Question

What types of molecules does the blood brain barrier (BBB) allow to pass into the brain? What is blocked? How does this protect the brain, but also leave it potentially vulnerable?

Answer 1

The blood–brain barrier (BBB) is a highly selective semipermeable border of endothelial cells that prevents solutes in the circulating blood from non-selectively crossing into the extracellular fluid of the central nervous system where neurons reside.

A) It allows  the

• hydrophobic molecules (O2, CO2, hormones) and
• small polar molecules
• lipid soluble molecules, such as barbituate drugs, rapidly cross through into the brain.
• Molecules that have a high electrical charge are slowed.

B) It blocks the  

• Large molecules do not pass through the BBB easily.
• Low lipid (fat) soluble molecules do not penetrate into the brain.
• restricts the passage of pathogens,
• the diffusion of solutes in the blood, and
• hydrophilic molecules into the cerebrospinal fluid

The blood-brain barrier (BBB) forms a layer of specialized endothelial cells around the brain that protects it—letting in only what is needed and keeping out what could be harmful. It crucially maintains the right ionic balance within the brain and blocks substances that would disrupt essential neural functions.

The blood-brain barrier may become leaky in select neurological diseases, such as amyotrophic lateral sclerosis, epilepsy, brain trauma and edema, and in systemic diseases, such as liver failure.

(Please like if answer is helpful for you thanks)