• protective mechanism that helps maintain a stable environment for the brain....the brain needs consistency----separated from the extra cellular environment.
• Blood borne substances with in the brain's capillaries are separated from the extra cellular space and neurons by:
1. The continuous endothelium of the capillary wall.
2. Thick basal lamina surface surrounding the external face of the capillary 3. Bulbous "feet" of the astrocyte that cling to the capillary.
• Least permeable capillaries in the entire body. Astrocytes help form these tight junctions by stimulating the endothelial cells to come in extremely close contact.
• The blood brain barrier is ONLY ineffective against fats, fatty acids, oxygen, and carbon dioxide and other fat-soluble molecules such as alcohols, nicotine, and anesthetics can affect the brain.
• We are missing the blood brain barrier in some areas such as:
1. Around the 3rd and 4th ventricles because this is the region of vomiting
center of the brain stem which monitors blood for poisonous substances.
2. Hypothalmus because it regulates the chemical environment and therefore needs to sample the chemical composition of blood
3. Absent in newborns and premature infants....only develops after birth, after skull has closed.