ependyymi

Ependyymi are the ependymal linings that line the ventricular system of the brain and the central canal of the spinal cord. They form the epithelial layer that covers these cavities and provides a selective interface between cerebrospinal fluid (CSF) and brain tissue.

The epithelium of the ependyymi is composed of ependymal cells, which are typically simple cuboidal to columnar. Many ependymal cells have motile cilia on their apical surface to help circulate CSF, and microvilli that increase surface area for exchange. In the walls of the ventricles the ependyma may be specialized, such as the choroid plexus epithelium, which participates in CSF production and modification. Tanycytes and other specialized ependymal cells are found in certain regions and can participate in transport between CSF and brain tissue.

Functions of the ependyymi include facilitating CSF movement, forming part of the blood-CSF barrier, and contributing to CSF homeostasis. While most ependymal cells are not high-rate producers of CSF, the choroid plexus epithelium within the ventricles is the principal site of CSF secretion. Some ependymal cells retain progenitor-like properties and may participate in neurogenesis or tissue repair under certain conditions.

Developmentally, the ependyma arises from the neural tube's neuroepithelium and lines the ventricular system and spinal canal. Clinically, ependymal-derived tumors called ependymomas can occur within the ventricles or spinal canal and may disrupt CSF flow, causing hydrocephalus. Inflammation or injury to the ependyma can also affect CSF dynamics.