Peritoneum

Bursae of  peritoneal cavity

 

           The PERITONEUM is serous membrane that covers the walls of abdominal cavity and viscera in abdomen and pelvis. It may be subdivided into parietal peritoneum and visceral peritoneum. Transition of parietal peritoneum into visceral peritoneum realizes by derivatives: ligament, mesentery and omentum. If organ covered by peritoneum from all sides, such position is called intraperitoneal; if from three sides - mesoperitoneal position; if only one side  - extraperitoneal or retroperitoneal.

Abdominal cavity is limited:

·        above - by diaphragm

·        anteriorly and laterally - by muscles, fasciae, skin

·        behind - by lumbar and sacral portions of backbone and lumbar muscles

·        from below – by bones, ligaments and muscles of pelvis.

Abdominal cavity contains the organs of digestive and urogenital systems and spleen.

Peritoneal cavity is complex of fissure between abdominal organs and walls lined by parietal and visceral sheets that contain serous liquid. It can be subdivided into superior storey and inferior storey, also cavity of lesser pelvis.

Superior storey of peritoneal cavity positioned between diaphragm and level of mesocolon of transverse colon. It contains:

hepatic bursa surrounds right hepatic lobe and gallbladder;

pregastric bursa accommodates left hepatic lobe and anterior wall of stomach;

omental bursa is situated behind lesser omentum and it is in touch with posterior stomach surface.

Lesser omentum is formed by double peritoneal sheet that forms of hepatogastric ligament and hepatoduodenal ligament. Lesser omentum carries common bile duct, portal vein and proper hepatic artery (DVA).

The lesser omentum (small omentum; gastrohepatic omentum; Latin: omentum minus) is the double layer of peritoneum that extends from the liver to the lesser curvature of the stomach and the start of the duodenum.

The primitive mesentery of a six weeks’ human embryo, half schematic. (Lesser omentum labeled at left.)

Schematic and enlarged cross-section through the body of a human embryo in the region of the mesogastrium, at end of third month

The lesser omentum is extremely thin, and is continuous with the two layers ofperitoneum

 which cover respectively the antero-superior and postero-inferior surfaces of the stomach and first part of the duodenum.

When these two layers reach the lesser curvature of the stomach and the upper border of the duodenum, they join together and ascend as a double fold to the porta hepatis.

To the left of the porta, the fold is attached to the bottom of the fossa for the ductus venosus, along which it is carried to the diaphragm, where the two layers separate to embrace the end of the esophagus.

At the right border of the lesser omentum, the two layers are continuous, and form a free margin which constitutes the anterior boundary of the epiploic foramen.

Anatomically, the lesser omentum is divided into ligaments, each starting with the prefix "hepato" to indicate that it connects to the liver at one end.

Most sources divide it into two parts:[1]

·                    hepatogastric ligament: the portion connecting to the lesser curvature of the stomach

·                    hepatoduodenal ligament: the portion connecting to the duodenum

In some cases, the following ligaments are considered part of the lesser omentum:

·                    hepatophrenic ligament: the portion connecting to the thoracic diaphragm[2]

·                    hepatoesophageal ligament: the portion connecting to the esophagus[3]

·                    hepatocolic ligament: the portion connecting to the colon

Between the two layers of the lesser omentum, close to the right free margin, are thehepatic artery, the common bile duct, the portal vein, lymphatics, and the hepatic plexus of nerves—all these structures being enclosed in a fibrous capsule (Glisson's capsule).

Between the layers of the lesser omentum, where they are attached to the stomach, run the right and left gastric arteries, as well as the gastric veins.

Hepatic bursa communicates with omental bursa by the medium of epiploic foramen (of Winslow). Last limited from above by caudate lobe of the liver, from below - by superior part of duodenum, anteriorly - hepatoduodenal ligament, behind - by parietal sheet of peritoneum.

Greater omentum develops from 4 peritoneal sheets, which continue from gastrocolic ligament and, freely hanging down, covers the abdominal organs in front. The gastrocolic ligament connects the transverse colon with the greater curvature of the stomach.

The greater omentum (also the great omentum, omentum majus, gastrocolic omentum, epiploon, or, especially in animals, caul) is a large fold of visceralperitoneum

 that hangs down from the stomach. It extends from the greater curvature of the stomach, passing in front of the small intestines and reflects on itself to ascend to the transverse colon before reaching to the posterior abdominal wall. The common anatomical term "epiploic" derives from "epiploon" from the Greek "epipleein" meaning to float or sail on, since the greater omentum appears to float on the surface of the intestines.

The functions of the greater omentum are:

·                    Fat deposition, having varying amounts of adipose tissue[1]

·                    Immune contribution, having milky spots of macrophage collections[1]

·                    Infection and wound isolation; It may also physically limit the spread of intraperitoneal infections.[1] The greater omentum can often be found wrapped around areas of infection and trauma.

The greater omentum is the largest peritoneal fold. It consists of a double sheet ofperitoneum

, folded on itself so that it is made up of four layers.

The two layers which descend from the greater curvature of the stomach and commencement of the duodenum pass in front of thesmall intestines, sometimes as low down as the pelvis; they then turn upon themselves, and ascend again as far as the transverse colon, where they separate and enclose that part of the intestine.

These individual layers may be easily demonstrated in the young subject, but in the adult they are more or less inseparably blended.

The left border of the greater omentum is continuous with the gastrolienal ligament; its right border extends as far as the commencement of the duodenum.

The greater omentum is usually thin, presents a cribriform appearance, and always contains some adipose tissue, which in obese people accumulates in considerable quantity.

The greater omentum is often defined to encompass a variety of structures. Most sources include the following two:[2][3]

·                    Gastrocolic ligament - to transverse colon (occasionally on its own considered synonymous with "greater omentum"[2])

·                    Gastrosplenic ligament - to spleen

The splenorenal ligament (from the left kidney to the spleen) is occasionally considered part of the greater omentum.[

The right and left gastroepiploic vessels provide the sole blood supply to the greater omentum. Both are branches of the celiac trunk. The right gastroepiploic is a branch of the gastroduodenal artery, which is a branch of the common hepatic artery, which is a branch of the celiac trunk. The left gastroepiploic artery is the largest branch of the splenic artery, which is a branch of the celiac trunk. The right and left gastroepiploic vessels anastomose within the two layers of the anterior greater omentum along the greater curvature of the stomach.

Development

The greater omentum develops from the dorsal mesentery that connects the stomach to the posterior abdominal wall. During stomach development, the stomach undergoes its first 90° rotation along the axis of the embryo, so that posterior structures are moved to the left and structures anterior to the stomach are shifted to the right. As a result, the dorsal mesentery folds over on itself, forming a pouch with its blind end on the left side of the embryo. A second approximately 90° rotation of the stomach, this time in the frontal plane, moves structures inferior if they were originally to the left of the stomach, and superior if they were originally to the stomach's right. Consequently, the blind-ended sac (also called the lesser sac) formed by the dorsal mesentery is brought inferiorly, where it assumes its final position as the greater omentum. It grows to the point that it covers the majority of the small and large intestine.

Omentectomy refers to the surgical removal of the omentum, a relatively simple procedure with no major side effects, that is performed in cases where there may be spread of cancerous tissue into the omentum. Examples for this conditions are ovarian cancer and advanced or aggressive endometrial cancer as well as intestinal cancer. The procedure is generally done as an add-on when the primary lesion is removed.

Inferior floor of peritoneal cavity extends from mesocolon of transverse colon to entrance into lesser pelvis.

Root of small intestine mesentery divides the inferior storey into right and left mesenteric sinuses.  They accommodate the loops of small intestine. Right mesenteric sinus is bordered by mesenteric root and ascending colon. In place, where ileum continues into cecum superior and inferior ileocecal recesses are situated. One can see retrocecal recess behind cecum. Right paracolic sulcus runs between ascending colon and parietal peritoneum of lateral abdominal wall. Mesenteric root, descending colon and sigmoid colon border left mesenteric sinus. Superior and inferior duodenal recesses are positioned in area of duodenojejunal junction. Mesocolon of sigmoid forms intersigmoidal recess. Left paracolic sulcus runs between descending colon and parietal peritoneum of left abdominal wall.

Parietal sheet of peritoneum covering back surface of anterior abdominal form plicae (folds) and fossae. The median umbilical fold contains the remnant of the embryonic urachus; the medial umbilical folds carry obliterated umbililal arteries; lateral umbilical folds contain inferior epigastric arteries. Supravesical fossae positioned between median and medial umbilical folds. Medial umbilical fossae located between medial and lateral umbilical folds. Lateral umbilical fossae located laterally from lateral umbilical folds. Medial and lateral umbilical fossae can be projected into superficial inguinal ring and deep inguinal ring.

Cavity of lesser pelvis

Peritoneal cavity in the male pelvis contains rectovesical excavation (pouch). Peritoneum in the female between uterus and urinary bladder form vesicouterinae excavation. Behind the uterus peritoneum descends into the rectouterine pouch (pouch of Douglas), which is the lowest point of the peritoneal cavity. That is why some liquid from all peritoneal cavity can collect here during some pathology. The entrance into the rectouterine pouch is narrowed by the rectouterine folds, in which the rectouterine muscles run.

  The glistening appearance of the deep surface of the abdominal wall and of the surfaces of the exposed viscera is due to the fact that the former is lined, and the latter are more or less completely covered, by a serous membrane, the peritoneum.

The Peritoneum (Tunica Serosa)—The peritoneum is the largest serous membrane in the body, and consists, in the male, of a closed sac, a part of which is applied against the abdominal parietes, while the remainder is reflected over the contained viscera. In the female the peritoneum is not a closed sac, since the free ends of the uterine tubes open directly into the peritoneal cavity. The part which lines the parietes is named the parietal portion of the peritoneum; that which is reflected over the contained viscera constitutes the visceral portion of the peritoneum. The free surface of the membrane is smooth, covered by a layer of flattened mesothelium, and lubricated by a small quantity of serous fluid. Hence the viscera can glide freely against the wall of the cavity or upon one another with the least possible amount of friction. The attached surface is rough, being connected to the viscera and inner surface of the parietes by means of areolar tissue, termed the subserous areolar tissue. The parietal portion is loosely connected with the fascial lining of the abdomen and pelvis, but is more closely adherent to the under surface of the diaphragm, and also in the middle line of the abdomen.

  The space between the parietal and visceral layers of the peritoneum is named the peritoneal cavity; but under normal conditions this cavity is merely a potential one, since the parietal and visceral layers are in contact. The peritoneal cavity gives off a large diverticulum, the omental bursa, which is situated behind the stomach and adjoining structures; the neck of communication between the cavity and the bursa is termed the epiploic foramen (foramen of Winslow). Formerly the main portion of the cavity was described as the greater, and the omental bursa as the lesser sac.

  The peritoneum differs from the other serous membranes of the body in presenting a much more complex arrangement, and one that can be clearly understood only by following the changes which take place in the digestive tube during its development.

Peritoneum is the serous membrane that forms the lining of theabdominal cavity or the coelom—it covers most of the intra-abdominal (or coelomic) organs—in amniotes and some invertebrates (annelids, for instance). It is composed of a layer of mesothelium supported by a thin layer of connective tissue. The peritoneum both supports the abdominal organs and serves as a conduit for their blood and lymphvessels and nerves.

The abdominal cavity (the space bounded by the vertebraeabdominal muscles,diaphragm and pelvic floor) should not be confused with the intraperitoneal space(located within the abdominal cavity, but wrapped in peritoneum). The structures within the intraperitoneal space are called "intraperitoneal" (e.g. the stomach), the structures in the abdominal cavity that are located behind the intraperitoneal space are called "retroperitoneal" (e.g. the kidneys), and those structures below the intraperitoneal space are called "subperitoneal" or "infraperitoneal" (e.g. the bladder).

Layers

Although they ultimately form one continuous sheet, two types or layers of peritoneum and a potential space between them are referenced:

·                    The outer layer, called the parietal peritoneum, is attached to the abdominal wall and the pelvic walls.[1]

·                    The inner layer, the visceral peritoneum, is wrapped around the internal organs that are located inside the intraperitoneal space. It is thinner than the parietal peritoneum.

·                    The potential space between these two layers is the peritoneal cavity; it is filled with a small amount (about 50 mL) of slipperyserous fluid that allows the two layers to slide freely over each other.

·                    The term mesentery is often used to refer to a double layer of visceral peritoneum. There are often blood vessels, nerves, and other structures between these layers. The space between these two layers is technically outside of the peritoneal sac, and thus not in the peritoneal cavity.

Subdivisions

Peritoneal folds are omenta, mesenteries and ligaments; they connect organs to each other or to the abdominal wall.[2] There are two main regions of the peritoneum, connected by the epiploic foramen (also known as the omental foramen or foramen of winslow):

·                    The greater sac (or general cavity of the abdomen), represented in red in the diagrams above.

·                    The lesser sac (or omental bursa), represented in blue. The lesser sac is divided into two "omenta":

·                                The lesser omentum (or gastrohepatic) is attached to the lesser curvature of the stomach and the liver.

·                                The greater omentum (or gastrocolic) hangs from the greater curve of the stomach and loops down in front of the intestinesbefore curving back upwards to attach to the transverse colon. In effect it is draped in front of the intestines like an apron and may serve as an insulating or protective layer.

The mesentery is the part of the peritoneum through which most abdominal organs are attached to the abdominal wall and supplied withblood and lymph vessels and nerves.

In addition, in the pelvic cavity there are several structures that are usually named not for the peritoneum, but for the areas defined by the peritoneal folds:

female

Development

The peritoneum develops ultimately from the mesoderm of the trilaminar embryo. As the mesoderm differentiates, one region known as the lateral plate mesoderm splits to form two layers separated by an intraembryonic coelom. These two layers develop later into the visceral and parietal layers found in all serous cavities, including the peritoneum.

As an embryo develops, the various abdominal organs grow into the abdominal cavity from structures in the abdominal wall. In this process they become enveloped in a layer of peritoneum. The growing organs "take their blood vessels with them" from the abdominal wall, and these blood vessels become covered by peritoneum, forming a mesentery.[citation needed]

Peritoneal folds develop from the ventral and dorsal mesentery of the embryo.[2]

Clinical aspects

Peritoneal dialysis

In one form of dialysis, called peritoneal dialysis, a glucose solution is sent through a tube into the peritoneal cavity. The fluid is left there for a prescribed amount of time to absorb waste products, and then removed through the tube. The reason for this effect is the high number of arteries and veins in the peritoneal cavity. Through the mechanism of diffusion, waste products are removed from the blood.

Primary peritoneal carcinoma

Main article: Primary peritoneal carcinoma

Primary peritoneal cancer is a cancer of the cells lining the peritoneum.

Classification of abdominal structures

The structures in the abdomen are classified as intraperitoneal, retroperitoneal or infraperitoneal depending on whether they are covered with visceral peritoneum and whether they are attached by mesenteries (mensentery, mesocolon).

Structures that are intraperitoneal are generally mobile, while those that are retroperitoneal are relatively fixed in their location.

Some structures, such as the kidneys, are "primarily retroperitoneal", while others such as the majority of the duodenum, are "secondarily retroperitoneal", meaning that structure developed intraperitoneally but lost its mesentery and thus became retroperitoneal.

Etymology - Peritoneum is derived from Greek via Latin. Peri- means around, while -ton- refers to stretching. Thus, peritoneum means stretched around or stretched over.

The SPLEEN lies in epigastrium and belongs to secondary lymphatic organs and is a big lymphatic node. Spleen is disposed in left hypochondriac region on the level of 9 th -11th ribs. Spleen has inferior margin and superior margin, anterior extremity and posterior extremity. It has a diaphragmatic surface (superior) and visceral surface (inferior). To the last adjoin stomach (facies gastrica), left kidney with suprarenal gland (facies renalis), left colic flexure (facies colica) and tail of pancreas (facies pancreatica). Place on visceral surface, where vessels and nerves enter and leave, is called as splenic hilus. Spleen is covered by peritoneum from all sides (lies intraperitoneally).

Spleen is covered by fibrous capsule, from which numerous small fibrous bands, trabeculae are given off in all directions into parenchyma, these uniting, and constitute the framework of the spleen. Parenchyma consists of splenic pulp, which has a white pulp and red pulp and its structure described in detail in histology course.

    To trace the membrane from one viscus to another, and from the viscera to the parietes, it is necessary to follow its continuity in the vertical and horizontal directions, and it will be found simpler to describe the main portion of the cavity and the omental bursa separately.

Vertical Disposition of the Main Peritoneal Cavity (greater sac)—It is convenient to trace this from the back of the abdominal wall at the level of the umbilicus. On following the peritoneum upward from this level it is seen to be reflected around a fibrous cord, the ligamentum teres (obliterated umbilical vein), which reaches from the umbilicus to the under surface of the liver. This reflection forms a somewhat triangular fold, the falciform ligament of the liver, attaching the upper and anterior surfaces of the liver to the diaphragm and abdominal wall. With the exception of the line of attachment of this ligament the peritoneum covers the whole of the under surface of the anterior part of the diaphragm, and is continued from it on to the upper surface of the right lobe of the liver as the superior layer of the coronary ligament, and on to the upper surface of the left lobe as the superior layer of the left triangular ligament of the liver. Covering the upper and anterior surfaces of the liver, it is continued around its sharp margin on to the under surface, where it presents the following relations: (a) It covers the under surface of the right lobe and is reflected from the back part of this on to the right suprarenal gland and upper extremity of the right kidney, forming in this situation the inferior layer of the coronary ligament; a special fold, the hepatorenal ligament, is frequently present between the inferior surface of the liver and the front of the kidney. From the kidney it is carried downward to the duodenum and right colic flexure and medialward in front of the inferior vena cava, where it is continuous with the posterior wall of the omental bursa. Between the two layers of the coronary ligament there is a large triangular surface of the liver devoid of peritoneal covering; this is named the bare area of the liver, and is attached to the diaphragm by areolar tissue. Toward the right margin of the liver the two layers of the coronary ligament gradually approach each other, and ultimately fuse to form a small triangular fold connecting the right lobe of the liver to the diaphragm, and named the right triangular ligament of the liver. The apex of the triangular bare area corresponds with the point of meeting of the two layers of the coronary ligament, its base with the fossa for the inferior vena cava. (b) It covers the lower surface of the quadrate lobe, the under and lateral surfaces of the gall-bladder, and the under surface and posterior border of the left lobe; it is then reflected from the upper surface of the left lobe to the diaphragm as the inferior layer of the left triangular ligament, and from the porta of the liver and the fossa for the ductus venosus to the lesser curvature of the stomach and the first 2.5 cm. of the duodenum as the anterior layer of the hepatogastric and hepatoduodenal ligaments, which together constitute the lesser omentum. If this layer of the lesser omentum be followed to the right it will be found to turn around the hepatic artery, bile duct, and portal vein, and become continuous with the anterior wall of the omental bursa, forming a free folded edge of peritoneum. Traced downward, it covers the antero-superior surface of the stomach and the commencement of the duodenum, and is carried down into a large free fold, known as the gastrocolic ligament or greater omentum. Reaching the free margin of this fold, it is reflected upward to cover the under and posterior surfaces of the transverse colon, and thence to the posterior abdominal wall as the inferior layer of the transverse mesocolon. It reaches the abdominal wall at the head and anterior border of the pancreas, is then carried down over the lower part of the head and over the inferior surface of the pancreas on the superior mesenteric vessels, and thence to the small intestine as the anterior layer of the mesentery. It encircles the intestine, and subsequently may be traced, as the posterior layer of the mesentery, upward and backward to the abdominal wall. From this it sweeps down over the aorta into the pelvis, where it invests the sigmoid colon, its reduplication forming the sigmoid mesocolon. Leaving first the sides and then the front of the rectum, it is reflected on to the seminal vesicles and fundus of the urinary bladder and, after covering the upper surface of that viscus, is carried along the medial and lateral umbilical ligaments on to the back of the abdominal wall to the level from which a start was made.