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The blood–brain barrier is formed by the brain capillary endothelium and excludes from the brain 100% of large-molecule neurotherapeutics and more than 98% of all small-molecule drugs. [23] Overcoming the difficulty of delivering therapeutic agents to specific regions of the brain presents a major challenge to treatment of most brain disorders.
The blood-brain barrier and the blood-spinal cord barrier: Pericytes and astrocytes endfeet (Astrocytic endfeet envelop the abluminal surface of brain capillaries, accounting for 70% to nearly 100% of their total surface area). [34] The inner blood retinal barrier (iBRB) [35] Pericytes and endfeet of glial cells like astrocytes and Müller cells.
The larger arteries throughout the brain supply blood to smaller capillaries. These smallest of blood vessels in the brain, are lined with cells joined by tight junctions and so fluids do not seep in or leak out to the same degree as they do in other capillaries; this creates the blood–brain barrier. [44]
Ligands can also be attached to the surface of a nanoparticle to target certain receptors located within the brain. Once the nanoparticle is through the blood brain barrier it releases the drug into the brain. [5] A specific example of this solution is the delivery of anti-HIV drugs to the central nervous system by TAT-conjugated nanoparticles. [6]
The blood–cerebrospinal fluid barrier (BCSFB) is a fluid–brain barrier that is composed of a pair of membranes that separate blood from CSF at the capillary level and CSF from brain tissue. [14] The blood–CSF boundary at the choroid plexus is a membrane composed of epithelial cells and tight junctions that link them. [ 14 ]
Firstly, the brain can be flooded with molecules that are floating through the blood stream that are usually blocked by the barrier. Secondly, when the tight junctions loosen, the homeostasis of the brain can also be thrown off which can result in seizures and the compromised function of the brain. [8]
This is called the precapillary sphincter. The precapillary sphincter has now also been found in the brain, where it regulates blood flow to the capillary bed. [3] The sphincter can open and close the entrance to the capillary, by which contraction causes blood flow in a capillary to change as vasomotion occurs. [4] [unreliable source?
The hypophyseal portal system is a system of blood vessels in the microcirculation at the base of the brain, connecting the hypothalamus with the anterior pituitary.Its main function is to quickly transport and exchange hormones between the hypothalamus arcuate nucleus and anterior pituitary gland.