Cerebrospinal Fluid (CSF) is Not Lined by Mesothelial Cells
The correct answer is C. CSF (cerebrospinal fluid) is the only fluid among the options that is not lined by mesothelial cells.
Mesothelial Cell Distribution in Body Cavities
Mesothelial cells form a protective monolayer that lines the serous cavities of the body, including:
- Pleural cavity - containing pleural fluid
- Pericardial cavity - containing pericardial fluid
- Peritoneal cavity - containing peritoneal fluid
These specialized epithelial cells create a non-adhesive barrier that protects against physical and biochemical damage in these cavities 1.
Cerebrospinal Fluid: Different Cellular Origin
Unlike the other fluids mentioned, cerebrospinal fluid is:
- Produced primarily by the choroid plexus epithelium and ependymal cells of the ventricles 2
- Contained within the subarachnoid space of the central nervous system
- Not lined by mesothelial cells but rather by specialized neural tissue
The CSF flows through the ventricular system and subarachnoid space, which has a completely different embryological origin and cellular composition than the mesothelium-lined cavities 3.
Characteristics of Mesothelial-Lined Cavities
Mesothelial cells lining the pleural, pericardial, and peritoneal cavities share important features:
- Express both epithelial markers (cytokeratins) and mesenchymal markers (vimentin) 1
- Produce glycocalyx, a hydrophilic protective barrier consisting mainly of glycosaminoglycans 1
- Play key roles in fluid transport and inflammation 4
- Secrete various cytokines including G-CSF, GM-CSF, M-CSF, IL-1, and IL-6 5
- Regulate electrolyte and fluid transport across serosal membranes 4
Diagnostic Implications
The distinction between mesothelial and non-mesothelial linings has important diagnostic implications:
- Cytological examination of pleural, pericardial, and peritoneal fluids may reveal mesothelial cells that can be identified by specific immunohistochemical markers 3
- Malignant mesothelioma specifically arises from mesothelial cells of the pleura, peritoneum, or pericardium, but not from the CNS 3
- Immunohistochemistry markers like calretinin, keratins 5/6, and WT1 are used to identify mesothelial cells in diagnostic samples 3
Clinical Relevance
Understanding the different cellular linings of body cavities is essential for:
- Interpreting cytological findings in fluid samples
- Differentiating between primary malignancies (like mesothelioma) and metastatic disease
- Understanding the pathophysiology of effusions in different body cavities
- Developing targeted treatments for conditions affecting specific body cavities
The mesothelium should be considered a specialized organ with distinct functions rather than just a membrane 1, while the cerebrospinal fluid system has its own unique cellular environment and functions related to the central nervous system.