What are the physiological characteristics of cerebral circulation? Regulation of cerebral circulati

The brain is located in the cranial cavity. The cranial cavity is bony and its volume is fixed. The cavity is filled with the brain, cerebrovascular and cerebrospinal fluid, and the sum of the volumes of the three is also fixed.

Because brain tissue is incompressible, the degree of cerebral vasomotor is quite limited, and the change in blood flow is smaller than that of other organs.

The endothelial cells of the capillary wall of the cerebral circulation are in close contact with each other and overlap to a certain extent, and there are no small holes in the tube wall. In addition, there is no direct contact between the capillaries and the neurons, but the glial cells are afraid of separation. This structural feature acts as a barrier to the diffusion of substances between the blood and brain tissue, known as the blood-brain barrier.

The physiological characteristics of cerebral circulation, that is to say, there are many blood vessels in the brain for the brain to think, and these blood vessels are used to provide energy, so the physiological characteristics of cerebral circulation are that your brain needs energy to attack, that is, blood circulation to be able to work normally.

There are five physiological characteristics of cerebral circulation:

1. Cerebral blood** comes from internal neck A and vertebral A.

2. The head is high and Xingheng education is whole|Reason.

3. Cerebral blood flow decreases with age.

4. The blood flow of gray matter is greater than that of white matter.

5. The cerebral blood flow is relatively stable, and the change range is very small.

1 Pinyin 2 English references.

3 Overview 4 Characteristics of cerebral circulation.

nǎo xún huán

cerebral circulation

Cerebral circulation is another extremely important local vascular system in the systemic circulation that supplies blood to brain tissue. The blood circles of the brain contain circles from the internal carotid and vertebral arteries. The vertebral arteries on the left and right sides merge into the basilar artery in the abdomen of the pont, which in turn communicates with the internal carotid arteries on both sides to form a cerebral artery ring, which then branches out for the cavity to dig up the parts of the brain.

Veins in the brain drain into the interdural venous sinuses, then into the internal jugular veins on both sides, and then back to the right atrium via the superior vena cava. The veins of the brain do not run with the arteries. The brain is rich in blood**, and the cerebral blood flow accounts for about 13 16 of the cardiac output.

The blood flow per 100 grams of brain tissue is 50-60 ml per minute.

The spike nucleus is located in the cranial cavity in the brain, so that the cerebral circulation has the following characteristics:

1) The volume of the cranial cavity is quite fixed, filled by the brain, blood vessels and cerebrospinal fluid, so the sum of the three is also quite fixed. If cerebral edema or cerebrospinal fluid volume increases, it causes an increase in intracranial pressure, which increases cerebral blood flow resistance and thus decreases cerebral blood flow when the intracranial pressure exceeds 30 mm Hg (1 mm Hg kPa). On the other hand, the cerebral blood vessels cannot be dilated significantly, and when the cerebral arteries are dilated, the veins of the brain will contract accordingly, so that the venous blood will flow out rapidly.

2) Because the cerebral blood vessels cannot be greatly dilated and contracted, the total cerebral blood flow mainly depends on the arterial blood pressure. When arterial blood pressure increases, cerebral blood flow increases; Otherwise, it will be reduced. Therefore, the relative constant arterial blood pressure is of great significance for maintaining normal blood in the brain.

3) The cerebral blood flow in normal people is relatively constant, with an average of about 750 ml minutes. The total cerebral blood flow in different functional states did not change much, only increasing or decreasing by 30 50. The blood flow in each part of the brain is related to its functional activity, and the blood flow in the more active brain area is higher than that in other brain areas.

The local regulation of the main receptor fluid factors of the cerebral blood vessels, such as hypoxia, carbon dioxide increase or pH decrease, etc., makes the cerebral blood vessels dilate and blood flow increases, among which the effect of carbon dioxide is the most obvious. Cerebrovascular innervation is innervated by sympathetic and parasympathetic nerves, but the effect is not obvious.

Cerebral circulation is regulated by a variety of factors, and even if the internal and external environment changes through the regulation mechanism, the cerebral blood flow can remain stable, which is of great significance for the normal function of the brain. For example, total cerebral blood flow does not increase due to stressful mental activity, nor does it decrease due to relaxation of mental activity or even sleep (and even increases some during sleep). Humoral factors, especially carbon dioxide pH, K+, and Ca2+ in cerebral blood flow, have obvious regulatory effects on cerebrovascular movement, while neuromodulation is weaker and occupies a secondary position.

Because cerebral circulation is within the cranial cavity, changes in intracranial pressure are bound to have an effect. In addition, the average arterial and venous pressure at the brain level, as well as the viscosity of the blood, have an impact on cerebral circulation. The arterioles in the brain, like the arterioles in other organs of the body, are directly affected by the oxygen and carbon dioxide levels of local tissues.

Carbon dioxide, oxygen and pH levels in the brain also have a certain effect on cerebral blood flow: the increase in the partial pressure of carbon dioxide causes a significant increase in cerebral blood flow; The increase in partial pressure of oxygen has the opposite effect. However, changes in the pH of cerebrospinal fluid and extracellular fluid in tissues have a major regulatory effect on cerebral blood flow.

Brain tissue has a high level of metabolism and more blood flow. In the quiet condition, the blood flow per 100 grams of brain is 50-60 ml min. The blood flow throughout the brain is about 750 ml min.

It can be seen that although the proportion of the brain accounts for only about 2% of body weight, blood flow accounts for about 15% of cardiac output. Brain tissue also consumes more oxygen. In quiet conditions, oxygen consumption per minute per 100 grams of brain; In other words, the oxygen consumption of the whole brain accounts for about 20% of the total body oxygen consumption.

I hope that friends will learn the correct breathing method, skillfully use simple breathing to regulate the blood circulation of the head, and restore the vigorous functions of the brain, eyes, mouth and nose.

Cerebral circulation is the most important component of circulation in a particular area. For example, the oxygen consumption of the human brain is about 1 5 of the total body oxygen consumption, and the blood flow of the human brain accounts for about 13% to 15% of the total cardiac output. Adequate cerebral blood flow is the primary condition for normal brain activity.

Insufficient blood flow to the brain** can quickly seriously affect brain function. The cerebral cortex is very sensitive to cerebral circulatory ischemia and hypoxia in the blood, and the lack of oxygen in the cerebral circulation blood for half a minute or completely blocking the cerebral blood flow for 10 seconds will lead to coma, and the lack of oxygen for 3 minutes may cause irreparable damage to the brain nerve cells, and the lack of oxygen for 6 minutes can cause death. It can be seen that cerebral circulation is related to the life and death of animals.

The cerebral circulation supplies nutrients to the central nervous system and eliminates its harmful metabolites, thereby maintaining its normal function.

Cerebral blood flow in vertebrates comes from two pairs of arteries, including one pair each of the vertebral artery and the internal carotid artery. The left and right vertebral arteries enter the cranial cavity from the foramen magnum to form the basilar artery, and then meet with the posterior communicating artery, the internal carotid artery, and the anterior communicating artery to form a cerebral artery ring, from which six cerebral arteries are supplied with blood to the brain and brainstem, and from the basilar artery to the cerebellum artery, one pair of arteries to the cerebellum, and the anterior spinal artery is sent out before the vertebral artery merges into the basilar artery. The internal carotid artery supplies blood to the anterior and middle parts of both cerebral hemispheres, and the vertebral and basilar arteries supply blood to the cerebellum and occipital and posterior fossa of the brain.

Blood injected into the internal carotid artery supplies only the ipsilateral cerebral hemisphere. There is no vascular crossing between the two cerebral hemispheres. Therefore, when one internal carotid artery is occluded, it often causes only ipsilateral cerebral ischemia, especially in the elderly.

The tissue structure of the arteries of the brain parenchyma is characterized by a thinner muscular layer but more elastic fibers and a different arrangement than arteries of similar size in other parts of the body.

The endothelial cells of the cerebral capillaries are closely connected to each other and do not have the same holes or windows as the capillaries of other tissues. About 80% of the surface of the cerebral capillaries is surrounded by circumferential feet. These structures form layers of barriers, making it difficult for many substances in the blood in the cerebral capillaries, especially the large molecular weight substances with low fat solubility such as proteins, antibiotics, and some macromolecular dyes, to pass through, and only allow most ions and small molecules such as glucose to pass through, thus forming the so-called blood-brain barrier.

Cerebral veins have thinner walls compared to cerebral arteries. Unlike veins in other parts of the body, there are no venous valves in the walls of the cerebral veins, and the return of venous blood depends on the potential energy of the high position. The return path of cerebral venous blood can be summarized as follows:

Most cerebral venous blood flows into the internal jugular vein through deep cerebral veins and cerebral sinusoids; Blood from the small cerebral veins passes through the pterygoid plexus of the eye, enters the venous conductor to the scalp, and finally flows into the paravertebral venous system in the spinal canal. The cerebral venous system has a large number of communicating branch venous plexuses, and even if both internal jugular veins are blocked, cerebral venous blood can still complete its return through the vertebral vein and external jugular venous system.