What is the Difference Between Blood Brain Barrier and Blood CSF Barrier

The main difference between blood brain barrier and blood CSF barrier is that the blood-brain barrier separates the lumen of the brain capillaries from the brain parenchyma at the level of endothelial cells, but the blood CSF barrier occurs in the choroid plexus of each ventricle of the brain at the level of epithelial cells. Furthermore, tight junctions mainly contribute to the reduced permeability of the blood-brain barrier. On the other hand, the capillaries of the choroid plexus do not contain tight junctions but, contain fenestrations. Still, a monolayer of tight-junctional epithelial cells delimits the choroid plexus. 

In brief, the blood brain barrier and blood CSF barrier are two types of restrictions for the free exchange of cells and molecules between blood and the perivascular extracellular surfaces of the brain. However, the rates of passage may greatly vary due to the different morphological structures. Still, both types of barriers contain tight junctions.  

Key Areas Covered 

1. What is Blood Brain Barrier
     – Definition, Anatomy, Type of Exchange
2. What is Blood CSF Barrier
     – Definition, Anatomy, Type of Exchange
3. What are the Similarities Between Blood Brain Barrier and Blood CSF Barrier
     – Outline of Common Features
4. What is the Difference Between Blood Brain Barrier and Blood CSF Barrier
     – Comparison of Key Differences

Key Terms 

Blood Brain Barrier, Blood CSF Barrier, Cerebrospinal Fluid (CSF) Flow, Passive Diffusion, Tight Junctions

What is Blood Brain Barrier 

The blood-brain barrier is a morphological structure of the brain, composing of capillaries, the basal membrane, and a perivascular layer of astroglial cells. If you look at the endothelial layer of some blood capillaries of the brain, it consists of tight junctions, which form a three-dimensional maze that is not completely impermeable. Thus, this is the type of blood capillaries that tend to form a blood-brain barrier; especially, at the endothelial level.

Figure 1: Blood-Brain Barrier and Blood CSF Barrier

Furthermore, the molecular size determines the permeability and selectivity for the proteins through the blood barrier. Also, the other types of molecules that pass through the blood-brain barrier include sugars, amino acids, and vitamins. 

What is Blood CSF Barrier 

Blood CSF barrier is another type of morphological structure of the brain that has dynamic aspects like the blood-brain barrier. Usually, apart from the blood capillaries that form the tight junctions at the endothelial level, there are other blood capillaries of the brain that contain fenestrations. And, these second type of blood vessels also contains a monolayer of tight-junctional epithelial cells. So, these are the types of blood vessels that contain the blood CSF barrier, which occurs at the epithelial level in the choroid plexus.

Figure 2: Choroid Plexus

Moreover, the dynamic aspects of the blood CSF barrier include the cerebrospinal fluid (CSF) flow in which blood-derived proteins, such as albumin, directly move from the blood vessels into the ventricles, the cisterns, and the cerebral and spinal subarachnoid spaces through diffusion and reaching CSF. Thus, along with the CSF flow, the concentration of the protein steadily increases, depending on the flow rate. On that account, the blood CSF barrier is important in CSF analysis. 

Similarities Between Blood Brain Barrier and Blood CSF Barrier  

• Blood-brain barrier and blood CSF barrier are two types of structural restrictions for the free exchange of cells and molecules between blood and the perivascular extracellular surfaces of the brain.  
• Although their main function is to defend the central nervous system, they allow the interchange of different substances.  
• Still,  the rates of passage may greatly vary due to the different morphological structures.   
• Although they allow passive diffusion of large particles, these barriers morphologically or functionally do not contain pores.  
• Both types of barriers contain tight junctions.   

Difference Between Blood Brain Barrier and Blood CSF Barrier 

Definition 

Blood-brain barrier refers to a semipermeable membrane that separates the blood from the cerebrospinal fluid and constructing a barrier to the passage of cells, particles, and large molecules. Blood CSF barrier, on the other hand, refers to a fluid-brain barrier composed of a pair of membranes, which separate the blood from the cerebrospinal fluid (CSF) at the capillary level and CSF from the brain tissue.  

Anatomy 

The main components of the blood-brain barrier are a layer of endothelial cells, basal membrane, and the protrusions of astrocytes, while the main components of the blood CSF barrier are choroidal epithelial cells, basal membrane, the endothelium of the pia matter capillaries. 

Level of Occurrence 

The blood-brain barrier occurs at the endothelial level, while the blood CSF barrier occurs at the epithelial level. 

Occurrence 

The blood-brain barrier separates the lumen of the brain capillaries from the brain parenchyma, while the blood CSF barrier occurs in the choroid plexus of each ventricle of the brain.  

The occurrence of Tight Junctions 

Tight junctions mainly contribute to the reduced permeability of the blood-brain barrier, while the capillaries of the choroid plexus do not contain tight junctions but, contain fenestrations. Still, a monolayer of tight-junctional epithelial cells delimits the choroid plexus. 

Method of Exchange 

The exchange of large molecules through the blood-brain barrier occurs through passive diffusion. In contrast, the exchange of molecules through the blood CSF barrier occurs through dynamic aspects such as CSF flow. 

Defined In Terms of  

Therefore, the blood-brain barrier is defined in terms of the morphology. However, the blood CSF barrier is defined in terms of function. 

Conclusion 

The blood-brain barrier is a type of morphological structure, which restricts the exchange of large molecules between the brain tissue and the blood. Typically, the blood-brain barrier occurs at the endothelial layer as its tight junctions occur at the endothelial layer. On the other hand, molecules exchange through the blood-brain barrier through passive diffusion. In contrast, the blood CSF barrier is a type of functional barrier in the brain, also restricting the exchange of molecules between the blood and the brain. Here, the tight junctions occur at the epithelial level. Therefore, the blood CSF barrier also occurs at the epithelial level. Importantly, the exchange of molecules occurs by the dynamic aspects, such as CSF flow in the blood CSF barrier. Hence, the main difference between the blood-brain barrier and blood CSF barrier is the structure and the method of exchange of molecules between the blood and the brain. 

References:

1. Reiber, H. “2 Blood–Brain Barrier and Blood–CSF Barrier Function.” Laboratory Diagnosis in Neurology, Georg Thieme Verlag KG, 2010, pp. 5–9. ISBN 9783131441010.

Image Courtesy:

1. “Protective barriers of the brain” By Stolp HB, et. al (CC BY-SA 3.0) via Commons Wikimedia    
2. “Slide2ff” By Anatomist90 – Own work (CC BY-SA 3.0) via Commons Wikimedia