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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]
A specialised form of epithelium, endothelium, forms the inner lining of blood vessels and the heart, and is known as vascular endothelium, and lining lymphatic vessels as lymphatic endothelium. Another type, mesothelium , forms the walls of the pericardium , pleurae , and peritoneum .
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]
They are joined at the lumen of the tube by junctional complexes, where they form a pseudostratified layer of epithelium called neuroepithelium. [ 1 ] Neuroepithelial cells are the stem cells of the central nervous system , known as neural stem cells , and generate the intermediate progenitor cells known as radial glial cells , that ...
The brain is small and simple in some species, such as nematode worms; in other species, such as vertebrates, it is a large and very complex organ. [4] Some types of worms, such as leeches, also have an enlarged ganglion at the back end of the nerve cord, known as a "tail brain". [17]
Brain cells make up the functional tissue of the brain. The rest of the brain tissue is the structural stroma that includes connective tissue such as the meninges, blood vessels, and ducts. The two main types of cells in the brain are neurons, also known as nerve cells, and glial cells, also known as neuroglia. [1]
The arachnoid mater makes arachnoid villi, small protrusions through the dura mater into the venous sinuses of the brain, which allow CSF to exit the subarachnoid space and enter the blood stream. Unlike the dura mater, which receives a rich vascular supply from numerous arteries, the arachnoid mater is avascular (lacking blood vessels).
The endothelium is a thin layer of single flat cells that line the interior surface of blood vessels and lymphatic vessels.[1]Endothelium is of mesodermal origin. Both blood and lymphatic capillaries are composed of a single layer of endothelial cells called a monolayer.