Example Physiology Essay
A Review of Oxidative Stress & Brain Aging
The human brain is the mainsource of nerve function in the body. It is the epicenter of the nervoussystem and controls all of the main neural functions of the human body (Lewiset al, 1998, 479-483). When assessing brain function, there are many differentareas that are addressed, but one main area of concern is the actual aging ofthe brain. As the brain ages, the functions that it performs are broken downand degraded. The nerves become slower and the motor functions are lessprecise. Short term and long term memory is negatively affected and theoverall brain function is broken down.
Many people attribute all of these detrimental affects to oldage and poor health, when in reality oxidative stress and free radicals are themain causes of loss of brain function. Throughout this paper, actual brainfunction patterns will be examined, followed by some common reasons for brainfunction degradation. Then oxidative stress and its effects on the human brainwill be looked at, along with a few of the common diseases and health problemsthat are associated with brain aging and loss of brain function.
The Brain: an Overview
The human brain is a mass of nerve tissue, synaptic gaps, andnerves (Lewis et al, 1998, 479-483). All of these parts work together to formwhat is known as the human brain. The brain is the main center of nervefunction in the body. The nervous system is controlled solely by the brainitself, which works as a kind of packaging center for the messages that aredelivered to each nerve cell by the body. However, the brain would notfunction properly if it were not for the job performed by each cell and itsconsequent parts. A cell is made up of the nerve cell itself, the synapse, anddendrite. Each dendrite is connected to the next dendrite by a small openingthat allows the passage of chemicals such as Potassium and in order forproper neural functioning. The chemicals move along the dendritic pathway andform a gradient at the synaptic gap. The gradient then allows the chemical totrickle across the gap, which then causes the nerve to deliver its message(usually a message for a muscle to contract). If a gradient does not exist,then the message is not sent and the function is not performed properly. If aproblem arises in the nervous system then it is usually due to the fact thatthe chemical gradient is incorrect at a particular synaptic gap, creatingeither a muscle seizure or some other undesirable reaction.
The main nerve cord of the body, known as the spinal column,is made up of layer upon layer of nerve cells. This mass of nerves serves asthe pathway for all of the major neural messages of the body. It allows thechemical messages packaged by the brain to be transported to various parts ofthe body, and vice versa. All of the neural messages of the human body aredelivered in a matter of seconds, that is why it does not seem as if there is along delay in between a particular stimuli and the consequent reaction.Branching out from the spinal cord itself are the various nervous pathways ofthe body. There are nerves that stretch all of the way to the fingertips andtoes, but they all return to the spinal cord to deliver various stimulusmessages. Each of the various nervous pathways is also made up of layers ofnerve cells. All of the nerve cells of the body work together to form messagesthat are interpreted by the brain. The brain is able to decide what priorityis needed to be appropriately assigned to each task and then takes action toperform those actions.
Brain Function
There are basically three main functions of the brain:memory, interpretation of data, and motor function control. Not only is thebrain a packaging and interpretation center for the neural messages of thehuman body, but it is also a storage bank for information. The brain storesinformation from everyday life using chemical reactions in the cerebrum tocreate memories. This information is then available for the rest of thebrain's life, regardless of whether a person can actually pull the informationup to examine it.
The brain serves its main purpose of data interpretation bydeciphering the messages and stimulus information that the human bodyencounters everyday. Each and every piece of information that the body comesinto contact with is sent through the brain to either store the information,cause a reaction to a stimulus, or to disregard it. This interpretationprocess is very exact, yet extremely fast. The entire process seemsinstantaneous, from the introduction of the information all the way to theinterpretation results/stimuli reaction.
Finally, the brain controls all of the muscles of the bodyand consequently all motor control of the human body. Every movement, be itvoluntary or involuntary is controlled by the brain. Each function of themuscles is perfectly coordinated and timed so that the abducting muscles workperfectly with the adducting muscles to produce useful movement. The braincoordinates each twitch of any muscle in the entire musculature system so thatno energy is wasted in useless movement. Because the body is constantly in adelicate balance, it is necessary for the brain to be even more precise thanthe world's most sophisticated computer when dealing with the body'shomeostasis. The body has many involuntary muscle movements that are necessaryfor life, but need not be thought about to be performed each time. A couple ofthese movements are such things as the contraction and expansion of thediaphragm in the stomach to allow respiration and the beating of the heart.However, other muscles and functions are also controlled by the brain, such asthe movement in walking, swimming, or running. The contraction of the bladderand other voluntary, yet unthought of muscle contractions are also controlledby the brain.
Stressors of the Brain
In every cell of the body, there are what are known as redoxreactions (OXIS Research, 2003, 2). Basically, a redox reaction is anoxidation-reduction chemical reaction in which one compound is oxidized (loseselectrons) and another compound is reduced (gains electrons) (Zumdahl, 1991,216-220). Redox reactions are essential for survival and for the properfunction of various organ systems in the body.
While redox reactions may be essential for survival, they canproduce what are known as free radicals (OXIS Research, 2003, 2). A freeradical is defined as any type of chemical existence that can stand alone andsurvive on its own without the need for any other chemicals to continue thelife of the chemical (OXIS Research, 2003, 2). Free radicals contain unpairedelectrons, which make the chemical very unstable (OXIS Research, 2003, 2). Theunpaired electrons tend to try to pair with any other free electrons to achievea stable outer electron ring (usually eight electrons). Therefore, theunstable free radicals are always trying to pair up with any and all organicchemicals that they come into contact with. Free radicals can be increased inthe body by exercise and environmental stresses. They tend to be stored in thefat cells of the body and are released when fat is burned. The free radicalsare then spread all throughout the body where they can then react with otherorganic substrates (OXIS Research, 2003, 1). These organic substrates includeDNA and various proteins as well (OXIS Research, 2003, 1). The oxidation ofthese molecules can damage them and cause a great number of diseases (OXISResearch, 2003, 1).
There are several different organ systems that arepredisposed to free radical damage. These organ systems include thecirculatory system, the pulmonary system, the eye, the reproductive system, andthe brain (OXIS Research, 2003, 2). While it is true that every organ systemcould be examined and an oxidative stress Achilles heel could be found, thebrain is especially susceptible to free radical damage (OXIS Research, 2003,2). Oxidative stress is a term that is used when dealing with a build up ofROS chemicals (OXIS Research, 2003, 2). ROS stands for Reactive Oxygen Speciesand refers to many chemical oxygen derivatives (OXIS Research, 2003, 2). Thebuild up of these chemicals can cause an imbalance of oxidant activity in thesystem (i.e. the brain) and can lead to several negative health effectsincluding premature aging of the system and any number of diseases (OXISResearch, 2003, 2).
The oxidative reactions that take place in the body andespecially the brain are regulated by a system known as the Antioxidant DefenseSystem, or ADS for short (OXIS Research, 2003, 2). This system is aconglomerate of many different approaches to keeping free radical productionand collection to a minimum in the body. The ADS contains antioxidantchemicals as well as a number of enzymes that can not only limit and controlthe overall production of oxidative reactions, but actually target damagedmolecules for the purpose of replacement or repair (OXIS Research, 2003, 2).The actual antioxidants are either internally synthesized or are ingested bythe organism via various fruits, vegetables, and grains (OXIS Research, 2003,2). Antioxidants are categorized into two different categories: Scavengeroxidants and prevention antioxidants (OXIS Research, 2003, 2). Scavengerantioxidants remove the ROS molecules from the body and include both smallantioxidants (Vitamin C and glutamine) and large antioxidants that need to besynthesized by cells in the body before they can be used to protect the organsystems (OXIS Research, 2003, 2). Prevention antioxidants such as ferritin andmyoglobin are designed to prevent the formation of new oxidants and freeradicals (OXIS Research, 2003, 2). They work by binding to the various freeradicals to protect the proteins that are essential in the organ system (OXISResearch, 2003, 2). This group includes such chemicals as metallothionine,albumin, and transferrin (OXIS Research, 2003, 2).
It is obvious that free radicals are at least a necessaryevil in the body when it comes to the completion of certain processes. Inorder for proper functioning of the various life systems of the human body, itis necessary to have the byproducts of the processes (generally free radicals)present in the system. However, this does not mean that free radicals are safeor needed. Most of the time the body's systems of removal (ADS, etc.) willtake care of the overabundance of free radicals, however at times it ispossible for even the ADS system to be overpowered by a great influx of freeradicals. This phenomenon can be due to the production of energy bymitochondria or some other natural process, but in most cases this large influxof free radicals is caused either by environmental stresses or from being nearvarious industrial processes. It is a great concern of researchers today thatthere are more free radicals being released into the environment by industrialactivities and other forms of pollution. These free radicals are easily boundto various food products that are produced by humans and have a detrimentalhealth effect on both animals and humans. If more free radicals are present inthe environment than in past historical records, there is a high risk ofingesting enough oxidants to produce an imbalance of free radicals that couldlead to the ADS system not being able to handle the extra oxidant load. This wouldthen result in a large epidemic of environmentally caused free radical damageand disease.
Degradation and the Effects on Brain Function
Due to the importance of the brain function to the body, itcan be seen why it is imperative that the brain be kept in good working orderso to speak. If the brain is allowed to degrade to the point that motorfunctions and memory is affected, then there could be long term health effectsthat can cause more problems than just brain functioning. If the brain isallowed to degrade to a point at which everyday muscular functions and otherphysiological functions begin to become harder to perform then there is apossibility that other more serious side effects could be on the horizon.Certain diseases are caused by brain degradation or are causation factors inbrain aging and degradation itself. One such disease is Alzheimer's Disease.
Alzheimer's disease is a brain disorder that has manysymptoms and causes the loss of memory, the ability to learn, and the abilityto carry out everyday activities. Towards the end of the disease progression,Alzheimer's can cause personality changes and even cause hallucinations andparanoia (Alzheimer's Association, 2005, 2). Alzheimer's is a form ofdementia: a category of diseases that cause the systematic destruction of braincells and lead to a decline in brain function and quality (Alzheimer'sAssociation, 2005, 2). It has many stages and eventually leads to the completebreakdown of the brain to the point of death (Alzheimer's Association, 2005,2). A person who has a dementia disease will eventually need full-time carebecause of the loss of a large portion of the brain function (Alzheimer'sAssociation, 2005, 2). While Alzheimer's and dementia are not the only neuraldisorders that have a progressive effect on brain function, they are two of themain problems that are faced in countries such as the United States andEngland. Researchers have not yet identified a known cause of Alzheimer'sdisease, however the field has progressed great strides in the past few years.As of right now, the disease is linked to a genetic predisposition to thedisease and generally bad aging habits (Alzheimer's Association, 2005, 2). Butthere is still some value to the school of thought adopted by a few doctorsthat believe that diseases like Alzheimer's, dementia, and Parkinson's diseaseare all due to not only genetic factors but also to environmental stresseswhich would include the introduction of free radicals into the body. Freeradicals can cause great disruption in the brain function mainly because theneurotransmitters and neurons that are present in the brain are very delicateand can be destroyed easily. The free radicals can bind to the variousproteins that are used to transmit messages and perform repairs in the braintissues, preventing them from performing their duties and causing a weakenedbrain state. Proteins are themselves very specific concerning bindingproperties and will only function correctly if they bind with the correctsubstrate (Staines et al, 1993, 130). Therefore, if the active site of theprotein is disrupted by a free radical, then that protein is completely changedand will not perform as it was intended.
Brain Aging: An uphill battle
Many diseases are linked to free radicals and othertypes of oxidants, however another factor of brain function needs to beexamined to get the entire picture concerning brain functions and memory. Thisfactor is, of course, brain aging. It is what some call an unfortunate fact oflife, but we all grow older. From the time of our birth all the way to ourdeath, our body is in a constant state of degradation and repair (Ebbing andGammon, 2002, 809). This is true for every part of the body including thebrain and carries great consequences for overall brain function and health.The brain is a delicate organ that stores the information that runs the rest ofthe body's functions. If it is allowed to age past a certain point and it isnot in good health, then it is possible for bodily functions and memory to bedetrimentally affected. As the brain ages, it becomes slightly more sluggishand tends to lose its edge so to speak. Because of the complexity of thebrain itself, aging tends to have a harsh effect on its ability to functioncorrectly. A major factor in the development of diseases such as dementia andother neural system diseases is often the aging of the brain. The older thebrain is, the less it functions correctly. As of now, there is not aparticular treatment or cure for dementia. The best that we can do is tosimply make the patient comfortable and to try to make their lives as easy as possiblewhen dealing with everyday life functions. It is the hope of researchers ofbrain aging that by forging new paths in the field of neural aging, that a curewill be found for such diseases as dementia and Alzheimer's.
For years it has been common practice to believe that brainand neural diseases were caused either by environmental stresses or from brainaging. Today, however the tide is swaying more towards the middle than toeither extreme. Researchers are starting to realize that the environment aswell as brain aging could be factors in the development of certain diseases anddisorders. Not only can both environmental factors and the age of the brainitself work together to cause stress on the brain, but some environmentalfactors can actually cause the brain to age prematurely as well. Thispremature aging is actually a worse form of aging than the actual aging processof the human body itself. Premature aging means that the brain is aging fasterthan it would naturally; in other words a brain that is supposed to only befive years old would look and function as if it were ten years old or older.The implications of this type of aging process are obvious. As the brain ages,neurons and neurotransmitters die and do not function as well as when the brainwas younger, leading to memory loss and slower reaction time.
Brain aging is caused by many factors including environmentalfactors, industrial processes, and of course the passage of time. Two of thesefactors can be regulated: environmental factors and industrial processes. Byregulating certain chemicals and industrial processes, it is possible to cutdown on the amount of premature aging that occurs in the brain (Sharon, 1998,167). Certain industrial processes such as the metallurgic processes used inalloy formation as well as welding are known causes of brain degradation andcausation factors in such diseases as Parkinson's and manganism (Landis and Yu,1999, 213-217). Certain chemicals that are present in these various processes areable to penetrate through the blood brain barrier and contact the brain tissuedirectly. This can lead to tumors and neuron death that then causes cognitiveproblems as well as body function problems. The only good way to prevent suchcontamination is to completely negate contact with these chemicals at all.Researchers know this and that is why environmental laws are being put intoplace that allow for the prevention of release of these chemicals.
Aging of the brain occurs whether or not there are externalenvironmental stressors present in the person's surroundings. It occursthroughout the entire lifespan of the organism. Earlier in history it wasbelieved that the aging of the brain caused the degradation of neurons nomatter the circumstances, however it is the common belief today that as long asa few guidelines concerning lifestyle choices are followed, it is possible forthe neurons of the brain to stay completely healthy and fully functional allthe way until death. Brain aging is defined as the breakdown of the brainitself. The grooves in the brain tissue will grow wider and the actual weightof the brain material will decrease dramatically. New studies are showing thatthe plaques and neural tangles that were previously believed to have been theculprits of Alzheimer's disease may actually not be the main disease causingfactors after all (Brady et al, 2000, 864). It is a growing school of thoughtthat the actual cause of dementia type diseases is actually result of complexchemical reactions in the brain (Brady et al, 2000, 864). This information isvery important to neural researchers because it can completely change the focusof their research and hopefully eventually lead to a cure for dementia andother diseases of this type.
Conclusions
It is apparent that the aging of the brain is a majorconcern, especially to researchers studying the effects of specific kinds ofneural diseases. It is believed that these diseases could have a myriad ofcauses, but brain aging may be a contributing factor in several or all ofthem. The overall aging of the brain is coming to the forefront of modernmedicine because not much is known about it. It is becoming evident that whatwas thought to be facts concerning brain aging before was little more than justeducated guesses. Now however, the technology is available that will allow theactual study of the brain and its functions to try to give a better picture ofthe breakdown of the organ. Once a specific timeline is established that showsthe breakdown of a healthy brain, it will be possible to quantitativelymeasure the degradation of a diseased brain. While this may not seem veryimportant, it is actually very useful information. This information can beused to explain to patients what they should expect to experience at specifictime periods of their disease and could help prepare them for what is to come.
Brain aging information can also be of use to the doctors that areadministering treatment, in as much that it would allow the doctor to determineat what stage the aging was in, and therefore what type of treatment toadminister.
Oxidative brain stress is a completely different matter thanbrain aging as far as research is concerned. While it is true that more isknown about free radicals and their effects on the brain than the agingprocess, it is important to understand why research of this kind needs to becontinued. The world is constantly changing and the chemicals and differentkinds of pollutants that are released are in a continuous state ofadvancement. Because of this it is necessary to continually be studying thephysiological and biological effects of each new chemical that is developed andput onto the market. By performing this kind of research early on in the developmentprocess, it is possible to determine if there are any harmful effects of usingthe new chemicals. The early research performed as a preliminary study couldlead to less disease and fewer health problems later on.
Overall, oxidative stress along with brain aging is newlyemerging field that has the job of trying to answer age old questions that areconcerned with brain and neural health. It is important to continue researchin both of these areas so that advancements in modern medicine can be pursued.Society owes a great debt to the researchers who have and will spend theirentire lives studying the effects of brain aging and oxidative stress on thefunctioning of the brain. Hopefully in the near future there will be greatadvancements made in the field of neural medicine to allow for better and moreeffective treatment of certain nervous system diseases.
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