Lecture 8: Stroke Flashcards
What does blood bring in and out of the brain?
- -Oxygen, carbohydrates, amino acids, fats, hormones and vitamins go in;
- -Carbon dioxide, ammonia, lactate and hormones go out.
How much does the brain weigh and how much blood does it consume?
Although the brain weighs ~2% of our body weight, it consumes about 15-20% of the body’s blood supply.
What is the Circle of Willis and what is it made up of?
- named after Thomas Willis, is a collection of arteries that supplies blood to the brain and surrounding structures.
- Internal carotid arteries: carries 80% of oxygenated blood to the brain. Most important. Splits into two at the level of the brain, so theres one in each hemisphere.
- Anterior cerebral arteries
- —> connected by Anterior communicating artery
- Posterior cerebral arteries
- —> connected byPosterior communicating arteries.
these communicating arteries are very important because they are like the bridge between the arteries on the left and right hemispheres of the brain
Why is the Circle of Willis important?
The arrangement of arteries creates anatomical redundancy, which allows for collateral circulation of blood to the brain It’s a safety mechanism (protects us from clogs and blockages )
Therefore, if one part of the circle is blocked or narrowed, blood flow from other vessels can often preserve blood flow and avoid ischemia (brain or part of brain is starved of oxygen).
What does the anterior circulation, posterior circulation, and communicating arteries do?
Anterior circulation: Supplies the anterior and medial parts of the brain (ex. frontal and parietal lobes)
Posterior circulation: Supplies the posterior brain and cerebellum (and midbrain)
Communicating arteries: forms Circle of Willis
What is a stroke and what are the two types?
A stroke is a medical condition in which an abnormality of the vascular supply causes damage to the central nervous system.
1) Ischemic
2) Hemorrhagic
- ruptured blood vessel
What is an ischemic stroke?
An ischemic stroke is (typically) caused by a blockage of arterial blood vessels.
Two main ways it could happen:
1) Thrombosis: obstruction of a blood vessel by local blood clot;
2) Embolism: obstruction due to an embolus (traveling particle or debris in the bloodstream) from elsewhere in the body; a thrombosis can turn into an embolism because part of it can break off and travel
What happens to the brain with an ischemic stroke?
- Brain tissue ceases to function if deprived of oxygen for more than 60 – 90 seconds, and will suffer irreversible damage after ~3 hours of ischemia.
- -Body not very good at generating ATP in absence of oxygen (lactate –> lactic acid –> acidosis);
- -Leads to failure of energy-dependent processes in brain cells (e.g. ion pumping); Na/K pump
- -Ultimately leading to apoptosis or necrosis. Typically necrosis because everything happens very fast
- -Causes infarction: tissue death (necrosis) caused by lack of blood supply to the affected area.
What is a hemorrhagic stroke?
– A hemorrhagic stroke refers to bleeding in or around the brain’s membranes, usually caused by a rupture of a blood vessel or abnormal vascular structure.
There are 4 main types:
1) Epidural: between skull and dura matter;
2) Subdural: between the dura matter and arachnoid space;
3) Sub-arachnoid: between arachnoid space and pia matter;
4) Intracerebral: bleeding within the brain itself. Either from the brain tissue (intraparenchymal hemorrhage) or from the brain’s ventricular system (intraventricular hemorrhage).
Why are epidural hemorrhagic strokes the worst type?
- theres anchor points between the dura matter and the skull which are very strong because they hold/connect the skull to the brain. Because of these anchor points, the blood can’t spread out so it causes a lot of pressure to one particular part of the brain. With subdural hematomas, the blood doesn’t pool in one particular area and cause pressure because there are no anchor points so the blood can spread and not cause as much pressure
- epidural strokes can cause displacement (structures are being pushed and pulled in different directions causing these networks to not be connected in the same way a before)
What are the specific symptoms associated with hemorrhagic strokes?
biggest thing that differs a hemorrhagic stroke from an ischemic stroke is Intracranial pressure that occurs in hemorrhagic stroke
- -Severe headache;
- -Dizziness;
- -Seizures;
- -Vomiting
- Pain
- Loss of consciousness
How does the WHO define a stroke?
The WHO defines a stroke as “neurological deficitof cerebrovascular cause that persists beyond 24 hours or is interrupted by death within 24 hours”
What are the clinical symptoms of a stroke?
– Very rapid and focal symptoms. Some symptoms may be permanent, others subside. Occurs unilaterally
– Weakness in face and/or limbs; very common because it occupies most of the brain (both the motor and sensation of these areas occupy many parts of the brain)
– Numbness (loss of sensation); NOT pins and needles
– Aphasia or dysarthria; aphasia is difficulty with speech because blood flow is cut from the language centres in the brain (wernickes area for language processing and brocas area for speech). dysarthria Is a weakness or loss of muscles that control your face and tongue (can’t articulate your words).
– Vision loss;
– Headache; Typically common with hemorrhagic stroke because this causes pressure, not ischemic stroke
FAST: Facial droop, Arm weakness, Speech difficulty = Time to call 9-1-1
Rarely, patients may experience:
- Loss of consciousness;
- Pain;
- Abnormal movement.
What is the neuropathology of an infarction?
- The release of osmotically active substances (e.g. arachidonic acid, electrolytes, lactic acid, etc.) from necrotic brain tissue into the fluid between neurons applies osmotic pressure into surrounding cells which causes cerebral edema (swelling in the brain)
- These surrounding cells will then start taking on water or getting rid of water to balance the concentration of solutes and solvents which leads to axon swelling
- Axons swelling can cause unravelling of myelin sheath
- Neuroinflammatory response to release substances, forms glial scar around infarct; all the glia cells will rush to site of damage and this causes glial scars. glial scars make it hard to rebuild the neural network there (neurogenesis) because all these glial cells are surrounding the area and not letting things get in or out
- By 3-4 days, interstitial fluid accumulates in and around the infarct; this is the most dangerous period
- -Cell death is caused by cerebral edema and herniations (swelling causes certain structures to be physically displaced), not by loss of brain tissue and this is why neurological functions return again
- Neovascularization occurs for ~2 weeks; body’s attempt to sprout out new arterial blood vessels but this can cause pressure and swelling
How can you recover a stroke patient?
Recovery of function can be achieved by restoration of perfusion (blood flow) by administering blood thinners or surgery, and the settling down of cerebral edema (acutely) and neuronal plasticity (long-term).
