Fig. 1

Locations and functions of the choroid plexuses and the blood brain barrier. a The choroid plexuses are discrete structures located in the cerebral ventricles, which are filled with cerebrospinal fluid. Fluid can flow from the ventricles into the cisterna magna and from there to the subarachnoid spaces of the brain and spinal cord. b A cast of the vascular system of a human brain. The blood–brain barrier, which comprises the lining of the smallest and most numerous branches of the vascular system, the microvessels, is present almost everywhere in the brain. c Diagram of a cross section of part of a single villus of a choroid plexus as would be seen by light microscopy. The apical brush border is well separated from most of the basolateral membrane. d Diagram of a cross section of a microvessel wall and adjacent parenchyma as could be seen in an electron micrograph. Note the difference in scales in c and d. a–d are reproduced with permission: a from [26] as relabelled in [15], b from [536] (promotional and commercial use of the material in print, digital or mobile device format is prohibited without the permission from the publisher Wolters Kluwer. Please contact healthpermissions@wolterskluwer.com for further information), c, d from [15]. For an image of part of a choroid plexus see Fig. 5