Under normal conditions, for every 100 grams of brain tissue at rest, 55.6 ml is obtained in 1 minute. blood, consuming 3.5 ml. oxygen. This means that the brain, which weighs only 2% of the total body weight, receives 850 ml per minute. blood, 20% oxygen and the same amount of glucose. An uninterrupted supply of oxygen and glucose is necessary to maintain a healthy brain substrate, the functioning of neurons and ensure their integrative function.
Carotid and vertebral arteries
The human brain is supplied with blood thanks to two paired main arteries of the head - the internal carotid and vertebral arteries. Two-thirds of all blood is supplied to the brain by the carotid arteries, and one-third by the vertebral arteries. The former form a complex carotid system, the latter make up the vertebrobasilar system. The internal carotid arteries are branches of the common carotid artery. Entering the cranial cavity through the internal opening of the carotid canal in the temporal bone, they enter the cavernous sinus and form an S-shaped bend. This part of the internal carotid artery is called the siphon. The anterior villous and posterior communicating arteries depart from the carotid artery. From the optic chiasm, the carotid artery divides into two terminal branches - the anterior and middle cerebral arteries. The anterior artery supplies blood to the frontal lobe of the brain and the inner surface of the hemisphere, and the middle cerebral artery supplies blood to a significant part of the cortex of the parietal, frontal and temporal lobes, as well as the subcortical nuclei and internal capsule.
The vertebral arteries arise from the subclavian artery. They enter the skull through holes in the processes of the vertebrae and enter the cavity through the foramen magnum. Both vertebral arteries in the area of the brain stem merge into a single spinal trunk - the basilar artery, which divides into two posterior cerebral arteries. These arteries supply the midbrain, cerebellum, pons and occipital lobes in the cerebral hemispheres. The vertebral artery also gives rise to two spinal arteries and the posterior inferior cerebellar artery.
Collateral arterial supply
It is divided into four levels: the system of the arterial circle of the cerebrum, the system of anastomoses above and inside the brain, blood supply through the capillary network of cerebral arteries, as well as the extracranial level of anastomoses. Collateral blood supply to the brain plays a critical role in compensating for disturbances in normal circulation in the event of blockage of any of the cerebral arteries. Although numerous anastomoses between the vascular beds also play a negative role. An example of this is cerebral steal syndromes. There are no anastomoses in the subcortical region, therefore, when the artery is damaged, irreversible destructive changes occur in the brain tissue in the area of their blood supply.
Brain vessels
They, depending on their functions, are divided into several groups. The great vessels are the internal carotid and vertebral arteries located in the extracranial region, and the vessels of the arterial circle. Their main purpose is the uninterrupted regulation of cerebral circulation in the event of changes in a person’s systemic blood pressure.
The arteries of the pia mater are vessels with a pronounced nutritional function. The size of their lumen depends on the metabolic needs of the brain tissue. The main regulator of the tone of these vessels is the metabolic products of brain tissue, especially carbon monoxide, which dilates brain vessels.
Intracerebral capillaries and arteries directly provide the basic function of the cardiovascular system. This is a function of exchange between blood and brain tissue. Such vessels are called “exchange”.
The venous system performs a drainage function. It is characterized by a significantly larger capacity compared to the arterial system. This is why the veins of the brain are also called “capacitance vessels.” They are not a passive element of the entire vascular system of the brain, but are directly involved in the regulation of blood circulation.
Venous blood flows out of the choroid plexuses through the deep and superficial veins of the brain. It goes directly through the great cerebral vein, as well as other venous sinuses of the meninges. Then from the sinuses the blood flows into the internal jugular veins, from them into the brachiocephalic veins. Eventually the blood enters the superior vena cava. This closes the circle of blood circulation in the brain.
The brain system regulates all other structures of the body, maintaining dynamic constancy in the internal environment and the stability of the main physiological functions. That is why the intensity of nutrition in nervous tissue is very high. Next, let's look at how the blood supply to the brain occurs.
General information
At rest, the brain receives approximately 750 ml of blood per minute. This corresponds to 15% of cardiac output. The blood supply to the brain (the diagram will be presented later) is closely related to functions and metabolism. Adequate nutrition of all departments and hemispheres is ensured due to the special structural organization and physiological mechanisms of vascular regulation.
Peculiarities
The nutrition of the organ is not affected by changes in general hemodynamics. This is possible due to the presence of various self-regulation mechanisms. Nutrition of the centers of coordination of nervous activity is carried out in an optimal mode. It ensures a timely and continuous supply of all nutrients and oxygen to the tissues. The blood circulation of the brain in the gray matter is more intense than in the white matter. It is most intense in children under one year of age. Their nutritional intensity is 50-55% higher than that of adults. In an elderly person it is reduced by 20% or more. About a fifth of the total blood volume is pumped by the vessels of the brain. The centers regulating nervous activity remain constantly active, even during sleep. Control of cerebral blood flow is achieved through metabolic activity in the nervous tissue. With an increase in functional activity, metabolic processes accelerate. Due to this, blood supply to the brain increases. Its redistribution is carried out within the arterial network of the organ. To speed up metabolism and increase the intensity of nerve cell activity, therefore, no additional increase in nutrition is required.
Blood supply to the brain: diagram. Arterial network
It includes paired vertebral and carotid canals. Due to the latter, 70-85% of the hemispheres are supplied with nutrition. The vertebral arteries contribute the remaining 15-30%. The internal carotid canals arise from the aorta. Then they pass on both sides of the sella turcica and the intertwining of the optic nerves. Through a special channel they enter the cranial cavity. In it, the carotid arteries are divided into middle, anterior and ophthalmic. The network also distinguishes between the anterior villous and posterior connecting canals.
Vertebral vessels
They arise from the subclavian artery and enter the skull through the foramen magnum. Then they branch out. Their segments approach the spinal cord and the membrane of the brain. Branches also form the inferior posterior cerebellar arteries. Through connecting channels they communicate with the middle vessels. As a result, a circle of Willis is formed. It is closed and located, accordingly, at the base of the brain. In addition to the Willis, the vessels also form the second circle - Zakharchenko. The site of its formation is the base of the medulla oblongata. It is formed due to the fusion of branches from each vertebral vessel into a single anterior artery. This anatomical diagram of the circulatory system ensures uniform distribution of nutrients and oxygen to all parts of the brain and compensates for nutritional disorders.
Venous drainage
Blood channels that collect blood, which is enriched with carbon dioxide, from nerve tissue are presented in the form of jugular veins and sinuses of the dura mater. From the cortex and white matter, movement through the vessels occurs towards the inferior, medial and superolateral surfaces of the hemispheres. An anastomotic venous network is formed in this area. Then it runs through the superficial vessels to the hard shell. A network of deep vessels opens into a large vein. They collect blood from the brain base and internal parts of the hemispheres, including the thalamus, hypothalamus, choroid plexuses of the ventricles, and basal ganglia. The outflow from the venous sinuses is carried out through the jugular canals. They are located on the neck. The superior vena cava is the last link.
Impaired blood supply to the brain
The activity of all parts of the organ depends on the state of the vascular network. Insufficient blood supply to the brain provokes a decrease in the content of nutrients and oxygen in neurons. This, in turn, leads to dysfunction of the organ and causes many pathologies. Poor blood supply to the brain, congestion in the veins leading to the development of tumors, circulatory disorders in the small and large circles and acid-base status, increased pressure in the aorta and many other factors accompanying diseases associated with the activity of not only the organ itself, but also the musculoskeletal system. - motor system, liver, kidneys, provoke lesions in the structure. In response to impaired blood supply to the brain, bioelectrical activity changes. An electroencephalographic study allows us to register and identify this kind of pathology.
Morphological signs of the disorder
Pathological disorders are of two types. Focal signs include infarction, hemorrhagic stroke, and intrathecal hemorrhage. Among the diffuse changes, there are small focal disturbances in the substance of varying degrees of age and character, small organizing and fresh necrotic areas of tissue, small cysts, gliomesodermal cysts and others.
Clinical picture
If the blood supply to the brain undergoes changes, subjective sensations may be observed that are not accompanied by objective neurological symptoms. These include, in particular:
- Paresthesia.
- Headache.
- Organic microsymptoms without pronounced signs of central nervous system dysfunction.
- Dizziness.
- Disorders of the higher functions of the cortex of a focal nature (aphasia, agraphia and others).
- Disorders of the sensory organs.
Focal symptoms include:
- Movement disorders (impaired coordination, paralysis and paresis, extrapyramidal changes, decreased sensitivity, pain).
- Epileptic seizures.
- Changes in memory, emotional-volitional sphere, intelligence.
Blood circulation disorders, by their nature, are divided into initial, acute (intrathecal hemorrhages, transient disorders, strokes) and chronic, slowly progressive manifestations (encephalopathy, discirculatory myelopathy).
Methods for eliminating disorders
Improved blood supply to the brain occurs after deep breathing. As a result of simple manipulations, more oxygen enters the organ tissue. There are also simple physical exercises that can help restore circulation. Normal blood supply is ensured if the blood vessels are healthy. In this regard, it is necessary to carry out measures to clean them. First of all, experts recommend reviewing your diet. The menu should contain dishes that help eliminate cholesterol (vegetables, fish, etc.). In some cases, it is necessary to take medications to improve blood circulation. It should be remembered that only a doctor can prescribe medications.
Nerve cells require an intensive supply of oxygen, so even 3-4 minutes without oxygen lead to the death of neurons. The nerve cells of the cerebral cortex are the most vulnerable, and the cells of the brain stem are the most resistant. The importance of adequate blood supply to the brain is evident from the fact that although the brain makes up only 2% of the body's weight, 15-20% of the blood pumped by the heart passes through it.
Arteries
Blood supply to the brain is provided on each side of the body by two arteries - internal carotid artery And vertebral artery. The left and right internal carotid arteries arise from the site of division common carotid artery at the base of the skull and, without branching, enter the cranial cavity through the carotid canal. Left And right vertebral artery They arise from the corresponding subclavian arteries and go towards the head through the openings in the transverse processes of the upper six cervical vertebrae. Having passed through the foramen magnum, they also enter the cranial cavity.
The four arteries anastomose with each other in arterial circle(circle of Willis). The arterial circle and all the arteries branching from it are located in the subarachnoid space. After passing through the foramen magnum, the two vertebral arteries run along the anterior side of the medulla oblongata, and from each of them is separated inferior posterior cerebellar artery, leading to the cerebellum, and spinal arteries (for example, the anterior spinal artery), which supply blood to the spinal cord. At the lower border of the pons, the two vertebral arteries join to form the main artery, from which they branch lower front And superior cerebellar artery. At the upper border of the pons, the main artery divides into left and right posterior cerebral arteries, which go backward and supply blood to the back of the cerebral hemispheres, mainly the lower surface of the temporal lobe and the occipital lobes.
From the two internal carotid arteries, immediately after entering the base of the skull, two ophthalmic arteries(each of which supplies one eye and part of the nose), and the internal carotid arteries themselves are further divided into the anterior and middle cerebral arteries. The two anterior cerebral arteries first run forward in the longitudinal fissure, then go back along the corpus callosum and supply blood to the medial surfaces of both hemispheres. The two middle cerebral arteries turn laterally between the temporal and frontal lobes and branch in the lateral sulcus, supplying most of the lateral aspect of the cerebral hemispheres. On their route between the frontal and temporal lobes, the middle cerebral arteries give off important branches supplying the internal capsule. The middle cerebral artery is the largest of the three cerebral arteries; it is a direct continuation of the internal carotid artery.
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The two anterior cerebral arteries are connected by the anterior communicating artery. The two posterior communicating arteries connect the middle and posterior cerebral arteries. They form an arterial circle connecting the vertebral and carotid arteries on the underside of the brain. This is of great clinical importance because if one of the four vessels supplying the brain with blood is blocked, the affected area can receive blood through the three remaining arteries. Aneurysms are often observed in the circle of Willis, i.e. pouch-like expansions of the vascular wall. In these places, the vascular wall is thin and with a sharp increase in blood pressure can easily rupture, with profuse hemorrhage into the subarachnoid space (subarachnoid bleeding).
If a blood clot forms in one of the arteries supplying blood to the brain (usually as a result of atherosclerosis of the vascular wall) or if a blood clot forms elsewhere (for example, in the heart) and then travels into the arteries of the brain through the bloodstream (this called an embolus), a blockage of the artery may occur, depriving the tissue of the normal supply of fresh blood. A lack of blood supply (ischemia) leads to insufficient oxygen and nutrients, which causes cell death (necrosis). Ischemic necrosis is called infarction.
Cerebral infarction is one of the two most common types of stroke (this is the name for any event that affects the blood vessels of the brain and causes an abrupt onset of usually irreversible or only partially reversible neurological deficit). Brain bleeding from ruptured arteries causes cell death near the site of the bleed—a common cause of stroke.
Vienna
The outflow of venous blood occurs mainly through superficial and deep cerebral veins And venous sinuses. The brain capillaries connect into veins, which go to the surface and join larger veins, which, like arteries, run in the subarachnoid space and give off anastomotic veins. The latter then flow into the large venous sinuses (for example, the superior sagittal sinus) formed by the dura mater.
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Blood from the lower part of the brain flows through the deep cerebral veins and eventually enters the straight sinus through the great cerebral vein. Superior sagittal sinus And straight (occipital) sinus join on the inner surface of the occipital bone (fusion of sinuses), after which blood enters right And left transverse sinuses, each of which in turn continues with the sigmoid sinus. Ultimately, the blood is directed to internal jugular vein, which exits the skull through the jugular foramen, located at the base of the skull on the side of the foramen magnum. In addition to other veins, the cavernous sinus, located around the sella turcica, receives the superficial facial veins (angular and nasofrontal veins); they also drain into the internal jugular vein.
Blood supply to the brain carried out by two internal carotid arteries and two vertebral arteries. The outflow of blood occurs through two jugular veins.
At rest, the brain consumes about 15% of the blood volume, and at the same time consumes 20-25% obtained during breathing.
Arteries of the brain
Carotid arteries
The carotid arteries form the carotid basin. They originate in the chest cavity: the right from the brachiocephalic trunk (lat. truncus brachiocephalicus), left - from the aortic arch (lat. arcus aortae). The carotid arteries provide about 70-85% of blood flow to the brain.
Vertebro-basilar system
The vertebral arteries form the vertebrobasilar basin. They supply blood to the posterior parts of the brain (cervical, and). The vertebral arteries originate in the thoracic cavity and pass to the brain in the bone canal formed by the transverse processes of the cervical vertebrae. According to various sources, the vertebral arteries provide about 15-30% of blood flow to the brain.
As a result of the fusion, the vertebral arteries form the main artery (basilar artery, a. basilaris) - an unpaired vessel, which is located in the basilar groove of the bridge.
Circle of Willis
Near the base of the skull, the main arteries form the circle of Willis, from which the arteries branch off, supplying blood to the brain tissue. The following arteries participate in the formation of the Circle of Willis:
- anterior cerebral artery
- anterior communicating artery
- posterior communicating artery
- posterior cerebral artery
Venous drainage
Sinuses of the dura mater
The venous sinuses of the brain are venous collectors located between the layers of the dura mater. Blood is obtained from the internal and external veins of the brain.
Jugular veins
Jugular veins (lat. venae jugulares) - paired, located on the neck and drain blood from the neck and head.
Additional images
The brain regulates all structures of the body, allowing the stable functioning of physiological functions. As a result, intensive nutrition of nervous tissue plays a huge role in the life of the body. The blood supply to the brain is provided by two internal carotid and two vertebral arteries.
Arterial blood supply system
The physiology of the human body has not yet been fully studied, but the greatest mystery for scientists remains the brain, which is always active, even if a person is at rest and sleep. Blood supply to the brain is provided by two systems:
- The vertebral arteries, which begin in the subclavian, pass into the transverse processes of the cervical vertebrae and, in the area of the first of them, leave this canal, entering the foramen magnum in the skull. Here the PAs are located at the base of the medulla oblongata. At the border of the latter and the pons of the brain, the arteries listed above merge into one trunk of the basilar artery. At the border of the pons, it divides into a pair of posterior cerebral arteries.
If there are pathologies in the cervical spine, compression of the artery is often observed, which sometimes leads to irreversible consequences.
- The internal carotid artery is separated from the common carotid artery, which in turn is separated from the aorta and subclavian artery. Due to this, normal conditions for blood flow are created in the left artery system.
When a blood clot breaks away from the left region of the heart, it more often passes into the left carotid artery than into the right, since there is a direct connection with the aorta. The ICA enters the skull using the canal of the same name.
A diagram of the blood supply to the brain can be seen below.
The connection between both systems is due to the arterial circle of the cerebrum, which is otherwise called the circle of Willis and is formed due to the following blood supply elements:
- posterior brain (vertebrates);
- connecting posterior (internal carotid arteries);
- middle cerebral (internal carotid arteries);
- cerebral anterior (internal carotid arteries);
- connecting anterior (internal carotid arteries).
The purpose of the arterial circle of the cerebrum is to support proper blood flow to the brain, which is necessary if there is a violation in one of the arteries.
The system for transporting substances from the capillary to the nervous tissue is called the “blood-brain barrier,” which protects against the penetration of pathogenic factors (toxins, microbes, etc.) into the brain.
In the normal state of the barrier, substances such as:
- iodine compounds;
- immune bodies;
- salt;
- antibiotics.
Thus, medications containing the substances listed above cannot affect the nervous system.
At the same time, the following are able to overcome the blood-brain barrier:
- morphine;
- alcohol;
- tetanus toxin;
- chloroform.
In order for drugs used to treat infectious diseases of the brain to easily overcome this barrier, they must be injected into the fluid that surrounds the brain. This process is carried out through a puncture in the lumbar region of the spinal column or in the area under the back of the head.
The outflow of blood is carried out through veins that flow into the sinuses of the dura mater. They are slit-like canals in the connective membrane of the brain. Their peculiarity is that their lumen is always open in any conditions. This ensures a stable outflow of blood and prevents it from stagnating. Through the sinuses, venous blood enters the jugular foramen, located in the cranial base, where the jugular vein begins. Through it, blood flows into the superior vena cava.
Functionality of the arteries that make up the circle of Willis
The anterior cerebral artery supplies blood to the following areas:
- superior part of the postcentral and precentral gyri;
- cerebral cortex;
- olfactory tract;
- basal and internal part of the frontal lobe;
- white matter of the parietal and frontal lobes;
- head and outer part of the caudate nucleus;
- part of the corpus callosum;
- portion of the pedicle of the internal capsule;
- part of the lenticular nucleus.
The middle cerebral artery is responsible for supplying blood to the following areas:
- cerebral cortex;
- part of the lenticular and caudate nuclei;
- white matter of the surface of the cerebral hemispheres;
- in the temporal lobe of Wernicke's center;
- visual radiance;
- parietal lobe;
- part of the frontal gyri and lobes.
The posterior cerebral artery supplies the following areas:
- cerebral cortex;
- white matter;
- hypothalamus;
- cerebral peduncle;
- part of the optic thalamus;
- caudate nucleus;
- corpus callosum;
- Graziole bun;
- quadrigeminal.
The vertebral arteries supply the following brain areas:
- parts of the cerebellum;
- medulla;
- spinal cord.
The posterior inferior cerebellar artery provides blood supply to the following sections:
- posterior inferior cerebellum;
- part of the medulla oblongata.
An interesting fact is that there is no portal system in the blood supply to the brain. That is, the branches of the circle of Willis do not penetrate the medulla, as is usually the case in the vital organs of the body. They spread along the brain surface, branching off into thin branches at right angles. This fact determines the uniform distribution of blood supply. Therefore, there are no large vessels in the brain, but only capillaries and small arteries.
Still, there are large arteries in the head, which are located on the surface of the brain in the arachnoid membrane. Their location is fixed, since the vessels are not only suspended on trabeculae, but also supported at a specific distance relative to the brain.
Peculiarities
An interesting fact is that hemodynamics and changes in it do not affect blood circulation, since it contains self-regulation mechanisms.
The blood circulation of the gray matter has greater intensity compared to the white matter. The most saturated blood flow occurs in babies whose age has not yet reached one year. A newborn baby has a greater blood supply than an adult. As for the elderly, in this category of people it decreases by twenty percent, and sometimes more.
Control of this process occurs in the nervous tissue, and it is determined by metabolism. Centers for regulating nervous activity operate throughout life, without ceasing their functioning even during sleep.
The intracerebral structure of capillaries has some features, namely:
- A thin elastic membrane surrounds the capillaries, as a result of which they cannot stretch.
- Capillaries do not contain Roger cells, which can contract.
- Transudation and absorption are carried out due to precapillaries and postcapillaries.
Different blood flow and pressure in the vessels cause fluid transudation in the precapillary and absorption in the postcapillary.
This whole complex process makes it possible for there to be a balance between absorption and transudation without the participation of the system that the lymph forms.
Pregnancy has a particular impact on the blood supply to the entire body and the brain in particular, during which most medications are contraindicated, otherwise the fetus may have pathologies.
Impaired blood supply
A person can independently check the blood supply to the brain - normally, the scalp should move freely in all directions.
Temporary disturbances in blood flow can occur under the influence of various factors. For example, with osteochondrosis, the cervical vertebra presses on the blood vessels, and this is the cause of migraines. Increased blood pressure, tension and anxiety can also slow down blood flow. In such a situation, symptoms are often supplemented by loss of consciousness, vomiting and sensation. Most often, it is the asymmetry of blood flow through the arteries of the spine that provokes a violation of the blood supply.
If the blood supply is insufficient, then there is a low percentage of nutrients and oxygen in the neurons, which leads to brain damage and the development of pathological processes. An electroencephalographic study can reveal such conditions occurring in the brain.
Focal signs of pathological disorders imply the development of the following conditions:
- hemorrhagic stroke;
- cerebral infarction;
- hemorrhages in the intrathecal area.
Such conditions manifest themselves in the form of the following clinical picture:
- epilepsy;
- decreased sensitivity;
- intellectual disabilities;
- problems with coordination of movements.
When the blood supply to the brain is disrupted, a person feels such conditions subjectively, but they are also accompanied by objective neurological symptoms, which include:
- headache;
- paresthesia;
- dizziness;
- problems with the functioning of organs responsible for sensitivity.
Circulatory disorders are divided into three stages:
- Initial.
- Spicy.
- Chronic.
Acute disruption of blood circulation manifests itself in the form of strokes, hemorrhages and other disorders. Chronic conditions include encephalopathy and discirculatory myelopathy.
The clinical picture of circulatory disorders in the brain is as follows:
- headache;
- dizziness;
- red face;
- pain in the eye area;
- a frequently occurring symptom is tinnitus;
- nausea;
- convulsions;
- turning the head in the direction of the lesion worsens the condition;
- confusion.
An interesting fact is that pain tends to increase.
Often these conditions are accompanied by the following symptoms: chills, elevated body temperature and high blood pressure.
Causes
The following pathologies can affect poor blood circulation in the brain:
- Atherosclerosis, which occurs more often in older people and those who suffer from impaired functionality of the cardiovascular system. During this process, sclerotic plaques accumulate in the arteries, which significantly impede blood circulation.
- Curvature of the spine, as well as a muscle pinched as a result, can also interfere with blood circulation.
- Hypertension.
- Stressful situations can also reduce blood flow.
- The cerebrospinal fluid also has a significant influence on the blood supply.
- Surgery or trauma to the skull.
- Injured spine.
- Improper venous outflow of blood from brain tissue.
Regardless of the reasons that lead to the difficulty of microcirculation, the consequences affect not only the brain, but also the functioning of internal organs.
Elimination of blood circulation disorders in the brain
Circulation can improve during deep breathing, due to which much more oxygen enters the tissues. To achieve a significant effect, you should use simple physical exercises, after consulting with your doctor.
Stable blood supply to the brain and spinal cord can be achieved exclusively through healthy blood vessels.
Thus, to achieve what you want, you need to do something that feeds the brain. For this purpose, those products that help eliminate cholesterol should be used.
