Abdominal Viscera
The viscera of the abdomen proper include the stomach, intestine, liver and biliary system, pancreas, spleen, kidneys, ureters, and suprarenal glands. Most of the stomach and intestine is anchored to the body wall by peritoneal mesentery, whereas the three paired glands (kidneys, suprarenals, and gonads before birth) lie retroperitoneally. The general relationships are shown in figures 26-1, 26-2, 26-3 and 26-4. The positions of the abdominal viscera vary with the individual and with gravity, posture, respiration, and degree of filling. Radiological studies have shown that "the normal abdominal viscera have no fixed shapes and no fixed positions, and every description of them must be qualified by a statement of the conditions existing at the time of observation. Moreover, profound change may be caused not only by mechanical forces but also by mental influences" (A. E. Barclay). Organs tend to descend when a subject is in the erect position, and the most mobile organs are those attached by mesenteries.
The following structures can sometimes be palpated in normal subjects: pulsations of the abdominal aorta, the lumbar vertebrae, the lower pole of the right kidney, possibly the liver, and occasionally the spleen. The body of the uterus can be palpated bimanually.
Peritoneum
The peritoneum is a smooth, glistening, serous membrane that lines the abdominal wall as the parietal peritoneum and is reflected from the body wall to various organs, where, as visceral peritoneum, it forms an integral part as the outermost, or serosal, layer. The pericardium, pleura, and peritoneum have a similar arrangement in the parietal and visceral layers, with a cavity between. The extraperitoneal tissue external to the parietal peritoneum is carried with the reflections to the organs and becomes a part of the serosal layer. Organs, like most of the intestine, that are almost completely invested by peritoneum are connected to the body wall by a mesentery. Other viscera, however, such as the kidneys, are retroperitoneal; i.e., they lie on the posterior abdominal wall and are covered by peritoneum only anteriorly.
The peritoneal cavity contains merely a thin film of fluid. The peritoneal cavity is completely closed in the male, whereas, in the female, it communicates with the uterine tubes and hence indirectly with the exterior of the body.
The peritoneum minimizes friction, resists infection, and stores fat. It allows free movement of the abdominal viscera. In response to injury or infection (peritonitis), it exudes fluid and cells and tends to wall off or localize infection.
The parietal peritoneum is supplied by nerves (e.g., phrenic and thoraco-abdominal) to the adjacent body wall, and most of it is very sensitive to pain. Painful stimuli to the central part of the diaphragmatic peritoneum are referred to the shoulder. The visceral peritoneum is insensitive.
General arrangement of peritoneum
The peritoneal reflection to the jejunum and ileum is termed the mesentery, whereas those to the colon are each known as a mesocolon. Some reflections are termed ligaments or folds, e.g., gastrohepatic ligament or rectouterine fold. Most such ligaments contain blood vessels, and most folds are raised by underlying vessels in their free edges. A broad peritoneal sheet or reflection is termed an omentum (the Greek word for which is epiploon). The general arrangement of the peritoneum is shown in figures 26-2, 26-3, 26-4 and 26-5.
Greater Sac.
An incision through the anterior abdominal wall and parietal peritoneum enters that part of the peritoneal cavity known as the greater sac. This extends from the diaphragm to the pelvic floor. Above the umbilicus, its anterior wall presents the falciform ligament, which contains the ligamentum teres (obliterated umbilical vein) in its free margin. Below the umbilicus, the anterior wall of the greater sac contains five folds: (1) the median umbilical fold (containing the urachus), which extends from the urinary bladder to the umbilicus; (2) two medial umbilical folds (each containing an obliterated umbilical artery), which extend from the sides of the bladder to the umbilicus; and (3) two lateral umbilical folds (each containing an inferior epigastric artery), which extend from the deep inguinal ring to the arcuate line. Three depressions on each side of the median plane are produced by the umbilical folds (see fig. 25-9).
The greater omentum
The greater omentum is a prominent peritoneal fold that hangs down from the stomach anterior to the transverse colon, to which it is attached. The greater omentum is a double fold that connects the stomach to the posterior abdominal wall (figs.26-6 and26-7), being derived from the dorsal mesogastrium in the embryo. The greater omentum is fused behind with, but is separable from, the transverse colon and mesocolon. If the greater omentum is elevated, the coils of the small intestine can be examined and the mesentery can be traced to its root. The root of the mesentery extends from the duodenojejunal flexure (above and to the left) to the ileocolic junction (below and to the right) (fig.26-6). If the greater omentum is followed to the transverse colon, the transverse mesocolon can be traced back to the posterior abdominal wall (see fig.26-5B). Hepatic and splenic flexure mark the beginning and end of the transverse colon, which lead to the ascending and descending colon, respectively. These usually have no mesocolon (i.e., they are secondarily retroperitoneal), although the ascending colon appears to be more mobile in vivo than is generally appreciated. The descending colon becomes the sigmoid colon distally, which has a mesentary called the sigmoid mesocolon. The attachment of the sigmoid mesocolon to the posterior abdominal wall is often shaped like an inverted V, the apex being at the pelvic brim, in anterior to the left ureter.
Traced superiorly from the umbilicus, the falciform ligament is found to be reflected onto the diaphragmatic surface of the liver (see fig. 28-3B), thereby preventing a hand placed between the liver and the diaphragm from passing from anterior to posterior or from right to left sides. The peritoneal reflection from the diaphragm to the liver diverges and forms the anteiror (upper) layer of the coronary ligament on the right and the anterior layer of the left triangular ligament on the left (see fig. 28-3C). The subdiaphragmatic portions of the greater sac on each side of the falciform ligament are known as the right and left subphrenic spaces, respectively, and are important clinically because abscesses may form there. Inferior to the coronary ligament, the recess of the greater sac between the liver and the right kidney is known as the hepatorenal pouch (fig. 26-6).
The fundus of the gallbladder is usually visible at the anteroinferior border of the liver. Traced upward, the gallbladder leads to the lesser omentum, which extends between the liver and (1) the stomach (gastrohepatic ligament), and (2) the duodenum (hepatoduodenal ligament). The free edge of the lesser omentum is its right border, which lies immediately anterior to the epiploic foramen opening into the lesser sac.
Lesser sac.
The lesser sac is an irregular part of the peritoneal cavity that lies mostly posterior to the stomach and lesser omentum (see figs. 26-3, 26-4 and 26-5). It communicates with the greater sac by the so-called epiploic foramen, which can be found by running a finger along the gallbladder to the free edge of the lesser omentum. Two fingers can usually be inserted into the opening. The epiploic foramen, which is the opening from the greater into the lesser sac, lies immediately posterior to the free, right edge of the lesser omentum. A finger in the opening and a thumb in front of the omentum would encircle the bile duct (at the right), the hepatic artery (at the left), and the portal vein posterior and between them). The inferior vena cava is situated posterior to the epiploic foramen, the liver is superior, and the first part of the duodenum is inferior (see fig. 26-3A).
The anterior wall of the lesser sac is formed by the peritoneum of (1) the lesser omentum, (2) the posterior surface of the stomach, and (3) the anterior two layers of the greater omentum (see fig. 26-5B). The posterior wall of the lesser sac is formed by (1) the peritoneum that covers the diaphragm, pancreas, left kidney and suprarenal gland, and duodenum and (2) the posterior two layers of the greater omentum (see fig.26-5B). The lesser sac can be entered surgically by penetrating (1) the lesser omentum, (2) the greater omentum between the stomach and transverse colon, or (3) the fused greater omentum and transverse mesocolon (see fig.26-4).
The superior recess of the lesser sac extends posterior to the liver, being invaginated by the caudate lobe (fig.26-4). Most of the lesser sac (the omental bursa of the embryo) lies posterior to the stomach.
A number of minor peritoneal folds, fossae, and recesses may be present, especially around the duodenum and cecum.
Development of the peritoneum (figs.26-5 and 26-8)
The stomach and intestine (gut tube) in the embryo are attached by a continuous mesentery to the posterior abdominal wall. This dorsal mesentery persists into adulthood in only every second portion of the gastro-intestinal canal, namely: in the stomach as the greater omentum; not in most of the duodenum; in the jejunum and ileum as the mesentery; seemingly not in the ascending colon; in the transverse colon as the transverse mesocolon; usually not in the descending colon; in the sigmoid colon as the sigmoid mesocolon; and not in the rectum. The embryonic dorsal mesentary of the duodenum, ascending and descending colons fuse mosre or less completely with the parietal peritoneum of the posterior abdominal wall. Therfore these organs are more-or-less firmly bound to the posterior wall and these organs are said to be "secondarily retroperitoneal." These organs may be mobilized by developing this plane of fusion which would not require transecting any major blood vessels since these would follow the plane of the embryonic mesentary.
The embryonic ventral mesentery, which is limited to the foregut, is more complicated. It is usually stated that the liver grows ventrally from the diaphragm into the ventral mesentary, thereby dividing it into (1) a portion from the anterior abdominal wall to the liver, i.e., the falciform ligament, and (2) a part from the liver to the stomach and duodenum, i.e., the lesser omentum. The complicated rotation and fixation of the intestine are summarized in figure 26-8. The general term "malrotation" is used for various anomalies of these processes.
Questions
26-1 What are the serous membranes?
26-2 How does the peritoneal cavity communicate with the exterior of the body?
26-3 What is the relationship of the transverse colon to the greater omentum?
26-4 What is the extent of the root of the mesentery?
26-5 Where may a subphrenic abscess be found?
26-6 What are the attachments of the lesser omentum?
26-7 What is the lesser sac of the peritoneum and how may it be approached surgically?
26-8 What and where is the epiploic foramen?
26-9 What is malrotation of the intestine?
Figure legends
Figure 26-1 General relations of abdominal viscera. In A, most of the small intestine and transverse colon, as well as the sigmoid colon and rectum, has been removed. The liver and spleen are visible above the right and left flexures of the colon, respectively. The transpyloric and the right and left lateral planes are indicated. In B, the position of the kidneys and ureters is shown. In C, which is a posterior view, the kidneys and spleen are represented. The right twelfth rib is shorter here than the left. Q represents the portion of the quadratus lumborum not under cover of S, the erector spinae.
Figure 26-2 Right and left lateral aspects of the trunk, showing the topography of the viscera. The clavicles and parts of ribs 2, 8, and 10 are shown. In the thorax, the outlines of the pleurae (interrupted line) and lungs are provided. In the abdomen, the peritoneum and peritoneal cavity are shown. In A, the liver (L), kidney (K), right flexure, and ascending colon can be seen. In B, the liver (L), stomach (St.), spleen (Sp.), kidney (K), left flexure, and descending colon can be seen. M, midaxillary line. (After Pernkopf.)
Figure 26-3 Horizontal sections through the abdomen. In A, the liver, right and left kidneys (R.K., L.K.), pancreas (P.), spleen (Sp.), and stomach (St.) are shown, as well as the aorta (Ao.) and splenic artery, inferior vena cava (I.V.C.), portal vein (P. V.), bile duct, and hepatic artery. The greater sac of the peritoneal cavity (around the liver, for example) can be traced through the epiploic foramen (arrow) into the lesser sac between the stomach and pancreas. L. V., lumbar vertebra. (After Symington.) B represents the principle of the arrangement of the peritoneum and its mesenteries.
Figure 26-4 Median section through the abdomen to show the peritoneal cavity. The lesser sac is situated behind the stomach and in front of the pancreas. The caudate lobe invaginates the lesser sac. Below the liver, the stomach, transverse colon, and small intestine are seen in section. The greater omentum and transverse mesocolon are fused posteriorly. The arrows indicate surgical approaches to the lesser sac. The relations in the pelvis are shown also in fig. 31-9.
Figure 26-5 Sagittal schemes of the greater omentum and transverse mesocolon (A) prenatally and (B) in the adult. The numerous short lines in 8 represent sites of fusion.
Figure 26-6 The attachments of the peritoneum to the posterior abdominal wall, viewed from in front. HR, the hepatorenal pouch. R and L, right and left subphrenic spaces. X, the superior recess of the lesser sac.
Figure 26-7 The attachments of the peritoneum to the abdominal viscera, viewed from behind. This is a mirror image of the previous view. The peritoneum on the back of the anterior abdominal wall has not been colored. A vertical segment of the transverse mesocolon and greater omentum has been removed. LO, the lesser omentum.
Figure 26-8 Scheme of mesenteric attachments and of the rotation of the gut. A, Early fetal period. Note that the colon crosses ventral to the duodenum. The small intestine is being reduced, that is, withdrawn into the abdominal cavity through the umbilical ring. B, Slightly later in the fetal period. The intestine is completely reduced. The axis of rotation of the gut is the superior mesenteric artery. C, The fixation of mesenteries in the adult. Note that every second part of the alimentary canal retains a mesentery.