Cerebral Vasculature Flashcards
What proportion of blood, glucose and oxygen does the brain take?
Even though it is 2% of body weight:
Cardiac output: 10-20%
Oxygen consumption: 20%
Liver glucose: 66%
:. If blood supply is impaired, brain is very vulnerable
What are the main arteries that carry blood from the heart to the brain?
Branch off the aorta:
Brachioceohalic artery -> splits into Right common carotid artery (and also subclavian)
Left common carotid
Carotids split around the level of the Adam’s apple into internal (enters skull) and external (supplies the structures of the face) carotid arteries
Also vertebral arteries. Go through transverse foramen of the cervical vertebrae and enters foramen magnum
What are the arteries supplying the brain?
Circle of Willis
Look up a diagram!!!
Main vessels from front to back are:
Internal carotid arteries
Vertebral arteries (these combine to form the basilar artery, sits in the base of the pond)
The basilar then splits into two posterior cerebral arteries
The main branch of the internal carotids is a middle cerebral artery each
Then there is an anterior cerebral artery
Also an anterior communicating artery
And two posterior communicating arteries
The circle theoretically means that if the blood supply is cut off for example from one internal carotid, there is a chance of compensatory flow from the other side
What are the veins draining the brain?
Cerebral veins
But most venous blood drains from the cranial cavity using venous sinuses in the dura mater. It has two layers which are mostly together. But when they separate they form the sinuses
The sinuses drain into the internal jugular vein
What are the venous sinuses of the brain?
Falx cerebri (down the longitudinal fissure) holds the superior saggital sinus along the top, and also an inferior saggital sinus. These lead back to the confluence of the sinuses
Great cerebral vein (of Galen) leads it from the brain itself posteriorly. This drains down the straight sinus to the confluence.
The confluence drains into the transverse sinuses
The transverse sinuses drain into the sigmoid sinuses. These leave the jugular foramen and become the internal jugular veins
What are the four types of intracranial haemorrhage? (Positions)
Important to note there is no extradural space (or epi) between the periosteal dura and cranium
- Extradural
- Subdural
- Subarachnoid
- Intracerebral
What are the details of an extradural bleed?
Trauma (maybe to the pterion, which has the main artery supplying the dura behind it, middle cerebral artery)
has immediate acute clinical effects. So symptoms very quickly
It is an ARTERIAL bleed so has HIGH PRESSURE, it strips the dura away from the skull and causes raised Intracranial pressure
Requires fast surgical action
Raised ICP can cause the brain to push down in the cranium and compress the brain stem, this may close down cardio respiratory centres
What are the details of a subdural haemorrhage?
There is a small space between dura and arachnoid
Largely due to trauma
Effects may be delayed, as it is a VENOUS bleed and has low pressure
What are the details of a subarachnoid haemorrhage?
Relevance is mostly at the base of the brain where the circle of Willis is
Where there are weaknesses in blood vessel walls: aneurisms
In hypertensive patients these may burst and bleed
What are the details of an intra cerebral haemorrhage?
These occur in the substance of the brain (parenchyma)
Usually seen in people who are hypertensive
And are spontaneous
What is a stroke?
Cerebrovascular accident (CBA)
Definition: rapidly developing focal disturbance of brain function of presumed vascular origin and of >24 hours duration
Thrombo-embolic (blockages) (85%) or haemorrhage (15%)
What is a transient ischaemic attack?
Rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24 hours
(Exactly the same as definition of stroke BUT it should resolve in less than 24 hours with no remaining defects)
A TIA may be a warning sign for another stroke further down the line
What does infarction mean?
Degenerative changes which occur in tissue following occlusion of an artery
Tissue dies when it loses blood supply
What’s is cerebral ischaemia?
Lack of sufficient blood supply to nervous tissue resulting in permanent damage if blood flow is not restored quickly
Not the same as anoxia, you have lost the whole blood supply so glucose as well etc
What is a thromboembolic stroke?
Thrombosis: formation of a blood clot
Embolism: plugging of a small vessel by material carried from a larger vessel (eg. Thrombi from the heart or atherosclerotic debris from internal carotid which is more common) (a thrombus is a form of embolism)
