Blood Brain Barrier and CSF Flashcards
What are the 3 meningeal layers?
Dura mater, arachnoid, pia mater
Describe the dura mater
Adjacent to the skull (and attached to it in places). It has two layers, periosteal and meningeal, and these are fused together
Describe the arachnoid
Membrane has an outer compact layer of ‘barrier’ cells and an inner ‘trabecular’ meshwork
Describe the pia mater
Thin membrane which is tightly attached to the basement lamina of the brain
Where are veins found within the meninges?
Inner layers of the dura (meningeal layer) and crossing the dura-arachnoid interface
Where are blood vessels found within the meninges?
Within the dura and arachnoid
What is an epidural haemorrhage?
Involves bleeding outside of the dura, and it is usually arterial so there is a rapidly increasing size, usually caused by acute skull trauma
What is a subdural haemorrhage?
Where there is bleeding between the dura and arachnoid, and this usually occurs from damage to bridging veins, (from dura and arachnoid) so the onset of symptoms is slow as the blood spreads diffusely over the brain surface. Usually caused by rapid acceleration or deceleration of the head
What is a subarachnoid haemorrhage?
Where there is bleeding in the subarachnoid space and this is often due to a ruptured aneurysm, and therefore is a form of stroke
What is the falx cerebri?
Sheet of dura that extends down between the two hemispheres in order to divide them
What are the tentoria?
a pair of approximately transverse sheets of dura which extend laterally below the base of the occipital cerebrum, and they divide the cerebrum above from the cerebellum below
What is the tentorial notch?
Gap between the two tentoria where the brainstem passes
Outline how different compounds cross the BBB
Tight junctions prevent the passage of macromolecules, glucose is via GLUT transporters, amino acids via transporters (different depending on amino acid being basic, acidic or neutral) and lipid-soluble molecules can diffuse across BBB
Describe the structure of the blood-brain-barrier
Astrocyte end-feet and the tight junction system between the endothelial cells lining cerebral capillaries (prevent proteins leaving blood) make up the BBB
Describe how cerebrospinal fluid is formed
Formed by the choroid plexus; a network of capillaries that are covered by ependymal cells that protrude into the ventricles of the brain, the choroid capillaries are fenestrated and ultrafiltrate of the blood passes through these fenestrations into the subependymal layer
Where is most of the CSF formed?
Choroid plexus of the lateral ventricles
Describe the composition of CSF
Very little protein, no cells and less glucose than plasma
Outline the flow of the cerebrospinal fluid
Lateral ventricles –> third ventricle –> fourth ventricle cisterna magna –> subarachnoid space absorbed in arachnoid granulations (penetrate dura at top of brain and enable drainage into SSS) –> joins venous blood in superior sagittal sinus
What type of vein runs in the skull?
Diploic
What is hydrocephaly?
Accumulation of CSF in ventricular system resulting from obstruction of normal CSF circulation, usually treated by inserting a tube into the 3rd ventricle that leads to the subarachnoid space in order to allow shunting
What type are most brain tumours?
Astrocytomas
Explain the role of astrocytes in brain homeostasis
Maintain local pH and glucose in correct range, secrete GF , secrete cytokines to regulate immune cell function, form astrocytic scars in CNS injury repair
