What is the blood brain barrier and how is it linked to Alzheimer's disease? 🧠 Our brains have a layer of specialised cells that protect it and regulate what enters and leaves the fluid surrounding our brains – this is called the blood brain barrier. The blood-brain barrier deteriorates in many diseases that cause dementia, including in Alzheimer’s disease. This leads to toxic substances entering the brain, incorrect use of vital nutrients like oxygen and glucose, and failure to remove waste pr