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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–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.
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 microcirculation has three major components: pre-capillary, capillary, and post-capillary. In the pre-capillary sector, arterioles, and precapillary sphincters participate. Their function is to regulate blood flow before it enters the capillaries and venules by the contraction and relaxation of the smooth muscle found on their walls.
The choroid plexus regulates the production and composition of cerebrospinal fluid (CSF), that provides the protective buoyancy for the brain. [2] [10] CSF acts as a medium for the glymphatic filtration system that facilitates the removal of metabolic waste from the brain, and the exchange of biomolecules and xenobiotics into and out of the brain.
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.
[4] [5] Pericytes help in the maintainenance of homeostatic and hemostatic functions in the brain, where one of the organs is characterized with a higher pericyte coverage, and also sustain the blood–brain barrier. [6] These cells are also a key component of the neurovascular unit, which includes endothelial cells, astrocytes, and neurons.
Blood–brain barrier – Semipermeable capillary border that allows selective passage of blood constituents into the brain; Blood–ocular barrier – Physical barrier between the local blood vessels and most parts of the eye itself; Blood–saliva barrier – Semipermeable biological barrier