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The blood–brain barrier (BBB) is a highly selective semipermeable border of endothelial cells that regulates the transfer of solutes and chemicals between the circulatory system and the central nervous system, thus protecting the brain from harmful or unwanted substances in the blood. [1]
The blood–brain barrier is formed by special tight junctions between endothelial cells lining brain blood vessels. Blood vessels of all tissues contain this monolayer of endothelial cells, however only brain endothelial cells have tight junctions preventing passive diffusion of most substances into the brain tissue. [1]
Pericytes play a crucial role in the formation and functionality of the blood–brain barrier. This barrier is composed of endothelial cells and ensures the protection and functionality of the brain and central nervous system. It has been found that pericytes are crucial to the postnatal formation of this barrier.
The glia limitans also acts as a second line of defense against anything that passes the blood–brain barrier. However, because the astrocytes surrounding the vessels are connected by gap junctions , it is not considered part of the BBB and material can readily pass between the foot processes.
The most common functional imaging signal is the blood-oxygen-level dependent signal (BOLD), which primarily corresponds to the concentration of deoxyhemoglobin. [13] The BOLD effect is based on the fact that when neuronal activity is increased in one part of the brain, there is also an increased amount of cerebral blood flow to that area which ...
The median eminence is generally defined as the portion of the ventral hypothalamus from which the portal vessels arise. [1] The median eminence is a small swelling on the tuber cinereum, posterior to and on top of the pituitary stalk; it lies in the area roughly bounded on its posterolateral region by the cerebral peduncles, and on its anterolateral region by the optic chiasm.
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The blood–ocular barrier is a barrier created by endothelium of capillaries of the retina and iris, ciliary epithelium and retinal pigment epithelium. [1] It is a physical barrier between the local blood vessels and most parts of the eye itself, and stops many substances including drugs from traveling across it. [ 2 ]