Pt4 CSF & BBB Flashcards
What are the meninges and what are the 3 layers?
-brain and spinal cord are surrounded by 3 layers of CT = “meninges”
1. Dura mater (outer)
2. Arachnoid (middle)
3. Pia mater (inner)
Describe dura mater.
-outermost layer
-fused with inner surface of skull
-thicker, protects CNS
Describe arachnoid.
-spiderweb appearance = network of trabeculae that join the pia mater
-thin, loose CT
-subarachnoid space:
>between arachnoid & pia mater
>traps CSF
>CSF circulates & is absorbed here
Describe pia mater.
-innermost
-adheres to surface of CNS
Describe the blood supply for the CNS.
-CNS has a high metabolic rate & receives 20% of total cardiac output (blood).
-more O2 needed for synapses & cell bodies than axons
-grey matter gets more blood than white
-association/integration areas have greater requirements than other areas
-forebrain is more vascular than other CNS regions
CNS & meninges are drained by veins & sinuses
Describe the ventricular system.
-4 expanded regions forming ventricles, interconnecting foramens and tubes
1. Lateral ventricles (2) = longitudinal in each hemisphere & connected with 3rd ventricle
2. Third ventricle = surrounding interthalamic adhesion and connected with the 4th ventricle
3. Fourth ventricle = connected with the subarachnoid space & central canal of spinal cord
Describe CSF and its functions.
found in ventricular system, central canal, & subarachnoid space
-clear, colorless fluid
Functions:
-protects brain and spinal cord against impact of bony walls
-waste control that removes harmful cellular metabolites
-brain distribution system for peptide hormones & growth factors
-maintain extracellular micro environment for neurons and glia
What are the two ways neurons and neuroglia cells receive materials?
- Capillaries in choroid plexus = micronutrients
- Interstitial capillaries = O2 & macronutrients like glucose
What is the choroid plexus?
-most of CSF formed here
-cauliflower like growth of capillaries covered by a thin layer of modified ependymal cells (choroid epithelium)
-fourth ventricle
What is the function of the choroid epithelium?
-selective tight junction barrier
-membrane transporters & selective channels
-controls composition of CSF
-created from blood plasma
-99% water, diff ions, almost no proteins
-micronutrients (folates, Vit C & B6)
What are the steps for the secretion of cerebrospinal fluid?
- H2O in choroid epithelial cells combines with intracellular CO2 produced by cell metabolism to form H+ & HCO3-
- At basal surface, H+ is exchanged for extracellular Na+ from blood
- Influx of Na+ = excess positive charge
- To neutralize this, Cl- & HCO3- move into ventricles
- Na+ pumped out through apical surface into ventricles
- H2O diffuses into ventricles = maintain osmotic balance
Describe the flow of CSF.
Lateral ventricles -> third ventricle-> cerebral aqueduct -> fourth ventricle -> subarachnoid space -> arachnoid villus -> dorsal sag sinus -> veins
OR
Fourth ventricle -> central canal
Describe CSF rate of formation.
-1 ml/hr in cats, 3 ml/hr dogs, 20 ml/hr humans
-constant formation = independent of changes in pressure
-most of CSF is absorbed from subarachnoid space into the venous sinuses through arachnoid villi
>finger like projections of arachnoid membrane that poke through dura mater in lumen of venous sinuses
Describe CSF absorption.
-pressure dependent & unidirectional
-CSF can flow from subarachnoid space to venous outflow system
>fluid (including waste products & foreign matter like blood) move into sinus
-venous blood can’t move back into subarachnoid space
Describe the CSF clinical correlations.
-pressure, cell count, chemical constituents of CSF can be sampled via spinal taps for diseases of CNS
>cisterns magna
-myelography
>injection of radiopaque dyes into CSE of subarachnoid space
-used with CT scan to access spinal canal
-hydrocephalus = abnormal dilation of ventricular system from an increased volume of CSF (congenital or acquired)
