The Blood-Brain Barrier and Cerebrospinal Fluid Dynamics

Question-and-answer flashcards covering BBB structure, function, choroid plexus, CSF dynamics, and CNS fluid exchange based on Fall 2021 notes.

What is the Blood-Brain Barrier (BBB) and its primary function?

A network including capillary endothelial tight junctions, astrocyte endfeet, and pericytes that limits entry of harmful substances from blood into the brain while allowing selective transport of essential substrates like glucose.

Which cells interact with the BBB to help maintain its impermeability?

Astrocytes (with endfeet surrounding vessels) and pericytes, in addition to endothelial cells forming tight junctions.

What are endothelial tight junctions and where are they located in the BBB?

360-degree fused membranes between adjacent endothelial cells in CNS capillaries that prevent paracellular diffusion.

How does pinocytotic diffusion in CNS endothelium compare to other tissues?

It is greatly reduced in the CNS; nonspecific pinocytosis is limited to protect the brain.

Can many large molecules or non-lipid-soluble drugs penetrate the BBB easily?

No; they cannot cross easily and often require active transport or lipid solubility to pass.

What is the Blood-CSF barrier and where is it located?

A barrier formed by tight junctions between choroid plexus epithelial cells in the ventricular system, regulating exchange between blood and CSF.

Where is the choroid plexus located and what is its main function?

Distributed throughout the ventricular system, lining the floors of ventricles; produces about 500–550 mL of CSF per day and forms the Blood-CSF barrier via tight junctions between choroid epithelial cells.

What is the nature of the choroid plexus capillaries and their implication for transport?

Capillaries are fenestrated, providing less restriction to intracellular transport, but the barrier to CSF is created by tight junctions between epithelial cells.

How do CSF and ECF interact within the CNS?

CSF can diffuse into extracellular compartments; ECF can diffuse into the subarachnoid space; there are no tight junctions at these interfaces, allowing mixing.

What is the function of CSF-ECF mixing in the CNS?

Aids in waste removal and metabolic waste clearance, acting as a substitute for lymphatic drainage; includes metabolic water.

How much CSF is produced daily and how many times does it turnover?

About 500–550 mL per day with complete turnover roughly 3–4 times per day.

How do CSF and blood plasma differ in solute composition (glucose, proteins, ions)?

CSF has lower glucose, proteins, and calcium/potassium; higher chloride, sodium, and magnesium than blood plasma.

Can brain-derived neurotransmitters cross the BBB and can circulating neurotransmitters cross into the brain?

Generally, blood-borne neurotransmitters cannot enter the CNS and CNS-produced neurotransmitters generally cannot exit into the blood.

Why is the BBB not uniform throughout the CNS?

There are regions with modified barriers; notably the choroid plexus and its Blood-CSF barrier differ from the typical BBB.

What is the role of pericytes in BBB formation and function?

Support cells with nutritive, phagocytic, and embryonic signaling roles that contribute to inducing endothelial cells to form tight junctions.