Peritoneal Cavity - Anatomy & Physiology

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Introduction

The peritoneum is the serous membrane which lines the abdominal cavity. It lies directly beneath the abdominal musculature (rectus abdominis and transverse abdominis). It is a type of loose connective tissue covered by mesothelium. Extensions of the peritoneum form the mesenteries that support the abdominal contents. It functions to lubricate abdominal viscera, enhance immune responses and wall off infection in the abdomen to prevent peritonitis.

Structure & Histology

The peritoneum is smooth and clear in the healthy animal.
It consists of a thin layer of loose connective tissue covered by a single layer of mesothelial cells. Collectively, the connective tissue and peritoneum are referred to as the serosa.
- Mesothelial cells are simple squamous and of mesodermal origin.
There are two layers of peritoneum lining the abdomen.
- The layer in contact with the abdominal wall
Many species have lymphoid tissue aggregates and fixed phagocytes in the omentum that are not covered by mesothelial cells
NB Post mortem change and autolysis result in increased volumes of red-brown fluid in the abdomen, not associated with other pathology, no roughening of surfaces of organs or peritoneum.

Function

Small volume of clear fluid for lubrication - in equilibrium with plasma but doesn't contain high molecular weight molecules like fibrinogen

Vasculature

Innervation

Lymphatics

Histology

Have microvili on their surface
Very fragile but regenerate very quickly
High fibrinolytic activity - protects against the formation of adhesions
Show reactive change with inflammation or effusions
May be confused with neoplastic cells

Species Differences

Peritoneum is normally smooth and clear,
Small volume of clear fluid for lubrication - in equilibrium with plasma but doesn't contain high molecular weight molecules like fibrinogen
Small animals
- Low volume of clear straw coloured fluid
- Specific gravity <1.015 to 1.018
- Total protein 25-39g/L
- Nucleated cell count <3x10e9/L
- Mesothelial cells/macrophages

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