CSF & Blood Brain Barrier Flashcards
Cerebrospinal fluid
-a clear fluid that surrounds the brain and spinal cord
Function of Cerebrospinal fluid
-buoyancy
-cushion the brain and spinal cord from injury
-prevention of ischemia
-nutrient delivery and waste removal system for the CNS
Manufacturing of CSF
-manufactured continuously in areas of the brain called ventricles and is absorbed by bloodstream
What is CSF derived from?
-derived from blood plasma
Contents of CSF
-the content is similar to blood plasma
-electrolytes, glucose, nitric oxide. Few proteins and cells present
Hydrocephalus
- An increased volume in the brain ventricles
- Connections between ventricles can get plugged (by tumours/growths) or narrowed
How does hydrocephaly occur?
-occurs because the CNS does not have any connective tissue or lymphatics, and has very little extracellular space (which is all the normal mechanisms that the body has to deal with excess fluid)
-The CNS is held within a confined space (brain in skull, spinal cord in vertebral canal) which does not allow for much expansion of tissues and even a small amount of fluid accumulation can increase pressure enough to cause damage
Where do the ventricles develop from?
-lateral ventricles develop from Telencephalon
-3rd ventricle (surrounds thalamus) develops from diencephalon
-aquaduct comes from mesencephalon (midbrain)
-4th ventricle comes from rhombencephalon
-central canal from spinal cord
ventricular system lining
-lined by ependymal cells (cuboidal)
-usually a smooth surface but some areas are more complex such as the choroid plexus (junction between cell types and location of CSF production)
-ciliated cells help move the CSF through ventricular system
Choroid Plexus
-junction between ependymal cells and blood vessels (blood-CSF barrier)
-production center for Cerebrospinal fluid
Plexi
-areas where the ependyma invaginates
-four in total
4 plexi
-Two lateral ventricles
-roof of 3rd ventricle (mesencephalon)
-roof of IV ventricle (metensephalon/myelencephalon)
Components needed for CSF production
-simple cuboidal epithelium with increased blood supply
-fenestrated capillaries allow for movement of molecules from blood to CSF
-tight junctions in ependyma (active and passive transport- everything needs to move through the ependyma by bidirectional flow from capillaries to ventricles)
>waste goes back into blood stream
>glucose comes into CSF
**Reason for sterile CSF environment, but also hard to use medicine to fight infections
CSF composition compared to blood
- increased H2O (99% vs. 93%
- slightly less glucose (although ependymal cells have lots of glucose transporters present
- far fewer proteins
- slightly more acidic (because there are less proteins to buffer)
- acellular (under normal conditions)
- similar osmolarity
Continued production of CSF
-replaced 4-5x daily
-regulated via pressure gradients (osmotic pressure) and autonomic nervous system so when CSF pressure is high, CSF production decreased
Movement of CSF
-moves via ciliated cells and pressure gradients (from rostral to caudal)
-rate of flow is influenced by rate of production
Clinical significance of CSF production and composition
-Brain tissue cannot expand therefore when there is head trauma (brain swelling), can reduce CSF and intracranial pressure by giving patient hypertonic saline or mannitol (20%)
> > these large molecules will draw water out of CSF and shrink the ventricles to provide more space
**Hypertonic blood will result in decreased CSF production
CSF movement steps
-Lateral ventricles to III ventricle to mesencephalic aqueduct to IV ventricle to central canal
**some of the CSF flows out of the lateral apertures of the IV ventricles into the subarachnoid space
Subarachnoid space and CSF
-arachnoid has long thin trabeculae, creating a space within the meningeal layer and the space between then trabeculae is the sub arachnoid space
-this spaces surrounds the entire CNS and is filled with CSF
Venous sinus
-large space connected to subarachnoid space which allows for CSF to drain and be recycled
CSF collection sites
1.cervical spinal puncture (cerebellomedullary cistern/cervical cistern)
2.lumbar spinal puncture (lumbar cistern)
Blood brain barrier vessels
Start in the meninges and dive into deeper CNS tissues
-Astrocytes are always surrounding the vasculature of CNS
- Creates a glial limiting membrane
Pericytes function
-provide support to endothelial cells in CNS
-paracrine signaling
- important for the development of the CNS vasculature
BBB purpose
-BBB protects the CNS from many substances and cells
- keeps out circulating immune cells, toxins, pathogens, most viruses, and drugs
**some drugs are able to penetrate the BBB (ie. heroin)
