A sagittal section through the abdomen. Visceral and parietal peritoneum is shown, respectively
From the viewpoint of the insertion of a peritoneal dialysis catheter (PDC) from the anterior abdominal wall, the area below the umbilicus should be encouraged, because the ventral mesogastrium is present in the area above the umbilicus. Usually the tip of a PDC is placed at the rectovesical/rectouterine pouch (of Douglas), which is the lowest area of the peritoneal cavity in the upright position (Fig. 11.2). On the other hand, in the supine position, the lowest area of the peritoneal cavity is posterior to the liver and spleen.
A schematic representation of the peritoneal sac (cavity). A peritoneal catheter is in place
In the physiological condition, the visceral peritoneum and parietal peritoneum are in contact. When massive ascites occurs, or peritoneal dialysate is administered, the peritoneal sac functions as a “peritoneal cavity” (Fig. 11.3). The peritoneal cavity is entirely closed in the male, while it is connected to the outside through the oviduct and uterus at the free end of the oviduct in the female. Therefore, bloody effluent fluid is occasionally observed in female peritoneal dialysis patients during menstruation.
A schematic representation of the development of embryo and peritoneal cavity between embryonic 3–4 weeks. (a) The early phase of embryonic third week. Intraembryonal mesoderm is divided into three parts: paraxial mesoderm, intermediate mesoderm, and lateral plate mesoderm. (b) The late phase of embryonic third week. The lateral mesoderm causes the intercellular cleft, which divides the lateral mesoderm into two layers, the parietal layer and the visceral layer. (c) The early phase of embryonic fourth week. Lateral folding makes the embryonic body cylindrical. (d) The and of embryonic fourth week. The formation of the peritoneal cavity as a closed space is completed by conglutination of the lateral body wall in the midline
As mentioned above, what connects the parietal and visceral peritoneum is the mesentery, the structure formed by the double-ply serosal membrane. The mesentery, which connects the organs, is called a “ligament,” and that which directly contacts with the stomach is called the “omentum.” These mesenteries, or superimposed peritonea, allow blood vessels and nerves to pass through (Table 11.1).
Superimposed peritoneum and intraperitoneal vasculature
Round ligament (remnant of the umbilical vein)
Short gastric artery/vein
Right gastroepiploic artery/vein
Small intestinal mesentery
Superior mesenteric artery/vein
Middle colic artery/vein
Inferior mesenteric artery/vein
Hepatogastric ligament (lesser omentum)
Left gastric artery/vein
Hepatoduodenal ligament (lesser omentum)
Proper hepatic artery, portal vein, common bile duct
Median umbilical fold
Remnant of the urachus
Medial umbilical fold
Remnant of the umbilical artery
Lateral umbilical fold
Inferior epigastric artery/vein
Of these double-ply serosal membranes, the greater omentum is a distinctive structure. The greater omentum, which is called the “policeman in the abdomen” (Morison 1906), covers the frontal surface of the peritoneal cavity widely, finds an emergent situation at an early stage, and acts as a defense mechanism, as, for example, by covering a perforating intestine. The greater omentum has on its surface a large number of opalescent spotty microstructures named “milky spots.” A precise description of the milky spots is provided later.
According to Collins, the surface area of the peritoneum (cm2) is 177 × kg body weight (Esperanca and Collins 1966). Other reports, however, suggest that there is considerable individual variation in the surface area (Wegener 1877; Rubin et al. 1988). About 90% of the peritoneum consists of visceral peritoneum (one-third of this consists of mesenterium and omentum), and only 10% is parietal peritoneum (40% of this covers the diaphragm) (Esperanca and Collins 1966) (Fig. 11.2). Moreover, the submesothelial basement membrane is thicker in the parietal peritoneum than in the visceral peritoneum (Jaquet and Sugarbaker 1996). As a result of such conditions, 80% of intra-abdominal fluid is adsorbed from visceral peritoneum in the physiological state (Torres et al. 1978).
Irrespective of its lesser surface area ratio, however, the parietal peritoneum plays not a small part in solute transport during peritoneal dialysis treatment. Alon et al. reported a case of successful peritoneal dialysis treatment after almost total enterectomy (Alon et al. 1988). In addition, Fressner et al. reported the importance of the parietal peritoneum that covers the diaphragm in solute transport of peritoneal dialysis treatment (Fressner and Dedrick 1994).
11.2 Sensory Innervation of the Peritoneum
Sensory nerves are grossly divided into two categories: somatic afferent nerves and visceral afferent nerves. Somatic afferent nerves transmit sharp and focal sensations, whereas visceral afferent nerves transmit dull and abrupt sensations. Accordingly, somatic pain transmitted by somatic afferent nerves is epicritic, and visceral pain transmitted by visceral afferent nerves is protopathic. Sensory nerves that are distributed to the parietal peritoneum are somatic nerves, while those that are distributed to the visceral peritoneum are visceral nerves. Therefore, signs of peritoneal irritation, such as muscular guarding and Blumberg’s sign, which is a typical finding of acute peritonitis, reflect peritoneal damage on the parietal side. From the viewpoint of innervation area, nerves that distribute to the parietal peritoneum are branches of lower intercostal nerves and subcostal nerves; therefore, referred pain that reflects their skin innervation area could be induced in cases of parietal peritoneal damage. Somatic sensory nerves distribute not only to the parietal peritoneum but also to a part of the mesentery (Uchida and Onda 1995); a pain that occurs with drainage of peritoneal solution from the peritoneal cavity is probably due to traction of the mesentery or parietal peritoneum caused by negative pressure around the tip of the peritoneal dialysis catheter.