Peritoneum Anatomy
The peritoneum is a
serous membrane with parietal and visceral layers, which encloses a space, the
peritoneal cavity. The parietal peritoneum lines the walls of the abdomen and
pelvis, while the visceral layer covers many of the abdominal and pelvic
organs. In the male, the peritoneal cavity is a closed sac, but in the female,
it communicates with the interior of the uterus and vagina via a microscopic
channel through each uterine tube. Normally, the peritoneal cavity contains
only a few millilitres (mL) of serous fluid, but in certain diseases, serous
fluid can accumulate (ascites), sometimes up to several litres.
The peritoneal cavity comprises the greater and lesser
sacs. The greater sac is very extensive and can be
traced from the diaphragm above into the pelvic cavity below. The omental bursa
(lesser sac) is located in the upper part of the abdomen behind the stomach and
communicates with the greater sac through a narrow opening, the omental
(epiploic) foramen.
The parietal peritoneum is applied to the inner aspect of
the abdominal and pelvic walls (Fig. 4.30) and
continues superiorly across most of the undersurface of the diaphragm. The
peritoneum lining the anterior abdominal wall is raised into several folds or
ridges. Below the umbilicus, the median umbilical
ligament often raises a midline ridge (median umbilical
fold), on each side of which the occluded part of the umbilical artery (medial
umbilical ligament) may produce a further peritoneal fold (medial umbilical
fold) (Fig. 4.31). Above the umbilicus, the round ligament of the liver (Fig. 4.30) is contained in a large fold of peritoneum,
the falciform ligament, which attaches the liver to the anterior abdominal wall
and the diaphragm (Fig. 4.57).
Posteriorly, the peritoneum covers several organs that
lie on the muscles of the posterior abdominal wall (Fig. 4.32). These
retroperitoneal organs include the ascending and descending parts of the colon,
the kidneys, ureters and suprarenal glands, and most of the pancreas and
duodenum. Also lying behind the peritoneum are the aorta and its branches and
the inferior vena cava and its tributaries.
Nerve supply
The parietal peritoneum of the abdominal wall is
innervated by the lower thoracic and first lumbar nerves. Inflammation spreading
from an organ such as the appendix to this peritoneum causes well-localized
pain and tenderness and rigidity of the abdominal muscles. The lower thoracic
nerves also innervate the peritoneum covering the periphery of the diaphragm.
Inflammation of this peritoneum consequently gives rise to pain in the lower
thoracic wall and abdominal wall. By contrast, the peritoneum on the central
part of the diaphragm receives sensory branches from the phrenic nerves (C3, C4
& C5) and irritation here may produce pain referred to the region of the
shoulder (the fourth cervical dermatome; Fig. 3.6).
Most of the abdominal organs have a covering of visceral
peritoneum and are suspended within the abdominopelvic cavity by mesenteries.
Although organs possessing mesenteries are often termed intraperitoneal, they
do not lie within the peritoneal cavity but merely project into it. Mesenteries
consist of double layers of peritoneum containing the vessels and nerves of the
intraperitoneal organs. Typically, a mesentery attaches to the posterior
abdominal wall, where its peritoneal layers are continuous with the parietal
peritoneum. Examples include the mesentery of the small intestine (Fig. 4.35)
and the transverse mesocolon.
The mesenteries of the stomach (the omenta) do not attach
to the abdominal wall but to other organs. The lesser curvature of the stomach is
connected to the liver by the lesser omentum, while the upper part of the
greater curvature is attached to the spleen by the gastrosplenic ligament (Figs
4.37 & 4.38). The major portion of the greater curvature gives attachment
to the greater omentum.
The greater omentum is an apron-like fold of peritoneum
with a free lower border (Fig. 4.33). Hanging behind
the anterior abdominal wall and in front of most of the small intestine, this
omentum is usually a conspicuous feature when the peritoneal cavity is opened.
Superiorly, it attaches to both the transverse colon (Fig. 4.34) and the
greater curvature of the stomach, enclosing the inferior part of the omental
bursa (see below). The free inferior border of the omentum ascends on the right
as far as the first part of the duodenum, while on the left it merges with the
gastrosplenic ligament. The position of the greater omentum is influenced by
previous episodes of intra-abdominal disease because it tends to adhere to
sites of inflammation such as the appendix or gall bladder.
The transverse mesocolon (Fig. 4.35) has a long
horizontal root, attached across the posterior aspect of the abdomen,
principally to the pancreas. This mesocolon slopes downwards and forwards into
the greater sac, dividing it into supracolic and infracolic compartments. Along
its lower margin, close to the anterior abdominal wall, runs the transverse
colon.
Infracolic compartment of the greater sac
This compartment lies below and behind the transverse
mesocolon and is usually covered anteriorly by the greater omentum. The
infracolic compartment consists of right and left spaces separated by the
mesentery of the small intestine (Fig. 4.35). The root of this mesentery begins
to the left of the midline near the transverse mesocolon and slopes downwards
into the right iliac fossa. The mesentery is extensively folded and is attached
to the jejunum and ileum. The left infracolic space communicates directly with
the cavity of the pelvis. By contrast, the right infracolic space is confined
inferiorly by the attachment of the lower part of the mesentery.
Behind the peritoneum on either side of the infracolic
compartment lie the ascending and descending parts of the colon. Lateral to
these are grooves lined by peritoneum, the right and left paracolic gutters (Fig.
4.68).
Another mesentery, the sigmoid mesocolon, lies in the
left lower part of the infracolic compartment. Its root is shaped like an
inverted ‘V’, with its apex overlying the bifurcation of the left common iliac
vessels and the left ureter. Behind the sigmoid mesocolon lies the
intersigmoid recess, which ends blindly at the apex of the ‘V’ but is continuous inferiorly with the
pelvic cavity.
Small folds of peritoneum may produce additional
peritoneal recesses (or fossae) near the ascending duodenum (paraduodenal
recesses) and the caecum (retrocae- cal and ileocaecal recesses). A loop of bowel
can become trapped in a peritoneal recess, producing an internal hernia, which may
lead to intestinal obstruction.
Nerve supply
The autonomic nerves that supply the abdominal organs
also innervate the visceral peritoneum surrounding the organs. Pain conveyed
by these nerves tends to be deeply felt and poorly localized.
Supracolic compartment of the greater sac
The supracolic compartment lies above and in front of the
transverse mesocolon (Fig. 4.36). Its superior part intervenes between the
diaphragm and the liver and is divided by the falciform ligament into two
subphrenic spaces. The compartment includes the deep recess between the right
lobe of the liver and the right kidney (the hepatorenal recess) and extends
across the midline below the left lobe of the liver and in front of the
stomach. Infection within the abdomen or pelvis can spread through the peritoneal
cavity and may accumulate near the liver, producing an abscess. Abscesses
between the diaphragm and the liver are termed subphrenic and those below the liver
subhepatic.
Omental bursa (lesser sac)
The omental bursa is the small part of the peritoneal
cavity behind the stomach (Figs 4.36 & 4.38). It communicates with the
greater sac through a narrow opening, known as the omental or epiploic foramen,
which lies between the first part of the duodenum and the visceral surface of
the liver (Fig. 4.37).
The omental bursa is isolated from the greater sac by the
stomach and several peritoneal folds. One of these folds, the lesser omentum,
connects the lesser curvature of the stomach to the posterior surface of the
liver (Fig. 4.37). Two further folds, the gastrosplenic and splenorenal
(lienorenal) ligaments, attach the spleen to the greater curvature of the
stomach and the left kidney, respectively (Fig. 4.38).
The omental bursa extends upwards behind the stomach and
the caudate lobe of the liver as far as the diaphragm. On the left, it
continues to the hilum of the spleen, terminating between the gastrosplenic and
splenorenal ligaments. Inferiorly, the omental bursa usually extends a short
distance below the greater curvature of the stomach between the gastric and
colic attachments of the greater omentum. To the right, it communicates through
the epiploic foramen with the hepatorenal recess of the greater sac.
