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Structure Related to Function of the Heart.

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Felicity Roussak 05/10/87 Structure Related to Function of the Heart The heart is the pumping station of the body. It is infact two completely seperate pumps, one pushing deoxygenated blood to the lungs to oxygenate it through diffusion through the alvoli in the lungs, the other to pump the freshly oxygenated blood around the body. The two pumps consist of an atrium and a ventricle, and are seperated by the septrum, a thick muscular wall down the middle of the heart, which prevents oxygenated and deoxygenated blood from mixing, and also aids contraction of the heart- more detail on this later. The two sides of the heart differ slightly because of their different fuctions. At the top of the heart, both have a thin walled atrium, which collects blood from the main veins of the body, the pulmonary vein on the left and the anterior and posterior vena cava on the right. ...read more.


- if there was as much then the capillaries in the surrouding tissue of the lungs would burst and drown the alveoli in blood. The left ventricle has a very thick muscular wall because it pushes blood around the body, and so needs a high pressure to move blood in arteries in the furthest regions of the body. When the ventricles are full, they then contract at the same time, starting from the bottom, pushing the blood upwards, through the semi-lunar valves - one on each side of the septrum. The right ventricle pumps blood into the pulmonary artery to the lungs, the left into the aorta which swells, then branches off to various parts of the body. This is called ventricular systole. When there is no blood left in the ventricles and therefore little pressure, and a high pressure in the arteries, the semi-lunar valves in the middle of the heart close to prevent backflow of blood (this makes a sound which can be heard by a stethoscope as the second thump of a heartbeat - 'Dub'). ...read more.


This sends an electrical wave of excitation spreading across both atria meaning they contract at the same time and push blood into the ventricles. The same wave of excitation will then reach and stimulate the Atrio-Ventricular node (or AV node) which causes ventricular contraction. However, blood from the ventricles needs to be pushed upwards to allow it to flow more easily into the arteries. Therefore, the new wave of excitation initiated by the AV node travels down special fibres in the septrum (mentioned before in aiding heartbeat) called Purkinje fibres, which collectively make up an insulating electrical conducting passage called the 'Bundle of His'. When it reaches the bottom of the heart, called the apex, the same wave of excitation then spreads upwards across the ventricle walls causing them to contract from the bottom up and push the blood towards the arteries. This process is called the cardiac cycle. In conclusion, the size of the muscular walls in the heart, the existance and positioning of valves and the conduction of electrical waves of excitation make the heart perfect for the job as a pump of blood around the body. ...read more.

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