Neuro Lecture 4: Blood Brain Barrier

blood brain barrier (BBB)

• network of systems working to keep damaging elements from blood out of brain

• allows certain substrates and amounts of glucose to exit blood vessel

tight junctions

• where cell membranes of adjacent cells are fused 360°

• will not allow intercellular diffusion of blood elements

• between endothelial cells of blood vessels

basal lamina

• continuous in arteries/capillaries

• discontinuous in blood vessels

reduced pinocytotic division means…

many drugs/molecules are unable to penetrate the BBB

active transport process

allows many solutes through endothelium

What restricts most molecules, proteins, and microorganisms from entering the CNS?

the BBB

glucose

• concentrations lower in neural tissue and are variable throughout day

• BBB reduces amount that reaches CNS

Are blood borne neurotransmitters able to enter the CNS?

no

astrocytic end feet

• extend from pia mater to arterial walls of central or cortical branches

• surround vascular component and may contribute to impermeability pf vascular core contribute to impermeability of vascular core

pericytes

specialized vascular support cells

abilities of pericytes

• nutritive functions

• hemolytic functions

• phagocytic functions

• embryonic induction of vascular endothelium (forms tight junctions)

What makes the BBB unique in the human body?

tight junctions

the BBB allows extracellular fluid (ECF) to…

enter extracellular compartments located in all 6 divisions of CNS

What percent of brain weight is ECF?

15%

How many mL of ECF are produced in 24 hours?

200 mL

cerebral spinal fluid (CSF)

free to diffuse through ventricular wall (ependymal-glial membrane) into chambers/extracellular compartments (bc no tight junctions between cells)

pialglial membrane

allows ECF to diffuse into sub-arachnoid space (bc no tight junctions between cells)

mix of CSF and ECF

• flows ventricle wall to sub-arachnoid space

• waste removal

• sub for lymphatic drainage

• also has metabolic waste water mixed in

Does the CNS have lymphatic drainage?

no

metabolic water

• water produced by neuronal metabolism

• removal of waster and non-captured neurotransmitters

How many mL of CSF does the choroid plexus produce in 24 hours?

550 mL

How many times per day does the choroid plexus have a complete turnover of CSF?

3-4

vascular element of choroid plexus

folded, ribbon-like structure with numerous villa

vascular structure of choroid plexus

• core encased by dense CT and capped by choroid cells (epithelial cells)

• choroid cells have tight junctions between them

choroid plexi

found throughout ventricular system lining floor of each cavity

in case of choroid plexus, capillary beds are fenestrated

• allows less restriction for intracellular transport of materials into CT surrounding them

• no tight junctions between endothelial cells, so less restricted intracellular transport

• tight junctions between choroid epithelial cells critical to tightness of barrier function

What has a lower concentration in CSF than in blood plasma?

glucose, proteins, albumin, and ions (Ca and K)

What has a higher concentration in CSF than in blood plasma?

Cl, Mg, and Na

Can blood-circulating neurotransmitters/neuroactive agents(epinephrine/nor-epinephrine) cross the BBB?

no

What can a shift in concentrations indicate?

a disease

bacterial meningitis

low glucose levels with high neutrophils count in CSF

hemorrhage in sub-dural space

RBC in CSF

multiple sclerosis

lymphocytes (as few as 50 cells/mL) in CSF may indicate MS