choroid plexus choroid plexus the choroid plexus, or plica choroidea, is a plexus of cells that arises from the tela choroidea in each of the ventricles of the brain. regions of the choroid plexus produce and secrete most of the cerebrospinal fluid (csf) of the central nervous system. the choroid plexus consists of modified ependymal cells surrounding a core of capillaries and loose connective tissue. multiple cilia on the ependymal cells move to circulate the cerebrospinal fluid. choroid plexuschoroid plexus shown in lateral ventriclecoronal section of lateral and third ventricles.detailsidentifierslatinplexus choroideusmeshd002831neuronames1377ta98a14.1.09.279 a14.1.01.307 a14.1.01.306 a14.1.01.304 a14.1.05.715ta25654, 5786, 5980fma61934anatomical terms of neuroanatomy structure location scheme of roof of fourth ventricle. the arrow is in the median aperture.1: inferior medullary velum2: choroid plexus 3: cisterna magna of subarachnoid space4: central canal5: corpora quadrigemina6: cerebral peduncle7: superior medullary velum8: ependymal lining of ventricle9: pontine cistern of subarachnoid space there is a choroid plexus in each of the four ventricles. in the lateral ventricles it is found in the body, and continued in an enlarged amount in the atrium. there is no choroid plexus in the anterior horn. in the third ventricle there is a small amount in the roof that is continuous with that in the body, via the interventricular foramina, the channels that connect the lateral ventricles with the third ventricle. a choroid plexus is in part of the roof of the fourth ventricle. microanatomy 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 (ventricular layer) that lines the ventricular system. progenitor ependymal cells are monociliated but they differentiate into multiciliated ependymal cells. 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 increase 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. function csf circulation the choroid plexus regulates the production and composition of cerebrospinal fluid (csf), that provides the protective buoyancy for the brain. csf acts as a medium for the glymphatic filtration system that facilitates the removal of metabolic waste from the brain, and the 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. blood–cerebrospinal fluid barrier