What Is The Peritoneum

Overview

Abdominal cavity is the large hollow space of the body which contains digestive tract, liver, pancreas, spleen, kidneys and adrenal glands located above the kidneys. The upper boundary is the diaphragm and lower boundary is the upper plane of the pelvic cavity.

Peritoneum is the serous membrane (that secretes serum) which lines the abdominal cavity and covers the abdominal organs. It helps to hold the organs in place and acts as a passage for the nerves, blood vessels and lymphatics. Peritoneum secretes a lubricating fluid to reduce friction when the organs rub against each other.

Peritoneum is a thin layer made up of 2 layers leaving a space in between them, which is known as peritoneal cavity. Here we shall look into the anatomy of the peritoneum, which includes the structure, relationship of peritoneum covering abdominal organs and their clinical importance.¹

Anatomy of the Peritoneum

Peritoneum is located in the abdominopelvic cavity, which is between the diaphragm and the pelvic floor. The 2 layers of the peritoneum are parietal peritoneum and visceral peritoneum, they are made up of simple squamous epithelial cells called mesothelium. It contains epithelial cells on the top layer which secretes and absorb fluid, filter out particles, carry blood and also contains lymph and nerve supply. The connective tissue is the underneath layer, which holds everything together.^1,2

Parietal peritoneum

Parietal peritoneum is the outer layer, which attaches the abdominal and pelvic wall. Peritoneum gets the somatic nerve supply, therefore the pain is localised, and it is sensitive to touch, pressure, lacerations and temperature. 

Visceral peritoneum

Visceral peritoneum covers the internal organs, which includes stomach, spleen, liver, parts of small and large intestines. It has the autonomic nerve supply and the pain is poorly localised.³

Peritoneal cavity

Peritoneal cavity is the space between the parietal peritoneum and visceral peritoneum. This includes the omentum, ligaments and mesentery. This space contains the lubricating fluid.

Intraperitoneal & retroperitoneal organs

1. Intraperitoneal organs

The abdominal viscera is divided according to the relationship to the peritoneum. Intraperitoneal organs are covered by the visceral peritoneum, which covers the organ both inside and outside. The organs are stomach, liver and spleen.

2. Retroperitoneal organs

Retroperitoneal organs are only covered by the parietal peritoneum, which means the organs are covered only in the anterior surface. The organs are suprarenal glands, aorta, duodenum, pancreas, ureter, colon, kidneys, oesophagus and rectum.

Peritoneal reflections

Peritoneum nearly covers all the viscera, in order to function properly peritoneum develops into a highly folded structure and pouches. They are described according to the folds and spaces, they are : 

1. Mesentery

Mesentery is a double layer which connects the intestines to the posterior abdominal wall, this provides passage for nerves, blood vessels and lymphatics.

2. Omentum

Omentum is a large double layer that covers the front of the abdomen like an apron. They are like sheets of visceral peritoneum.

• Greater omentum

It consists of layers of visceral peritoneum, where it layers from the greater curvature of the stomach to the posterior part of the duodenum and then folds up and connects to the anterior part of the transverse colon. It plays a role in immunity, as they can migrate to the infected viscera.

• Lesser omentum

It is a double layer visceral peritoneum, where it connects the lesser curvature of the stomach to the posterior part of the duodenum and then to the liver.

3. Peritoneal ligaments

Peritoneal ligament is a double fold peritoneum that connects the viscera to the abdominal wall.

Function of peritoneum

Peritoneum has several functions and researchers are still learning about it. Some of the functions are : 

• Insulation: Peritoneum is a layer that forms and protects the abdominopelvic organs

• Lubrication: In the peritoneal cavity there is a lubricating fluid that helps the organs move freely without rubbing each other

• Passage: Peritoneum serves as a passage for the blood vessels, lymphatics and the nerves
• Immunity : Peritoneum recognises injury or infection, and sends in the white blood cells or repair its injury on its own. It plays a role in filtering the fluid in the peritoneal cavity and drains the waste products, in case of kidney failure.

Disease conditions and disorders

Peritonitis

Inflammation of the peritoneum is known as peritonitis, which is caused by infection occurring inside the peritoneal cavity. Peritonitis should be treated immediately, as the infection in the peritoneal cavity can be absorbed into the blood and can cause septicemia (also known as blood poisoning, when the infection enters the bloodstream).⁴

Ascites

Ascites is a condition where excess fluid is stored in the peritoneal cavity. It is a common symptom of cirrhosis (liver disease), hypertension in portal vein, congestive heart failure and cancer.⁵

Hernia

Hernia is a condition when a part of the inside protrudes through an opening or weakness in the muscle or tissue that contains it.

Abdominal adhesions

Abdominal adhesions occur after an abdominal surgery that cuts through the peritoneum and causes scar. These scars can block the free movement of the organs and in the case of intestines it can lead to bowel obstruction.

Sclerosing mesenteritis

It is a rare condition that affects the fatty tissue of the mesentery, the chronic inflammation of tissue can lead to scarring (fibrosis). Fibrosis can stop the blood flow through the tissue and can cause bowel obstruction.

Mesenteric lymphadenitis

It is a condition where the lymph nodes that connect the bowel to the wall of the stomach become swollen and inflammed. It occurs due to infection and can cause fever and pain.

Cancer

Cancer in the abdominopelvic organs can easily spread to the peritoneum, called peritoneal carcinomatosis. Cancer can occur in the peritoneum also and can spread to the organs that it covers.⁶

Diagnosis

The healthcare provider may conduct a physical examination and ask about any pain or difficulty occurring while examining the abdomen. Other tests are: 

• Peritoneal fluid analysis

In this procedure a hollow needle is taken and inserted into the peritoneal cavity and a small amount of fluid is collected. This fluid is examined in the laboratory for checking any infection or cancer. This helps to diagnose peritonitis or ascites.

• Peritoneal biopsy

In this procedure needle biopsy is inserted into the abdomen and a peritoneal tissue is taken and examined. This is also done during laparoscopy, where a tiny incision is made on the abdomen and a camera attached at the end of the tube is inserted to the abdominal cavity. This helps in viewing the abdominal and reproductive organs and is also used to collect samples of tissue for testing.

Treatment and management

• Peritoneal dialysis

Peritoneum helps in filtering waste products and sometimes it is used in dialysis to treat kidney failure. Dialysis removes the waste products and excess fluid from the blood. During dialysis the health provider fills the peritoneal cavity with fluid solution and the peritoneum filters the fluid, later the fluid is drained out by the health provider.⁴

• Hyperthermic intraperitoneal chemotherapy (HIPEC)

HIPEC is a new alternative chemotherapy, where the concentrated, heated chemotherapy solution is directly delivered into the peritoneal cavity. This technique is used to treat in case of localised peritoneal cavity cancer.

• Cytoreductive surgery

Cancer in the abdominopelvic cavity is usually treated with chemotherapy and surgery. Cancer is most commonly seen in the omentum of the peritoneum. Cytoreductive surgery helps in removing as many of the cancer cells as possible. In some cases part of the affected peritoneum is removed (omentectomy, surgical removal of omentum), or removal of the entire peritoneum (peritonectomy).

FAQs

What are the symptoms of peritoneum diseases?

Common symptoms of the disease affecting the peritoneum are abdominal pain, tenderness, bloating sensation, fever and fullness of the abdomen.

What are the diseases of peritoneum?

Peritoneum is a serous membrane that lines the abdominal cavity and covers the abdominal organs. Common peritoneal diseases are ascites, hernia and peritoneal cancer.

Can you have peritonitis and not know about it?

Yes, patients can have peritonitis and not have any symptoms, they are termed as “silent peritonitis”. The person may not have any abdominal pain, fever or tenderness.

Can the peritoneum be removed?

In case of abdominopelvic cavity cancer the surgeon may suggest chemotherapy or cytoreductive surgery, in which the surgeon removes the whole peritoneum.

Summary

Peritoneum is the serous membrane (that secretes serum) which lines the abdominal cavity and covers the abdominal organs. It helps to hold the organs in place and acts as a passage for the nerves, blood vessels and lymphatics. Peritoneum secretes a lubricating fluid to reduce friction when the organs rub against each other. Peritoneum is located in the abdominopelvic cavity, which is between the diaphragm and the pelvic floor. The 2 layers of the peritoneum are parietal peritoneum and visceral peritoneum, they are made up of simple squamous epithelial cells called mesothelium. Peritoneum recognises injury or infection, and sends in the white blood cells or repair its injury on its own. It plays a role in filtering the fluid in the peritoneal cavity and drains the waste products, in case of kidney failure.