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Definition:
Stroke is a serious medical disease characterized by sudden onset of weakness , numbness , difficult speech , loss of speech , vision problem and any other manifestation of sudden interruption of blood flow to the specific area of brain.
Explanation:
stroke cause due to a blood clot formed in blood vessel and reduce blood flow to brain. Due to it brain tissue become damaged or die. The stroke also known as brain attack. Brain attack occurs when something blocks blood supply to the part of brain or when the blood vessel in the brain bursts. In this case, parts of the brain become damaged or die. The brain attack cause lasting brain damage, long-term disability, or even death. Brain controls many vital function in our body such as movement, store information and the source of thought, emotion and circulation. Brain also controls many other function of body such as breathing, digestion, etc. To work properly your brain needs oxygen, energy and nutrients. Brain makes up only 2% of human body weight, it uses 20% of the total oxygen when human breathe. Carotid arteries and vertebral arteries deliver oxygen-rich blood to all parts of your brain.
Types of stroke:
There are two types of stroke
1) Ischemic stroke
2) Hemorrhagic stroke

1) Ischemic stroke:
An ischemic stroke occurs when blood clots or other particles block the blood vessels to the brain. Fatty accumulation are called plaque also cause blockages by building up in the blood vessels. Most strokes are ischemic stroke which are about 87%

2) Hemorrhagic stroke:
A hemorrhagic stroke happens when an artery in the brain flow blood out of blood vessel or ruptures. The leaking blood puts too much pressure on brain cells, which damages them. Both type of stroke cause brain cell death.
There are two types of hemorrhagic strokes
a) Intracereberal hemorrhage : Intracerebral hemorrhage is very common type of brain stroke. It occurs when an artery in the brain bursts and fill the surrounding tissue with blood.
b) Subarachnoid hemorrhage: Subarachnoid hemorrhage is a less common type of hemorrhagic brain attack. It cause due to bleeding in the area between the brain and the thin tissues that cover it.

Anotomy and Physiology:
Stroke is define is a neurological deficit caused by impairment in the perfusion to the brain. stroke in the posterior circulation for example may result in double vision, vertigo and dysphagia while stroke involving the left anterior circulation may manifest itself as aphasia and right hemiparesis. 20% of the cardiac output is delivered to brain although the average weight of brain is 1.3kg. Anteriorly the brain is supplied by two internal carotid arteries and posteriorly blood supplied by two vertebral arteries which lies in subarachnoid space. The right common carotid arteries are arise from brachiocephalic artery while the left common carotid artery is arise directly from an aortic arch, while the external carotid supplies the face internal carotid directly penetrate the base of skull, will not any other branches till there, through the carotid canal to supply the anterior aspect of cerebrum. The first branch of internal carotid artery at the level cavernous sinus is ophthalmic artery which enter the orbit through the optic canal together the optic nerve and supplies the retina and choroid via its terminal branches, the central retinal artery and posterior cilliary artery.

Pathophysiology:
A stroke cause when the blood flow to an area of the brain is disturbed, resulting in some exetent of permanent neurological damage. There are two major types of stroke which are ischemic due lack of supply of blood and lack of supply of oxygen to an area of the brain and the other is hemorrhagic stroke occur due to bleeding from a burst vessel or leak out of blood from blood vessel in the brain.
Pathophysiology of ischemic stroke: The common way for ischemic stroke is lack of sufficient blood flow to the brain tissue due to block or narrowing of arteries which carry blood to the brain or within brain. When blood flow to the brain stop occurs then ischemic cascade is initiated. This is a chain of biochemical reaction which occur in brain and any other aerobic tissue which usually occur for three to four hour and can last for a day even after normal blood flow can return to the brain tissue.
Important steps:
1) Without adequate blood flow to brain there is low oxygen or no oxygen so brain cell lost their ability to produce energy especially adenosine tri phosphate ATP.
2) Due to low supply brain cell start anaerobic respiration which produce less amount of ATP and release lactic acid by product.
3) Lactic acid which is release in anaerobic respiration is irritant which is the ability to destroy the normal brain cell by disturbing acid base balance inside the brain.
4) The transport pump which are ATP dependent ion loss function and causing the cell membrane to depolarize which leading to large influx of ca** ion into the cell and efflux of potassium ion out of cell.
5) Calcium level increase in inside cell and trigger the release of excitatory aminoacid neurotransmitter glutamate
6) Glutamate stimulate AMPA receptors and calcium permeable NMDA
7) High level of calcium inside the cell more excites the cell and activates protease, lipase enzyme and produce free radical.
8) Cell membrane is broken by phospholipase enzyme and allow more ion and harmful substance to move inside the cell
9) Due to it mitochondria break down and release toxin and apoptotic factor in the cell.
10) Cell start apoptosis
11) If cell die due to necrosis it release toxic chemical and glutamate into the around environment. Toxic poison substances overactivate nearby neuron and glutamate around the cell.
12) The loss of vascular structure integrity cause in breakdown of protective blood brain barrier (BBB) and contribute with cerebral oedema which can cause secondary formation of brain injury.

Pathophysiology of hemorrhagic stroke:
Hemorrhagic stroke are due to rupture of blood vessel leading to compression of brain tissue from an expending hematoma. This can lead to damage and injure brain tissue. The pressure may cause the loss of blood supply to the effect area of brain tissue with resulting infraction and the blood released by blood vessel the brain hemorrhage appear to have direct toxic effect on the brain tissue and vasculature.

Sign and Symptoms:
? Sudden numbness or weakness in face, arm or leg especially on one side of body
? Sudden confusion, difficulty understanding speech or trouble speaking
? Sudden trouble seeing in one or both eye
? Sudden trouble walking, dizziness or loss of balance, or lack of coordination
? Sudden severe headache with no cause

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