LAN Networks Coursework Example | Topics and Well Written Essays - 250 words

LAN Networks - Coursework Example They will use the Ethernet cables to connect all the computers, DVR, VoIP phone, and game console to the network. They can then hook the router to the modem to connect to the internet. In this way all the devices can access the internet provided that the router is configured and allows them. The justification for the above requirements is that the family is in possession of several devices that need internet connectivity. The recommended devices will make this possible. The modem is connected to the router so that the router access the internet through the ISP assigned IP address. This dynamically assigns each of the devices IP addresses thus enabling the m to access the internet. The enterprise-level company will require a large server room with several servers, routers, bridge, and network switches to connect to the several hundred business users of their network. Each device will connect to the switches via wired or wireless access. Wired access will include Ethernet cable, at least a cat5e twisted pair of the fiber optic Ethernet cable. The network switch will be used for routing information from their network to the internet. The routers will be the gateway to the network thus will be used to connect the enterprise’s LAN and the internet thus giving them access to a good firewall. The bridges will be used to direct the traffic over the network. The three most common types of server applications are email servers, List server, and Telnet servers. Email servers are computers that keep records of each and every mail that comes in and leaves the network. List servers are computers that for the users or one way list that gives announcements, newsletters or even advertising. Telnet servers are computers that help the users to sign in to host computers and perform tasks as if they are working on their computers. Even though the servers can be combined, I will not combine all of them. I will implement two

Emphysema Research Paper Example | Topics and Well Written Essays - 2500 words

Emphysema - Research Paper Example According to National Institute of Health, NIH (2014), COPD encompasses varied lung diseases that include emphysema, chronic obstructive airways disease and chronic bronchitis. This paper focuses on emphysema, the main type of COPD as noted by Klaassen (2013). Emphysema is a type of chronic lung disease. It normally causes people to have breathing difficulties due to blowing out air being limited and majorly affects people between the ages of 45 and 60 (NIH, 2014). It is estimated that over 10 million people in America are likely to have emphysema with 2011 having had 4.7 million Americans diagnosed with the condition according to statistics from the American Lung Association (2013). Historically, men exhibit higher prevalence for emphysema than women, though the past five years has seen the prevalence in women increase by 63% while prevalence among men has decreased by 6%. Together with bronchitis, emphysema is ranked fourth among the leading causes of death in America, killing abou t 16,242 people every year. The pathogenesis of emphysema largely remains unclear. However, it has been generally accepted that emphysema occurs when delicate linings of air sacs which occur in the lungs get irreversibly damaged. It involves the inflammatory changes that occur in small airways accompanied by loss of small vessels and alveolar septal structures. This, according to NIH (2014), occurs due to gradual destruction of air sacs in the lungs making the patient slowly deprived of breath. There is also the postulate by Nici and ZuWallack (2012) that emphysema results from protease-antiprotease imbalance. For proper maintenance of lungs, there needs to be a delicate balance in the activity of protease and antiprotease. Interference with this balance results to lungs being destroyed or inappropriately repaired, eventually leading to emphysema. Additionally, the destruction of elastin fragments resulting

Five Forces Anaysis Of Dell Inc Essay Example | Topics and Well Written Essays - 2500 words - 1

Five Forces Anaysis Of Dell Inc - Essay Example This research paper presents five forces analysis of Dell Inc to analyze major factors and competitive elements and to assess how successful and effective is the company. The five force analysis, introduced by Michael Porter, can be used as a tool to measure the competitive rivalry and to assess whether the company has achieved sustainable competitive advantages or not. The five force Model The modern economy and international business environments have recently been largely influenced by various critical factors including globalization, fierce competition and advanced technology etc and therefore, as Michael Porter argued, business strategy equates to how a firm competes with other firms in the industry. According to his findings, strategy is not just a series of models and methods at corporate level, but rather it includes analyzing potential entrants, suppliers, buyers, substitutes and competitors (Stahl and Grigsby, 1997, p. 145). The five forces model has widely been applied as an important functional area of management and business academics. Almost all managers and large companies depend on porter’s five force analysis to find their marketing strengths and competitive advantages. Harvard professor Michael E. Porter has developed Five Force model in 1980s to help companies identify what specific forces determine the profits in an industry. Any particular firm in an industry faces various forces within the industry affecting the profitability significantly. Some of such determining factors are competitive rivalry, potential entrants, threat of substitutes, bargaining power of buyers as well as suppliers. If a business is able to understand and analyze all these factors, then it would also be able to develop a business-level strategy to allow business either to take advantage or protect the business from these forces (Ahlstrom and Bruton, 2009, p. 131). Porter argued that each of the five forces determines how the firm would be able to perform in its marketing landscape. The stronger each of these forces is, the more limited is the ability of well-established companies to increase prices and earn greater amounts of profits. Competition rivalry, substitutes, pot ential entrants, power of suppliers and buyers thus directly impact the profitability as well as effective and smooth functioning of the business (Hill and Jones, 2007, p. 45). The five factors can greatly influence various aspects of the strategies of a company. for instance, if consumers of the company have considerable bargaining power, it will largely impact the business strategy of that company. Similarly, if more number of suppliers are available and there is increased possibility of getting better supplies for comparatively cheaper amounts, the company will be more likely to achieve relatively better competitive advantage as well (Kurtz, MacKenzie and Snow, 2009, p. 57). Competitive rivalry is one of the five forces and is influenced by the other four forces. A company that operates in a market where there are larger numbers of substitutes, more powerful buyers and suppliers and there are chances for new entrants faces relatively more severe competition. A company would be ab le to flourish if it is able to fence off new entrants and substitutes. Dell Inc: Company Profile For several

Communication an organisations Essay Example for Free

Communication an organisations Essay This assessment is to demonstrate an understanding and appreciation of the topics taught in leading and motivating a team effectively module of the ILM Level 3 Course in Leadership and Management. The document will be split into two main sections, the first section will focus on how to communicate an organisations vision and strategy to the team as well as provide an analysis on its importance. The second section will look at the role motivation in the development of a team. Section 1: How to communicate an organisations vision and strategy to the team One of the definitions of the word team (in its verb form) is, come together to achieve a common goal (Oxford University Press, 2014). It is this common goal or purpose that turns a group of individuals into a team without a common purpose or goal to strive toward a team cannot function effectively. For example in a football team each player needs to know their place and role in the team, but also the strategy and vision for wider team, is the team an attacking team, a defensive team, do they attack via the wings etc. without knowing the common goal of the team the players will look to their own role and not know how to support the wider team and therefore are less likely to achieve their common goal. The same holds true within an organisation not just at an individual person level but at a departmental level, if teams do not know the wider vision or strategy of the organisation they can become siloed and retreat upon themselves and just focus on delivering the â€Å"day job† rather than support the organisation in a more holistic role. With the above in mind, it’s clear to see that for a team to perform it needs clarity in its purpose, and from a business point of view this should be given by the vision and strategy of the organisation. The vision tells us what the organisation wants to be, it doesn’t focus on the how that is the role of the strategy, the vision is a simple statement of what it wants to achieve. Below is an example vision statement from Amazon. Our vision is to be earths most customer-centric company where customers can find and discover anything they might want to buy online†¦ at the lowest possible prices. It’s a fairly short statement but allows staff and managers to know that the focus of Amazon is on three things †¢Being Customer Focused †¢Providing Online Services †¢Cost effectiveness (for Amazon and the customer) With the vision clearly stated it helps teams understand the direction in which the organisation wants to go, the next step is to explain how team fits in this vision and will help deliver it. Once the vision of an organisation is understood, it’s important about going about explaining how it will achieve this and this is referred to as the strategy. The strategy should be a series of plans that detail how elements of the vision will be achieved; for example Amazon’s vision could be split into two strategies; being customer centric and providing online services with cost effectiveness being a theme that runs across both strategies. These plans would then be broken down into more tactical detail such as action plans and SMART objectives to be carried out an operational level. For example a call centre team will have several objectives/KPI such as Calls answered in less than 5 seconds in a given month or First Time Call Resolution 95% (Year to Date), which without much explanation simply look like tools to ensure staff are doing their jobs when in fact they are SMART objectives that relate to the customer focused strategy of Amazon’s vision and how effec tively that strategy is working. It is the performance of these objectives that dictate future strategy, poor performance may result in a change of strategy (i.e. outsourcing) where as good performance could result in the current strategy being maintained or even expanded (i.e. expansion to provide alternative services) and as such it is vital that staff are informed not only of their objectives and targets but how and why they exist, and what their overall effect on the business is. As we can see the role the vision and strategy plays in the performance of a team or individual is huge but it can be a two edged sword if the vision and strategy are either poorly communicated, misunderstood or simply unknown. As such communication is key, to ensure that the common sense and purpose that the vision and strategy provides is embedded and understood. There are many methods of communication available within an organisation in aid of establishing a common purpose, but the first method is that the vision statement should be one that staff and customers can relate too and  understand, if the vision doesn’t make sense the job to communicate it to staff will be twice as hard. A good basis for ensuring good communication is using the seven principles of communication; to ensure the message is clear, concise, concrete, correct, coherent, complete and naturally courteous. Once the message has been developed, it’s a matter of choosing the medium in which it is delivered; there are various methods such as email, telephone, meetings, seminars, presentation, 1-2-1s, newsletters all of which to be effective must be used at the right time and place. As the vision is a supposed to provide a common purpose and understanding of what the company wants to be, it suggests that the best way to communicate this message is via more group/communal methods such as Team meetings, Away days or newsletters where the same message can be relayed to multiple staff at a time and avoids confusion or contamination of the key messages trying to be delivered, that can occur in mores personal communications such as 1-2-1 meetings. For example a team meeting where a contact centre manager for Amazon relays the vision of the company and how the team’s work fits in and helps deliver it to their 10 staff, is likely to be more effective than having 10 1-2-1 sessions in which they deliver they try to deliver the same message which is likely to alter between sessions due to personal relationships coming into play, more two way conversation disrupting the flow of the message, the recipient choosing to understand the message how they see it rather than how it was said and then finally the confusion that can occur when team members compare conversations. This is not to say that group communication is always the best method to use as it does also have its downsides such as; it’s less likely people will ask questions in team/group meetings and could result in misunderstandings/confusion, if the person delivering the message is not clear and does not understand the message being delivered it will have a negative impact on the recipients, they can become side tracked by issues that arise during the meeting and people forget the message being delivered. My own skills actually lend themselves to small groups or 1-2-1 sessions as I struggle to manage wider groups at times, especially when the meeting goes off topic or several conversations start within the meeting. However as I only manage two staff at the moment this hasn’t hampered my ability to communicate a common sense of purpose to my staff as I have my own concepts on what our role is in the  business, however as highlighted in our learner session in July we did struggle as a group to find the group’s vision and strategy, which in itself is a failing in that without knowing the true vision and strategy of the business how can I communicate that to my staff and could potentially be providing them with a purpose that is counter to the organisations own goals. In reflection this had led me to book in some time to read the new business plan, and in readiness I’ve booked a team meeting together with my staff to go over it and highlight were we as a team fit in it. I’ve also took some time recently to review our action plans and KPI’s on Covalent, which is a software we use to link action plans and KPI’s together to strategies to see how our objectiv es are linked to the wider organisation and through that hopefully provide better clarity and coherent information to my staff. Hopefully my management of meetings will improve through this course, as one of the modules in on managing meetings effectively. In conclusion I use to think my communication skills were quite good, however through this exercise I’ve noted that while my method of delivery and communication style may be good it doesn’t mean much if you don’t truly know the message you are trying to convey which until I’m up to speed on the business plan and our place in it I can’t say I know what that message should be without retreating into the â€Å"day job† which as mentioned at the beginning is a symptom of a team who doesn’t know the organisations vision or strategy. Section 2: Know how to motivate and develop the team Section 2.1: Describe the main motivational factors in a work context and how these may apply to different situations, teams and individuals. There are multiple models and theories for motivation such as Maslow’s hierarchy of needs, Alderfers ERG theory, Acquired Needs Theory by McClellan and Two Factor Theory by Hezberg to name a few and while most can be used to explain motivational factors in a work context some such as Maslow’s and Alderfer’s theory require more adaption or to make it fit as such I’ll be using Hezberg’s Two factor theory to describe the main motivational factors in the work context. According to Herzberg, two kinds of factors affect motivation,  and they do it in different ways: Hygiene factors: These are factors that are taken for granted and can be seen as having no positive satisfaction by themselves, however if they were taken away would cause a dramatic down turn in morale and motivation. An example is a policy of free tea and coffee for staff by itself unlikely to motivate staff but if it was removed would have a negative impact. Motivator factors: These are factors whose presence motivates. Their absence does not cause any particular dissatisfaction, it just fails to motivate. An example would be recognition at work for a job well done, achieving a promotion. Looking at the above it would seem that simply applying the motivator factors would cause an increase in motivation and simply ensuring the hygiene factors stayed in place is the sure fire way to succeed in motivating your staff, however the below example shows how by applying one rule to an individual can affect the team as a whole. Person A is doing a good job and as such you wish to increase motivation by recognising their work, which you do by offering a promotion/raise or bonus, this however can impact on the rest of the team as Pay and Benefits also come under Hygiene factors and as such by rewarding one and not everyone in the team this can cause a demotivation or job dissatisfaction. Section 2.2: Explain the importance of a leader being able to motivate teams and individuals and gain their commitment to objectives. Section 2.3: Explain the role that the leader plays in supporting and developing the team and its members and give practical examples of when this will be necessary

How Is Inactivity And Obesity Effecting Children Young People Essay

How Is Inactivity And Obesity Effecting Children Young People Essay The rise of inactivity and its consequences The prevalence of sedentary lifestyles is increasing in America and much of the developed world. In the US (our core geographic area of focus for this project) this trend coupled with poor eating choices has notably manifested itself in rising obesity rates across the country over the past two decades as depicted in Exhibit 1. As of 2008, over 68% of Americans were categorized as being overweight, with nearly half of that group being defined as obese or morbidly obesei. Between 1980 and 2002 overweight rates for children aged 6 11 more than doubled from 7% to 16%ii. Today that number is estimated to be closer to 20%iii. Shortened life spans. More than 14% of deaths in the US in 2003 resulted from obesity related conditions; and Diminished motivation to be active. Being overweight or obese makes physical activity more challenging, thus requiring greater commitment and effort to be active compared to a healthy weighted individual. The more overweight people become due to reduced levels of activity the less likely they are to engage in future activity. Furthermore, obesity is often tied to depression which causes individuals to experience lower levels of energy and motivationiv. Teenagers the gateway to addressing rising inactivity levels . The number of years a consumer leads an active life; The variety of sports or fitness related activities the consumer engages in over those years; and The products that the two factors above drive demand for. In order to optimize across all drivers we honed in on teenagers (primarily 13-15) as our focus segment. We view other groups, such as adults and, retirees, and so forth, who have a shorter customer lifetime value and being, as being more set in their ways, both in terms of habit and product affinities. In arriving at this focal segment we have taken the following factors into consideration: According to the Eight Stages of Development, adolescents learn about and define who they are between the ages of approximately 12 and 19. If being athletic, or at least active, is not established as central to ones identity, the probability of prioritizing athletic activity later in life is likely diminished. If more children define themselves as being active during this influential period, the market for healthy, sustainable athletes will likely increase over time. From a commercial perspective, the potential lifetime value of an active teenager is likely to be higher than that of an average U.S. adult. Firstly the cost of acquiring an active youth is lower, as there are fewer barriers to exercise/activity as outlined above. Secondly, the number of years that teenagers have to be active is significantly greater as they not only start younger but may potentially live longer due to their adoption of healthy and active lifestyles. Teenagers generally have lower opportunity costs of activity and learning to exercise than adults. A combination of the greater amounts of leisure time available to them and their propensity to experiment with new things makes teenagers more likely to be comfortable learning about and engaging in activity. Teenagers also tend to have many opportunities to choose to engage in activities. These include physical education (PE) programs, sports teams, community teams, and informal pick-up games. Section 2 of this report presents key underlying influences and trends that currently inhibit and have the potential to further diminish activity levels among teenagers. Section 3 of this report then discusses the selection criteria that potential solutions must satisfy in order to most effectively address the problem of teen inactivity. Finally Section 4 lays out a potential solution aimed at leveraging key influences to encourage more active lifestyles among teenagers. Section 2: Factors underlying teenage inactivity Family influences In order to address the rising levels of inactivity among teenagers, it is necessary to first identify and understand the primary network of influencers that ultimately impact their decision making behavior and involvement in activities. Dual income single parent households Traditionally parents have been one of the strongest sources of influence over teenagers, and have played a crucial role in shaping their overall growth and development. However insights from interviews conducted with families in the Boston area suggest that shifts in the overall structure and composition of the average American family have decreased the amount of influence that parents exert over their children. In particular, the steady increase in the number of dual income earners1 and the rise in the number of single parent households highlight that parents today are facing increasing time constraints. A significant consequence of this phenomenon is that teenagers are increasingly subject to less direct parental oversight, as working parents often outsource the supervision of their children to external parties such as baby-sitters, nannies and daycare centers. While parents have a vested interest in encouraging their children to lead active lives in order to promote overall health and well-being, external parties are more likely to encourage teenagers to engage in sedentary, home-based activities that are easier to supervise. Examples of such activities include watching TV, surfing the internet or playing video games. Decline of parental role models Another implication of parental time constraints is that parents have less face-to-face time with their children and consequently fewer opportunities to educate them on the merits of leading an active lifestyle and adopting healthy eating habits. Given these time constraints parents themselves are also less likely to demonstrate the very behaviors that they aim to instill in their children. Thus, an absence of role models that are leading active lives in the household could further explain why teenagers are tending towards more sedentary lifestyles. Additionally, if parents spend less time prioritizing the on-going supervision and support of their childrens activity levels, teenagers may feel less motivated to participate in sports or other physical activities at school. For example our interviews with parents suggest that parental inability to attend games to cheer for their children or even provide the basic resources that support their childrens involvement in sports, such as providing rides to practice, may result in teenagers being less inclined or able to pursue active lifestyles. Evolution of family dining A further implication of parental time constraints is that working parents are increasingly relying on convenience and on-the-go food solutions for meal preparation. These habits can have a profound impact on the overall health and well-being of their children as evidenced by Child Development research which suggests there is a link between the number of years a working mother spends in the workforce and their childs BMI.v The increase in child obesity has attracted a great deal of media attention which has, in turn, resulted in a heightened sense of awareness of health wellness issues among parents. The observation that child obesity persists in the face of this awareness suggests that parents are precluded from developing solutions because they lack the necessary tools to motivate their children in the face of time constraints. This insight highlights an area of opportunity for Nike to provide tools to: Assist parents in incentivizing their children to lead more active lives; and Assist parents in motivating their children in a way that fits into their busy schedules. Crime parental attitudes An emphasis on helicopter parenting2, which has gained popularity in recent times, combined with the persistent coverage of criminal activity in the media has resulted in a heightened sense of paranoia around crime levels and neighborhood safety among parents. The implications of helicopter parenting are straightforward. As parents become more concerned about the overall safety of their neighborhoods they are more likely to only allow outside activity with adult supervision. However, due to their personal time constraints, they often encourage their children to stay indoors or commute to school by car, rather than engage in outdoor activities or walk, for example. In this case, parents appear to be prioritizing the short term benefits of child safety over the long term risks of obesity and other future health problems due to reduced activity levels Friend influences Increasing prominence of friends as influencers Siblings, particularly older ones, have traditionally been a powerful source of influence over teenagers. Younger siblings generally tend to emulate the behavior and habits of their older siblings, especially if there is a positive relationship between the two. However as the size of U.S. households continue to decline, the average teenager is growing up with fewer siblings to rely on and learn behaviors from. As a result of teenagers being exposed to fewer siblings and busier parents, peers and friend groups have gained more prominence in the influence and authority they have over teenagers lives. School influences In light of the factors discussed above, such as the limited amount of time parents spend with their children; external environments can serve as important influences on teenagers. Schools are not only a physical representation of where teenagers spend most of their time outside the home, but are also the arena within which their social networks converge. Teacher attitudes resource constraints Given that teenagers are highly exposed to their social networks at school, their fear of failing at physical activities can often overshadow their desire to try something new or different to shine in front of their peers causing them to shy away from any activity. For example, a school that has a reputation for being a leader in a certain sport, say basketball, may place significantly more emphasis on winning than inclusion. In such environments, children have less room to fail, that is to say, not to be good at basketball. Such overtly competitive situations can lead to divisions (ball players vs. non ball players) which amplify less skilled students feelings of inadequacy. Teachers serve as de facto parents in the school environment. Their attitudes towards general wellness and encouraging teenagers can be powerful drivers of childrens sustained engagement in activities. However, the continuous budgetary pressures schools face often result in understaffing, which causes teachers to stretch themselves very thinly across large student bodies. In these situations, teachers may not be able to provide the level of encouragement and personal attention necessary for children to enthusiastically engage in activities. If a child does not enjoy participating in an activity, the child is unlikely to engage in that activity again in the future. Tension between academics activity Teenagers are increasingly living in an achievement-oriented society, wherein the results of their efforts today can have a profound impact on their future options. In light of this, parents are getting their children involved in an array of extracurricular activities, such as debating clubs and honors classes, in order to increase their childrens chances of getting into good colleges. This additional competition on teenagers time often leads to reduced levels of activity. City influences Rural vs. urban settings The natural resources and climate of a region can impact activity levels depending on the type of sports they encourage. For example, hiking is an activity that requires minimal financial resources to participate and would likely encourage higher levels of activity. However, the relatively higher cost of participation in skiing may deter people from adopting the sport and therefore drive lower levels of activity. Media Technology influences Celebrity influence Proliferation of media distribution channels Celebrities and pop culture icons have become significant influencers of social behavior as children spend less time with their parents. The emergence of distribution channels such as Twitter has increased teenagers ability to gain direct access to celebrities. Given parents limited ability to monitor their childrens internet and mobile phone usage, teenagers are now accessing messages of varying quality. For example, children are no longer confined to watching PBS, which has focus on activity and wellness. They can now watch the latest craze on YouTube or access celebrity gossip on other outlets, which typically place a premium on glamorous lifestyles over healthy ones. Such messages can have a great degree of influence on children, who are particularly impressionable. Addictive characteristics of technology Perpetually connected to the internet and their mobile devices, teenagers today have become attuned to interacting with their environments using technology. Activity which requires them to disengage from electronic devices may be seen as dull and involve de-addiction from perceived high stimuli technology driven experiences. Physical vs. virtual interaction The advent of mobile phones and online social networks has reduced teenagers need to meet in person, as they can rely on the immediacy of virtual communication. The increased usage of these platforms has fundamentally changed the ways in which teenagers interact with one another by allowing them to remain socially engaged without needing to physically walk or bike over to see a friend.

Mental Health Panopticon Essay -- prison systems

Prisons act as a total institution where inmates are put on a strict schedule and fall under one of the most gruesome forms of social control. Because of this, many inmates rebel resulting in prisons having to increase security and impose stricter punishments. As a result of this, less effort has been put into helping mentally ill inmates. The term panopticon, coined by Bentham illustrates the concept that the prison design would allow guards to see into cells but not allowing prisoners to see out. Thus, this would allow guards to have omniscient power over the inmates. Fortunately, this never worked as a prison, however prison has created a type of mental health panopticon. This allows for mentally ill parents to feel like they are always being observed; similarly to that of an experiment. Despite prisons best attempt to equally serve all inmates to the best of their ability, prioritizing security and punishment has lead to a mental health panopticon. As a result, prisons environm ents have exacerbated negative behaviours, created an inhumane environment for prisoners and lack the means to aid in mental health. First, the prison system exacerbates negative behaviour such as drug use, self-harming behaviour and suicidal thoughts and actions. One of the most significant ways that the prison community worsens drug use, self-harming behaviour and suicidal thought is providing minimal amount of harm reduction. Accordingly, Lines makes note that higher instance of HIV/HVD and other transmitted disease are a cause on mental health issues within prison, this harm reduction measures would improve the overall health of individuals in prison (Lines at Al. 2005). Thus, the prion systems all intersects: much like society, the happier the i... ...t work. Instilling fear into people works to conform behavior to a degree but it ultimately creates prisons with exacerbated negative behaviours inhume and unfit environments. Works Cited Brown, Michelle. (2012). Empathy and Punishment. Punishment & Society 14(4): 383-401. Lamb, H. Richard., Weinberger, Linda E., & Gross, Bruce H. (2004). Mentally ill persons in the criminal justice system: Some Perspectives. Psychiatric Quarterly 75(2): 107-126. Lines, Rick., Jurgens, Ralf., Betteridge, Glenn., & Stover, Heino. (2005). Taking action to reduce injecting drug-related harms in prisons: The evidence of effectiveness of Out of control [Television series episode]. (2010). In The fift estate. CBC. Retrieved from http://www.cbc.ca/fifth/episodes/2009-2010/out-of-control Sapers, H. (2008). A Preventable Death. Available at: http://www.oci-bec.gc.ca/rpt/index-eng.aspx

Development of the Cardiovascular System in Vertebrate Embryos

The cardiovascular system is the first organ system to become fully functional in the vertebrate embryo and its development occurs in a similar way in all vertebrates. It is derived from angioblastic tissue, which arises from mesenchyme, an aggregation of mesenchymal cells derived from the mesodermal tissue of embryos. The main processes involved in the development of the embryonic cardiovascular system are Vasculogenesis, Angiogenesis, Hematopoiesis, Erythropoiesis and Heart Formation. All processes occur under the influence of stimuli from genes and paracrine factors, oligosaccharides, multifunctional cytokines and enzymes.Vasculogenesis and AngiogenesisTwo distinctive mechanisms, vasculogenesis and angiogenesis implement the formation of the vascular network in the embryo. Embryonic vasculogenesis gives rise to the heart and the primordial vascular plexus within the embryo and its surrounding membranes as the yolk sac circulation. In mammals, it occurs in parallel to hematopoiesis , the formation of blood cells. Vasculogenesis refers to the in situ differentiation and growth of new blood vessels from mesenchymal cells known as angioblasts which aggregate to form isolated angiogenic cell clusters known as blood islands (angiocysts) within the extra-embryonic and intra-embryonic mesoderm. Small cavities appear within these blood islands by the confluence of intercellular clefts.The peripheral cells within these blood islands flatten to form endothelial cells, triggered by the binding of the Vascular Endothelial Growth Factor (VEGF) to the first of its two receptors, the VEGF-R2 (Flk1) protein, which is responsible for the differentiation of mesodermal cells into endothelial cells and the subsequent proliferation of the endothelial cells. The core cells give rise to blood cells (haematoblasts). The newly formed endothelial cells arrange themselves around the cavities in the blood islands, forming the primitive endothelium. Cellular vacuoles within the developing endothelial cells coalesce and fuse together without cytoplasmic mixing to forma the blood vessel lumen of the initial endothelial tube.Extracellular matrix deposition by fibroblasts promotes capillary-like tube formation under the influence of the binding of VEGF to its second receptor, VEGF-R1 (Flt1). This is followed by the interaction of the endothelial blood vessel with the supporting mesodermal cells. The Angiopoietin-1 growth factor binds to the Tie2 receptor tyrosine kinase on the cell membrane of the endothelial cells, allowing the blood vessel to recruit the peri-endothelial cells that will surround it as pericytes and the smooth muscle tissue of the blood vessel, thus maintaining the stability of the blood vessels.The growth and multiplication of this primordial vascular plexus occurs through the process of angiogenesis in which new blood vessels arise from pre-existing vascularity. This process requires the combination of two signals, Angiopoietin 2 and VEGF, in order t o promote the loosening of the support cells and the ability of newly exposed endothelial cells to multiply by budding and sprouting into new vessels. Replacement of Ang1 by Ang2 on the Tie2 receptor tyrosine kinase destabilizes the vessel integrity thus facilitating vessel sprouting in response to the VEGF signal. The new endothelial tubule then interacts with the surrounding mesenchymal cells in part as a response to Ang1 which acts on the endothelial cell Tie2 in order to trigger the association of the new tubule with the periendothelial cells.Hematopoiesis and ErythropoiesisBlood develops from endothelial cells (haematoblasts) by a process known as hematopoiesis initially in various parts of the embryonic primitive mesenchyme (yolk sac and allantois), and then in the liver and later on in the spleen, bone marrow and lymph nodes. In embryonic development it is known as primitive hematopoiesis. All blood cells develop from pluripotential stem cells committed to three, two or one h emopoietic differentiation pathways but morphologically undistinguishable. These pluripotent stem cells divide infrequently to generate either more pluripotent stem cells (self-renewal) or committed progenitor cells (colony-–forming cells, CFCs) which are irreversibly determined to produce only one or a few types of blood cells.These colony-forming cells are known as Lymphocyte Forming Colony (LCFC), Megakaryocyte Forming Colony (MCFC), Erythrocyte Forming Colony (ECFC) and Monocyte Granulocyte Forming Colony (MGFC). The progenitor cells are stimulated to proliferate by specific growth factors (colony-stimulating factors, CSFs) but progressively lose their capacity for division and develop into terminally differentiated blood cells which usually live for only a few days or weeks. Erythrocytes (red blood cells) develop by the process of erythropoiesis. In embryos, erythrocytes are nucleated and express embryonic globin chains.Heart FormationIn vertebrate embryos the heart tube , the earliest formed heart structure, arises in the heart field, an embryonic clustering of cells which arises soon after gastrulation. These early stages of development are almost identical among all vertebrates unlike the subsequent septation of the chambers and of the outflow tract which varies between species.The heart field is that region of the precardiac mesoderm that contains the cardiac progenitor cells (endocardial and myocardial precursor cells) and is competent in responding to inductive signals.Precardiac cells from the epiblast lateral to the primitive streak invaginate through the streak and migrate cranio-laterally to form part of the lateral plate. This pattern is maintained in the eventual anteroposterior placement of structures in the heart, with the most cranial cells contributing to the bulbus cordis at the extreme anterior end of the heart and the most caudal cells contributing to the sinoatrial region and the extreme posterior end.As mentioned above, the cell progeny of this region contributes to all layers of the heart tube (myocardium, endocardium and parietal pericardium), as well as to the endothelial cells in the vicinity of the heart. In the lateral plate the cells maintain their anteroposterior position.The lateral plate splits to form two epithelial layers, the somatic mesoderm (which also includes migratory precursors for limb musculature) and the splachnic mesoderm which remains an epithelial sheet and includes the cardiac precursors.The embryo then folds ventrally carrying the splachnic mesoderm with it and bringing it ventral to the foregut which is generated as the lateral folds meet in the ventral midline. The precursors of the endocardium are included in the splachnic mesoderm and begin to form clusters on the foregut side of the epithelial sheet.The heart fields fuse at the midline to form a primary heart tube, the process beginning cranially and proceeding caudally. This tubular heart consists of an outer myocardial man tle and an endocardial inner lining. Between these two concentric epithelial layers an acellular matrix, the cardiac jelly, is found. As the ventricular region of the heart begins to bend to the right (â€Å"cardiac looping†), the cardiac jelly disappears from the future major chambers of the heart (atria and ventricles) and begins to accumulate in the junction between the atria and ventricles (atrioventricular junction, AVJ) and in the developing outflow tract (OFT).This results in the formation of the endocardial cushion tissues in the AVJ which later contribute to the formation of AV (atrioventricular) septal structures and valves, septation of the OFT and formation of the semilunar valves of the aorta and pulmonary artery.The vertebrate heart tube is aligned along the antero-posterior axis. Arterial flow is directed from the ventricle at the anterior end of the heart, through the ventral aortic vessel and branchial arches and subsequently travels posteriorly to the dorsal vessel. Blood flow returns to the heart through the venous system to the atrium lying at the posterior end of the heart chamber.Formation of the Mammalian Embryonic Cardiovascular System1)   Formation of the primitive cardiovascular systema)   Extra-embryonic blood vesselsThe wall of the yolk sac mesenchyme proliferates and forms isolated cell clusters known as blood islands. Peripheral cells within these islands flatten and differentiate into endothelial cells in order to form endothelial tubes. Centrally- located cells develop into primitive blood cells (hematoblasts). Endothelial tubes approach and fuse with each other forming a primitive vascular network. This primitive endothelial network appears in the chorionic membrane and body stalk and connects to the vitelline circulation.b)   Intra-embryonic blood vesselsThe endothelial tube network appears in the intraembryonic mesenchyme to  form an intraembryonic endothelial   tube network. The intraembryonic and extra  e mbryonic tube networks connect to each other forming a diffuse endothelial   tube network which either fuses or disappears to form a primitive cardiovascular  system.2) Development of the HeartThe primitive cardiovascular system consists of the primary heart tube, formed from the fusion of the two bilateral heart fields of the precardiac mesoderm. The primary heart tube gives rise to the endocardium. Blood flows through this primitive heart tube in a cranial position. The mesenchyme surrounding the tube condenses to form the myoepicardial mantle (the future myocardium). Gelatinous connective tissue, the cardiac jelly, separates the myoepicardial mantle from the endothelial heart tube (the future endocardium).A series of constrictions (sulci) divides the heart into sections: the sinus venosus, in which the common cardinal veins, the umbilical veins and the vitelline veins drain; the primitive common atrium; the primitive common ventricle; and the bulbus cordis through which blood flows to the paired dorsal aortae. The paired dorsal aortae arise when the branchial or pharyngeal arches are penetrated by six pairs of arteries called aortic arches. These arteries arise from the aortic sac and terminate in a dorsal aorta. Initially, the paired dorsal aortae run along the whole length of the embryo but soon fuse to form a single dorsal aorta just caudal to the branchial or pharyngeal arches.The arterial and venous ends of the heart tube are fixed by the branchial or pharyngeal arches and the septum transversum, respectively. At this stage the heart is beating and the contractions are of myocardial origin and likened to peristalsis.The primitive atrium loops up behind and above the primitive ventricle and behind and to the left of the bulbus cordis forming the bulboventricular loop.. This looping process brings the primitive areas of the heart into the proper spatial relationship for the further development of the heart.Embryonic venous circulation consists of thr ee pairs of veins: the vitelline veins which drain blood from the yolk sac, the umbilical veins which bring oxygenated blood from the chorion (early placenta), and the common cardinal veins which return blood to the heart from the body of the embryo. Arterial circulation consists of three paired arteries: the intersegmental arteries, which form 30-35 branches of the dorsal aortae and carry blood to the embryo, the vitelline arteries which pass to the yolk sac and later to the primitive gut, and the umbilical arteries which carry oxygen-depleted blood to the placenta.3)  Ã‚  Ã‚  Ã‚  Ã‚   Formation of the Heart ChambersAs mentioned above, during cardiac looping the cardiac jelly disappears fromthe future major chambers of the heart and begins to accumulate in the  Ã‚  Ã‚   atrioventricular junction (AVJ) and developing outflow tract (OFT). This results in the formation of the endocardial cushion tissues in the dorsal and ventral walls of the AVJ. These cushions are invaded by mese nchymal cells, approach each other and fuse, dividing the atrioventricular canal into the right and left atrioventricular canals.The primitive atrium is divided into right and left atria by the formation, modification and fusion of the septum primum and the septum secundum. The septum primum grows towards the fusing endocardial cushions from the roof of the primitive atrium creating a curtainlike septum, the foramen primum between the free edge of the septum and the endocardial cushions.This foramen becomes progressively smaller and eventually disappears when the septum primum fuses with the fused endocardial cushions (atrioventricular septum). The septum secundum grows from the ventrocranial wall of the atrium to gradually overlap the foramen secundum in the septum primum, forming an incomplete separation between the atria in the form of an oval opening, the foramen ovale.The sinus venosus initially opens into the center of the dorsal wall of the primitive atrium and its left and r ight horns are of about the same size. The right horn progressively begins to enlarge in respect to the left horn until it receives all the blood from the head and neck via the superior vena cava and the placenta and caudal regions of the body via the inferior vena cava. The left horn forms the coronary sinus.The wall of the left atrium is formed by the incorporation of the primitive pulmonary vein which develops as an outgrowth of the dorsal atrial wall. As the atrium expands, the primitive pulmonary vein and its branches are gradually incorporated into the wall of the left atrium forming four pulmonary veins with separate openings.The division of the primitive ventricle into the right and left ventricles is initially indicated by a muscular ridge with a concave free edge in the middle of the ventricular floor near its apex. Initially, most of its increase in height results from the dilation of the ventricles on its each side. Later, however there is active proliferation of myoblas ts, forming the thick muscular part of the interventricular septum.At the beginning a crescentic interventricular foramen exists between the free edge of the interventricular septum and the fused endocardial cushions allowing communication between the right and left ventricles. This foramen closes as the result of the fusion of tissue from three sources: 1) the right bulbar ridge, 2) the left bulbar ridge and 3) the endocardial ridges. The membranous part of the interventricular spetum is derived from tissue extension from the right side of the endocardial cushions. It merges with the aorticopulmonary septum and the thick muscular part of the interventricular septum. When the interventricular foramen closes, the pulmonary trunk is in communication with the right ventricle and the aorta communicates with the left ventricle.Active proliferation of mesenchymal cells in the walls of the bulbus cordis gives rise to the formation of the bulbar ridges. Similar ridges form in the truncus ar teriosus and are continuous with the bulbar ridges. Both the bulbar and the truncal ridges have a spiral orientation and result in the formation of a spiral aorticopulmonary septum when the bulbar and truncal ridges fuse. This septum divides the bulbus cordis and the truncus arteriosus into the aorta and pulmonary trunk.Due to the spiral orientation of the aorticopulmonary septum, the pulmonary trunk twists around the aorta. The bulbus cordis is incorporated into the walls of the ventricles. In the left ventricle it forms the walls of the aortic vestibule just inferior to the aortic valve. In the right ventricle it forms the infundibulum or conus arteriosus.Ventricular trabeculation begins in the apical region of the ventricles soon after  cardiac looping. The trabeculation serves primarily as a way of increasing the  oxygenation of the myocardium in the absence of   a coronary circulation. The  compactation of the trabeculae adds to the proportion and thickness of the  co mpact myocardium.