Respiration is the process by which gases move in and out of our body and includes the process commonly known as breathing (including both inhalation and exhalation). We breathe in air from the atmosphere containing about 21% oxygen and 78% nitrogen. The air (or oxygen) goes through our body using the respiratory system and we finally exhale carbon dioxide.
We inhale the air from atmosphere through our nose (or mouth). This air then passes through the back of our throat, windpipe (or trachea), bronchial tubes, lungs, brochioles and alveoli. At the alveoli, the oxygen from the inhaled air is passed onto the blood stream. The blood is transported to various parts of the body by the pumping action of the heart and ultimately this oxygen reaches the cells. Cellular metabolism uses this oxygen, generates biomass and ATP (among other products) and releases carbon dioxide. The blood carries this carbon dioxide back to the lungs, where it is exhaled.
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Breathing is a process of exchanging gas in and out of organisms. For example, in humans the air gas we need to function is oxygen and we are excreting carbon dioxide into our surroundings. First, the oxygen-rich air goes into our nasal cavities; then it passes thorough the tracheae, bronchi, and then the bronchioles. The oxygen-carbon dioxide exchange happens in the alveoli. Now the oxygen molecules are transferred into the bloodstream that will eventually transport the oxygen to different cells in the body. The oxygen we breathe is used by the cells in order to perform its metabolic functions or cellular respiration. In return, carbon dioxide is excreted in the cells as the end product of cellular respiration.
After we inhale air through our noses, it passes through the nasal cavity where it is both filtered and heated. From here, it proceeds down the throat into the trachea, then into the two bronchi supplying the two lungs. The air further enters into smaller air tubes known as bronchioles before finally reaching the very tiny air sacs known as alveoli, where the gas exchange takes place. The alveoli are surrounded by capillaries carrying carbon dioxide rich blood, but they themselves contain oxygen rich blood. Because of the difference in concentration, the oxygen rich blood from the alveoli diffuses into the blood capillaries, and the carbon dioxide from the blood in the capillaries goes into the alveoli, where it is pushed back up the air tubes and finally out through exhalation. Once in the capillaries, the now oxygen rich blood is transported to the pulmonary vein that then takes the blood to the left side of the heart. The left side of the heart pumps the oxygenated blood to the rest of the body for use by cells in tissues and all body organs. The cells utilize the oxygen and produce carbon dioxide, which is carried in blood back to the lungs and ends up in the capillaries surrounding the alveoli. It diffuses into the alveoli for expulsion from the body through exhalation as oxygen diffuses into the capillaries for transportation to the heart and the rest of the body. This cycle repeats itself and the process is referred to as respiration.