Introduction
The abdominal cavity is enclosed by the nal walls and is completely filled by the abdomi-nal viscera. The abdomiabdomi-nal viscera include the stomach and intestines, their associated glands and ducts (liver and pancreas), blood and lymph vessels, the spleen, the kidneys, and the supra renal glands. The kidneys, the ureters, and the supra-renal glands lie on the posterior abdominal wall, posterior to the fascia lining the abdominal cavity.
The other structures lie anterior to this fascia and are surrounded to a greater or lesser extent by the peritoneal cavity.
The peritoneum is a tough layer of elastic areo-lar tissue lined with simple squamous epithelium.
It lines the largest of the serous sacs of the body—
the peritoneal cavity. It is similar to the pleura and pericardium in consisting of parietal and vis-ceral layers which enclose the peritoneal cavity, and are separated from each other by a thin film of peritoneal fluid. This fluid lubricates the smooth peritoneal surfaces and facilitates movement of those parts of the abdominal viscera which are en-sheathed by the visceral layer.
The parietal peritoneum is a simple layer on the internal surface of the abdominal walls. The visceral peritoneum is more complex in ar-rangement. It surrounds many segments of the intricately folded and tightly packed gut tube, the liver, and the spleen. The organs surrounded by the visceral peritoneum are referred to as intraperi-toneal. The visceral peritoneum also forms mesen-teries (sometimes called ligaments) which connect intraperitoneal organs to the body wall. Note that
Fig. 11.1 A diagram to show the arrangement of the parietal peritoneum lining the abdominal cavity and the visceral peritoneum on the gut tube and mesentery. Note the structures which lie behind the peritoneum—the retroperitoneal structures.
Parietal peritoneum Parietal peritoneum Visceral peritoneum around gut tube
Visceral peritoneum forming mesentery
A P R L Parietal
peritoneum
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The abdominal cavity
Posterior to the peritoneal cavity, there are three distinct layers of structures, each with its own blood and lymph vessels and nerves. From behind forwards, these are:
1. The posterior abdominal wall, consisting of the vertebral column and the muscles attached to it [see Fig. 10.1]. It contains the lumbar vessels and nerves. (The posterior abdominal wall is described in Chapter 13.)
2. On the posterior abdominal wall, but deep to its fascial lining, lie the kidneys, ureters, suprare-nal glands, and great vessels—the abdomisuprare-nal aorta and inferior vena cava. The aorta and inferior vena cava lie on the anterior surface of the vertebral column [see Figs. 11.13, 11.59]. The kid-neys, suprarenals, and their ducts lie on either side of the vertebral column. The gonads are displaced downwards from this layer, but their blood and lymph vessels and nerves still traverse it, as do the paired suprarenal and renal vessels.
3. The unpaired gut tube lies in a plane anterior to the kidney, suprarenal, and great vessels.
(i) The retroperitoneal parts of the gut tube (duo-denum, pancreas, ascending and de-scending colon, and their blood vessels) lie posteriorly, immediately anterior to the plane of the kidney.
(ii) The intraperitoneal parts of the gut tube which remain free—the stomach, jejunum, ileum, and of the posterior abdominal wall comes to run
di-rectly over these structures [Fig. 11.2]. These struc-tures are now ‘retroperitoneal’. As a result, the blood and lymph vessels and the nerves which originally ran in these mesenteries now lie on the posterior abdominal wall.
The paired viscera—the suprarenal glands, kid-neys, and gonads—and their vessels lie on the posterior abdominal wall behind the parietal peri-toneum. The retroperitoneal parts of the gut tube (duodenum, ascending colon, descending colon, pancreas) lie anterior to the paired viscera.
See Dissection 11.1 for directions on how to open the peritoneal cavity.
DISSECTION 11.1 Preliminary survey of the peritoneal cavity
Objective
I. To explore the contents of the peritoneal cavity.
Instructions
1. Open into the peritoneal cavity, taking care to avoid cutting any structure within the peritoneum.
2. Take time to explore the peritoneal cavity without damage to the peritoneum or the structures cov-ered by it.
Fig. 11.2 (A) Schematic diagram showing three segments of the gut tube suspended in the peritoneal cavity by mesenteries during early development. (B) In late development, gut segments 2 and 3 and their mesenteries have adhered to the posterior abdominal wall and lie posterior to the parietal peritoneum, anterior to the kidney and other structures associated with the urogenital apparatus. Gut segment 1 remains intraperitoneal and is suspended by its mesentery.
Mesentery 1
Mesentery 1
Mesentery 3
Mesentery 2 Gut segment 1
Gut segment 1 Gut segment 2
Gut segment 2 Gut segment 3
Gut segment 3 A. EARLY DEVELOPMENT
B. LATE DEVELOPMENT
Mesentery 2 Mesentery 3
Kidney
Kidney
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Introduction
into the superior part of the pelvis above the urinary bladder and the uterus and anterior to the rectum [see Figs. 17.5, 17.6]. In the male, the peritoneal cav-ity is a closed sac. In the female, the uterine tubes open into it. A direct communication thus exists in the female between the pelvic cavity and the exte-rior through the uterus and the vagina.
transverse and sigmoid colon—lie most ant-eriorly. They do so by retaining the mesenteries which attach them to the posterior abdominal wall (dorsal mesenteries). They are supplied by unpaired visceral vessels. These are the most mobile parts of the intra-abdominal gut tube and are surrounded by the visceral peritoneum.
The peritoneum surrounding the gut passes to the posterior abdominal wall from a narrow strip on the gut tube. It forms a double-layered fold of peritoneum. This double fold of peri-toneum is called the mesentery, or ligament.
Between the two layers of the fold is a variable amount of extraperitoneal fatty areolar tissue in which blood vessels, lymph vessels, and nerves run to and from the gut tube. Where the layers meet the posterior abdominal wall, they become continuous with the parietal peri-toneum, and the areolar tissue between them is continuous with the extraperitoneal tissue of the abdominal walls.
In addition to the dorsal mesentery which all parts of the free gut tube have, the stomach and proxi-mal 2–3 cm of the duodenum also have a ventral mesentery. The ventral mesentery attaches this part of the gut tube to the anterior abdominal wall.
During development, the liver develops in this ventral mesentery and divides it into two parts.
One part—the lesser omentum—connects the stomach and proximal duodenum to the liver. The other part—the falciform ligament—connects the liver to the anterior abdominal wall. The fal-ciform ligament is the only attachment of the ab-dominal viscera to the anterior abab-dominal wall.
When the anterior abdominal wall is removed, the only parts of the viscera immediately visible are the liver, the free gut tube (stomach, jejunum, ileum, transverse colon, and sigmoid colon), and the ascending and descending parts of the colon [Fig. 11.3].
The cavity of the lesser pelvis extends postero-inferiorly from the abdominal cavity [Figs. 11.4, 11.5]. It lies below the linea terminalis of the bony pelvis. The pelvic cavity is bounded antero-inferiorly by the pubic symphysis, and posteriorly and superi-orly by the curved sacrum and coccyx. The inferior limit of the lesser pelvis is the diamond-shaped peri-neum. A fibromuscular diaphragm—the pelvic dia-phragm—stretches between the pubic symphysis and the coccyx and separates the pelvic cavity from the perineum [Fig. 11.5]. The peritoneal cavity extends
Fig. 11.3 The abdominal viscera after removal of the anterior abdominal wall and the greater omentum. Note that the eighth costal cartilage reaches the sternum in this case.
Stomach 5
6 6
7 7
8 8
9 9
10 10
Liver Transpyloric
plane
Umbilicus Ascending
colon
Transverse colon Subcostal plane
Intertubercular plane Jejunum and ileum
Descending colon
Fig. 11.4 An outline of the abdominal and pelvic cavities as seen in the median section.
Epigastric region Diaphragm
Subcostal plane Vertebral
column Umbilical region
Umbilicus
Intertubercular plane Hypogastric region
Cavity of lesser pelvis
Plane of superior aperture of lesser pelvis
Pubic symphysis
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Fig. 11.5 A sagittal section through the abdomen and pelvis along the inferior vena cava.
Liver Xiphoid process
Lesser sac
1st part of duodenum Inferior vena cava
Levator ani M. (Pelvic diaphragm) Rectum
Sigmoid colon
Urinary bladder Pubic bone
Scrotum