Information processing Essay Example for Free

Information processing Essay Discuss how information processing varies between individual, team and racquet athletics.  Sport contains mainly perceptual motor skills so it is important to select the correct skill for the situation. The process used to select the correct skill is called the information processing system or the DCR process, because we Detect information, Compare it with previous experiences and then react.  Welford said that all information is taken in as stimuli through our senses. It is then stored in the short term memory before being sorted, if the stimulus is relevant to the current skill then it is stored in the short term memory where it is compared to previous experiences in the long term memory. Then a decision is made as to what action to take based on this comparison. The action that was performed and the outcome from this action are then stored in the long term memory for future reference. Welfords model is shown below:  This model makes a performer react in the way that they do to a situation but there are many factors that can influence what action the performer decides to take. These include; time available, number and intensity of stimuli, experience, anticipation, fitness and motivation of the performer. The effect these factors have on a performer will vary from individual, racquet and team sports.  The time that you have available to process the incoming stimuli differs in each sport. For example in rugby, which is externally paced, you have a small amount of time to process the stimuli and make a decision because there are usually many defenders around you. Tennis players also have very little time to react because the ball is usually travelling at a high speed and if they dont make a decision and return the ball they will lose the point. However in golf, an internally paced sport, the player can take as long as they need to make a decision because there ar e no opponents directly around them. There are three main types of stimuli that enter the sensory input these are;  Vision: is where a player will react to a visual stimulus such as the position of the ball or an opponent. These stimuli are easier to detect and react to if the stimulus is brighter. For example in tennis the ball is bright yellow which makes it easier to see. But there are also unwanted stimuli such as ball boys moving or crowd movements these stimuli are obviously irrelevant but they are still initially taken in which slows down the whole process. In an individual sport there are fewer visual stimuli for example in a 100m race the only real visual stimulus is where the finish line is in relation to you. Audition: this is all stimuli that are heard, for example when a team mate calls for the ball in rugby. Auditable stimuli are hard and processed easier and faster if they are loud and clear. There are also irrelevant auditable stimuli such as crowd noise these will slow down the information processing model.  Proprioception: this is made up of three components;  Equilibrium: this is an awareness of your body position and balance. We can tell if we are about to fall over and where we are in relation to objects. Team sports are more likely to have an uneven playing surface which means that your balance will have to be constantly adjusted as you are running. But in individual and racquet sports the playing surface is fairly constant with the exception of golf, where a stance may have to be altered to adjust to the surface. Kinaesthesis: this is where the body senses the muscle movement and contraction it is sometimes known as muscle memory. It is if the movement feels right to the performer. It is developed through practice and experience one example would be a conversion kick in rugby the player may take there step away from the ball in the same way they usually do but they may just feel that they are not in the right place. It doesnt apply as much in team games as in individual and racquet sports apart from set plays.  Tactile sense: this is the feeling of pressure this is important for all sports. It can be affected be the weather conditions because cold weather affects our ability to feel effectively. The short term sensory store is where all information is stored for a split second before it is processed. All relevant and irrelevant information is stored in here before it is replaced and lost. This does not differ between sports only what enters it does.  The perception stage is where all the information that has come from the short term sensory store is processed. This is when irrelevant information is thrown away and useful stimuli such as where the ball is, is kept to make a decision and stored in the STM. This will vary between individual, racquet and team sports because of the amount of stimuli. In team sports there are more stimuli so it takes longer to sort through whereas there are relatively small amounts of stimuli in individual sports so it wont take as long to sort them out. It also differs depending upon whether the performer is experienced or not as it will be easier for a expert to sort through the stimuli because they have more experience. We sort through the st imuli with selective attention and take only the important pieces of information because only around 7-10 pieces of information can be stored in the STM. The information passed on from the perception stage is then stored in the STM. Because only 7-10 pieces of information can be stored an experienced player may chunk information together so that the position of all players is one piece, but a beginner may not be able to do this so each player may be a separate piece. Team sports would be much more affected because of the amount of information so not all stimuli can be stored so a poor decision may be made but less poor decisions will be made in an individual or racquet sport because there is less information. The LTM holds information on movement patterns and the results of using them in certain situations and can hold them for a lifetime. Team sports have many memories but individual sports may have less.  The decision making process is where whats happening now (in the short term memory) with what has happened previously (in the long term memory). In the LTM the performer will be looking for similar situations and actions and their outcomes. This makes team games decision making process a lot longer because of the vast amount of information and possible actions to take. Whereas in an individual sport there is much less information and less possible actions. The motor output is the performance of the chosen skill. One example may be for a badminton player to put in a drop shot because the opponent is at the back of the court. The action is referred to the muscle movement in the LTM. The action and its consequences are then stored in the long term memory for future reference.  Individual sports, because they are individually paced, make them the simplest in the IP model. Also because there are fewer stimuli there is a shorter reaction time which gives the performer more time to carry out the IP model which should result in a better decision. Racquet sports are externally paced due to the fact that there is an opponent; this means that there is less time for the performer to react. There are some irrelevant stimuli which will slow down the IP model which means it takes longer to decide than in an individual sport but not as long as in a team sport because there are fewer possibilities for what action to take.  Team sports are externally paced which reduces the time available to react. Also there are much more irrelevant stimuli in team sports, this will lengthen the IP. The IP will also be lengthened due to the complexity of most team games because there are more situations and possible responses to choose from. Bibliography Advanced PE for Edexcel Heinemann by F. Galligan et al.

The Importance of Sleep, Nutrition, and Exercise Essay -- Health Nutri

The Importance of Sleep, Nutrition, and Exercise Many students today ask why they are so tired all the time. It also seems that people in college become more stressed out either because of grades or because of work. All people need to do is get the right amount of sleep, eating well, and exercise in order to feel better about themselves and feel good in general. This is not a short process. Most experts say that it takes about twelve weeks in order to see results. But, it is guaranteed that after that duration of time one will see a vast improvement in oneself. Sleep is something that most people take for granted. It is the one thing that people are willing to compromise even more then food or money. It is estimated that between 40 to 60 million Americans are sleep deprived. Different people can get by with different amounts of sleep. There are some that can survive the next day with only a few hours. Then there are always others who cannot be called after 9:00 because they need those good solid 10 hours. The average person actually needs anywhere from between 7-9 hours a night. Why does one need sleep? When human bodies do not get enough sleep they tend to lose strength, the immune system decreases, and there is an increase in blood pressure. As students, it can effect concentration, memory, logical reasoning, and ability to do math. Now that the problem is known here is how to fix it. Dr. Stanley Coren, a professor of psychology at the University of British Columbia, focuses on consistency. The body needs consistency. This can be fulfille d by simply going to bed at the same time every night and waking up at the same time every day. But, it is important to note that making up for lost sleep on the weekends is a big negative. It is preferable that if one likes to sleep on the weekends wake up at the same time Saturday and Sunday. When going to bed it should take about 15 to 20 minutes to fall asleep. If a half-hour has gone by and one still is not asleep one should get up and do something relaxing (i.e. take a warm bath, read, watch TV, etc.). Rita Mattson, a Certified Personal Trainer and Stress Management Counselor, makes the suggestion of drinking warm milk before retiring to bed because milk contains a high dosage of L-tryptophan which is a natural sedative. Sleep is just as important as any other part of taking good care of ones self. Another... ...ssue) provide a delicate support frame for the breasts that can be damaged by too much bouncing and stretching. There are two types of sports bras: compression bras and encapsulation, harness-type bras. The first works better for smaller breasted women because of the fit and the second tends to work better for larger women. When choosing the correct one for you take into account: the fit, how much support it is giving for the exercise that is going to be done, fabric (does it absorb moisture well), seams and stitching to avoid chaffing, and mobility. After taking all these into account one can be assured that he is well prepared for the exercise routine.   Ã‚  Ã‚  Ã‚  Ã‚  In conclusion, all the factors mentioned above can lead to a less stressful life. Sleep can help the body relax to deal with everyday pressure. People who eat a diet low in refined carbohydrates, sugar and caffeine, and high in whole grains, have shown a greater ability to cope with stress as in contrast to those who consume the opposite. Exercise, as well, is a way to release stress and tension (i.e. running, kickboxing, stair stepping, etc.). If one keeps all the factors in mind a healthier happier life can be achieved.

Attracting Cockroaches with Different Substances

Reason: The reason I did this project was because I am absolutely fascinated by cockroaches. I think they are really interesting. It also makes me happy that I’m the only person I know of who is not scared of cockroaches. We have cockroaches that will come into our house to escape from the cold outside, so I thought, why not get rid of some of them? But I had to know what kind of bait to put out for them in order to accomplish this. So that is how I came up with this. Hypothesis: If the peanut butter, the butter, the cheese, and the bread are tested, then the butter will attract the most cockroaches. If the peanut butter, the butter, the cheese, and the bread are tested, then the bread will attract the least amount of cockroaches. Experiment What I did: Well, first I put four 4 by 10 sticky traps on our counter. Then, I got out some butter, some peanut butter, some bread, and some cheese out. After that, I got a tablespoon and scooped the substances out. I put the tablespoon of each substance on its own sticky trap. The butter on one, the peanut butter on another, and so on and so forth. Then I turned off the light and went to bed. When I got up, I got my data book out and went out to our counters. When I turned on the light, I counted how many cockroaches were on each sticky trap and I recorded my results. I tested this out ten times, and each time I recorded my results. Discussion Comparing: It was very interesting because according to my research, cockroaches like moist substances that they can easily pick up. But instead of going for the moist substances I put out, they went for the dry ones! Another thing I didn’t look at before was the temperature. The temperature really affected my results. According to my research, cockroaches can be seen the most inside houses when it is cold outside. And my results proved that it was true. When I did my project, it showed that as the temperature got colder, more and more cockroaches got stuck on the sticky trap. Uncontrolled Events: I think one uncontrolled event was the temperature. The temperature fell while I was doing my project. Usually, cockroaches will come indoors to escape from the cold outdoors. More cockroaches came in when the temperature dropped. Another thing I couldn’t control would be the exact place I put the sticky traps. I mean, I did put them on the counter, but I couldn’t put them all in the exact same place. What if a cockroach was just making his way across the counters when he got stuck on the sticky trap? What I would have done differently: If I had to do my project again, I would add in the temperatures of the night as well, because it really does affect my results. Either that, or I would make sure the temperature was pretty much the same each night. If it wasn’t around the temperature that I wanted, I would wait for the next night. I would also have added more bait to test because four traps really isn’t that much. Other Experiments that can be done: Some other experiments that can be done would be like, how the temperature effects on how active the cockroaches are, or what traps trap cockroaches best. You could also see if cockroaches are more active at night or in the daytime. According to my research though, cockroaches like to come out at night, while it’s still dark out, because to them, light means that somebody is there and can hurt them. But when it’s dark out, that’s the signal that everybody is asleep. One last test somebody could do, would be how long a cockroach could survive without food or water. Would it be affected if they had been fed a lot before the experiment started? What if they had only been fed a little bit before the experiment started? Conclusion Results: My results showed that the roaches went for the bread and cheese more than the butter and peanut butter, so my hypothesis was wrong. Each night, hardly any cockroaches went for the butter and peanut butter. They would mostly all go to the bread and cheese.

Essay on Hamlets Procrastination And Co - 919 Words

Hamletamp;#8217;s Procrastination and Cowardicenbsp;nbsp;nbsp;nbsp;nbsp;In William Shakespeareamp;#8217;s play Hamlet, Hamlet is a loyal prince who vows to avenge his fatheramp;#8217;s murder. When Hamlet discovers the painful truth about his fatheramp;#8217;s death, he is left with feelings of hatred and resentment in his heart towards the murderer, Claudius. Although Hamlet is a very noble and sophisticated man, he struggles with the issue of avenging his fatheramp;#8217;s death. He swears his revenge will be quick, however, this is not the case. Since Hamlet is more into philosophizing than action, he thinks about his intention to kill Claudius. The more he thinks about his intention, the less he is able to execute it. The†¦show more content†¦69). nbsp;nbsp;nbsp;nbsp;nbsp; At this point, there is no doubt present in Hamletamp;#8217;s mind; he is determined to kill the King. His attitude soon changes when he realizes that he is plotting to commit treason and the enormous burden that comes along with that. He is scared. The reason for his first delay of action, according to Hamlet, is that he is doubting the existence of the ghost and whether it really was the spirit of his late father or just an evil spirit. Hamletamp;#8217;s excuse for doubting the ghost is displayed in his actions; amp;#8220;Be thou a spirit of health or goblin damnamp;#8217;d, Bring with thee airs from heaven or blasts from hell, Be thy intents wicked or charitable, Thou comamp;#8217;st in such a questionable shape; (Shakespeare, p. 59). Because Hamlet doubts the ghost, he cannot and does not kill the King at this point in the play. Time continues to pass by as Hamlet is indecisive. The conviction and determined attitude that Hamlet possessed earlier has now been lost and his procrastination becomes quite evident. 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His madness. Ift be so, Hamlet is of the faction that is wrongd; His madness is poor Hamlets enemy. (V.ii.230-235) Hamlets self-description in his apology to Laertes, delivered in the appropriately distanced and divided third-person, explicitly fingers the greatest antagonist of the play†¹consciousnessRead MoreStephen P. Robbins Timothy A. Judge (2011) Organizational Behaviour 15th Edition New Jersey: Prentice Hall393164 Words   |  1573 Pageswork—such as Starbucks, Adobe Systems, Cisco, Whole Foods, Google, American Express, Amgen, Pfizer, and Marriott—have a big advantage. A recent survey of hundreds of workplaces, and more than 200,000 respondents, showed the social relationships among co-workers and supervisors were strongly related to overall job satisfaction. 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KRAUS Surname Meaning and Family History

The last name Kraus is a descriptive German surname meaning with curly hair, from the Middle High German krus, meaning curly. Surname Origin: German Alternate Surname Spellings:  KRAUS, KRAUß, KRAUSS, KRAUßE, KRAUSSE, KRUSE, KRAUSE Famous People with the Kraus  Surname Adolph Kraus  - Jewish leader and lawyerCharles A. Kraus  - American chemistGertrud Kraus  - pioneer of modern dance in IsraelHans Werner-Kraus  - German U-boat commanderJoseph Martin Kraus  - classical composerGeorg Melchior Kraus  - German painter Where is the Kraus  Surname Most Common? According to surname distribution from Forebears, the Kraus  surname is most common in Germany, where it ranks 52nd in the nation, followed by Austria (95th), Luxembourg (170th), and Czech Republic (199th). Krause with the e, however, is even more popular in Germany—coming in as the 27th most frequent surname. WorldNames PublicProfiler indicates a similar distribution, with the greatest percentage of individuals named Kraus  in Germany, followed by Austria and Luxembourg. German surname distribution maps at Verwandt.de show Kraus as most common in southeastern Germany in areas such as Forchheim and Augsburg, while Kraus is much more frequent in northwestern and western Germany, around Hannover and Recklinghausen. Genealogy Resources for the Surname KRAUS Meanings of Common German Surnames: Uncover the meaning of your German last name with this free guide to the meanings and origins of common German surnames.Kraus  Family Crest - Its Not What You Think: Contrary to what you may hear, there is no such thing as a Kraus  family crest or coat of arms for the Kraus surname.  Coats of arms are granted to individuals, not families, and may rightfully be used only by the uninterrupted male line descendants of the person to whom the coat of arms was originally granted.The Kraus/Krause  DNA Surname Project: Individuals with the Kraus  surname or variants such as Krause are invited to participate in this group DNA project in an attempt to learn more about ancient Kraus family origins. The website includes information on the project, the research done to date, and instructions on how to participate.KRAUS  Family Genealogy Forum: This free message board is focused on descendants of Kraus  ancestors around the world.FamilySearch - KRA US  Genealogy: Explore over 1.1  million results from digitized  historical records and lineage-linked family trees related to the Kraus surname on this free website hosted by the Church of Jesus Christ of Latter-day Saints.KRAUS  Surname Mailing List: Free mailing list for researchers of the Kraus  surname and its variations includes subscription details and a searchable archives of past messages.DistantCousin.com - KRAUS  Genealogy Family History: Explore free databases and genealogy links for the last name Kraus.GeneaNet - Kraus  Records: GeneaNet includes archival records, family trees, and other resources for individuals with the Kraus  surname, with a concentration on records and families from France and other European countries.The Kraus  Genealogy and Family Tree Page: Browse genealogy records and links to genealogical and historical records for individuals with the Kraus  surname from the website of Genealogy Today.

Diabetes Mellitus And Contemporary Naturopathic Medicine

Diabetes Mellitus and Contemporary Naturopathic Medicine The world is plagued with an overwhelming amount of chronic health conditions. Many people accept this as a part of life, sometimes just assuming it will happen to them because their parents or grandparents suffered with the same condition. Many of these chronic conditions are linked and can shorten your lifespan and increase the amount of pain that a person has to deal with daily. Usually a person suffers with more than one of these conditions. Diabetes Mellitus also known as Type II Diabetes effects children, young adults, adults as well as the elderly. Diabetes Mellitus can be helped by using naturopathic medicine, yoga and tai chi. The benefits of naturopathic medicine, yoga†¦show more content†¦Preventive care practices are essential to better health outcomes for people with diabetes.4 Due to the steady rise in the number of persons with DM, and possibly earlier onset of type 2 DM, there is growing concern about: The possibility of substantial increases in prevalence of diabetes-related complications in part due to the rise in rates of obesity The possibility that the increase in the number of persons with DM and the complexity of their care might overwhelm existing health care systems The need to take advantage of recent discoveries on the individual and societal benefits of improved diabetes management and prevention by bringing life-saving discoveries into wider practice The clear need to complement improved diabetes management strategies with efforts in primary prevention among those at risk for developing type 2 DM. naturopathic medicine of one of the important CAMs may help reduce the number of people that may be diagnosed with diabetes mellitus and help the people that have already been diagnosed. Modern Naturopathic medicine Diabetes mellitus effects every age

Development of the Cardiovascular System in Vertebrate Embryos Free Essays

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. We will write a custom essay sample on Development of the Cardiovascular System in Vertebrate Embryos or any similar topic only for you Order Now All processes occur under the influence of stimuli from genes and paracrine factors, oligosaccharides, multifunctional cytokines and enzymes. Vasculogenesis and Angiogenesis Two 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 to 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 Erythropoiesis Blood 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 hemopoietic 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 Formation In 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 mantle 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 System 1)   Formation of the primitive cardiovascular system a)   Extra-embryonic blood vessels The 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 vessels The endothelial tube network appears in the intraembryonic mesenchyme to  form an intraembryonic endothelial   tube network. The intraembryonic and extra  embryonic 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 Heart The 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 three 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 Chambers As mentioned above, during cardiac looping the cardiac jelly disappears from the 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 mesenchymal 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 right 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 myoblasts, 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 arteriosus 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  compact myocardium. How to cite Development of the Cardiovascular System in Vertebrate Embryos, Papers