Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Anatomy and Physiology of the Digestive System
Morphofunctional Features of the Peritoneum

The Abdominal cavity, cavitas abdominis, is the largest body cavity. It is a space bounded by Muscles and lined with the endoabdominal fascia. Its walls are formed by the Diaphragm superiorly; the anterolateral group of Abdominal muscles anteriorly and laterally; the lumbar spine along with the adjacent psoas major and quadratus lumborum muscles posteriorly; and the internal walls of the greater and lesser pelvis, as well as the perineal muscles, inferiorly.

The Peritoneum is a serous membrane that lines the walls of the ABDOMINAL CAVITY AND covers some of the Organs located within it. The peritoneum lining the inner surface of the abdominal wall is called the parietal peritoneum, while that covering the organs within this cavity is called the visceral peritoneum.

The visceral peritoneum covers Internal Organs to varying degrees. There are three TYPES OF RELATIONSHIPS between organs and the serous membrane. In intraperitoneal positioning, an organ is covered by the peritoneum on all sides. These Digestive System organs typically possess a mesentery that anchors them to the posterior abdominal wall and provides mobility. Such organs include The Stomach, Small Intestine (except for the duodenum), Appendix, transverse colon, sigmoid colon, initial part of the rectum, and Spleen. The cecum is an exception: although located intraperitoneally, it lacks a mesentery.

In mesoperitoneal positioning, an organ is covered by the peritoneum on three sides, while the fourth is fused to the abdominal wall via adventitia; Examples include the ascending and descending colons, Liver, and Uterus.

In extraperitoneal positioning, an organ is covered by the peritoneum on only one side, with the remaining three sides surrounded by an adventitial coat. These organs are fixed and immovable. They include the duodenum, Pancreas, Kidneys, Adrenal Glands, and Ureters.

The parietal peritoneum transitions into the visceral peritoneum continuously. This forms a closed, slit-like space known as the peritoneal cavity. It is an irregularly shaped, slit-like space between the parietal and visceral peritoneum, or between individual Regions of the visceral peritoneum, filled with serous fluid. The indefinite shape of the peritoneal cavity is due to the Variability in size, position, and volume of the peritonealized internal organs.

It should be noted that in women, the peritoneal cavity communicates with the external environment through the lumens of the uterine tubes. Consequently, under certain conditions, pathogens can enter the peritoneal cavity via these tubes.

The serous membrane produces a fluid, the volume of which in the peritoneal cavity is 20–30 ml. This fluid is essential for moistening the membrane, which helps reduce friction between internal organs during their displacement. In addition, the fluid helps anchor (hold) them relative to one another.

Derivative structures of the peritoneum include peritoneal ligaments, mesenteries, omenta, and folds.

Peritoneal ligaments are segments of the peritoneum where the parietal layer transitions into the visceral layer, or where the visceral peritoneum passes from one organ to another. Examples of such structures include the coronary and falciform ligaments of the liver, which attach this organ to the diaphragm.

Mesenteries are double folds (duplications) of the peritoneum that connect an organ to the posterior abdominal wall (Fig. 7.16). They contain the Vessels and nerves that supply and innervate the organ. Practically all intraperitoneal organs have their own mesentery (except for the cecum). The largest are the mesenteries of the small intestine and the transverse colon. The ROOT of the transverse mesocolon runs horizontally at the level of the second lumbar vertebra; the root of the mesentery of the small intestine runs from left to right and superiorly to inferiorly, extending from the level of the second lumbar vertebra to the PROJECTION OF THE right sacroiliac joint.

Class="center">

Fig. 7.16. Topographic structures of the peritoneal cavity (sagittal section):

1 — diaphragm; 2 — caudate lobe of the liver; 3 — epiploic foramen; 4 — pancreas; 5 — retroperitoneal space; 6 — duodenum; 7 — peritoneal cavity; 8 — root of the mesentery of the small intestine; 9 — sigmoid colon; 10 — rectum; 11 — rectovesical pouch; 12 — Testis; 13 — tunica vaginalis of testis; 14 — Penis; 15 — prostate; 16 — Pubic Symphysis; 17 — Urinary Bladder; 18 — small intestine; 19 — omental bursa; 20 — parietal peritoneum; 21 — transverse colon; 22 — gastropancreatic fold; 23 — stomach; 24 — lesser sac (vestibule / pre-gastric recess); 25 — lesser omentum; 26 — liver; 27 — Pericardium; 28 — Sternum; 29 — Thymus

An omentum is an elongated mesentery of the stomach, between the layers of which are accumulations of adipose tissue and Blood vessel plexuses. There are the lesser and greater omenta. The lesser omentum extends between The Liver and the lesser curvature of the stomach. The greater omentum originates from the greater curvature of the stomach as a peritoneal fold, descends between the anterior abdominal wall and the intestines almost to the pubic bones, and then turns upward to fuse with the ascending fold. The omentum plays an important protective role in the abdominal cavity by helping to wall off areas of inflammation from unaffected Tissues (it adheres to sites of inflammation and localizes them).

Folds are duplications of the parietal peritoneum formed by underlying Blood Vessels, ducts, and ligaments. For example, the median umbilical ligament extends upward along the midline from the apex of the urinary bladder to the umbilicus, forming the median umbilical fold. This fold encloses the obliterated embryonic urachus.

The peritoneal cavity has two compartments (floors). The boundary between them is the transverse mesocolon. The upper compartment contains the stomach, liver, Gallbladder, spleen, pancreas, and duodenum. Here, a series of slit-like spaces exist between the abdominal wall and the organs. For instance, the right subphrenic recess is a cleft between the diaphragm and the right lobe of the liver; the left subphrenic recess lies beneath the diaphragm to the left of the coronary ligament of the liver. The subhepatic recesses are slit-like spaces located on the visceral surface of the liver. The splenic recess lies beneath the left side of the diaphragm, between it and the spleen. The Vestibule of the omental bursa is located posterior to the lesser omentum. It can be accessed through the epiploic foramen, which lies posterior to the hepatoduodenal ligament.

The lower compartment extends from the transverse mesocolon to the floor of the lesser pelvis. It contains the small and large intestines, the urinary bladder, and in women, the uterus, uterine tubes, and Ovaries. The lower compartment also features A number of slit-like spaces; for example, the right and left paracolic gutters lie between the lateral abdominal walls and the ascending and descending colons, respectively. The rectovesical pouch in men is located in the pelvic cavity. It is bounded anteriorly by the urinary bladder and posteriorly by the anterior wall of the rectum. In women, the lesser pelvis contains two pouches: the rectouterine pouch (pouch of Douglas) and the vesicouterine pouch. These are located where the peritoneum reflects from the uterus onto the rectum and urinary bladder, respectively. The former is situated posterior to the uterus, and the latter anterior to it.