http://medical-dictionary.thefreedictionary.com/Hematoencephalic+barrier

barrier /bar·ri·er/ (bar´e-er) an obstruction.

alveolar-capillary barrier , alveolocapillary barrier see under membrane.

blood-air barrier alveolocapillary membrane.

blood-aqueous barrier the physiologic mechanism that prevents exchange of materials between the chambers of the eye and the blood.

blood-brain barrier , blood-cerebral barrier the selective barrier separating the blood from the parenchyma of the central nervous system. Abbreviated BBB.

blood-gas barrier alveolocapillary membrane.

blood-testis barrier a barrier separating the blood from the seminiferous tubules, consisting of special junctional complexes between adjacent Sertoli cells near the base of the seminiferous epithelium.

placental barrier term sometimes used for the placental membrane, because it prevents the passage of some materials between the maternal and fetal blood.

Dorland's Medical Dictionary for Health Consumers. © 2007 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

blood-brain barrier

n. Abbr. BBB

A physiological mechanism that alters the permeability of brain capillaries so that some substances, such as certain drugs, are prevented from entering brain tissue, while other substances are allowed to enter freely.

The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.

Blood-brain barrier

A blockade of cells separating the circulating blood from elements of the central nervous system (CNS); it acts as a filter, preventing many substances from entering the central nervous system.

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Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.

blood-brain barrier (BBB)

Etymology: AS, blod + bragen + ME, barrere

an anatomic-physiologic feature of the brain thought to consist of walls of capillaries in the central nervous system and surrounding astrocytic glial membranes. The barrier separates the parenchyma of the central nervous system from blood. The blood-brain barrier prevents or slows the passage of some drugs and other chemical compounds, radioactive ions, and disease-causing organisms such as viruses from the blood into the central nervous system.

Mosby's Medical Dictionary, 8th edition. © 2009, Elsevier.

blood-brain barrier,

n barrier formed by epithelial cells in the capillaries that supply the brain and central nervous system. This barrier selectively allows entry of substances such as glucose, some ions, and oxygen, while blocking entry of other substances. Also called

Jonas: Mosby's Dictionary of Complementary and Alternative Medicine. (c) 2005, Elsevier.

blood-brain barrier,

n an anatomic-physiologic feature of the brain thought to consist of walls of capillaries in the central nervous system and surrounding glial membranes. It prevents or slows the passage of some drugs, other chemical compounds, radioactive ions, and disease-causing organisms such as viruses from the blood into the nerve tissues of the central nervous system.

Mosby's Dental Dictionary, 2nd edition. © 2008 Elsevier, Inc. All rights reserved.

blood-brain barrier

A mechanism that prevents some substances in the blood from reaching the brain. It is achieved by brain capillaries, which unlike other capillaries elsewhere in the body, are composed of endothelial cells sealed together in continuous tight junctions and surrounded by astrocytes that contribute to the selective passage of substances. Lipid-soluble substances such as alcohol, caffeine, nicotine and most anaesthetics, as well as glucose, oxygen and water, pass rapidly into brain cells, whereas proteins, most antibiotics and ions do not enter or enter very slowly. The mechanism protects brain cells against harmful substances and pathogens. See central nervous system.

Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann

blood-brain barrier

Physiology A selectively permeable structural and functional barrier that exists between the capillaries and the brain; water, O₂ and CO₂ readily cross the BBB, glucose is slower, Na+, K+, Mg++, Cl–, HCO₃– and HPO₄– require 3-30-fold more time to equilibrate with the CSF than with other interstitial fluids; urea penetrates very slowly; catecholamines and bile salts essentially do not cross the BBB–kernicterus is due to accumulation of bile salts in the brains of neonates whose BBB is yet immature; integrity of the BBB is impaired in hepatic encephalopathy

McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.