Visceral Peritoneum

The visceral peritoneum is the inner layer of the peritoneal membrane that covers the external surfaces of most abdominal and pelvic organs. It is continuous with the parietal peritoneum at the sites where organs protrude into the peritoneal cavity. Unlike the parietal layer, which lines the body wall, the visceral peritoneum intimately invests organs, forming part of their serosal surface. It plays a critical role in organ mobility, serous fluid secretion, immune response, and in anchoring neurovascular structures via mesenteries and ligaments. Despite being a thin and transparent membrane, it is fundamental to abdominal anatomy and function.

Structure

The visceral peritoneum is composed of a single layer of mesothelial cells supported by a thin layer of connective tissue. It forms the outermost layer of intraperitoneal organs, blending seamlessly with the serosa of those organs.

Composition

• Mesothelium: Simple squamous epithelium
• Underlying connective tissue: Contains capillaries, lymphatics, and autonomic nerves

The mesothelial cells secrete a small amount of serous fluid that lubricates organ surfaces, allowing them to move frictionlessly during digestion and respiration.

Location

The visceral peritoneum invests organs that lie within the peritoneal cavity. It does not lie within the cavity itself but folds around organs to form the inner lining of the cavity walls.

Organs Covered

• Stomach
• Small intestine (jejunum and ileum)
• Liver
• Transverse colon and sigmoid colon
• Spleen
• Uterus, ovaries, and superior part of bladder (in females)

The degree of peritoneal coverage varies by organ. Some organs are completely encased (intraperitoneal), while others are only partially covered (retroperitoneal).

Functions

The visceral peritoneum contributes to multiple physiological and anatomical functions:

• Frictionless organ movement: Secretes serous fluid to allow smooth gliding of abdominal organs
• Protective barrier: Acts as a selective filter and physical shield against infection and injury
• Supports immune defense: Contains resident macrophages and lymphatic channels
• Structural support: Participates in forming mesenteries and ligaments that suspend and stabilize organs

Mesenteries and Peritoneal Reflections

The visceral peritoneum is continuous with the parietal peritoneum at reflections that form:

• Mesenteries: Double layers of peritoneum that attach organs to the posterior abdominal wall (e.g., mesentery of the small intestine, transverse mesocolon)
• Omenta: Greater and lesser omentum connect stomach to other organs
• Peritoneal ligaments: E.g., gastrosplenic, hepatogastric, and phrenicocolic ligaments

These structures carry blood vessels, lymphatics, and nerves between the body wall and the organs.

Blood Supply

The visceral peritoneum receives its blood supply from the arteries of the organ it covers:

• Stomach: Left and right gastric, gastroepiploic arteries
• Small intestine: Branches of superior mesenteric artery
• Colon: Superior and inferior mesenteric arteries
• Liver: Hepatic artery and portal vein branches

Venous drainage also parallels the arterial supply and returns blood via organ-specific venous systems.

Innervation

Unlike the parietal peritoneum, which receives somatic innervation, the visceral peritoneum is supplied by autonomic nerves from the same plexuses that innervate the underlying organs:

• Celiac plexus (foregut)
• Superior mesenteric plexus (midgut)
• Inferior mesenteric and pelvic plexuses (hindgut and pelvis)

Because of its autonomic innervation, pain in the visceral peritoneum is poorly localized, dull, and crampy. For example, early appendicitis presents as vague periumbilical pain due to midgut visceral innervation.

Lymphatic Drainage

Lymph from the visceral peritoneum drains with the lymphatics of the underlying organ into:

• Mesenteric lymph nodes
• Celiac, superior, and inferior mesenteric nodes
• Pelvic or para-aortic nodes (depending on the organ)

This lymphatic continuity contributes to the rapid spread of infections or carcinomas through the peritoneal surfaces.

Clinical Significance

Visceral Pain and Referred Symptoms

• Visceral peritoneum pain is diffuse and referred to dermatomes related to embryological origin (e.g., foregut pain to epigastrium, midgut to umbilical region)
• Peritoneal irritation can cause reflex muscle guarding or vomiting

Peritoneal Carcinomatosis

• Cancer may spread across the visceral peritoneum (e.g., ovarian, gastric, or colorectal cancers)
• Deposits may form on peritoneal surfaces, leading to ascites and intestinal obstruction

Peritoneal Dialysis

• The peritoneal cavity (lined by both parietal and visceral peritoneum) is used in dialysis for renal failure patients
• Glucose-rich dialysate exchanges solutes via the peritoneal membrane’s semi-permeable properties

Peritoneal Adhesions

• Inflammation or surgical trauma to the visceral peritoneum can lead to fibrous bands that tether loops of bowel, potentially causing obstruction

Ascites and Infection

• In liver disease, peritoneal surfaces may accumulate fluid (ascites)
• Spontaneous bacterial peritonitis involves infection of this fluid and often affects the visceral layer

Comparison: Parietal vs Visceral Peritoneum

Feature	Parietal Peritoneum	Visceral Peritoneum
Location	Lines abdominal wall	Covers organs directly
Innervation	Somatic (sharp, localized pain)	Autonomic (dull, poorly localized pain)
Blood supply	Body wall arteries	Organ-specific arteries
Lymph drainage	Body wall lymph nodes	Follows organ lymphatics
Clinical example	Rebound tenderness in appendicitis	Early vague visceral pain in appendicitis