Choroid Plexus - Structure of The Choroid Plexus

Structure of The Choroid Plexus

The choroid plexus (CP) consists of many capillaries, separated from the ventricles by choroid epithelial cells. Liquid 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.

There are four choroid plexi in the brain, one in each of the ventricles. The CP consist 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 CP epithelial layer has tight junctions in 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 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.

In addition to CSF production, the CP act as a filtration system, removing metabolic waste, foreign substances, and excess neurotransmitters from the CSF. In this way the CP has a very important role in helping to maintain the delicate extracellular environment required by the brain to function optimally.