CVOs can be classified as either sensory or secretory organs serving homeostatic functions and body water balance.[3][7] The sensory organs include the area postrema, the subfornical organ, and the vascular organ of lamina terminalis, all having the ability to sense signals in blood, then pass that information neurally to other brain regions. Through their neural circuitry, they provide direct information to the autonomic nervous system from the systemic circulation.[1][10][14][15] The secretory organs include the subcommissural organ (SCO), the pituitary gland, the median eminence, and the pineal gland.[7][11] These organs are responsible for secreting hormones and glycoproteins into the peripheral blood using feedback from both the brain environment and external stimuli.[7]
Circumventricular organs contain capillary networks that vary between one another and within individual organs both in density and permeability, with most CVO capillaries having a permeable endothelial cell layer, except for those in the subcommissural organ.[1][16] Furthermore, all CVOs contain neural tissue, enabling a neuroendocrine role.
Although the choroid plexus also has permeable capillaries, it does not contain neural tissue; rather, its primary role is to produce cerebrospinal fluid (CSF), and therefore is typically not classified as a CVO.[1]
^Gross, P. M (1992). "Chapter 31: Circumventricular organ capillaries". Circumventricular Organs and Brain Fluid Environment - Molecular and Functional Aspects. Progress in Brain Research. Vol. 91. pp. 219–33. doi:10.1016/S0079-6123(08)62338-9. ISBN9780444814197. PMID1410407.
^ abFry, W.M.; Ferguson, A.V. (2009). "Circumventricular Organs". Encyclopedia of Neuroscience. Elsevier. pp. 997–1002. doi:10.1016/b978-008045046-9.00462-9. ISBN978-0-08-045046-9. Neurons in the sensory CVOs are ideally positioned at the blood–brain interface to monitor major constituents of body fluids.
^Kaur, C; Ling, EA (September 2017). "The circumventricular organs". Histology and Histopathology. 32 (9): 879–892. doi:10.14670/HH-11-881. PMID28177105.
^Hofer H (1958). "Zur Morphologie der circumventriculären Organe des Zwischenhirns der Säugetiere". Verhandlungen der Deutschen Zoologischen Gesellschaft. 55: 202–251.
^Wislocki, George B.; King, Lester S. (1936). "The permeability of the hypophysis and hypothalamus to vital dyes, with a study of the hypophyseal vascular supply". American Journal of Anatomy. 58 (2): 421–472. doi:10.1002/aja.1000580206. ISSN0002-9106.
^ abcdeGross PM, ed. (1987). Circumventricular Organs and Body Fluids, Volumes I-III. CRC Press, Inc. p. 688. ISBN978-0849367984.
^Rodríguez Esteban M.; Blázquez Juan L.; Guerra Montserrat (2010). "The design of barriers in the hypothalamus allows the median eminence and the arcuate nucleus to enjoy private milieus: The former opens to the portal blood and the latter to the cerebrospinal fluid". Peptides. 31 (4): 757–76. doi:10.1016/j.peptides.2010.01.003. PMID20093161. S2CID44760261.
^Morita S.; Miyata S. (2012). "Different vascular permeability between the sensory and secretory circumventricular organs of adult mouse brain". Cell and Tissue Research. 349 (2): 589–603. doi:10.1007/s00441-012-1421-9. PMID22584508. S2CID15228158.