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Why are the blood vessels of the brain so special? Reveal the amazing structure of the blood-brain barrier!
This system allows the passive diffusion of small molecules through it, while selectively actively transporting a variety of essential nutrients, ions, organic anions, and macromolecules, such as glucose and amino acids, which are critical for neural function.
The main feature of the blood-brain barrier is its tightly connected endothelial cells, the gaps between which hardly allow large or hydrophilic molecules to enter or exit freely. The formation of the blood-brain barrier prevents some pathogens and large water-soluble molecules from entering the cerebrospinal fluid, while hydrophobic molecules (such as oxygen, carbon dioxide and hormones) and small non-polar molecules can diffuse freely.
Special structures and functions
The structure of the blood-brain barrier consists of tight junctions in endothelial cells that limit the transmission of substances. The tight junctions that connect endothelial cells form a line of defense at the border, which is composed of various transmembrane proteins such as occludin, claudins and junctional adhesion molecules (JAMs), which are further stabilized by other protein complexes.
This allows the blood-brain barrier to more effectively restrict the entry of substances than the capillary endothelial cells in other parts of the body, greatly enhancing the brain's ability to protect against external dangers.
Development and Operation
The blood-brain barrier is already functional at birth, and studies have shown that P-glycoprotein is already present in the embryonic endothelium. Endothelial cells in newborns are functionally similar to those in adults, suggesting that a selective blood-brain barrier is already functioning at birth.
According to a series of studies, loss of claudin-5 during development leads to a breakdown in the blood-brain barrier, a finding that suggests its critical role in the adult blood-brain barrier.
Protective role of the blood-brain barrier
The blood-brain barrier effectively protects brain tissue from circulating pathogens and other potential toxins. This is also why blood-brain infections are so rare. Infections in the brain are often difficult to treat because antibodies are too large to cross the blood-brain barrier, and even some antibiotics cannot get through.
Therefore, in some cases, drugs need to be administered directly into the cerebrospinal fluid to effectively enter the brain.
Special Transmission Area
Some specialized structures of the brain, called periventricular organs (CVOs), have highly permeable capillaries that are distinct from the blood-brain barrier. These structures, such as the regional retroperitoneum, subperitoneal glands, and choroid plexus, allow rapid detection of signals in the blood and facilitate entry of brain-derived signals into the circulation.
These permeable capillaries are bidirectional blood-brain communication points for neuroendocrine function and therefore play a key role in maintaining neuroendocrine balance.
Future treatment research
In therapeutic research, the blood-brain barrier poses a particular challenge to targeted therapy because most large molecule therapies and more than 98% of small molecule drugs cannot cross this barrier. Scientists are exploring various mechanisms to overcome this barrier, including the use of biochemical approaches or physical methods such as high-intensity focused ultrasound to enable drugs to enter the brain more effectively.
In addition, research is also exploring non-invasive methods such as inhalation, which can effectively deliver drugs to the brain.
While many treatments are being investigated, the dirty and more complex structure and function of the blood-brain barrier continues to challenge the field's development. In the face of neurodegenerative diseases such as Alzheimer's disease and epilepsy, researchers are still trying to figure out what problems are associated with the blood-brain barrier and how to solve them.
Faced with the challenges posed by the blood-brain barrier, the scientific community needs to continue to explore new treatments. How can we effectively break through the obstacles of this structure to promote more brain therapies?
