The peritoneum is a serous double-walled membrane that lines the abdominal wall (parietal peritoneum) and is reflected without a continuity solution on the viscera to cover them in varying length (visceral peritoneum), similar to what the pleura does in the chest. . However, the disposition of the pleura is easy to understand when compared to that of the peritoneum. This is mainly because the abdominal viscera undergo, in the course of their development, complex changes before reaching their final shape and position. In these changes the peritoneum is taken with the viscera, undergoing torsions, fusions and coalescences. On the other hand, many abdominal organs are extremely mobile and the peritoneum must be available in order to fix them and, at the same time, allow their mobility.
The infraumbilical anterior parietal peritoneum presents the median umbilical fold, odd and the medial and lateral umbilical folds, even. All of them are produced by the presence of structures in the extraperitoneal tissue:
- median umbilical ligament, resulting from the uracus (embryonic structure that goes from the bladder to the navel) fibrous, produces the median umbilical fold
- the obliterated umbilicals produce the medial umbilical folds, one on each side
- the lower epigastric aa produce the lateral umbilical folds, one on each side
While the median and medial umbilical folds reach the navel, the sides do not.
Between the median umbilical fold and the medial umbilical folds is the supravesical fossa; between the medial and lateral is the medial inguinal fossa and laterally to the lateral umbilical fold is the lateral umbilical fossa.
Above the navel there is also a fold, formed by the sickle cell ligament, which will be seen later.
Among the parietal and visceral leaflets is the peritoneal cavity, virtual in a normal state, but real under certain circumstances, such as air or liquid spills (pneumoperitoneum, hemoperitoneum, bile spills, gastric or intestinal contents, etc.) or artificial air or liquid for diagnostic or treatment purposes. Also, the surgical or traumatic opening of the peritoneum, after sectioning the parietal planes, by allowing air to enter, transforms the peritoneal cavity from virtual to real.
Due to the disposition of the abdominal viscera, as well as their embryonic development, the peritoneum presents some specific formations:
- the mesos that are reflections of the posterior parietal peritoneum, consisting of two laminae, which relate the abdominal wall with its respective viscera, fixing it and at the same time giving it mobility. The space between the two layers of the meso is filled with extraperitoneal tissue, through which vessels, nerves and lymphatics pass towards the viscera. The existing mesos are the mesentery, for the jejunum and ileum, the transverse mesocolon, for the transverse neck and the mesosigmoid, for the sigmoid neck.
- the ligaments that are or double-layered peritoneal reflections that go from the parietal peritoneum (except the posterior, because then they would be mesos) to a viscera or peritoneal reflections between one viscera and another.
- the oments are broad, wide peritoneal reflections, which are arranged between two viscera. The existing oments are the smallest oment between the liver and the smallest curvature of the stomach and the first portion of the duodenum and the largest omentum that goes from the largest curvature of the stomach to the transverse neck and this is disposed as an “apron”, before the intestinal loops. .
These concepts are generalizations and as such, they admit exceptions. Thus, there are ligaments that attach to the posterior wall, such as the lienorenal and posterior lamina of the sickle cell ligament and ligaments called mesos, without leaving the posterior wall, such as the mesoappendix or mesosalpinx.
Abdominal viscera are classified according to their relation to the peritoneum in peritoneal, extraperitoneal and intraperitoneal.
Peritoneal cells are those that are almost completely surrounded by visceral peritoneum, leaving this coating only in a narrow band that corresponds to the region where the meso or ligament is delaminated to cover the viscera, becoming visceral peritoneum.
Extraperitoneal cells are those located outside the parietal peritoneum, which can line one or more sides of the viscera, but without involving it almost completely (in this case it would be peritonized). As a result of the changes that occurred during embryonic development, there are two types of extraperitoneal viscera: the primitively extraperitoneal viscera that, since the beginning of their development were located externally to the peritoneum and the secondly extraperitoneal viscera that were initially peritonized and subsequently became extraperitoneal as a result of the overlap from your meso to the posterior parietal peritoneum. The plates thus in contact (posterior plate of the meso and parietal peritoneum) join and are replaced by a conjunctive plate. The anterior lamina of the meso now becomes part of the posterior parietal peritoneum and the viscera becomes extraperitoneal. This phenomenon of juxtaposition and subsequent replacement is called coalescence and the conjunctive that replaced the peritoneal laminae is called coalescence fascia.
This definitive situation can be artificially reversed (by anatomical or surgical dissection) as the coalescent fasciae allow easy cleavage, which allows the manipulation of the posterior wall of these viscera through an incision in the anterior abdomen wall.
Since most of the extraperitoneal organs are located posterior to the posterior parietal peritoneum, it is common to call them retroperitoneal.
The only intraperitoneal viscera is the ovary, as it is located in the peritoneal cavity. In this region, the cavity is no longer virtual but real. In addition, as the fallopian tube opens both to the peritoneal cavity and to the uterus and it communicates with the vagina, the peritoneal cavity is, in this way, in communication with the external environment. Thus, while in males the peritoneal cavity is closed, in females it is an open cavity, which justifies the fact that infections of the female genital organs reach and involve the peritoneum.
SUPRA AND INFRAMESOCOLIC FLOORS
The peritoneal cavity is divided into supra and inframesocolic stages, separated by the transverse mesocolon and in a third portion, the pelvic portion, located below the upper narrow of the pelvis. The supra and inframesocolic floors will be seen below while the pelvic portion will be seen when studying the pelvis.
It is important to note that the transverse mesocolon is not a mere posteroanterior horizontal septum, as it has an oblique, infero-anterior disposition, and is highly mobile, in such a way that the relationships determined by it vary according to the situation.
The supramesocolic floor contains the liver, stomach, spleen, sickle cell ligament, minor omentum and most of the major omentum. It is subdivided by the liver into subphrenic and subhepatic recesses:
- the right and left subphrenic (or suprahepatic) recesses are virtual spaces between the hepatic visceral peritoneum and the diaphragmatic parietal peritoneum, separated from each other by the sickle cell ligament. The right recess is later limited by the anterior lamina of the coronary ligament, while the left recess is later limited by the left triangular ligament.
- subhepatic (or hepato-renal) recess is located between the peritoneum of the visceral face of the right lobe of the liver and the posterior parietal peritoneum that lines the right kidney. Subsequently, it is limited by the posterior lamina of the coronary ligament.
The inframesocolic floor is divided into upper (or right) and lower (or left) parts by the root of the mesentery and contains the jejunal and ileal loops, framed by the ascending, transverse and descending necks. Lateral to the ascending and descending necks there are two longitudinal depressions, the paracolic grooves.
These compartments and grooves in the peritoneal cavity determine how and where materials (peritoneal fluid, blood, pus, etc.) contained in the peritoneal cavity must accumulate or displace. Accumulations occur at the points of greatest slope, which are the hepatic-renal recess, in both sexes and in the supine position and the retovesical excavation, in males and the rectum uterine excavation, in females. Also the curvatures of the spine contribute to the determination of these points of accumulation, creating natural slopes for the flow. The paracolic grooves and the left division of the inframesocolic floor drain into the pelvis. In addition, the paracolic grooves also drain into the hepatic-renal recess and receive, especially the right, the contents of the omental sac, through the epiplomatic foramen. The right division of the inframesocolic floor is a closed space,
OMENTS AND LIGAMENTS
At the beginning of embryonic development, the primitive intestine has two connections with the body wall. Later it is attached to it by the broad dorsal meso, which runs from the terminal esophagus to the cloacal part of the posterior intestine. Previously it is attached to the ventral meso that exists at the height of the terminal esophagus, stomach and the initial part of the duodenum. The growth of the liver, between the two layers of the ventral meso separates them from each other, transforming them into hepatic visceral peritoneum. What persists from the ventral meso form:
- the sickle cell ligament, between the anterior abdominal wall and the liver. The free, inferior border of the sickle cell ligament contains the umbilical vein, which, after birth, is obliterated and forms the round ligament of the liver.
- the lesser omentum, between the liver, superiorly and the lesser curvature of the stomach and the first portion of the duodenum, inferiorly. The free margin of the minor omentum, right in the adult, contains the bile duct, a. hepatic and v. door and constitutes the anterior wall of the epiplomatic foramen, which gives access to the omental sac. The lesser omentum is usually divided into hepatic-gastric ligaments, between the liver and stomach and hepatic-duodenal ligaments, between the liver and the 1st portion of the duodenum.
- between the liver and the diaphragm the coronary ligament forms. Between its two slides, one anterior (or superior) and another posterior (or inferior) is the naked area of the liver, non-peritonized. The two blades meet on the right, forming the right triangular ligament and on the left, forming the left triangular ligament.
As these structures are all derived from one, the ventral meso, they are continuous with each other. Thus, the sickle cell ligament continues to the right and to the left as the anterior lamina of the coronary ligament and the posterior lamina of this remains as the lesser omentum. Hence some authors claim to be the left triangular ligament formed by the left laminae of the sickle cell ligament and the minor omentum.
Part of the dorsal meso will become attached to the primitive posterior parietal peritoneum as a result of the growth, folding and rotation that the primitive intestine undergoes during its development. What persists forms the mesentery, the transverse and sigmoid mesocoli, the greater omentum and the gastrophrenic, gastrolienal and splenorenal ligaments:
- the greater omentum hangs from the stomach and passes anterior to the transverse neck. Its lateral edges are free, but its anterior wall, formed by two peritoneal laminae, curves posteriorly constituting the posterior wall, which ascends to be fixed in the transverse neck. The embryo consists of four peritoneal laminae (the two anterior and the two posterior), but during development there is a fusion, to a varying degree, of the anterior wall with the posterior one, with the transverse neck and with the transverse mesocolon. The resulting part of these fusions, which goes from the stomach to the transverse neck, is the gastrocolic ligament.
- the gastrophrenic ligament connects the bottom of the stomach and the abdominal esophagus to the diaphragm.
- the gastrolienal ligament extends from the greater curvature of the stomach to the spleen, where its anterior lamina remains as the visceral peritoneum of this organ.
- the splenorenal (or lienorenal) ligament runs from the spleen to the posterior parietal peritoneum related to the left kidney. It is formed by the continuation of the visceral peritoneum of the spleen and the posterior lamina of the gastrolienal ligament.
As a consequence of these changes that occur with the organs and with the ventral and dorsal mesos, the omental sac is formed. It is a virtual space, wide and irregular, located mostly behind the stomach and minor omentum. It is a dependency on the peritoneal cavity with which it communicates through the epiplomatic foramen. This is bordered anteriorly by the free border of the lesser omentum and posteriorly by the posterior parietal peritoneum covering the v. inferior pit. On the left, the omental sac is limited by the gastrolienal and splenorenal ligaments. Inferior it extends into the lower recess of the omental sac, between the anterior wall and the posterior wall of the greater omentum. The dimensions of this recess depend on the degree of fusion of these walls (see description of the greater omentum). Occasionally the lower recess may be isolated from the rest of the omental pouch due to the presence of adhesions. Superiorly the pocket continues between the liver and the diaphragm as the upper recess of the omental pocket.
The peritoneum is a true organ, with its own functions and pathologies. Of its functional characteristics, the main ones are:
- secretion of peritoneal fluid, which reduces friction between the viscera
- resistance to infection by the action of macrophages in the peritoneal fluid and also by its ability to confine an infection. When it is not very intense, the peritoneum, especially through the greater omentum, which moves, isolates it by tamponade and / or adhesion.
- the accumulation of fat, especially in the greater omentum, which acts as a nutritional reserve
- the absorption and elimination of substances to and from the circulation, which can be used in therapeutic processes (peritoneal dialysis, medication administration). This same property explains the absorption of bacterial toxins in cases of serious infections affecting the peritoneum
- the peritoneum is very sensitive, causing severe pain when traumatized, detached or severely distended. The parietal peritoneum is innervated by the nerves of the adjacent walls: the diaphragmatic part by the phrenic nn, the rest by the thoracoabdominal nn and branches of the lumbosacral plexus. The painful stimuli of the parietal peritoneum can be directly related to the stimulated region or can be referred to, such as, for example, the painful stimulation of the central part of the diaphragmatic peritoneum that is referred to in the shoulder. The visceral peritoneum does not present innervation for pain, but feelings of distension or traction can be felt diffusely.