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All circumventricular organs except the subcommissural organ contain fenestrated capillaries, [2] a feature that distinguishes them from most other parts of the brain. [7] The SFO can be divided into six anatomical zones based on its capillary topography: two zones in the coronal plane and four zones in the sagittal plane. [3]
The brain pia mater is reflected from the surface of the brain onto the surface of blood vessels in the subarachnoid space. In the brain, perivascular cuffs are regions of leukocyte aggregation in the perivascular spaces, usually found in patients with viral encephalitis. Perivascular spaces vary in dimension according to the type of blood vessel.
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. [28] Overcoming the difficulty of delivering therapeutic agents to specific regions of the brain presents a major challenge to treatment of most brain disorders.
A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the innermost layer of an artery or vein), consisting of a thin wall of simple squamous endothelial cells. [2]
The VOLT is one of the three sensory circumventricular organs providing information to other brain regions. [6] [10] VOLT capillaries do not have a blood–brain barrier, and so neurons in this region can respond to circulating factors present in the systemic circulation. [11] [9]
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]
The glia limitans perivascularis abuts the perivascular space surrounding the parenchymal blood vessels and functions as a supportive constituent of the blood–brain barrier. In contrast, the non-parenchymal blood vessels present in the subarachnoid space are not covered by the glia limitans.
The capillaries in the portal system are fenestrated (have many small channels with high vascular permeability) which allows a rapid exchange between the hypothalamus and the pituitary. The main hormones transported by the system include gonadotropin-releasing hormone , corticotropin-releasing hormone , growth hormone–releasing hormone , and ...