| Choroid plexus | |
|---|---|
 Choroid plexus shown in the fourth ventricle | |
 | |
| Details | |
| Identifiers | |
| Latin | plexus choroideus |
| MeSH | D002831 |
| NeuroNames | 1377 |
| TA98 | A14.1.09.279 A14.1.01.307 A14.1.01.306 A14.1.01.304 A14.1.05.715 |
| TA2 | 5654,5786,5980 |
| FMA | 61934 |
| Anatomical terms of neuroanatomy | |
Thechoroid plexus, orplica choroidea, is aplexus ofcells that arises from thetela choroidea in each of theventricles of the brain.[1] Regions of the choroid plexus produce and secrete most of thecerebrospinal fluid (CSF) of thecentral nervous system.[2][3] The choroid plexus consists of modifiedependymal cells surrounding a core ofcapillaries andloose connective tissue.[3] Multiplecilia on the ependymal cells move to circulate the cerebrospinal fluid.[4]
There is a choroid plexus in each of the fourventricles. In thelateral ventricles, it is found in thebody, and continued in an enlarged amount in theatrium. There is no choroid plexus in theanterior horn. In thethird ventricle, there is a small amount in the roof that is continuous with that in the body, via theinterventricular foramina, the channels that connect the lateral ventricles with the third ventricle. A choroid plexus is in part of the roof of thefourth ventricle.[citation needed]
The choroid plexus consists of a layer ofcuboidal epithelial cells surrounding a core ofcapillaries andloose connective tissue.[3] Theepithelium of the choroid plexus is continuous with theependymal cell layer (ventricular layer) that lines the ventricular system.[5] Progenitor ependymal cells are monociliated but theydifferentiate into multiciliated ependymal cells.[6][7] Unlike the ependyma, the choroid plexus epithelial layer hastight junctions[8] 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.[citation needed] 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.[9]
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 muchactive transport of substances into, and out of, the CSF as it is made.[citation needed]
The choroid plexus regulates the production and composition ofcerebrospinal fluid (CSF), that provides the protective buoyancy for the brain.[2][10] CSF acts as a medium for theglymphatic filtration system that facilitates the removal of metabolic waste from the brain, and the exchange ofbiomolecules andxenobiotics into and out of the brain.[10][11] 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.[citation needed]
The choroid plexus is also a major source oftransferrin secretion that plays a part iniron homeostasis in the brain.[12][13]
Theblood–cerebrospinal fluid barrier (BCSFB) is a fluid–brain barrier that is composed of a pair of membranes that separate blood from CSF at the capillary level and CSF from brain tissue.[14] The blood–CSF boundary at the choroid plexus is a membrane composed ofepithelial cells andtight junctions that link them.[14] There is a CSF-brain barrier at the level of the pia mater, but only in the embryo.[15]
Similar to theblood–brain barrier, the blood–CSF barrier functions to prevent the passage of most blood-borne substances into the brain, while selectively permitting the passage of specific substances (such as nutrients) into the brain and facilitating the removal of brain metabolites and metabolic products into the blood.[14][16] Despite the similar function between the BBB and BCSFB, each facilitates the transport of different substances into the brain due to the distinctive structural characteristics of each of the two barrier systems.[14] For a number of substances, the BCSFB is the primary site of entry into brain tissue.[14]
The blood–cerebrospinal fluid barrier has also been shown to modulate the entry of leukocytes from the blood to the central nervous system. The choroid plexus cells secretecytokines that recruitmonocyte-derived macrophages, among other cells, to the brain. This cellular trafficking has implications both in normal brain homeostasis and inneuroinflammatory processes.[17]
Duringfetal development, somechoroid plexus cysts may form. These fluid-filled cysts can be detected by a detailedsecond trimester ultrasound. The finding is relatively common, with a prevalence of ~1%. Choroid plexus cysts are usually an isolated finding.[18] The cysts typically disappear later during pregnancy, and are usually harmless. They have no effect on infant and early childhood development.[19]
Choroid plexus cysts are associated with a 1% risk of fetalaneuploidy.[20] The risk of aneuploidy increases to 10.5-12% if other risk factors or ultrasound findings are noted. Size, location, disappearance or progression, and whether the cysts are found on both sides or not do not affect the risk of aneuploidy. 44-50% ofEdwards syndrome (trisomy 18) cases will present with choroid plexus cysts, as well 1.4% ofDown syndrome (trisomy 21) cases. ~75% of abnormal karyotypes associated with choroid plexus cysts are trisomy 18, while the remainder are trisomy 21.[18]
Choroid plexus translates from the Latinplexus chorioides,[21] which mirrorsAncient Greekχοριοειδές πλέγμα.[22] The wordchorion was used byGalen to refer to the outer membrane enclosing the fetus. Both meanings of the word plexus are given as pleating, or braiding.[22] As often happens language changes and the use of bothchoroid orchorioid is both accepted.Nomina Anatomica (nowTerminologia Anatomica) reflected this dual usage.[citation needed]
This article incorporates text in thepublic domain frompage 798 of page 841 of page 816 of the 20th edition ofGray's Anatomy(1918)
The embryonic CSF-brain barrier, shown in Figure 1(f). In the ventricular zone is a temporary barrier between the CSF and brain parenchyma. In early brain development, strap junctions are present between adjacent neuroepithelial cells; these form a physical barrier restricting the movement of larger molecules, such as proteins, but not smaller molecules. At later stages of development and in the adult brain, these strap junctions are no longer present when this interface becomes ependyma.
