Production of the Cerebrospinal Fluid

Ventricular System of the Brain &CSF Circulation

Illustration from Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/

The ventricular system in the brain consists of four cavities that are interconnected and function together to ensure that many of the biological needs of the body's systems are met. The four cavities that exist in the human brain are what are referred to as the ventricles, and the ventricles represent a range of different sizes. These structures develop early in the embryological development in humans and are an offshoot of the neural canal in the early stages of an embryo's growth. These ventricles perform a vital function for the body through the production of the cerebrospinal fluid (CSF) by the choroid plexuses that are located within them. This paper will briefly give an illustrated introduction to the development, structure, and functioning of this vital bodily function.

Development and Structure

The brain ventricular system is composed of a highly conserved set of cavities that contain cerebrospinal fluid (CSF), a protein-rich fluid essential for brain function, yet, little is known about the function of embryonic CSF (eCSF), or the mechanisms of CSF production, retention, and circulation that regulate brain ventricle shape and size (Chang, 2012). Researchers however are continually learning more about the specific manner in which these structures begin to form in the early development of an embryo. For example, some research has used zebrafish as subjects so that they can dissect the brain at different stages of development to study it and have identified insights such as the fact that Na, K-ATPase regulates three aspects of brain ventricle development essential for normal function - neuroepithelial formation, permeability, and CSF production (Chang, 2012). Figure 2 - https://embryology.med.unsw.edu.au/embryology/index.php/Neural_-_Ventricular_System_Development

Yet, despite whatever limitations may exist today in the understanding of how this system forms, much of the development is understood in a more general sense. For example, the ventricular system develops from the single cavity formed from the hollow neural tube and this fluid-filled space is separated from the amnion following fusion of the neural tube and closure of neuropores; the neuropores are at different regions sites within the wall (floor of lateral ventricle and roof of the third and fourth ventricles) differentiate to form choroid plexus a modified vascular structure which will produce cerebrospinal fluid (CSF) (Embryology, 2016). In the adult, the choroid plexus produces about two thirds of the CSF, the rest is produced by ventricular ependymal cells and cells lining the subarachnoid space.

CSF Functioning

In adults, CSF is produced from arterial blood plexuses of the lateral and fourth ventricles by a combined process of diffusion, pinocytosis and active transfer, while a small amount is also produced by ependymal cells (Agamanolis, 2013). The choroid plexus consists of tufts of capillaries with thin fenestrated endothelial cells and unlike any of the body's other organs and tissues, these cells have no visicles that are used for transportation, rather they have tight junctions between these cells that have receptors and ion channels on the surface that forms what is known as the blood-brain barrier (BBB) (Agamanolis, 2013). This barrier plays and important role in keeping toxic substances out of the brain and also allowing for the removal of any unwanted substances. Once the CSF is produced by the choroid plexus (mainly in the third and fourth ventricles), it then flows into the subarachnoid space through the foramina of Luschka (there are two of these) and the foramen of Magendie (only one of these) (Chudler, N.d.). Once the production of this fluid is complete and it is released, it has four primary functions in the body (Chudler, N.d.): Figure 3 - http://neuropathology-web.org/chapter14/chapter14CSF.html