Choroid plexus

The choroid plexus is a plexus of cells that produces the cerebrospinal fluid in the ventricles of the brain. The choroid plexus consists of modified ependymal cells.Coronal section of inferior horn of lateral ventricle.Choroid Plexus Histology 40xChoroid plexusChoroid plexus The choroid plexus is a plexus of cells that produces the cerebrospinal fluid in the ventricles of the brain. The choroid plexus consists of modified ependymal cells. There is a choroid plexus in each of the four ventricles of the brain. In the lateral ventricles it is only present in the inferior horn. Choroid plexus is also located in the interventricular foramina, the channels between the lateral and the third ventricles. The choroid plexus in the fourth ventricle is beneath the cerebellum. The choroid plexus consists of a layer of cuboidal epithelial cells surrounding a core of capillaries and loose connective tissue. The epithelium of the choroid plexus is continuous with the ependymal cell layer that lines the ventricles. The cells of the choroid plexus are non ciliated but, unlike the ependyma, the choroid plexus epithelial layer has tight junctions between the cells on the side facing the ventricle (apical surface). These tight junctions prevent the majority of substances from crossing the cell layer into the cerebrospinal fluid (CSF); thus the choroid plexus acts as a blood–CSF barrier. The choroid plexus folds into many villi around each capillary, creating frond-like processes that project into the ventricles. The villi, along with a brush border of microvilli, greatly increases the surface area of the choroid plexus. CSF is formed as plasma is filtered from the blood through the epithelial cells. Choroid plexus epithelial cells actively transport sodium ions into the ventricles and water follows the resulting osmotic gradient. The choroid plexus consists of many capillaries, separated from the ventricles by choroid epithelial cells. Fluid filters through these cells from blood to become cerebrospinal fluid. There is also much active transport of substances into, and out of, the CSF as it is made. The choroid plexus mediates the production of cerebrospinal fluid (CSF). CSF acts as a medium for filtration system that facilitates the removal of metabolic waste from the brain and exchange of biomolecules and xenobiotics into and out of the brain. In this way the choroid plexus has a very important role in helping to maintain the delicate extracellular environment required by the brain to function optimally. The choroid plexus is also a major source of transferrin secretion that plays a part in iron homeostasis in the brain. The blood–cerebrospinal fluid barrier (BCSFB) is a fluid–brain barrier that is composed of a pair of membranes that separate blood from CSF and CSF from brain tissue. The blood–CSF boundary at the choroid plexus is a membrane composed of epithelial cells and tight junctions that link them. The brain–CSF boundary is the arachnoid membrane, which envelops the surface of the brain. Similar to the blood–brain barrier, the blood–CSF barrier functions to prevent the passage of most blood-borne substances into the brain, while selectively permitting the passage specific substances into the brain and facilitating the removal of brain metabolites and metabolic waste into the blood. Despite the similar function between the BBB and BCSFB, each facilitates the transport of different substances into the brain due to the distinct structural characteristics between the two barrier systems. For a number of substances, the BCSFB is the primary site of entry into brain tissue.