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| Peritoneum |
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| The epiploic foramen, greater sac or general cavity (red) and lesser sac, or omental bursa (blue). |
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| Horizontal disposition of the peritoneum in the upper part of the abdomen. (Areas outlined in blue and red correspond to above diagram.) |
| Gray's |
subject #246 1149 |
| MeSH |
A01.047.025.600 |
| Dorlands/Elsevier |
p_14/12629236 |
In higher vertebrates, the peritoneum is the serous membrane that forms the lining of the abdominal cavity - it covers most of the intra-abdominal organs. It is composed of layer of mesothelium supported by a thin layer of connective tissue.
[edit] Structure
The peritoneum is the serous membrane of the abdominal cavity. (The corresponding serous membranes in the pleural and pericardial cavities of the thorax are called the pleura and the pericardium respectively.) The peritoneum both supports the abdominal organs and serves as a conduit for their blood and lymph vessels and nerves.
[edit] Layers
Although they ultimately form one continuous sheet, two types or layers of peritoneum are referenced to and a potential space between them:
- The outer layer, called the parietal peritoneum, is attached to the abdominal wall.
- The inner layer, the visceral peritoneum, is wrapped around the internal organs that are located inside the abdominal cavity.
- The potential space between these two layers is the peritoneal cavity; it is filled with a small amount (about 50 ml) of slippery serous 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. It should be noted that the space between these two layers is technically outside of the peritoneal sac, and thus not in the peritoneal cavity.
[edit] Subdivisions
There are two main regions of the peritoneum, connected by the epiploic foramen:
- 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 intestines before 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 with blood and lymph vessels and nerves.
Structures include:
| SOURCES |
STRUCTURE |
FROM |
TO |
CONTAINS |
|
OMENTA |
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| dorsal mesentery |
* greater omentum |
greater curvature of stomach (and spleen) |
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| dorsal mesentery |
** gastrosplenic ligament |
stomach |
spleen |
short gastric artery, left gastro-omental artery |
| dorsal mesentery |
** gastrophrenic ligament |
stomach |
diaphragm |
- |
| dorsal mesentery |
** gastrocolic ligament |
stomach |
transverse colon |
- |
| dorsal mesentery |
** splenorenal ligament |
spleen |
kidney |
splenic artery, tail of pancreas |
| ventral mesentery |
* lesser omentum |
lesser curvature of the stomach (and duodenum |
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| ventral mesentery |
** hepatogastric ligament |
stomach |
liver |
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| ventral mesentery |
** hepatoduodenal ligament |
duodenum |
liver |
hepatic artery proper, hepatic portal vein, bile duct |
|
MESENTERIES |
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| dorsal mesentery |
* Mesentery proper |
small intestine – jejunum and ileum |
posterior abdominal wall |
superior mesenteric artery |
| dorsal mesentery |
* transverse mesocolon |
transverse colon |
posterior abdominal wall |
middle colic |
| dorsal mesentery |
* sigmoid mesocolon |
sigmoid colon |
pelvic wall |
sigmoid arteries |
| dorsal mesentery |
* mesoappendix |
mesentery of ileum |
appendix |
appendicular artery |
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OTHER LIGAMENTS AND FOLDS |
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| ventral mesentery |
* falciform ligament |
liver |
thoracic diaphragm, anterior abdominal wall |
round ligament of liver, paraumbilical veins |
| left umbilical vein |
* round ligament of liver |
liver |
umbilicus |
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| ventral mesentery |
* coronary ligament |
liver |
thoracic diaphragm |
|
| ductus venosus |
* ligamentum venosum |
liver |
liver |
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* phrenicocolic ligament |
left colic flexure |
thoracic diaphragm |
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| ventral mesentery |
* left triangular ligament, right triangular ligament |
liver |
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* umbilical folds |
urinary bladder |
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* ileocecal fold |
ileum |
cecum |
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* broad ligament of the uterus |
uterus |
pelvic wall |
mesovarium, mesosalpinx, mesometrium |
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* ovarian ligament |
uterus |
inguinal canal |
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* suspensory ligament of the ovary |
ovary |
pelvic wall |
ovarian artery |
[edit] 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.
[edit] Clinical aspects
[edit] Pathology
- Pneumoperitoneum is the presence of gas within the peritoneal cavity, as may occur when a perforation forms in the stomach or intestines, and heralds a perilous situation.
- Peritonitis refers to inflammation of the peritoneal lining or cavity, as may occur with either a perforation or by spread of infection through the wall of one of the abdominal organs. This too is a serious condition, and often requires emergency surgery.
- Ascites is an accumulation of excess fluid within the peritoneal cavity.
[edit] Peritoneal dialysis
In one form of dialysis, the peritoneal dialysis, a glucose solution is run 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.
[edit] 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 have a mesentery or not. Some structures, such as the kidneys, are "primarily retroperitoneal", meaning that structure developed intraperitoneally but lost its mesentery and thus became retroperitoneal. Structures that are intraperitoneal are generally mobile, while those that are retroperitoneal are relatively fixed in their location.
[edit] Intraperitoneal
- Stomach
- First part of the duodenum [5 cms].
- Pancreas(Tail)
- Jejunum
- Ileum
- Appendix
- Cecum
- Transverse colon
- Sigmoid colon
- Rectum, upper 1/3
- Liver
- Spleen
- In women:
- Uterus
- Fallopian tubes
- Ovaries
[edit] Retroperitoneal
- The rest of the duodenum
- Rectum, middle 1/3
- Kidneys
- Pancreas(Head and Body)
- Suprarenal glands (adrenal glands)
- Ureters, renal vessels and gonadal blood vessels
- Ascending colon
- Descending colon
[edit] Infraperitoneal
- Rectum, lower 1/3
- Urinary bladder
[edit] Etymology
Peritoneum is derived from Greek. Peri- means around, while -ton- refers to stretching. Thus, peritoneum means stretched around or stretched over.
[edit] Additional images
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Topography of thoracic and abdominal viscera.
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[edit] References
- Tortora, Gerard J., Anagnostakos, Nicholas P. (1984) Principles of Anatomy and Physiology, Harper & Row Publishers, New York ISBN 0-06-046656-1
[edit] External links
