Peritoneum. Omenta. Abdominal cavity

Abdominal cavity (cavitas abdominis) is the largest cavity of the human body. It is located between the thoracic cavity and the pelvis.

Peritoneum (peritoneum) is a serous coat lining the walls of the abdominal cavity and covering some organs located in it. It secretes and absorbs serous fluid.

The peritoneum is divided into 2 layers:

1. Parietal layer, which covers the internal surface of the abdominal wall

2. Visceral layer, which covers the organs of the abdominal cavity.

The space between the sheaths is called the peritoneal cavity (cavitas peritonealis). This cavity is filled with serous fluid.

The peritoneum forms various spaces inside the abdominal cavity, separating the organs from each other.

Abdominal cavity (cavitas abdominalis) is a space that is delimited by the endo-abdominal fascia (fascia endoabdominalis).

Endo-abdominal fascia (fascia endoabdominalis)

Space located behind the peritoneum is called the retroperitoneal space (spatium retroperitoneale).

Retroperitoneal space (spatium retroperitoneale)

Space located in the area of the urinary bladder is called the anteroperitoneal space (spatium anteroperitoneale).
Space located below the peritoneum is called the subperitoneal space (spatium subperitoneale)

There are three options for covering the visceral peritoneum of internal organs.

The intraperitoneal location means that the organ is covered with the peritoneum from all sides. Examples: stomach, ileum, jejunum, caecum, appendix, transverse colon, sigmoid colon, and initial part of the rectum.
The mesoperitoneal location means that the organ is covered with the peritoneum on three sides. Mesoperitoneal organs include the ascending colon, descending colon, the middle part of the rectum, liver, filled urinary bladder and gallbladder, as well as uterus.
The extraperitoneal location means that the organ is covered with the peritoneum on only one side.

Let’s consider a number of derivatives of the peritoneum.

Ligaments of the peritoneum
Mesenteries
Omenta
Folds

Mesenteries are double-sheath ligaments, or duplicators of the peritoneum, fixing the organ and serving as conductors of vessels and nerves. It should be remembered that the organ with the mesentery is always located intraperitoneally.

The root of the mesentery is the place where the mesentery of an organ is fixed to the posterior wall of the abdominal cavity.

Let’s take a closer look at where the roots of the mesenteries of various organs are located.

Root of the mesentery of the transverse colon (radix mesocolon transversum) begins on the right at the level of the 2nd lumbar vertebra and ends on the left at the level of the 1st lumbar vertebra.
Root of the mesentery of the jejunum and ileum (radix mesenterii) arises from the 2nd lumbar vertebra and ends in the projection of the right sacro-iliac joint.
Root of the mesentery of the sigmoid colon (radix mesocolon sigmoidei) is attached to the left at the level between the 4th and 5th lumbar vertebrae.

Root of the mesentery of the jejunum and ileum (radix mesenterii)

Root of the mesentery of the rectum (radix mesorecti) is attached at the level between the 1st and 3rd sacral vertebrae.
Root of the mesentery of the vermiform process (radix mesoappendicis) is attached to the terminal part of the ileum.

The omentum is an elongated mesentery of the stomach, between the sheaths of which there are accumulations of adipose tissue in the form of lobules, as well as plexuses of blood vessels.

There are two omenta in the human body:

Greater omentum
Lesser omentum

Let’s consider them in greater detail.

The lesser omentum (omentum minus) is a duplication of the peritoneum stretched between the liver, the small curvature of the stomach and the superior part of the duodenum.

It consists of two ligaments that pass into one another:

Hepatogastric ligament (lig. hepatogastricum)

Hepatogastric ligament (lig. hepatogastricum)

Hepatoduodenal ligament (lig hepatoduodenale). The portal vein, proper hepatic artery, common bile duct, lymphatic vessels, and nerves pass through its thickness.

Hepatoduodenal ligament (lig hepatoduodenale)

Greater omentum (omentum majus) is an elongated dorsal mesentery of the stomach.

It consists of three ligaments:

Gastrocolic ligament (lig. gastrocolicum), which connects the stomach and transverse colon.

Gastrocolic ligament (lig. gastrocolicum)

Gastrosplenic ligament (lig. gastrolienale / gastrosplenicum), which connects the stomach and spleen.

Gastrosplenic ligament (lig. gastrolienale / gastrosplenicum)

Gastroprhenic ligament (lig. gastrophrenicum), which connects the stomach and the diaphragm.

Gastroprhenic ligament (lig. gastrophrenicum)

Peritoneal folds are duplications of the parietal peritoneum formed by vessels, ducts, ligaments, or fat deposits passing under it.

The following structures are located on the anterior abdominal wall:

Median umbilical fold (plica umbilicalis mediana), which contains the median umbilical ligament (lig. umbilicale medianum), which is a closed urinary duct of the fetus (urachus).

Median umbilical fold (plica umbilicalis mediana)

Medial umbilical fold (plica umbilicalis medialis) contains the medial umbilical ligament (lig. umbilicale medianum), which is a closed umbilical artery (a. umbilicalis).

Medial umbilical fold (plica umbilicalis medialis)

Lateral umbilical fold (plica umbilicalis lateralis) contains the inferior epigastric arteries and veins.

Lateral umbilical fold (plica umbilicalis lateralis)

On the internal surface of the anterior abdominal wall, above the inguinal ligament, three pairs of pits are present between the above mentioned folds

Supravesical fossae (fossa supravesicalis), which are located on the sides of the medial umbilical fold.

Supravesical fossae (fossa supravesicalis)

Medial inguinal fossa (fossa inguinalis medialis), which is located medial to the lateral umbilical fold and corresponds to the external opening of the inguinal canal.

Medial inguinal fossa (fossa inguinalis medialis)

Lateral inguinal fossa (fossa inguinalis lateralis), which is located laterally to the lateral umbilical fold and corresponds to the internal opening of the inguinal canal.

Lateral inguinal fossa (fossa inguinalis lateralis)

Under the inguinal ligament, there is another fossa called the femoral fossa (fossa femoralis). It corresponds to the internal opening of the femoral canal.

Let’s go even lower, into the lesser pelvis. The following structures are present in the lesser pelvis:

Rectovesical fold (plica rectovesicalis) in men
Recto-uterine fold (plica rectouterina) and vesico-uterine fold (plica vesicouterina) in women.

There are also fossae (or depressions) on the posterior wall of the peritoneal cavity. Retroperitoneal hernias may form in them.

The superior duodenal recess (recessus duodenalis superior)

and the inferior duodenal recess (recessus duodenalis inferior) are located near the duodenojejunal flexure

Behind the cecum, there is the retrocaecal recess (recessus retrocaecalis).

An intersigmoid recess (recessus intersigmoideus) is located near the sigmoid colon.

In addition, the so-called floors can be distinguished in the peritoneal cavity. According to the conventional classification, there are two floors: upper and lower. The border between them is the transverse colon and its mesentery.

There are three so-called bursae on the upper floor:

The hepatic bursa (bursa hepatica), which contains the right lobe of the liver. It has a subphrenic recess (recessus subphrenicus)

and a subhepatic space (recessus subhepaticus)

The pregastric bursa (bursa pregastrica) is located anteriorly to the stomach and lesser omentum

The omental sac (bursa omentalis) is located posteriorly to the stomach and lesser omentum.

It contains three recesses:

Superior omental recess (recessus omentalis superior)

Inferior omental rece (recessus omentalis inferior)

Splenic recess (recessus lienalis)

The omental bursa communicates with the hepatic bursa by the omental (or Winslow) foramen (foramen epiploicum)

In the inferior floor of the peritoneal cavity, there are two lateral canals and two mesenteric sinuses.

Right lateral canal (canalis lateralis dexter) is located between the right wall of the abdomen and the ascending colon.

Left lateral canal (canalis lateralis sinister) is located between the left wall of the abdomen and the descending colon.

The root of the mesentery of the small intestine divides the lower floor into the right mesenteric sinus (sinus mesentericus dexter)

and the left mesenteric sinus (sinus mesentericus sinister).

The right sinus is closed, and the left one communicates with the pelvic cavity inferiorly.

Where the peritoneum passes from the bladder to the rectum, men have the recto-vesical pouch (excavatio rectovesicalis)

In women, the peritoneum, passing from the bladder to the uterus, forms the vesico-uterine pouch (excavatio vesicouterina),

and moving from the uterus to the rectum it forms the recto-uterine pouch (excavatio rectouterina)

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