Case 16- Anatomy and infection Flashcards
Structure of the blood brain barrier
1) The blood vessels that pass through the brain are surrounded by an endothelial layer.
2) The endothelial cells are linked together by tight junctions.
3) The tight junctions provide a physical barrier preventing unwanted molecules from passing between the endothelial cells into the brain.
4) Otherwise there would be a lot of gaps between the blood cells.
5) Surrounding the endothelial layer is a layer of glial cells called astrocytes.
Importance of tight junctions
1) Tight junctions only allow specific substances to cross the cell membrane, they provide a polarity in the cell membrane where there are different proteins in the apical and basal cell membrane.
2) Prevents stuff from passing in between the endothelial cells.
3) Anything that enters the brain from the blood has to pass through the endothelial cells.
Astrocytes- blood brain barrier
Provides structural support for the brain as well as providing nutrients to neurones and providing a safe environment for neurones to survive (gets rid of toxins, provides ideal pH)
Astrocytes and end feet
The Astrocytes send End-feet which wrap around the capillary wall and help monitor the endothelial cells. Communication between the Astrocytes and endothelial cells to make sure that everything is being controlled properly
The three structures that form the blood brain barrier
Astrocytes, endothelial cells and tight junctions isolate the brain from the rest of the blood system
What can cross the blood brain barrier
- Astrocyte specific transporters- i.e. Glucose, potassium, channels, aquaporins etc
- Basal membrane specific transporters i.e. glucose, amino aicds, ion transporters
- Apical membrane specific transporters (series of protein transporters) i.e. glucose, amino acids, ion transporters
What is not allowed to enter the blood brain barrier
Because of the polarity of the membrane you have different transporters on the apical membrane then on the basal membrane. Specific proteins let certain substances enter. The blood-brain barrier protects the integrity and environment of the CNS. Often drugs cant pass through the blood brain barrier. It even tightly controls and restricts immune cells from crossing. It immune privileged and has its own immune cells, the microglia. Drugs that we want to affect the brain must be able to cross the blood brain barrier.
Ventricles
1) The neural tube forms cavities in the brain called ventricles which contain CSF
2) 70% of CSF is made by the choroid plexus, 30% is made by Ependymal cells (epithelia lining the ventricles)
3) The ventricles are continuous with the spinal cord
The third ventricle
The third ventricle is connected to the lateral ventricle through the intraventricular foramen. The third ventricle sits between the two thalamic nuclei in the centre of the brain and connects the fourth ventricle (which lies under the cerebellum) through the cerebral aqueduct. The two thalami form the walls of the third ventricle.
Structure from the lateral ventricles to the 4th ventricle
1) The two lateral ventricles are in a C shape with one in each hemisphere, the top of the ‘C’ shaped lateral ventricles are positioned under the corpus callosum and the frontal and parietal lobes of the cerebral cortex.
2) The third ventricle is in the middle of the brain and there is a hole running through it.
3) Below the third ventricle, a thin tube called the cerebral aqueduct runs down towards the base of the brain, it opens out into the 4th ventricle underlying the cerebellum.
4) The Cerebral aqueduct runs from the top of the brainstem through the pons and medulla.
5) The ventricles then continue into the spinal cord where they become the central canal which runs down the center of the spinal cord.
Structure from the 4th ventricle downwards
1) Within the 4th ventricle CSF flows out through the lateral and median Aperture.
2) The CSF flows into the Cristerna magna and then surrounds the brain.
3) It then flows from the Subarachnoid space, through the Arachnoid villi into the superior sagittal sinus where it joins the blood stream.
4) Also flows into the central canal and down the spinal cord. The CSF is produced in all the ventricles but mostly the lateral one.
Choroid plexus
Ependymal cells line the walls of the ventricle and form specialist tissue called the choroid plexus. Its the main tissue that produces and secretes CSF in the ventricles.
Flow of CSF
1) A small pressure is produced when CSF is made, this pushes CSF from the lateral ventricles, through the interventricular foramen to the third ventricle.
2) Then goes down the cerebral aqueduct to the 4th ventricle.
3) It then flows out through other foramen and over the whole surface of the brain.
Purpose of CSF
1) The brain is bathed in CSG which cushions the brain from the skull during excessive movement. Also protects the spinal cord.
2) CSF is removed by flowing into the bloodstream through bumps in the meninges (arachnoid mater) called arachnoid granulations.
3) CSF is continuously produced and removed in the bloodstream.
4) Flow of CSF also allows for removal of unwanted waste products from the brain into the bloodstream.
5) Allows brain to float, reduces traction on nerves and blood vessels connected to the brain. Provides stable environment for CNS
What does the CSF contain
Macromolecules (proteins), nutrients (sugar, amino acids etc), waste products (urea, lactic acid), electrolytes (sodium, potassium and chloride ions) etc. Abnormal levels can indicate disease.
What can a lumbar puncture diagnose
- Diseases such as Alzheimer’s disease and Parkinson’s disease - diseases linked to abnormal protein deposition in the brain, and thus a high level of these proteins appearing in the CNS.
- Autoimmune diseases such as multiple sclerosis - high level of white blood cells, antibodies etc indicitive of an immune response.
- Cancers of the brain and spinal cord - presence of malignant cancerous cells.
- CNS infections like meningitis and encephalitis
Normal lumbar puncture
Appearance- clear Glucose- 60-80% of plasma glucose Protein- Normal White cells- <5 lymphocytes/mm^3 0 polymorphs/mm^3
Bacterial infection- lumbar puncture
Appearance- cloudy
Glucose- low (<1/2 plasma)
Protein- High (>1g/l)
White cells- 10-5,000 polymorphs/mm^3
Viral infection- lumbar puncture
Appearance- clear/cloudy
Glucose- 60-80% of plasma glucose
Protein- normal/raised
White cells- 15-1,000 lymphocytes/mm^3
Tuberculosis lumbar puncture
Appearance- slightly cloudy, viscous
Glucose- low (<1/2 plasma)
Protein- high (>1g/l)
White cells- 10-1,000 lymphocytes/mm^3
When do you see low glucose in lumbar puncture
Mumps, Tuberculosis and herpes encephalitis
Lumbar puncture procedure
- You extract a sample of CSF from the lumbar region of the spinal cord- in the cauda equina region
- Because the nerves in this region are separate when a nerve is inserted it has space to push the nerves aside without causing any damage
- The risk is still there its just reduced.
