Blood supply to the brain

Stroke A stroke occurs when there is an interruption of blood supply to the brain. An ischemic stroke occurs when a clot prevents blood flow in the brain. A hemorrhagic stroke is when there is a rupture of a blood vessel in the brain. In either case, the brain cells in the affected area die. This area is called an infarct. Medical treatment is required to arrest the damage. More effective treatment can be administered within 6 hours of the onset of stroke. A stroke may result in weakness, paralysis, impairment of speech and memory, or even death. Medical treatment includes the use of anticoagulants to treat stroke victims. 

Blood supply to the brain and the role of the blood-brain barrier... 

Although the brain constitutes only 2% of body weight, it receives approximately 15% of the blood supply and consumes nearly 20% of the total oxygen and glucose available to the body. In order to supply these essential nutrients for brain function, there must be a consistent and rapid blood supply to the brain in order that the brain cells may function. This is supplied by the cerebral arteries derived from the internal carotid arteries which branch over the surface of the brain and send smaller branches into the deeper subcortical structures. The capillaries are highly branched and it has been calculated that every nerve cell is no more than 40-50 fim from a capillary. 

Neurotransmitters are produced in our brains from the contents of our diets by means of a many-step process. First, nutrients (labeled i in Fig. i—i), such as amino acids, sugar, fats, and peptides (strings of amino acids bound together), are extracted and absorbed from the food we eat and are transported out of the arterial blood supply to the brain—that is, they are actively carried through the blood—brain barrier and transported into the neurons. Enzymes (2) convert these nutrients into different neurotransmitters. The neurotransmitter molecules are actively transported into what are called synaptic vesicles (3), or very tiny spheres with hollow centers into which about 10,000 molecules of a typical neurotransmitter can be stored for later release from a neuron. 

The brain uses a substantial proportion of body oxygen and there is a generous blood supply to the brain from the carotid and vertebral arteries. Interruption of brain blood flow for more than a very short time causes neuronal damage and ultimately cell death. Cerebral blood flow is normally controlled by autoregulation. 

The collateral blood supply to the brain is described by Liebeskind (2003). Common sites of collateral blood supply to and within the brain are ... 

The brain requires an especially copious blood supply. Large arteries in the side and back of the neck carry blood to the brain, but when these arteries become narrowed or blocked by fatty deposits (a condition called atherosclerosis), the blood supply to the brain may be reduced to an insufficient amount. A balloon catheter may be used by the physician to clear the blockage. In this procedure, called angiography, a catheter is guided to the site of blockage. The tiny balloon on the end of the catheter is inflated to press the blockage out of the way. 

Syncope fainting caused by inadequate blood supply to the brain. 

Prostaglandins are known to inhibit the aggregation of platelets. They may thus be of therapeutic value by preventing the formation of blood clots, which can cut off the blood supply to the brain or the heart and cause certain types of strokes and heart attacks. Even if this behavior were the only useful property of prostaglandins, it would justify considerable research effort. Heart attacks and strokes are two of the leading causes of death in industrialized countries. More recently, the study of prostaglandins has been a topic of great interest because of their possible antitumor and antiviral activity. 

Fig. 1.5 Blood supply to the brain, (a) Vessels that contribute to the arterial circle of WrUis at the base of the brain. Note contributions from the vertebral and internal carotid systems. Throughout its length, each vessel that participates in the arterial circle gives off nrtmerous small, tmnamed branches that penetrate the brainstem, (b) Distribution of blood supply to the lateral surface of the cerebrum is illustrated. The middle cerebral artery is the prominent vessel, the anterior cerebral artery vascularizes the territory on either side of the falx cerebri and a narrow strip of superior surface of the cerebrum, (c) Sagittal section that depicts the distribution of blood flow to the cerebrum. Note that the anterior and middle cerebral arteries carry blood from the internal carotid arteries, whereas the blood to the posterior cerebral arteries comes from the vertebral/basilar artery system (See also Color Insert)...

With regard to tissue blood supply, the organization of the brain and brainstem differs from that of the rest of the body in that there are no anastomoses within the nervous tissue. Each arterial branch is a functional end artery if it were to be occluded, the territory of the brain that it supplied would become hypoxic and ischemic. Because the blood supply to the brain and brainstem is critical for normal cognitive function, a more complete description of the arterial supply follows. 

As a second example of the process that may be followed when modeling the human body with FEA, let us consider blood flow through the carotid artery. This is the main blood supply to the brain (through the internal carotid artery) and is the site of stenoses. Plaque formation (artherosce-losis) narrows the common carotid artery at the origin of the external carotid artery (which flows toward the face) until blood flow is reduced to the brain. 

Phosphorus occurs in human brain at higher concentration than in any other body part except bones and teeth (Table 11.8). Like muscle, brain contains phosphocreatine and ATP, which together contain about two thirds of the total amount of P present. Remaining compounds include NADP, phospholipid hydrolysis products and various sugar phosphates (Table 11.9). A blood supply to the brain is essential to maintain adequate quantities of ATP, which are needed to sustain mental activity. 

According to the World Health Organization (WHO), a stroke is caused by the interruption of the blood supply to the brain, usually because a blood vessel bursts or is blocked by a clot. This cuts off the supply of oxygen and nutrients, causing damage to the brain tissue. 

The general principle that hypertension demands treatment, and that the aim of treatment must be to produce a normal blood pressure, is a rule with exceptions there is an increasing realization in recent years that if we are to treat the patient rather than the symptom, the exceptions must be borne in mind. Any lowering of systolic and diastolic blood pressure in the hypertensive patient to more normal levels, after all, carries with it the risk of aggravating the patient s condition, since the high blood pressure may have become essential for maintaining the blood supply to the brain, kidney and heart (F). 

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