Question

A) Where does the blood brain barrier (BBB) exist? (state where it anatomically is) B) How are the capillaries at the BBB different from capillaries at the blood-CSF barrier, include where this blood-CSF barrier exists)  C) Why do they have this difference? D) Where does CSF flow as it circulates and what is its function? What anatomy is involved with the return of CSF to blood?

Answer 1

A. The blood-brain barrier is the barrier between the cerebral capillary blood and the interstitial fluid of the brain. It is made up of capillary endothelial cells and basement membrane, neuroglial membrane, and glial podocytes.

Circumventricular organs (CVOs) are individual structures located adjacent to the fourth ventricle or third ventricle in the brain, and are characterized by dense capillary beds with permeable endothelial cells unlike those of the blood-brain barrier.

B &C : Th blood–CSF boundary at the choroid plexus is a membrane composed of epithelial cells and tight junctions that link them. There is a CSF-brain barrier at the level of the pia mater, but only in the embryo.

BBB separates the lumen of the brain capillaries from the brain parenchyma. The main contribution to the BBB property of reduced permeability comes from the tight junctions among endothelial cells lining the capillaries. so it is call neurovascular unit also comprises the pericytes, a basement membrane surrounding both pericytes and endothelial cells and astrocyte end-feet processes from nearby astrocytes.

Blood-CSF barrier is found in the choroid plexus of each ventricle of the brain. Unlike the endothelium in the brain parenchyma, capillaries of the choroid plexus have no tight junctions and are fenestrated.

unlike the BBB, the blood-CSF barrier is located at epithelial level, while capillaries are relatively leaky and permeable to small molecules, thus allowing, among other processes, the rapid delivery of water through the bloodstream to the surrounding epithelial cells for CSF production in the choroid plexus.

D. The cerebrospinal fluid is produced from arterial blood by the choroid plexuses of the lateral and fourth ventricles by a combined process of diffusion, pinocytosis and active transfer. The circulation of CSF is aided by the pulsations of the choroid plexus and by the motion of the cilia of ependymal cells.

Cerebrospinal fluid has three main functions: CSF protects brain and spinal cord from trauma.

CSF supplies nutrients to nervous system tissue.

CSF removes waste products from cerebral metabolism.