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heart essay

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Introduction

Heart Assignment The human heart is located in the middle of the thorax but slightly to the left. The left ventricle is slightly larger than the right so it takes up more space in the left side of the thorax and therefore makes the left lung smaller. The heart is part of the circulatory system and is a powerful muscular sac that pumps blood around the body through blood vessels by repeated contractions. The heart on average beats 72 beats per minute (BPM). In the systemic ...blood travels from the heart via arteries then to the capillaries, which deliver oxygen to all organs in the body, then back up to the heart via the veins. In the pulmonary system blood travels from the lungs to the heart and then back to the lungs again. The heart consists of four chambers: the upper right and left atria and the lower right and left ventricles. The two upper chambers are called Atrium or Atria (plural) which are thin walled chambers that receive blood. The two lower chambers are called Ventricles which are thick walled chambers that pump blood out away from the heart. The human heart is separated into two distinct pumps, the right side and the left side, which both comprise of an Atrium and a Ventricle that contract and relax simultaneously. ...read more.

Middle

Blood flows rapidly in pulses and is under high pressure (10 - 16kPa). Veins and venules (smaller veins) carry de-oxygenated blood to the heart, with the exception of the pulmonary vein. They are medium sized compared to the arteries and capillaries and have little elastic tissue, but the lumen is quite large compared to the diameter of the actual vein. They have a thin soft muscular wall which is not permeable. Do have valves all the way through them and as they are not capable of constriction. Blood flows slowly and is under low pressure (1 kPa). Capillaries join arteries and veins together and blood changes from oxygenated to de-oxygenate in them. The blood pressure reduces from 4 - 1 kPa. They are the smallest of vessels with no elastic tissue and a large lumen. They have no muscular wall (as the wall is ultra thin) and do not have valves or pulses. They are not capable of constriction. They are permeable so oxygen and nutrients can pass through easily. The hearts muscular tissue 'myocardium' is responsible for making the heart contract and relax. The myocardium is not controlled by the nervous system but by impulses from within the heart itself; via the Sinoatrial node (SA node), although it can be affected by the autonomic nervous system. ...read more.

Conclusion

Once the level of carbon dioxide is lowered the PH of the blood increases back up and once again this then triggers the Carotid receptors to stimulate the cardio-inhibitory centre (again in the medulla oblongata in the brain) to reduce heart beat back to normal. Blood pressure is affected by changes in the cardiac output. Pressure needs to be kept to a relatively high level in order to keep the blood travelling to tissues that require it. Pressure is also controlled by the diameter of the vessels. Vasoconstriction is when the vessels narrow and the blood pressure rises whereas vasodilation is when the vessels widen and pressure drops. Both conditions are controlled by the vasomotor centre in the medulla oblongata in the brain. Coronary heart disease is the most common disorder of the heart. It is basically when the two coronary arteries that supply the heart with blood become filled with fatty deposits which limit the blood supply, which can be fatal. There are three ways a coronary artery can become blocked: Coronary thrombosis - when a blood clot becomes lodged and blocks the artery. Atherosclerosis - when the arteries narrow due to the walls becoming thicker with deposits. This condition is also referred to as thickening of the arteries, which can in turn lead to thrombosis. Spasm - when there is repeated contractions of the artery wall. ...read more.

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