infraperitoneal depending on whether they are covered with visceral peritoneum and whether they are attached by mesenteries (mensentery, mesocolon). Infraperitoneal / Intraperitoneal Retroperitoneal Subperitoneal Stomach, First part of the duodenum [5 cm], The rest of the jejunum, ileum, duodenum, ascending cecum, appendix, colon, descending Rectum (lower 1/3) transverse colon, colon, rectum (middle sigmoid colon, 1/3) rectum (upper 1/3)