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Structure and Function in the Mammalian Heart

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Structure and Function in the Mammalian Heart Mammals have a double circulatory system; blood passes through the heart twice during a complete circuit. Having a double circulatory system means that our pressure is maintained and oxygen is efficiently obtained from our lungs. The heart contains four chambers: two upper chambers called the atria and two lower chambers called the ventricles. The two sides of the heart are divided by the septum which prevents blood flowing between the two separate sides. The heart is composed of cardiac muscle which can tirelessly contract and relax rhythmically. Because of having thinner cardiac muscle than the ventricles, the atria produce less force when they contract. On the other hand, blood is pushed out with greater force once it is in the ventricles because of the thicker cardiac muscle in the walls of the ventricles. The muscle of the left ventricle is thicker since blood is pushed through to the rest of the body from here. ...read more.


This is clearly seen as one observes the pathway of blood as it enters and leaves this vital organ. From the vena cava, blood goes into the right atrium. When the atrium muscle contracts, blood is pushed through the open atrioventricular valve into the right ventricle (tricuspid valve). At this point, the muscle of the right ventricle contracts which forces the atrioventricular valve to shut. This pushes blood up into the pulmonary artery so that it can be oxygenated in the lungs. In the lungs, the blood collects oxygen and releases the waste gas carbon dioxide. The pulmonary valve is pushed open by the force of blood in the artery. The pulmonary vein brings blood back to the heart once it is oxygenated. Once the blood enters the left atrium, the atrium muscle contracts pushing blood through the open atrioventricular valves and into the left ventricle. When the muscle of the left ventricle contracts, the atrioventricular valve is forced shut. Blood is pumped out of the heart under high pressure to the rest of the body through the aorta. ...read more.


(Compton's Interactive Encyclopaedia CD ROM) For the reason that cardiac muscle is capable of instigating its own contraction, it is referred to as myogenic. The heart beats around 70 times per minute in adults. The coordination of the heart beat is controlled by the sino-atrial node which is referred to as the natural pacemaker of the heart. The SAN, located in the right atrium sends a signal to the heart muscle causing the muscle to contract. The signal composed of waves of electrical activity, spreads over the atria's surface causing it to contract, pushing blood to the ventricles. This results in the atrial systole. The time delay in the AVN provides enough time for the ventricles to fill up before being forced into the arteries. (Indge B. A New Introduction to Biology) In conclusion, I found learning about the function and internal structure of this muscular organ to be extremely interesting especially the way the chambers of the heart contract and relax simultaneously to form a rhythmic sequence. This cannot be performed efficiently without the valves doing their job of controlling blood flow through the four chambers of the heart. ...read more.

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Overall the candidate gives a very detailed response demonstrating a good subject knowledge. However, there is no clear introduction to this essay which is a mistake, you should always take the time to write an introduction as this sets the ...

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Response to the question

Overall the candidate gives a very detailed response demonstrating a good subject knowledge. However, there is no clear introduction to this essay which is a mistake, you should always take the time to write an introduction as this sets the tone for the rest of your work. A good introduction needs to give a brief description of your topic, in this case you could state the purpose of the human heart. You should also think about ways in which you can engage the reader, they are many ways in which you can do this including; stating an interesting fact or providing background information that is relevant to your topic.

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The candidate has gone into a great amount of detail and it is evident from the information they have included in their work that they have taken the time to research this topic, as they have discussed this topic at an advanced level. Furthermore they have used the correct terminology throughout their work which demonstrates a good level of understanding. By taking the initiative to research your topic you show an ability to learn independently which is a useful skill and you demonstrate enthusiasm and interest in your subject which is always a good thing. The candidate has sensibly included a bibliography with references the books they have used and links to webpages, this is important as it shows the steps you have taken to prepare for your essay. On another note, the candidate has concluded there work and they have done so with a personal response which is great as your teacher/examiner is interested in what you have learnt and what you have to say. Though in general a conclusion should include a summary of the key points from within your essay with references to why these are important, this helps to tie together any loose ends and bring your essay to a close.

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This essay is very well written and the candidate demonstrates a good understanding of the topics covered. With the exception of the term ‘back flow’ which should be two words and not one, there are no issues with spelling or grammar. You should make sure you double and treble check your work to avoid any basic errors.

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