PERITONEUM: anatomy, functions, pathologies


Features and functions

What is the peritoneum? The peritoneum it is a serous membrane, which is an epithelial tissue formed by a layer of very thin cells, said mesothelium. This type of tissue is present only in the walls of three cavities of our body: in the pleura, that lines the lungs, in pericardium, that covers the heart, and precisely in the abdomen, where it takes the name of peritoneum. What do these cavities have in common and what meaning do they have? They all surround organs in continuous movement: the lungs, the heart and the intestine, which performs contractions (peristaltic movements) that allow the digestive material to proceed and be digested and absorbed.

Therefore one function of these membranes is that of to protect the organs from the friction that their movement creates, and it does so by producing a liquid film. However, the peritoneum envelops not only the intestine, but also other abdominal organs that do not move. What is it for then? To anchor them to the abdominal wall.

But that's not all. There are in fact two "extensions" of the peritoneum, called oments. The first is said small omentum, a thin band stretched between the liver and stomach / duodenum. The great omentum instead it is inserted on the lower face of the stomach, and moves downwards in front of the ileal skein, and then wraps around itself and returns almost to the point of origin (to the transverse colon, which is immediately below the stomach). It is therefore a sort of pocket, rich in adipose tissue and immune cells.

These peculiarities allow the maintenance of the temperature (the adipose tissue acts as a thermal insulator) and the protection in case of infections or the presence of foreign materials in abdomen. In fact, in the latter case, the omentum is able to envelop the foreign agents, triggering an inflammatory process in an attempt to eliminate or otherwise isolate them (this is what happens, for example, if the materials used by the surgeon were left in the cavity). Furthermore, the adipose tissue is a soft tissue, able to cushion any trauma.

We can therefore summarize the functions of the Peritoneum:

  • Cancellation of friction produced by intestinal peristalsis
  • Immunological protection against foreign, infectious or inert agents
  • Protection from external trauma
  • Thermal protection
  • Anchoring of the organs to the abdominal wall
  • Offer a flow plane to blood and lymphatic vessels, as well as to nerves, directed to the various abdominal organs.


Where is the peritoneum located? We have to imagine the peritoneum like a big sack lining the inside abdominal cavity and upper pelvic, delimited by skeletal structures (spine and pelvis) and muscles. Structures that we can imagine as ropes branch off from this sac, which can accommodate blood and lymphatic vessels and nerves within them, or contain nothing and have the sole function of anchoring. At the end of these cables, in fact, there are organs, which are covered by the same fabric of which the great sac is made. Here then we will call the external sac "Peritoneum or Parietal Leaf", while the bags that wrap the individual organs constitute the "Peritoneum or Visceral Leaf".

The connecting cables between the two will be called “Months” if they carry vessels, otherwise simply “Ligaments”, which join together the different organs, or more rarely connect an organ (but not its vessels) to the wall. Here then is the Mesentery, which anchors the small intestine and in which the branches of the superior mesenteric artery run; or the Mesogastrium, which anchors the stomach, and so on. We will have the Hepatoduodenal, Hepatorenal etc. ligaments.


Saggittal section of the human body highlighting the peritoneum that surrounds the abdominal organs.

But what are these intraperitoneal organs? The liver with the gallbladder, spleen, stomach, almost the entire small intestine, cecum and appendix, transverse colon, sigma, first portion of the rectum, tube uterine and ovary.

The other abdominal organs are located behind the posterior wall of the parietal peritoneum; they are therefore coated only on their anterior face, and are therefore defined as "retroperitoneal": they are Pancreas, ascending and descending Colon and middle third of the Rectum; but also abdominal aorta and inferior vena cava.

The Bladder and Uterus are called "Infraperitoneal" instead, as they are covered only on their upper side by the parietal Peritoneum, and the very last portion of the rectum. A recess is formed between the rectum and the bladder / uterus, the Douglas cavity, which can be reached by a doctor during rectal exploration and is very useful for identifying initial inflammatory states with the production of fluid.

Finally, let's not forget about the kidneys: they are in effect abdominal organs, but they are "extra-peritoneal", as they are isolated by a layer of fat from the peritoneum.

What about the ovaries? They are found in the peritoneal sac, to which they are connected, but from which they are not completely covered: they are therefore free in the peritoneal cavity.

What changes between intra- and extra-peritoneal? First of all, whoever is inside the peritoneum is relatively free to move, and is affected by respiratory excursions due to the presence of the diaphragm. This is very useful in medical examinations: if there is an abdominal mass, when it moves with the breath it is intra-peritoneal (for example, liver tumor), otherwise not (for example, kidney tumor).

In addition, an inflammatory disease of an intraperitoneal organ will trigger a reaction of the peritoneum, which will increase the production of fluid, which in some cases will be so abundant that it can be felt on palpation.

Main pathologies


Peritonitis is aacute inflammation of the peritoneum. The most common causes are:

  • Perforation of intraperitoneal hollow organs such as stomach, gallbladder and intestines. When does this happen? For example, a gastric ulcer can puncture the wall, releasing acid which has a powerful inflammatory effect (chemical peritonitis) and releasing air (pneumoperitoneum). A gallstone can erode the gallbladder wall, inflaming it (Cholecystitis), until it can puncture: the release of bile acids will cause chemical peritonitis. Or again, the presence of large inflamed intestinal diverticula: diverticula are dilations of the wall in which intestinal material can accumulate, with inflammation and in the most serious cases perforation, with the release of fecal material and bacteria of the intestinal flora, and therefore Septic Peritonitis . Finally, in the course of pancreatitis, pancreatic enzymes (with a very strong erosive power) can be introduced into the cavity, with Enzyme Peritonitis.

We can therefore summarize the causes of peritonitis in:

  • Chemistry (stomach and gallbladder perforation)
  • Enzyme (from severe pancreatitis)
  • Septic (from intestinal perforation)
  • Spontaneous (from superinfection of ascites, peritoneal effusion)

THE symptoms of peritonitis are very strong pain, fever, nausea, vomiting, up to the arrest of peristalsis with dehydration. In the absence of prompt treatment, it is a picture with a poor prognosis, with death occurring from hypovolemic-acidosic shock.

Very common example: theappendicitis it is caused by accumulation of feces and bacteria in the appendix. This buildup will cause inflammation of the intestinal walls, with dull and widespread pain throughout the abdomen, as the painful information is carried by nerve fibers that are unable to tell us exactly where the problem lies. If the inflammation continues, it will affect the peritoneum, which instead is innervated by fibers that tell us exactly where the pain is: here an intense pain appears, located at the bottom and on the right. If nothing is done, we can have the walls perforated (septic peritonitis).

There spontaneous bacterial peritonitis instead it is a form of peritonitis that arises due to superinfection of the ascitic fluid, in the absence of perforations or other abdominal trauma. It appears to be linked to bacterial translocation from the bladder to the peritoneal cavity and is very common in people with advanced liver cirrhosis.

Laboratory tests:

  • Increased hematocrit (linked to dehydration or haemoconcentration)
  • Increase in white blood cells, ESR and CRP (indices of inflammation or inflammation)
  • Increase in blood creatinine and blood urea nitrogen (Kidney pain)
  • Increase of enzymes such as GOT, LDH, GTP (Indicators of cell death)
  • Reduction of coagulation factors and increased Gamma-GT and hypoalbuminemia (hepatic distress)
  • In severe cases, metabolic acidosis (state of tissue ischemia and shock).


Ascites is the abundant accumulation of fluid in the abdominal cavity, it is also called peritoneal effusion and is due to:

  1. Loss of the ability of the blood to retain liquids, due to decreased production of albumin, a protein that has the function of retaining the liquid part of the blood in the blood vessels (like a sort of magnet). This happens with liver diseases, such as cirrhosis: in fact the liver is the only producer of these proteins.
  2. Increased amount of blood in the abdominal veins: This happens when there is an obstacle in the way of the Vena Porta, which is the vein that carries blood from the intestine to the liver. When does an obstacle arise?
    • For a stiffening of the liver, which thus compresses the portal vein: Cirrhosis or multifocal hepatocarcinoma or other infiltrative-cystic liver diseases.
    • When the heart cannot pump all the blood it receives, or in the case of heart failure, also called heart failure.
    • When the heart cannot accommodate all the blood that comes from the hollow veins: pericarditis constrictive, pulmonary hypertension.
  3. Abundant production of inflammatory exudate, mostly secondary to cancer: in this case it is referred to as neoplastic ascites.

Laboratory tests

The findings are typical of dehydration and, in the case of exudate, inflammation (see above). Direct analysis of the liquid taken from the abdomen through paracentesis is important: determination of the protein concentration (high in the exudate, reduced in the transudate), cell count (leukocytosis if inflammatory), and search for any bacteria.

Peritoneal tumors:

Tumors of the peritoneum can be primary or secondary (metastases). Primary peritoneal tumors are peritoneal mesothelioma and peritoneal pseudomyxoma (which actually derives from the caecal appendix), while the secondary ones give rise to the so-called peritoneal carcinosis (or peritoneal carcinomatosis) and are secondary to neoplasms of the colon, liver or ovary. Symptoms and signs are nonspecific: fever, fatigue, shortness of breath, sometimes diffuse and dull abdominal pain.

Diagnosis is mostly instrumental (CT, PET, MRI), while blood tests are inconclusive.

Learn more: peritoneal dialysis

Dialysis is a support for patients with renal insufficiency. One of the functions of the kidney is to purify the blood. When this function fails, the blood can be purified by hemodialysis or peritoneal dialysis. The latter takes advantage of the fact that the peritoneum is highly vascularized; therefore, by introducing a dialysis solution ("pure") in the abdomen, exchanges are established through the peritoneal membrane between "pure" liquid and "impure" blood, which thus gets rid of toxic substances. Obviously it is a procedure that takes place over hours and is useful only in certain cases of chronic renal failure, never acute.


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