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Blood-Brain Barrier (BBB) The brain is protected by Harmful substances are shielded from the brain by the Blood-Brain Barrier.
 * Bone
 * Meninges
 * Cerebrospinal fluid

BBB is the most significant element responsible for the preservation of CNS homeostasis. Brain edema formation after stroke has been linked to the inability of the BBB to maintain necessary ion gradients. Alterations in BBB ion homeostasis have been linked with epilepsy. Changes in BBB function have been described in several neurological disorders, including stroke, multiple sclerosis and Alzheimer’s disease.In Alzheimer’s disease, β-amyloid induces cytokine release and monocyte migration across an in vitro BBB in vivo β-amyloid deposition leads to degeneration of the microvascular basement membrane and alterations in BBB permeability.

Development of the Blood-Brain Barrier The counterpart of this situation in later life is the syndrome, in which there is a congenital deficiency of glucuronyl transferase. These individuals can have very high free bilirubin levels in the blood and develop encephalopathy.
 * It is often stated that the BBB is immature at birth.
 * In severely jaundiced infants with high plasma levels of free bilirubin and an immature hepatic bilirubin-conjugating system, free bilirubin enters the brain and, in the presence of asphyxia, damages the basal ganglia (kernicterus).

Function of the blood-brain barrier
 * Controls delivering of nutrients to and removing metabolites from the CNS compartment.
 * It is a barrier for ionic currents and hydrophilic compounds able to cross it only through special membrane transporters.
 * The BBB regulates the ion balance of the brain. Brain edema after stroke has been linked to the inability of the BBB to maintain necessary ion gradients.
 * Protects the CNS from abrupt changes in blood biochemistry that occur after meals, physical excercises, or in pathological conditions.
 * BBB is an extremely important „guardian” that regulates access of drugs to the CNS under both physiological and pathological circumstances.
 * BBB components are responsible for the biochemical modification of chemicals that enter the CNS. Moreover, some drugs, even if they can cross the BBB, are immediately removed from the CNS.
 * Divides neurotransmitters and in general, neuroactive substances into two pools of Central & Peripheral systems

BBB building blocks: Endothelial cells Astrocytes Pericytes

Nanotechnology approaches to crossing the blood-brain barrier