The choroid plexus consists of invaginated folds of pia mater, rich in dilated fenestrated capillaries, that penetrate the interior of the brain ventricles. It is found in the roofs of the third and fourth ventricles and in part in the walls of the lateral ventricles.
The choroid plexus is composed of loose connective tissue of the pia mater, covered by a simple cuboidal or low columnar epithelium made of ion-transporting cells .
The main function of the choroid plexus is to elaborate cerebrospinal fluid, which contains only a small amount of solids and completely fills the ventricles, central canal of the spinal cord, subarachnoid space, and perivascular space. Cerebrospinal fluid is important for the metabolism of the central nervous system and acts as a protective device against mechanical shocks.
Cerebrospinal fluid is clear, has a low density (1.004–1.008 g/ mL), and is very low in protein content. A few desquamated cells and two to five lymphocytes per milliliter are also present. Cerebrospinal fluid is continuously produced and circulates through the ventricles, from which it passes into the subarachnoid space. There, arachnoid villi provide the main pathway for absorption of cerebrospinal fluid into the venous circulation.
Choroid Plexus & Cerebrospinal Fluid-Histology of Nervous System