Choroid Plexus

Ependymal Cells
Colored scanning electron micrograph (SEM) of the lining of the brain, showing ependymal cells (yellow) and ciliary hairs (green).

STEVE GSCHMEISSNER/Science Photo Library/Getty Images

The choroid plexus is a network of capillaries and specialized ependymal cells that are found in the cerebral ventricles. The choroid plexus serves two important functions in the body. It produces cerebrospinal fluid and helps to provide a barrier that protects the brain and other central nervous system tissue from toxins. The choroid plexus and the cerebrospinal fluid that it produces are necessary for proper brain development and central nervous system function.


The choroid plexus is located in the ventricular system. This series of connecting hollow spaces house and circulate cerebrospinal fluid. Choroid plexus structures are found in certain locations within both lateral ventricles, as well as within the third ventricle and fourth ventricle of the brain. The choroid plexus resides within the meninges, the membrane lining that covers and protects the central nervous system. The meninges are composed of three layers known as the dura mater, arachnoid mater, and pia mater. The choroid plexus can be found in the innermost layer of the meninges, the pia mater. The pia mater membrane contacts and directly covers the cerebral cortex and spinal cord.


The choroid plexus is composed of blood vessels and specialized epithelial tissue called ependyma. Ependymal cells contain hair-like projections called cilia and form a tissue layer that encases the choroid plexus. Ependymal cells also line the cerebral ventricles and spinal cord central canal. Ependymal cells are a type of nervous tissue cell called neuroglia that helps to produce cerebrospinal fluid.


The choroid plexus serves two important functions necessary for proper brain development and protection against harmful substances and microbes.

Cerebrospinal Fluid Production
Choroid plexus ependymal cells are vital for the production of cerebrospinal fluid. Ependyma tissue surrounds the capillaries of the choroid plexus separating them from the cerebral ventricles. Ependymal cells filter water and other substances from capillary blood and transport them across the ependymal layer into the brain ventricles. This clear fluid is the cerebrospinal fluid (CSF) that fills the cavities of the cerebral ventricles, the central canal of the spinal cord, and the subarachnoid space of the meninges. CSF helps to cushion and support the brain and spinal cord, circulate nutrients, and remove waste from the central nervous system. As such, it is vital that the choroid plexus function properly. Underproduction of CSF would stunt brain growth and overproduction could lead to excess accumulation of CSF in brain ventricles; a condition known as hydrocephalus.

Blood–Cerebrospinal Fluid Barrier
The choroid plexus, along with the arachnoid membrane of the meninges, forms a barrier between the blood and the cerebrospinal fluid. This barrier is called the blood–cerebrospinal fluid barrier. Together with the blood-brain barrier, the blood-cerebrospinal fluid barrier serves to prevent harmful substances in the blood from entering the cerebrospinal fluid and causing damage to central nervous system structures. Numerous white blood cells, including macrophages, dendritic cells, and lymphocytes can also be found in the choroid plexus. Microglia (specialized nervous system cells) and other immune cells enter the central nervous system through the choroid plexus. These cells are important for preventing pathogens from entering the brain. In order for viruses, bacteria, fungi, and other parasites to infect the central nervous system, they must cross the blood-cerebrospinal fluid barrier. Some microbes, such as those that cause meningitis, have developed mechanisms for crossing this barrier.


  • Liddelow, Shane A. “Development of the Choroid Plexus and Blood-CSF Barrier.” Frontiers in Neuroscience 9 (2015): 32. PMC.
  • Lun, Melody P., Edwin S. Monuki, and Maria K. Lehtinen. “Development and Functions of the Choroid Plexus–cerebrospinal Fluid System.” Nature reviews. Neuroscience 16.8 (2015): 445–457. PMC.