Blood Brain Barrier

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Blood Brain Barrier

• Unit 8 / Week 2
• Prof. Lammers

R.E.B, 4MedStudents.com, 2003
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What is Blood Brain Barrier?

• The BBB is formed by the single layer of
  endothelial cells that line the inner surfaces of
  capillaries in the brain.
• It is a semi-permeable capillary membrane that
  is, it allows some materials to cross, but
  prevents others from crossing. In most parts of
  the body the capillaries, are lined with
  endothelial cells. The endothelial tissue has
  small spaces between each individual cell so
  substances can move readily between the inside
  and the outside of the vessel. However, in the
  brain, the endothelial cells fit tightly together
  and substances cannot pass out of the
  bloodstream. (Some molecules, such as glucose,
  are transported out of the blood by special
  methods such as active transport.)

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Functions and Properties of the BBB

• The BBB has several important functions
• Protects the brain from "foreign substances" in
  the blood that may injure the brain.
• Protects the brain from hormones and
  neurotransmitters in the rest of the body.
• Maintains a constant environment for the brain.

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Functions and Properties of the BBB

• General Properties of the BBB
• Large molecules do not pass through the BBB
  easily.
• Low lipid (fat) soluble molecules do not
  penetrate into the brain. However, lipid soluble
  molecules rapidly cross the BBB into the brain.
• Molecules that have a high electrical charge to
  them are slowed.
• Therefore
• The BBB is selectively permeable to Oxygen,
  Carbon dioxide and glucose
• The BBB is not permeable to
• hydrogen ions

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Transport at the BBB

• There are five basic mechanisms by which solute
  molecules move across membranes
• simple diffusion
• facilitated diffusion
• simple diffusion through an aqueous channel
• active transport through a protein carrier
• Endocytosis

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Transport mechanisms at the BBB. 1 paracellular
diffusion , 2 transcellular diffusion , 3 ion
channel 4 ion-symport channel 5 ion-antiport
channel 6 facilitated diffusion , 7 active
efflux pump 8 active-antiport transport , 9
receptor mediated endocytosis