The Blood Supply To The Brain: Anatomy, Phases And Course

Our brain needs large amounts of blood to function.

Blood supply to the brain

Our brain is a complex machine that needs to be irrigated, in order to function properly, with a red fuel that we all know: blood. And for this, it uses a set of strategically arranged arteries that are going to be in charge of keeping the brain and the rest of the organs well nourished.

In this article we will see how blood circulation occurs in the brain and what are the main artery systems that make it possible.

How does blood circulate in the brain?

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 brains were not going to be any different. Although it represents just over 2% of body weight, it consumes a sixth of cardiac output and 20% of the oxygen that our body needs at rest.

The brain is constantly active (even when we sleep), hence the vascularization or blood supply 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 go up the neck to penetrate the skull.

The circulation of blood in the brain occurs through two symmetrical systems, on both sides of the neck: in the anterior part, the common carotid arteries; and on the back, the vertebral arteries, which make a large part 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 anterior portion of the brain, which we call the brain.

The vertebral arteries penetrate the skull and join to form a common trunk known as the basilar artery, which is responsible for supplying the cerebellum and brain stem. The internal carotid arteries and the basilar artery divide, in turn, into smaller and smaller branches, and are distributed throughout the brain surface.

The carotid system

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 out 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 are 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 branches (including the internal artery of the striatum), as well as the anterior communicating artery of the brain, and can be classified into 5 segments. It irrigates a large part of the inner surface of the cerebral hemisphere.

2. Middle cerebral artery

The middle cerebral artery or Silvian artery (so named because as soon as it emerges from the internal carotid artery, it enters the Silvio fissure ) is a branch of the internal carotid artery, and is responsible for supplying blood through two segments: a basal and cephalic portion.

This artery has the most complex branching pattern of all the cerebral arteries, and presents cortical (orbital, frontal, parietal, and temporal) and central (striated) branches. It has two main branches: a basilar, which is responsible for irrigating part of the caudate nucleus and the thalamus ; and the cortical portion, which supplies a large part of the cerebral cortex.

When the middle cerebral artery becomes blocked, 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

Willis polygon

The vertebrobasilar system is in charge of 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, brain stem, cerebellum, and much of the occipital and temporal lobes of the brain. When blood flow is reduced or completely stopped by a stroke or tear, the consequences for the individual are often disastrous, given the importance of the brain structures involved in subsequent irrigation.

1. Posterior cerebral artery

The posterior cerebral arteries originate in the interpeduncular cistern and come from the bifurcation of the basilar artery. Its main branches include 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 parietoccipital and calcarine arteries. The parieto-occipital artery continues through the parieto-occipital groove 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 of the visual cortex in the occipital lobe.

2. The polygon of Willis

The cerebral arterial circle or polygon of Willis (named after 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 system of blood circulation is formed by the union of the two systems that we have seen previously: the carotid system and the vertebrobasilar system. This is what is called an anastomosis system, that is, an interconnection network of arteries in the form of an arterial polygon responsible for supplying blood to the brain and adjacent areas.

Like the rest of systems, the polygon of Willis can be divided into its front and back. The anterior is formed by the internal carotid artery and supplies blood to the anterior part of the brain, supplying 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 primary function of the circle of Willis is to allow an alternate pathway to exist in the event that an occlusion occurs or the blood supply is stopped on its usual path. In addition, it also allows blood flow between the two sides of the brain (right and left hemisphere) to be equalized.

In short, 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 the cerebral irrigation and vascularization.

Bibliographic references:

  • Hendrikse J, van Raamt AF, van der Graaf Y, et al. Distribution of cerebral blood flow in the circle of Willis. Radiology 2005; 235: 184 –89
  • Kandel, ER; Schwartz, JH & Jessell, TM (2001). Principles of neuroscience. Fourth edition. McGraw-Hill Interamericana. Madrid
  • Scheel P, Ruge C, Petruch UR, Schoning M. Color duplex measurement of cerebral blood flow volume in healthy adults. Stroke. 2000; 31: 147-150

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