Anatomy and Physiology P4 Essay

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Cardiovascular system The structure of the heart The heart is the size of a curled up fist. It is located in the thoracic cavity which is situated between the lungs. It is surrounded by the pericardium which is a tough membrane which contains a layer of fluid which prevents friction. The heart is a double pump made up of four chambers, two upper chamber called the atriums and two lower chambers called ventricles. Each chamber of the heart has blood vessels entering or leaving them. The veins enter the atria and the arteries leave the ventricles. The left side of the heart pumps oxygenated blood from the lungs to the body. The right side however pumps deoxygenated blood from the veins to the lungs to be oxygenated. The two sides of the heart are separated by a septum. The cardiac cycle The cardiac cycle is what happens in the heart during one heartbeat. The average number of beats per minute is 70 at rest. The higher the heart rate is the shorter the cardiac cycle will be. The cardiac cycle can be split into 6 parts: 1. Both of the atria (the upper sections of the heart) contract. This increases the pressure which forces the blood into the ventricles (lower sections of the heart). 2. When the ventricles are full of blood the pressure in the ventricles will have increased which forces the atrio-ventricular valve shut. 3. The ventricles contract making the pressure within the ventricle to rise. This forces the semi-lunar valve open which allows the blood into the aorta and pulmonary artery. 4. When the ventricles contract it forces blood into the aorta and the pulmonary artery. The arteries have elastic walls which expand. 5. The muscles in the ventricle begins to relax as the blood leaves the ventricles. The blood falls backwards for a fraction of a second forcing the semi lunar valve to close. 6. When the ventricles relax and go

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