We can think of the blood-brain barrier as a heavily guarded institution, with entrance surveillance and security at every gate. Some visitors were unblocked, others had to show ID and be escorted inside after passing through security screening equipment. There are also some visitors who are turned away or not even allowed to approach.
Neuroscientists may use a range of extreme words when describing the brain. First and foremost, the brain is the most vulnerable organ in the human body. If you hold the brain in your hand, you will find that its texture is about the same as jelly. Due to the high amount of fat in the brain, it has a very soft texture and is easily damaged.
During evolution, nature also gave the brain the tightest protection. The brain is surrounded by several layers of protective membranes (meninges), and outside is a thick and hard skull. After an accidental blow to the head, we usually make an "ouch" or make a face, and then we're fine. But if it weren't for the skull and meninges, this seemingly innocuous minor bump could seriously damage the brain, leading to brain dysfunction and even death.
Inside the skull, the brain is immersed in clear, colorless cerebrospinal fluid. Without cerebrospinal fluid, the brain cannot even support its own weight. Cerebrospinal fluid "lifts" the brain, cushioning shocks from sudden head movements or impacts on hard surfaces. Cerebrospinal fluid circulation removes toxins and waste products produced in the brain, keeping the brain clean and functional.
However, force damage is not the only danger to an organ so vulnerable. It also needs to be protected from the inside, as many substances circulating in the blood can be extremely damaging to the brain.
Under the arrangement of nature, a special barrier between blood and brain tissue plays a role in preventing these harmful substances from entering the brain. The brain is the only organ in the body that has its own safety system, a network of blood vessels known as the blood-brain barrier. The blood-brain barrier is the last protective layer of the brain. It is composed of flat cells, and the cells are closely connected. It is an almost impenetrable cell barrier. Only those substances that are considered safe and useful can pass through the blood-brain barrier and enter the brain.
We can think of the blood-brain barrier as a heavily guarded institution, with entrance surveillance and security at every gate. This strategy allows the brain to take complete control of the situation - which substances are easy to get in, which substances can only pass under supervision, and which substances are dangerous and must be kept out.
Day in and day out, the blood-brain barrier protects the brain from damage from infection and inflammation by limiting the passage of foreign, potentially harmful substances such as bacteria, toxins, and even certain drugs. Meanwhile, whether chemical messengers produced elsewhere in the body, including some autologous hormones that may interfere with brain activity, enter the brain is precisely controlled by the blood-brain barrier.
In addition, various substances necessary for the functioning of the brain can pass through the blood-brain barrier. Amazingly, most of the substances that are allowed to cross the blood-brain barrier are inseparable from the air, the soil, and the food that grows in the ground. With every breath we take, every meal we eat, so much of the material in this planet we live on—its rivers, valleys, oceans, and skies—is becoming part of our brains, and it's shocking people's hearts.
First, water is a guest. Water is free to enter brain tissue at any time, as are some gases (such as oxygen), which are required for cellular respiration.
Besides water and air, what other substances can pass through the blood-brain barrier? Nutrients. Proteins, fats and carbohydrates, as well as vitamins and minerals, play a role in maintaining brain function, promoting cellular activity and preventing defects.
The human brain has evolved over millions of years to the point where highly specialized, nutrient-specific channels have formed in the blood-brain barrier, allowing this most important organ in our body to obtain what it needs to grow and stay alive. All nutrients.
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