How the Blood-Brain Barrier Protects the Brain - Essay Example

BLOOD BRAIN BARRIER By Course Professor’s Name Institution Affiliation Date Blood-brain barrier The blood contains many substances some needed for the brain whereas others limit it from playing its role. It is essential to restrict the entry of the unwanted materials by providing a neutral environment so as to ensure the brain can carry out its function. The blood brain barrier is responsible for regulating the substances in the blood that enters the brain and leaving others out. The paper will discuss the role of brain-blood barrier and how the structure helps it in its functioning. Introduction The central nervous system role in the body is to carry out neural signalling (Acker, 2014, p10). The reliability of the brain in the discharge of neural signalling depends on the elements available in the system. The sensitivity is due to the functioning of the neurons that depend heavily on the composition of chemical and electric signals. It is important to maintain a neutral environment within the central nervous system, and the blood-brain barriers ensure such environment. The paper will discuss how the structure of the blood-brain barrier helps it in controlling the substances that enter the central nervous system from the brain and those that are left out. The importance of the regulation will also be discussed as well as the entrance of drugs into the brain. Paul Ehrlich first noted the capability of the brain and spinal cord not being stained by dye injected into the blood in the year 1885 (Kliegman, 2016, p671). All the other body organs were stained leading him to conclude that the nervous tissues are incapable of absorbing the dye. Further development in the research was observed in 1913 when Edwin Goldmann, a student of Ehrlich injected dye into the cerebrospinal fluid (Kliegman, 2016, p672). The results showed that the central nervous system was stained leading to the conclusion that there is a permeable barrier between the brain and cerebral spinal fluid and an impermeable barrier between the central nervous system and the blood. Structure of blood brain barrier The endothelial cells of the blood-brain barrier are different those of other parts of the body in several ways helping the structural composition in playing its function. The blood-brain barrier endothelial cells contain both tight junctions and adherens junctions. The tight junctions regulate the polar solutes and the macromolecules contained in the blood plasma from dissolving into the brain extracellular fluid through diffusion (Kliegman, 2016, p673). The number and the distribution of tight junctions vary across the endothelial cells. They contain Claudin and Occludin proteins that are widely spread across the intercellular cleft (Neuwelt, 2013, p132). The arrangement of these proteins is equally essential to the functioning of the tight junctions as is their presence. Claudin 1 and 2 are the main types of Claudin protein found in the tight strands. Researchers have identified more than twenty types of protein. The type of Claudin contained in blood brain barrier is Claudin 1 and 5 (Neuwelt, 2013, p 133). Although Claudin is the main component of tight junctions, concentration of Occludin in the central neural system is higher as compared to that of non-neural tissues (Acker, 2014, p28). Occludin is a critical component of the brain endothelial cells as it modulates paracellular permeability. The structure of Occludin helps tights junctions in carrying out their regulating functions. The Occludin and Claudin strand are known to contain mediums that are flexible allowing the tight junctions to diffuse ions and hydrophilic molecules. Another protein found in the tight junctions is the junction adhesion molecule. The adherens junctions, on the other hand, are responsible for giving support to the cell. They contain cadherin-catenin protein complex that also spread across the intercellular opening (Kobiler et al. 2001, p20). The adherens junctions help in the formation of the tight junction, therefore; interference in their structure leads to a disruption of blood brain barriers. Blood-brain barrier carrier two dual functions namely; acting as a barrier and a carrier. It acts as a barrier in four main ways. The endothelial junctions help blood brain barrier to act as a paracellular barrier by restricting the movement of soluble compounds. The low concentration of endocytosis and transcytosis limit the free movement of substances into the cell cytoplasm (Neuwelt, 2013, p132). The other barrier function of blood brain barrier is acting as an enzymatic barrier aided by having complex enzymes such as acetylcholinesterase, capable of degrading other compounds (Neuwelt, 2013, p271). It also acts as a carrier by transporting essential nutrients to the brain. The blood-brain barrier restricts movement of only some molecules whereas facilitating that of others. Some of the molecules that are allowed to move into the brain are glucose and also amino acids. Some soluble lipid with small molecules and other gases in the blood including oxygen and carbon (IV) oxide move from the blood plasma into the brain (Kobiler et al. 2001, p21). Importance of restriction of molecules The discrimination of materials that enters the brain from the blood is important to prevent the brain from fluctuations in the blood compositions and toxicity since the brain is highly sensitive (Kliegman, 2016, p674). Such alteration to the blood composition can be caused by normal activities such as eating and practicing. The restriction is important as it limits the number of possible infections to the brain thus minimal recorded cases of brain infections. Some pathogens and antibodies are capable of causing infections to the brain, therefore, essential to regulate the amount of substances in the blood that can enter the cerebrospinal fluid. Other components of the blood are toxic capable of causing harm to the brain cells. Such toxic materials include the botulinum neurotoxins found n contaminated food (Acker, 2014, p35). The restriction property of the blood-brain barrier protects the brain from damage in such instances. The regulation mechanism of the blood-brain barrier is important as it enhance the provision of the brain with the essential requirements such as oxygen, glucose, and amino acid as well as restricting the entry of other elements to prevent its damage (Neuwelt, 2013, p106). There are times when the barrier accidentally breaks down allowing substances to move into the brain causing damage. Other pathogens can pass the blood brain barrier spreading infections to the brain. Such pathogen is the Borrelia contributing to Lyme disease (Kliegman, 2016, p675). Movement of drugs through the blood-brain barrier The entry of drugs into the brain is restricted the same way disease-causing pathogens are restrained. Researchers have been forced to innovate ways that these drugs can be able to pass through the blood-brain barrier without harming its structure. One way drugs targeted at treating brain disorder is administering them directly at the cerebrospinal fluid (Di & Kerns, 2015, p50). The strategy avoids injecting the drug into the blood therefore the drug enters the brain by moving through the cerebrospinal fluid barrier. Another way to cross barrier is by using a solution that draws water from the brain’s endothelial cells. It results in the cells contracting hence creating a gap through the blood-brain barrier (Di & Kerns, 2015, p67). The gap can then be used by the medication to pass through from the blood to the brain. The capability of the cells to absorb water thus reducing to their original size makes the strategy favourable as the discrimination will prevent any harm to the brain. The method has been successfully applied severally in treatment of persons with brain tumours. An example of such a solution is the mannitol although serious some side effects have been experienced (Di & Kerns, 201, p67). Using molecule as Trojan horse experiment to facilitate the movement of the molecule from the blood across the blood-brain barrier into the brain is another solution although experiments are still on-going. Nanocapsules have also being used as Trojan horse in experiments although their effectiveness is still questionable (Di & Kerns, 2015, ). Blood-brain barrier in new-born babies There is a developing concern on the maturity of infants’ blood brain barrier raising issues on the administration of drugs to either the young ones or pregnant women. The infants’ barrier is implied by many paediatricians and neurologists to be immature therefore assumptions that it is incapable of playing its function. A lot of research has been done on the structure of the barrier of infants in rats to assess if there is any difference. Early research by Ehrlich that used dye experiments to detect the presence of barriers between the blood plasma and the brain were done on infants’ brain, and most of the results were similar to those of adults (Neuwelt, 2013, p170). Recent studies on the same matter have identified well-formed tight junctions in the endothelial cells of infants. However, the knowledge available regarding the permeability of developing blood-brain barrier is limited up to date. It has presented problems to medication of pregnant mothers thus doctors advise them to avoid taking drugs. For ill expectant mothers, the challenge presented is to choose between what is important for the development of the baby while minimizing potential brain damage (Neuwelt, 2013, p174). Summary The brain is highly sensitive requiring a neutral environment for it to execute its signalling function. The structure of blood-brain barrier helps protect some material from entering the brain from blood plasma whereas allowing the required elements such as glucose, amino acids, and blood gases. Those gases include oxygen and carbon (IV) oxide. The endothelial cells of the blood-brain barrier contain tight junctions, responsible for the regulating functions, and edherens junctions, responsible for giving support to these cells. Knowledge on the permeability of blood-brain barrier in infants is limited leading to challenges in medication for pregnant mothers. References ACKER, P. (2014). Blood Brain Barrier a Medical Thriller. Cork, BookBaby. DI, L., & KERNS, E. H. (2015). Blood-brain barrier in drug discovery: optimizing brain exposure of CNS drugs and minimizing brain side effects for peripheral drugs. Kliegman, R., In Behrman, R. E., & Nelson, W. E. (2016). Nelson textbook of pediatrics. KOBILER, D., LUSTIG, S., & SHAPIRA, S. (2001). Blood-Brain Barrier Drug Delivery and Brain Pathology. Boston, MA, Springer US. NEUWELT, E. A. (2013). Implications of the blood-brain barrier and its manipulation. Plenum Medical. POLIN, R. A., FOX, W. W., & ABMAN, S. H. (2011). Fetal and neonatal physiology. Volume 2 Volume 2. Philadelphia, Elsevier Saunders. Read More