The respiratory system's main function is to supply oxygen to the blood in order for the blood to then bring oxygen to all the parts of the body. The act of breathing is how the respiratory system functions. When a person breathes, oxygen is inhaled and carbon dioxide is exhaled. The respiratory system is able to get oxygen to the blood through this exchange of gases.
The mouth, nose, trachea, lungs, and diaphragm are all involved in the process of respiration. Oxygen first enters the respiratory system through the nose and mouth. It then goes through the larynx, where the sounds of speech are produced, and the trachea, which is a tube that enters the chest cavity. In this cavity, the trachea splits into two smaller tubes which are called the bronchi. Each bronchus splits again and forms the bronchial tubes.
These tubes lead into the lungs where they again divide into several smaller tubes which connect to tiny sacs called alveoli. An adult's lungs typically contain about 600 million of the spongy, air-filled sacs which are surrounded by capillaries. Oxygen is inhaled and passes into the alveoli and is diffused through the capillaries into the arterial blood. Blood from the veins containing waste releases its carbon dioxide into the alveoli. Carbon dioxide follows the same route out of the lungs when an individual exhales.
It is the job of the diaphragm to help pump carbon dioxide out of the lungs and pull oxygen into the lungs. The diaphragm consists of a sheet of muscles which lie across the bottom of the chest cavity. As the diaphragm contracts and then relaxes, breathing takes place in the body. With each contraction of the diaphragm, oxygen is pulled into the lungs. As the diaphragm relaxes, carbon dioxide is pumped out of the lungs.
Humans breathe anywhere from 12 to 20 times every minute, day after day. Breathing begins at the nose and mouth. Air is inhaled into the nose or mouth and it travels down the back of the throat and into the trachea (or windpipe). As noted above, the trachea then divides into air passages which are called bronchial tubes.
For the lungs to perform at their peak, these airways need to be open during inhalation and exhalation. They also need to be free from inflammation or swelling or excessive amounts of mucous. As the bronchial tubes pass through a person's lungs, they divide into smaller air passages which are called bronchioles, and bronchioles end in tiny sacs called alveoli. The body contains more than 300 million alveoli.
Alveoli are surrounded by a mesh work of small blood vessels called capillaries. Oxygen coming from inhaled air passes through the walls of the alveoli and into the bloodstream.
After absorbing oxygen, the blood leaves the lungs and is then carried to the heart. The heart promptly pumps it through the body to provide oxygen for the cells of all the body's organs and tissues. As the cells use the oxygen, carbon dioxide is produced and absorbed into the blood. The blood then carries the carbon dioxide back to the lungs through the capillaries, where it is removed from the body upon exhaling.
The process of breathing is helped by a rather large, dome-shaped muscle under the lungs which is called the diaphragm. When a person breathes in, the diaphragm contracts downward, creating a vacuum which causes a rush of fresh air into the lungs. The opposite happens with exhalation, when the diaphragm relaxes upward, pushing on the lungs and allowing them to deflate.
The act of breathing alters the volume of the chest, or thoracic cavity. The lungs "suck" on to the inner chest wall so that as the cavity expands, the lungs become larger. The expanding forces are mainly provided by the intercostal muscles and the diaphragm. When the body is at rest, the diaphragm carries out the majority of the work. Volume and rate of breathing automatically increase if the body needs more oxygen, as when a person is exercising. This forced inspiration of air can suck in an extra 2 liters. During exertion, the breathing rate can triple, producing a total air exchange which is 20 times greater than at rest.
Breathing out is largely a passive act. As with a stretched elastic band, the enlarged lungs shrink and recoil when the diaphragm, intercostals and other inhalation muscles relax. Expiration which is forced brings further muscles into play to actively compress the lungs beyond their usual resting volume.
Luckily, the respiratory system has built-in methods to aid it in preventing harmful substances in the air from entering the lungs. Small hairs in the nose called cilia help filter out the large particles. Cilia are also found along the air passages and move in a sweeping fashion to keep the air passages clean. However, when harmful substances such as cigarette smoke are inhaled, the cilia are unable to function properly, causing health problems such as bronchitis.
The mucus which is produced by cells in the trachea and bronchial tubes helps keep air passages moist and aids in the battle to stop bacteria, viruses, dust, and allergy-causing substances from entering the lungs. Impurities which reach the deeper parts of the lungs can be moved out of the lungs via mucous which is coughed out or swallowed. Coughs and sneezes propel a tiny spray of mucous droplets from the respiratory system for a distance of up to 3m, or 10 feet.
The body is not able to store oxygen, so a continuing supply is needed. Inside the cells, oxygen reacts with glucose to free its energy.
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