Blood-brain barrier

The blood-brain barrier (BBB) is a selective permeable barrier composed of endothelium that separates central nervous system from circulating blood.

Some parts of the brain sit outside the blood brain barrier. Collectively, they are known as the circumventricular organs and include sensory and secretory organs important for neuroendocrine function including the pineal glad and the posterior pituitary. The olfactory bulb also sits outside the blood brain barrier.

Several diseases have been associated with a weakened blood-brain barrier including epilepsy and multiple sclerosis.