Blood Irrigation In The Brain: Anatomy, Phases And Route
Our brain is a complex machine that needs to be irrigated, in order to function correctly, with a red fuel that we all know: blood. And to do this, it uses a set of strategically arranged arteries that will be responsible for keeping the brain and the rest of the organs well fed.
In this article we will see how blood circulation occurs in the brain and what are the main arterial systems that make it possible.
The human brain is a complex organ and is responsible for a multitude of bodily functions that we need to survive. All machinery needs fuel to function, and our brain was not going to be different. Although it represents just over 2% of the body weight, it consumes one sixth of the cardiac output and 20% of the oxygen that our body needs at rest.
The brain is constantly active (even when we sleep), which is why vascularization or blood irrigation is such an important process for an organ like this. The entire brain is supplied by four large arteries, which emerge from the aorta artery and ascend through the neck until penetrating the skull.
Blood circulation in the brain occurs through two symmetrical systems, on both sides of the neck: on the anterior side, the common carotid arteries; and on the back, the vertebral arteries, which make much of their journey within the cervical vertebrae.
The common carotid arteries are divided into two branches, the external carotid, which mainly nourishes extracranial structures (tongue, pharynx, face, cervical muscles, etc.) and the internal carotid, which penetrates the skull and supplies blood to most of the arteries. the anterior portion of the brain, which we call the cerebrum.
The vertebral arteries penetrate the skull and join to form a common trunk that we know as the basilar artery , which is responsible for irrigating the cerebellum and brain stem. The internal carotid arteries and the basilar artery divide, in turn, into increasingly smaller branches, and are distributed throughout the brain surface.
The carotid system
The carotid system is responsible for the anterior circulation of blood in the brain and provides practically 80% of the blood flow received by the brain.
It is formed by the common carotids (right and left) which, once they have penetrated the skull, form the internal carotids, branching into the anterior and middle cerebral arteries. These reach the cerebral cortex, reaching the frontal, parietal and temporal lobes.
1. Anterior cerebral artery
The anterior cerebral artery originates from the internal carotid artery The arteries on each side are connected by the anterior communicating artery and both form part of the cerebral arterial circle or circle of Willis, which we will talk about later.
This artery has cortical (orbital), frontal (parietal) and central (including the internal artery of the striatum) branches, as well as the anterior communicating artery of the brain, and can be classified into 5 segments. It supplies a large part of the inner surface of the cerebral hemisphere.
2. Middle cerebral artery
The middle cerebral artery or sylvian artery (so called because as soon as it detaches from the internal carotid artery it enters the Sylvian fissure) is a branch of the internal carotid artery, and is responsible for supplying blood through two segments: one basal portion and another cephalic portion.
This artery has the most complex branching pattern of all cerebral arteries , and presents cortical (orbital, frontal, parietal and temporal) and central (striated) branches. It has two main branches: a basilar branch, which is responsible for supplying part of the caudate nucleus and the thalamus; and the cortical portion, which supplies much of the cerebral cortex.
When the middle cerebral artery is obstructed, hemiparesis (paralysis of one side of the body) occurs, affecting parts of the body such as the face, arm or leg, and generating sensory and visual alterations.
The vertebrobasilar system
The vertebrobasilar system is responsible for the posterior circulation of blood in the brain It is made up of the vertebral arteries (right and left), which are integrated into the basilar artery, once they have penetrated the brain, and branch into the posterior cerebral arteries that supply the occipital lobes (located in the posterior area of ​​the brain). .
This system facilitates the irrigation of part of the spinal cord, the brain stem, the cerebellum, and much of the occipital and temporal lobes of the brain. When blood flow is reduced or stopped completely by a stroke or tear, the consequences for the individual are often disastrous, given the importance of the brain structures involved in subsequent blood flow.
1. Posterior cerebral artery
The posterior cerebral arteries originate from the interpeduncular cistern and come from the bifurcation of the basilar artery Among its main branches are the posterior communicating artery, the medial and lateral posterior choroidal arteries, as well as the calcarine artery.
Upon reaching the cortex, this artery divides into the parieto-occipital and calcarine arteries. The parieto-occipital artery continues through the parieto-occipital sulcus and is responsible for supplying blood to the medial portion of the parietal and occipital lobes; and, for its part, the calcarine artery continues its course through the calcarine fissure, performing irrigation functions for the visual cortex in the occipital lobe.
2. The Willis polygon
The cerebral arterial circle or circle of Willis (named in honor of the English physician Thomas Willis, a pioneer in the study of comparative anatomy), is a heptagon-shaped structure located in the lower part of the brain, surrounding the stem of the brain. pituitary gland, optic chiasm and hypothalamus.
This blood circulation system is formed by the union of the two systems that we have seen previously: the carotid system and the vertebrobasilar system It is what is called an anastomosis system, that is, an interconnecting network of arteries in the form of an arterial polygon responsible for supplying blood to the brain and adjacent areas.
Like the rest of the systems, the circle of Willis can be divided into its anterior and posterior part. The anterior is formed by the internal carotid artery and supplies blood to the anterior part of the brain, irrigating most of the cerebral hemispheres, as well as some deep areas such as the caudate nucleus and putamen. The posterior area of ​​the arterial polygon is made up of the vertebral arteries and is mainly responsible for supplying blood to the cerebellum, the trunk and the posterior area of ​​the cerebral hemispheres.
The main function of the circle of Willis is to allow an alternative route to exist in case an occlusion occurs or blood flow to its usual route is stopped. In addition, it also allows blood flow to be equalized between the two sides of the brain (right and left hemisphere).
Definitely, This network of arteries facilitates a correct distribution of blood flow in our brain especially in the event that we suffer any type of damage or stroke that implies a decrease or paralysis of cerebral irrigation and vascularization.
