Cerebrospinal Fluid and Blood-Brain Barrier Physiology

Comprehensive vocabulary flashcards covering the production, composition, and circulation of CSF, the morphology and transport of the BBB, circumventricular organs, and CNS metabolism.

Cerebrospinal Fluid (CSF)

A clear, sterile, and colorless fluid that surrounds and bathes the entire central nervous system (CNS).

Choroid plexus

The primary site of cerebrospinal fluid secretion, responsible for approximately $70\%$ of its production.

CSF Sodium ($Na^+$) concentration

$135-150\,mmol/l$.

CSF Potassium ($K^+$) concentration

$2-3\,mmol/l$, which is significantly lower than the plasma concentration of $4.8\,mmol/l$.

CSF Chloride ($Cl^-$) concentration

$115-130\,mmol/l$, which is higher than the plasma concentration of $108\,mmol/l$.

CSF Protein concentration

$0.1-0.4\,g/l$, which is extremely low compared to the plasma concentration of $63-83\,g/l$.

CSF Glucose concentration

$2.2-4.2\,mmol/l$, which is lower than the plasma range of $3.3-5.6\,mmol/l$.

Homeostasis (CSF Function)

Acts as a chemical buffer to maintain neuronal excitability and serves as a transport medium for nutrients, metabolites, and neurotransmitters.

Mechanical Protection (CSF Function)

Provides a buoyant environment where the brain "floats," preventing tissue compression against the skull by gravity.

Foramen of Monro

The channel through which CSF circulates from the lateral ventricles into the third ventricle.

Aqueduct of Sylvius

The passage that carries CSF from the third ventricle to the fourth ventricle.

Foramina of Magendie and Luschka

The openings through which CSF exits the fourth ventricle to enter the subarachnoid space.

Arachnoid villi

Diverticula of the subarachnoid space that pierce the dura mater to project into dural venous sinuses for CSF absorption.

Arachnoid granulations

Large structures formed by grouped arachnoid villi involved in CSF drainage.

Blood-Brain Barrier (BBB)

A highly selective barrier consisting of continuous endothelium with tight junctions, a thick basal lamina, and astrocytic feet.

Passive Diffusion (BBB)

The transport mechanism for small molecules ($H_2O$, $O_2$, $CO_2$, $NH_3$, ethanol) and lipid-soluble molecules like steroid hormones.

Carrier-Mediated Transport (BBB)

The specific transport mechanism required for glucose (insulin-independent) and amino acids to cross the BBB.

Circumventricular Organs (CVOs)

Specialized, highly vascularized areas of the brain that lack a blood-brain barrier, allowing them to monitor blood composition or release hormones.

Subfornic organ / Vascular organ of lamina terminalis

Circumventricular organs containing osmoreceptors that regulate thirst and ADH secretion.

Area postrema

A chemoreceptor zone located on the floor of the fourth ventricle that acts as part of the vomiting center.

Median eminence

A secretory circumventricular organ that serves as the site for hypothalamic hormone release into the peripheral blood.

CNS Metabolic Rate

The brain accounts for $2\%$ of total body weight but consumes $20\%$ of the body's total energy.

CNS Energy Substrate

The main substrate is glucose; the brain is highly sensitive to hypoglycemia and oxygen interruptions.