Cerebrospinal fluid is secreted into each ventricle of the brain by choroid plexuses. These are vascular area where there is a proliferation of blood vessels surrounded by ependymal cells in the lining of ventricle walls. CSF passes back into the blood through tiny diverticula of arachnoid mater,called arachnoid villi,which project into the venous sinuses. The movement of CSF from the subarachnoid space to venous sinuses depends upon the difference in pressure on each side of the walls of the arachnoid villi,which act as one-way valves. When CSF pressure is higher then venous pressure,CSF passes into the blood and when the venous pressure is higher the arachnoid villi collapse,preventing the passage of blood constituents into the CSF. There may also be some reabsorption of CSF by cells in the walls of the ventricles.
From the roof of the fourth ventricle CSF flows through foramina into the subarachnoid space and completely surrounds the brain and spinal cord. There is no intrinsic system of CSF circulation but it’s movement is aided by pulsating blood vessels,respiration and changes of posture.
CSF is a clear,slightly alkaline fluid consisting of:
- Water
- Mineral salts
- Glucose
- Plasma proteins:small amounts of albumin and globulin
- Urea
- Creatinine
- A few leukocytes
