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The choroid plexus (CP) (from Greek ''khorion'' "membrane enclosing the fetus, afterbirth"; ''plexus'': Mod.L., lit. "braid, network") is a plexus of cells that produces the cerebrospinal fluid in the ventricles of the brain. The choroid plexus consists of modified ependymal cells. CSF is recycled (flushed) 4 times per day in order to clean out metabolites and toxins like beta amyloid. Hence the choroid plexus must produce about 500 milliliters of CSF daily (or 21 mL per hour). When a "dangling choroid plexus" is seen located in a dilated lateral ventricle on ultrasound, the fetal anomaly spina bifida is suspected. ==Structure== There are four choroid plexuses in the brain, one in each of the ventricles. The CP consists of a layer of cuboidal epithelial cells surrounding a core of capillaries and loose connective tissue. The CP epithelial layer is continuous with the ependymal cell layer that lines the ventricles, but unlike the ependyma, the epithelial layer has tight gap junctions between the cells on the side facing the ventricle (apical surface). These gap junctions prevent the majority of substances from crossing the cell layer into the CSF; thus the CP acts as a blood–CSF barrier. The CP 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 CP. CSF is formed as plasma is filtered from the blood through the epithelial cells. CP epithelial cells actively transport sodium, chloride and bicarbonate ions into the ventricles and water follows the resulting osmotic gradient. Choroid plexus is present in all components of the ventricular system except for the cerebral aqueduct, frontal horn of the lateral ventricle, and occipital horn of the lateral ventricle.〔 Choroid plexus is found in the superior part of the inferior horn of the lateral ventricles. It follows up along this boundary, continuous with the inferior of the body of the lateral ventricles. It passes into the interventricular foramen, and is present at the top of the third ventricle. There is also choroid plexus in the fourth ventricle, in the section closest to the bottom half of the cerebellum. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Choroid plexus」の詳細全文を読む スポンサード リンク
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