Functions and Mechanisms of the Blood-Brain Barrier

Abstract

The research outlines the important functions of the blood-brain barrier and why it does not exist in all parts of the body. The blood-brain barrier plays a major role in controlling the Central Nervous System which is a critical part of the brain. Additionally, the paper provides an insight into the mechanisms behind the blood-brain barrier and the factors that facilitate its functions. Some of the reasons why the blood-brain barrier does not exist in all parts of the brain are due the non-barrier regions of the brain and tight junctions that exist between each of these adjacent cells prevent the diffusion of polar solutes and other endo-enzymes among other factors.

Key Words: Blood-Brain barrier (BBB), Central Nervous System (CNS), brain cells

The Blood-Brain Barrier

                 The body of a human being is fully controlled from the central nervous system composed of the brain and the spinal cord that in coordination, processes coded information and coordinates other activities of the body (Sharif et al., 2018). In a more simple term, the central nervous system (CNS) of a human being can be related functionally to the central processing unit of a computer, without the CPU there is no computer, and likewise, without the CNS the whole body of a human being is compromised. It, therefore, requires that the networks of the brain remain neutral and the chemical composition of the brain membranes remains optimal and uncompromised at all times for the effective functioning of the whole central nervous system. This, therefore, means that the CNS naturally, has a system that maintains and regulates the flow of any input and output medium via the circulating blood and ensures that only the essential nutrients get through while potentially harmful products are removed accordingly.

                The blood-brain barrier (BBB) therefore comes in strategically to regulate the movement of molecules from the blood into the CNS and protecting it from any neurotoxins that would compromise the optimal and neutral functions of the brain. Ions and other neurotransmitter systems of the brain are regulated by BBB to prevent the entry of neurotoxins. It is composed of brain monolayer endothelial cells, perivascular macrophages, and a basal membrane that acts as a diffusion barrier that functions to regulate specific proteins and other transporter enzymes (Friedman and Kaufer, 2015).  The basement membrane provides structural support for the capillary and proteins. The BBB helps in regulating all the brain immune responses and monitoring the functions of the central immune cell population by transporting metabolic and immune barriers through signals from the brain. It provides a psychological balance between the central nervous system, circulation of nutrients, signaling and controlling the movement of microorganisms into the brain. 

                     Being this important in the brain, the BBB as anyone would imagine should be strategically located at all entry “gates” of the brain to ensure that at no given point does molecules enter or leave the brain unchecked. Ironically this isn’t the case since BBB structure is only located at a specific strategic position in the middle of the ventricular system, therefore, the other parts of the brain such as the pituitary glands, pineal glands and endothelium of choroid plexus do not contain BBB. Some of the reasons for this mystery are that the non-barrier regions of the brain are for hormonal control whereby these regions allow entry of molecules. Tight junctions that exist between each of these adjacent cells prevent the diffusion of polar solutes and other endo-enzymes and regulate the efflux of solute which is also a very important aspect of the brain functionality (Sharif et al., 2018).

                    Since BBB only allows some molecules to cross but prevent other large molecules from crossing, other parts such as neurohypophysis or posterior pituitary release other important neurohormones such as oxytocin into the blood. These non-BBB areas are important in regulates the brain fluids and the anterior pituitary through the release of neurohormones. Specific enzymes within the non-BBB are important in transporting complex nutrients such as glucose and amino acids that are not allowed by the BBB  into the brain (Friedman and Kaufer, 2015). As much as BBB may be the most predominant site for transportation of oxygen, amino acids and glucose, the non-blood barrier areas also play an important role in regulating the brain calcium ion homeostasis. Certain hormones are allowed entry into the brain through the non-blood barriers such as the choroid plexus that induces insulin into the brain. They help in carrying out activities for the influx of molecules such as thiocyanate and penicillin as well as the neurotransmitter metabolites.

                 The BBB is an important part of the brain that also controls the immunes of the brain as well as protecting it from pathogens and other diseases that may be in the blood. This would mean that any damage to the BBB can lead to serious malfunction of the brain or even other chronic mental diseases such as cerebral ischemia (Sharif et al, 2018). Since only a few drugs cross the BBB, the problem can be solved when new approaches of drug delivery are put in place in the area of drug manufacturing. Traditionally, old rigorous and risky methods of delivering therapeutic drugs such as drilling of a hole in the head of a patient have been used despite their high-risk factors. This must give way for news modern, safe approach in the field of pharmaceutics. New technologies should aim at reformulating drugs based on the knowledge of the functional and locations of the BBB in the brain.

                In conclusion, the BBB plays a very important role in the CNS by regulating the movement of molecules between the brain and the blood circulatory system. Despite having this crucial role, BBB is not located in all parts of the brain as one would imagine but only at one location of the brain cells. This is so to allow for the non-barrier regions of the brain to allow entry of large molecule for hormonal control as well as the diffusion of polar solutes and other endo-enzymes of which are also a very important aspect of the brain functionality.

References

• Friedman, A., & Kaufer, D. (2015). The blood-brain barrier in health and disease. Seminars In Cell & Developmental Biology, 38, 1. doi: 10.1016/j.semcdb.2015.03.006
• Sharif, Y., Jumah, F., Coplan, L., Krosser, A., Sharif, K., & Tubbs, R. (2018). Blood-brain barrier: A review of its anatomy and physiology in health and disease. Clinical Anatomy, 31(6), 812-823. doi: 10.1002/ca.23083