The structure of the choroid plexus and the physiology of the choroid plexus epithelium.

The choroid plexuses (CPs) are leaf-like highly vascular structures laying in the ventricles. The main function of choroid plexuses is the production of the cerebrospinal fluid (CSF). Although CPs have a unique distribution of ion transporters/channels, the mechanism of CSF production is similar to the production of fluids in other epithelia and is based on energy released from ATP hydrolysis, which drives unidirectional flux of ions accompanied by movement of water by osmosis. The CPs have an important role in the homeostasis of nutrients in the CSF since the kinetic parameters of glucose and amino acid (AA) transport across the CPs are the main reason for the low concentration of these molecules in the CSF. The CPs appear to be source of CSF-borne hormones and growth factors, including insulin-like growth factor II (IGF II), vasopressin (VP) and transforming growth factor beta1 (TGF-beta1). The CPs also synthesise the thyroid transporting protein transthyretin and transferrin and can chelate heavy metals.