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Heart & Lungs
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The Heart a simple introduction
The heart is basically a pump that is usually about the size of a man fist. An average heatlhly human heart weighs about 200-425 grams. The heart is a hollow muscular organ that is composed of cardiac muscle. Cardiac muscle is classed as involuntary muscle. The sinalatrial node controls it. The heart (myocardium is located behind the sternum slightly to the left. It is attached to our body by ligament to the spinal column, diaphragm and other parts of the body. Our hearts are encased in a double membrane structure that contains serous fluid. This double membrane is called the pericardium and it helps to reduce friction when the heart contracts. Within our heart there is four chambers the left atrium, left ventricle, right atrium and the right ventricle. A wall of muscle called septum separates these four chambers. The left side of the heart is larger than the right side .The reason for this size difference is because the left side of the heart has to pump blood around the body, whereas the right side of the heart only need to pump blood a short distance to the lungs. The heart also has a number of valves tricuspid valve, pulmonary valve, mitral valve and the aortic valve. Our heart is attached to different arteries and veins these are called Aorta, pulmonary artery, pulmonary vein and the vena cavae. The heart starts to beat about 21 days after conception at about 75-80 bpm (beats per minute). It beats faster up to about the 9th week and then begins to slow down again. Our heart has been beating since 21 days after we were conceived and in normal circumstances will beat till the moment of our death. In a hearts lifetime it may have continually beat more than 3.5 billion times. Average heart beats about 100,000 times a day pumping a huge 7,571 litres of blood. This amazing organ is able to maintain our body�s need for receiving oxygen and removing carbon dioxide and other waste products when we are at rest it is able to increase there needs when ever are body requires it. For example when we begin to walk or run the heart will speed up to meet our body�s need for supplying oxygen and removing carbon dioxide from our body. All of the muscles of the myocardium are connected and when the sino-atrial node, which is, located in the upper wall of the right atrium sends an electrical impulse the heart contracts. The left side of the heart is responsible for receiving oxygen and nutrient rich blood that gets pumped around to the body where it is needed. The right side of the heart is responsible for receiving and pumping blood that contains waste products to the lungs and kidneys, so it can be removed from our body. Oxygenated blood from the lungs enters the heart through the pulmonary vein. It then enters the left atrium where it gets squeezed into the left ventricle and it is then pumped though the aorta to supply the body with essential nutrients and oxygen. The blood diffuses with carbon dioxide and other waste products and then returns to the heart though the vena cava. It then renters the right atrium where it gets squeezed into the right ventricle. It finally gets pumped to the lungs where it can diffuse with oxygen to repeat its journey once again. Although the heart is a powerful pump by itself it would not be able to pump blood round the body. The arteries help transport blood away from the heart and to the cells. They are able to do this because they are tubs surrounded by smooth muscle that contracts to move blood to where it is needed. Veins are similar but they allow blood to travel to the heart they have thinner walls and one-way valves to prevent blood going back. The heart not only works as a pump but also secretes a peptide hormone that is called atrail natriurectic factor. Atrail natriurectic factor is released and stored by cells that are present in the atria of the heart. This peptide hormone is able to affect the blood vessels, adrenal glands, kidneys and regions of the brain that regulate blood pressure and volume. Provided that we lead a healthy lifestyle and eat a good balanced diet, exercise regularly, don�t smoke and don�t have any hereditary heart conditions. Our heart is likely to work for the rest of our lives. However a large proportion of the world�s population does not lead a healthy lifestyle, eat poor diets, smoke and do not exercise enough. These above factors do put a lot of stress on the heart and coronary heart disease is responsible for the premature death of many people. It is also on the increase and is likely to keep increasing until the modern world makes some changes.
The Lungs
After about 10 weeks after conception the lungs would have developed but they will not be fully developed or be used. The lungs remain filled with water until after birth. This is when we take our first breath and from that moment onwards the lungs become essential for us to stay alive. From this moment of us taking our first breath the lungs become stronger and the functioning of the lungs improves. They continue to improve there functioning until our late teens-early twenties. After this the functioning of our lungs begins to slowly decline by about 1% a year. But with a smoker they decline by about 2 % a year. The lungs are an essential organ that are needed for respiration. The main function of our lungs is to provide oxygen from outside body and to remove carbon dioxide from within our body to the outside environment. The lungs have a spongy like texture that can easily expand. Our two lungs make up one of the largest organs in our body. Each of our lungs is about 10-12 inches long. These paired organs are separated by a mediastinum; the mediastinum contains the heart, trachea, esophages and blood vessel. These two organs are located in our chest inside the thoracic cavity. The lungs are protected by the rib cage and a double sac that is called pleura encloses each lung. The inside layer of this sac is called vis ceral pleura and adheres tightly to the lungs. The outer layer of this sac parieta thoracic is attached to the inner wall of the thoracic cavity. The two layers of this sac are separated by a very thin space that is called the pleural cavity. This pleural cavity is filled with fluid called pleural fluid. This special fluid allows the two sacs to slide over each other without becoming separated easily. The two lungs are not equal in size and the left lung is the smaller of the two lungs. The left lung is smaller than the right to provide room for the heart. The lungs are attached to the heart and trachea by structures that are called the �roots of lungs�. The root of lungs is made up of the bronchi, pulmonary vessels, bronchial vessels, lymphatic vessels and nerves. These structures leave and enter at the part of the lung called the hilus. Our lungs are divided into lobes by a horizontal and oblique fissures. The larger right lung has three lobes and the smaller left lung has two lobes but does have a unique feature the cardiac notch. The cardiacnotc helps to create the lingula of the left lung. There is a space that is below the lungs. The diaphragm this is a dome shaped muscle seals the space. When our brain signals our body to breathe in our diaphragm contracts. Air that contains 21% oxygen, 79% nitrogen is drawn into the nasal cavity or the oral cavity or sometimes both. It then travels down though the pharynx, larynx and to the trachea. From the trachea the air divides and travels into the primary brochi. This flow of air will keep dividing until it reaches the bronchioles it subdivides 23 times. When the air finally reaches the bronchioles it travels to the alveoli. The alveoli are composed of many tiny sacs that are in close contact with blood filled capillaries. Alveoli are covered in a surfactant fluid that reduces surface tension. The air that has been inhaled in diffuses with carbon dioxide that is in the blood. The blood that now contains high levels of oxygen is transported to the heart. Homogloblin that are in the blood carry the oxygen. The poisonous gas carbon dioxide travels back to the nasal cavity or the oral cavity where it is exhaled into the outside environment. It is not only carbon dioxide that is exhaled but also oxygen and nitrogen. Although we do breath in 21% O2 we only use 4 % of it. This is because when CO2 reaches the unacceptable level of 4% we automatically breathe out. An average person takes about 15-25 breaths a minute. Each day we breath about 25,000 times and by the time we reach 70 years of age we will have taken 600 million breaths. When we exercise the body�s need for O2 increases and the amount of CO2 that needs to be removed from our body also increases so our rate of breathing speeds up to meet this need. The environment inside of our lungs in moist, warm and humid. However this is also a perfect environment for bacteria to grow. This is why we get a lot of infections in the lungs and why a lot of infections start in the lungs.
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