Serous Membranes and Cavities Flashcards

Serous membranes line the closed body cavities, including the pleural, pericardial, and peritoneal cavities.

A serous membrane consists of a parietal membrane lining the cavity wall and a visceral membrane covering the organs within the cavity.

Serous fluid is found between the parietal and visceral membranes.

The primary function of serous fluid is lubrication, which prevents friction between the membranes during organ movement.

Serous fluids are formed as ultrafiltrates of plasma. The mesothelial cells lining the membranes do not contribute additional material.

Production and reabsorption of serous fluid are influenced by hydrostatic pressure, colloidal (oncotic) pressure, and capillary permeability.

An effusion is defined as an increase in the amount of serous fluid between the membranes.

Primary causes of effusions include increased hydrostatic pressure, decreased oncotic pressure, increased capillary permeability, and lymphatic obstruction.

Fluids for laboratory examination are collected by needle aspiration, such as thoracentesis, pericardiocentesis, and paracentesis.

EDTA tubes are used for cell counts and differentials.

Sterile heparinized or SPS tubes are used for microbiology and cytology.

pH specimens must be kept anaerobic in ice.

Chemical tests performed on serous fluids are often compared with plasma concentrations because the fluids are essentially plasma ultrafiltrates.

Effusions are generally classified as transudates or exudates.

Transudates result from systemic disorders affecting fluid balance, such as heart failure or nephrotic syndrome.

Exudates arise from conditions directly involving the membranes, such as infections or malignancies.

Traditional tests include appearance, total protein, LDH, cell counts, and clotting.

Fluid:blood ratios for protein and lactic dehydrogenase are the most reliable differentiators.

Turbidity often indicates infection or inflammation.

Bloody fluid can suggest trauma or malignancy.

Milky fluid may indicate chylous or pseudochylous material.

Normal pleural fluid contains macrophages, lymphocytes, and a small number of neutrophils and mesothelial cells.

Increased neutrophils suggest bacterial infection or pancreatitis.

Elevated lymphocytes can indicate tuberculosis, viral infections, or autoimmune disorders.

Mesothelial cells line the serous cavities and can be found in serous fluids.

Detecting malignant cells is a primary concern.

Common chemical tests include glucose, pH, ADA, and amylase.

Decreased glucose can be seen in tuberculosis, rheumatoid inflammation, malignancy, and infections.

Low pH may indicate the need for chest-tube drainage.

Elevated ADA is indicative of tuberculosis.

Gram stains, cultures, and acid-fast stains are performed for suspected infections. Serological tests like ANA and rheumatoid factor can help differentiate immunologic origins.

Tumor markers (CEA, CA 125) are used for effusions of malignant origin.

Pericardial effusions can be transudates or exudates. Laboratory tests focus on differentiating transudates and exudates.

Ascites is peritoneal effusion.

The serum-ascites albumin gradient (SAAG) is often used.

A SAAG of 1.1 g/dL or greater strongly suggests a transudate of hepatic origin, commonly seen in cirrhosis.

Peritoneal lavage may be performed to detect intra-abdominal bleeding in trauma cases.

Turbid peritoneal fluid typically indicates bacterial or fungal infections (peritonitis).

A green or dark-brown color suggests bile leakage, often from gallbladder or pancreatic issues.

Ascitic fluid glucose is decreased in bacterial peritonitis, tuberculosis, and malignancy.

Elevated amylase levels can indicate pancreatitis or gastrointestinal perforation.

Alkaline phosphatase elevation suggests intestinal perforation.