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Take a deep breath and hold it for as long as you can. Use the second's hand of a watch to time yourself. You may be surprised to find that you have to take a breath before a minute or two has passed. Humans may be able to go for days without food or water, but we can only live for a few minutes without air.
We live at the bottom of a layer of air called the atmosphere. Earth's atmosphere contains oxygen, the gas is needed to get energy from the foods we eat, fuel our muscles, keep our hearts pumping, and perform many other important functions for survival. When breathing in, or inhaling, oxygen rushes into the body. When breathing out, or exhaling, the body is getting rid of a waste gas called carbon dioxide.
The human respiratory system consists of the nose, pharynx (throat), the larynx (voice box), the trachea (windpipe), the bronchi (air tubes), and the lungs
The journey of air to the lungs begins by inhaling through the mouth or nose. The entrance to the nose is the vestibule. The nose is made up of a strong, flexible cartilage. A piece of cartilage, called the septum, divides the nose into two nostrils. The insides of the nostrils are lines with tiny hairs called cilia that help to filter air and trap dust particles. A special type of tissue called the ciliated columnar epithelium lines the inside of the nose. .
The nostrils open into the nasal cavity. The walls of the nasal cavity produce a moist, sticky material called mucous, produced by goblet cells. Mucous traps germs and bits of dust that get past the nostrils. Mucous also helps warm and moisten the air that is breathed. Tear ducts from the eyes lead into the nasal cavity. When crying, tears drain into the nasal cavity. That is why the nose runs when a person cries.
Sinuses are air spaces in the skull that are linked to the nasal cavity. Sometimes sinuses become infected or swell up because of an allergy to pollen, dust, or other substances. A feeling of congestion and a headache may occur. Steam or a humidifier can help relieve the pressure of a sinus infection (Serrano, 1994).
At the top of the nasal cavity are two thumbnail-sized spots called the olfactory centers, olfactory meaning "smells." There are millions of these in the nose. A smell is sensed by different odor receptors. There are hundreds of different kinds of odor receptors. The act of sniffing moves air up to these nerve endings. The olfactory centers carry impulses from the nerve endings to the brain, which tells us whether we are smelling roses or rotten eggs (Lew, 2010).
Cilia stick out from the olfactory cells in the nose. The cilia wave back and forth like grass in the wind. They respond to chemicals in the air and send signals to the olfactory centers. The centers organize the signals into patterns as different smells.
Humans can distinguish about ten thousand different smells. The brain learns to tell one from the other very quickly (Dr. Alvin, 1994). The sense of smell can help to keep someone safe. For example, the smell of something burning can alert them to a fire before it is seen.
After passing through the nasal cavity, air travels into the throat, or pharynx. The pharynx is a muscular tube lined with mucous that starts behind the nose and stretched downward about five inches through the neck, it contains the tongue, and teeth and is also part of the digestive system. The oropharynx is the front part of the larynx. The upper part, through which air passes from the nose on its way to the lungs, is the nasopharynx. The soft palate, or the roof of the mouth, separates the oropharynx from the nasopharynx. Hanging down from the back of the soft palate is a small, soft tag of flesh called the uvula (Serrano, 1994).
From the sides of the nasopharynx, the Eustachian tubes lead to the inner ears, by allowing air to pass back and forth from the nasopharynx; these tubes stabilize air pressure on the eardrums, sometimes allowing a respiratory infection to spread to the ears, causing an ear infection (Center for Disease and Control, 2010). The tonsils and adenoids lie at the back of the nasopharynx, these glands defend the body against infections are a part of the lymph system.
The larynx, or voice box, is located at the bottom of the pharynx. The air tube leading to the lungs has a small flap called the epiglottis. The flap opens when air is inhaled but closes when food is swallowed. Trying to do both at the same time may result in choking. Two thin folds of tissue, called vocal cords, stretch across the voice box. Vocal cords are found in the glottis. When inhaling, the cords relax and allow air to easily pass through. When speaking or singing, tiny muscles stretch the vocal cords tightly. Air pushed out of the lungs makes the cords move back and forth quickly. The rapid movements, or vibrations, make a sound. The tighter the cords are stretched, the higher pitched the sound they produce. The front and side walls of the box are referred to as the Adam's apple.
Below the voice box, air moves into the windpipe, or trachea. The rings of the stiff cartilage that forms the trachea can be felt by placing two fingers below the lower part of the neck. These rings are connected by muscles, which allow bending and stretching and still keeps the windpipe open.
Toward the middle of the chest, the trachea splits into two narrow tubes called the bronchi. One tube leads into the right lung and the other into the left lung. Each bronchus splits into smaller and smaller bronchial tubes that look like the branches on a tree. Finally, each tiny air tube ends in a little branch of air sacs called alveoli.
The lungs contain more than six hundred million alveoli (Lew, 2010). The branches look like clusters of grapes. However, if all the tiny alveoli were spread out flat, they would cover a much larger surface than all the skin on a human body.
A network of small blood vessels called capillaries surrounds each air sac. The walls or membranes of the alveoli and the capillaries are very thin and close to one another. Molecules of oxygen and carbon dioxide can pass through the walls in either direction.
In a process called diffusion, substances move from an area of high concentration to an area of lower concentration. When inhaling, air that to the as traveling to the alveoli, has a large amount of oxygen in it. The blood in the capillaries traveling from the heart has a small amount of oxygen. That means that many oxygen molecules diffuse through the alveoli and capillary walls and into the blood. Oxygen is picked up by a substance in the red blood cells called hemoglobin. Blood, now rich in oxygen, is carried back to the heart, where it is pumped to all the cells of the body. At the same time, carbon dioxide molecules diffuse through the capillary and alveoli walls into the alveoli. When exhaling, carbon dioxide is released into the air.
The lungs fill up most of the space inside the chest. Each lung is enclosed and protected in an airtight lining called a pleural sac. The inside of the chest is also lined with a pleural sac. The linings are smooth and moist, allowing the lungs to move easily within the chest while breathing. The left and right lungs are joined together in the center in an area called the hilum. The left lung is a little smaller than the right lung due to the heart taking up space on the left side.
The amount of air the lungs can hold is called lung capacity. Lung capacity normally increases until a person's teens or early twenties and declines gradually with aging. An average person has a lung capacity of about twelve pint of air. When resting, a person breathes in and out about ten to fifteen times a minute. With each breath, about a pint of air enters and leaves the lungs. When exercising, a person breathes more quickly and deeply so more air goes in and out of the body every minute.
The chest is enclosed by the ribs, spinal column, breastbone, and all the muscles in between. The bottom of the chest is enclosed by a strong sheet of muscle and connective tissue called the diaphragm. When inhaling, the muscles of the diaphragm pull together and move downward. At the same time, the ribs and breastbone move forward and upward. The movements enlarge the size of the chest cavity. Outside air pushes through the air tubes to take up the extra room.
A few seconds later the muscles of the diaphragm relax and move upward to their rest position. The chest muscles also relax, and the ribs and breastbone move backward and downward. The chest cavity becomes smaller, and there is less room in the lungs. When exhaling, air is pushed out. Even when breathing out there is still some air left in the lungs. When breathing normally, the diaphragm moves up and down only about a half of inch, but when exercising, the diaphragm moves up and down three or four inches.
Some people snore when they sleep. Snoring happens when the throat muscles relax and vibrate, and the airway is partly blocked. Snoring is worse when people sleep on their backs, so sleeping on their side or with a pillow may help them. Some people naturally snore a lot; others do not snore much at all.
A sneeze is a sudden burst of exhaled air that comes out of the nose or mouth. It is generally caused by an irritation in the mucous lining. A powerful sneeze pushes air out of your nose or mouth at speeds of up to one hundred miles an hour (Lew, 2010). Mucus, dust, and germs are carried along with the air and can travel as much as ten feet.
A cough is an uncontrollable burst of air like a sneeze, but the air only comes out of the mouth. Air rushes out of the lungs and passes over the vocal cords, making a sound. Coughing often occurs to help spit up, or expel mucous from the airway.
Hiccups are caused by a sudden twitching of the diaphragm that forces air into the lungs. At the same time, the epiglottis flaps snap shut. This sudden closing blocks off the air and produces the hiccup noise. Breathing deeply and slowly or taking a long drink of water can sometimes help stop the hiccups (Lew, 2010).
The lungs and the other parts of the respiratory system can be irritated by dust, smoke, pollen and infections caused by germs and viruses. An inflammation of the larynx, pharynx, and tonsils results in a sore throat. An inflammation of the larynx also makes it difficult to speak, and the voice sounds hoarse. These symptoms usually only last a few days and can be helped by resting and drinking warm liquids. A doctor may prescribe antibiotics to help clear up an infection caused by germs (Dr. Alvin, 1994).
There are more serious respiratory issues that can occur. Tonsillitis is an inflammation of the tonsils, caused by a virus or germ called streptococcus, or strep.
Bronchitis is an irritation of the lining of the bronchial tubes. People with bronchitis cough a great deal and often are short of breath because of the excess mucus caused by an illness. Bronchitis may be either acute or chronic. Acute bronchitis often develops from a cold or other respiratory infection, which usually improves within a few days. Chronic bronchitis, a more serious condition, is a constant irritation or inflammation of the lining of the bronchial tubes, often due to smoking, which is included in chronic obstructive pulmonary disease (COPD) (Mayo Clinic, 2010).
Pleurisy is an infection of the pleural sac membranes around the lungs, causing the sacs to become inflamed. Also called pleuritis, pleurisy typically causes sharp pain, almost always when a deep breath is taken (Mayo Clinic, 2010).
Pneumonia is an infection of the air sacs in the lungs that results in inflammation. Bacteria, viruses, fungi or parasites can cause pneumonia. Pneumonia is a particular concern if you're older than 65 or have a chronic illness or impaired immune system. It can also occur in young, healthy people. Pneumonia can range in seriousness from mild to life-threatening. Pneumonia often is a complication of another condition, such as the flu. Antibiotics can treat most common forms of bacterial pneumonias, but antibiotic-resistant strains are a growing problem. The best approach is to try to prevent infection (Mayo Clinic, 2010).
Tuberculosis or TB is an infection that causes damage to the lung tissues. It is caused by a bacterium called Mycobacterium tuberculosis. The bacteria usually attack the lungs, but TB bacteria can attack any part of the body such as the kidney, spine, and brain. If not treated properly, TB disease can be fatal. TB disease was once the leading cause of death in the United States (Center for Disease and Control, 2010).
Emphysema is a long-term progressive disease in which the lungs become less elastic, often due to years of cigarette smoking. It causes shortness of breath due to over inflation of the alveoli. In people with emphysema, the lung tissue may become impaired or destroyed. Emphysema is called an obstructive lung disease because airflow on exhalation is slowed or stopped because over-inflated alveoli do not exchange gases when a person breaths due to little or no movement of gases out of the alveoli (emedicinehelp, 2010).
Asthma is one of the most common chronic non-curable inflammatory diseases of the respiratory system. It affects every one of all age groups, but most often starting in childhood. Asthma causes periods of wheezing, tight chest, shortness of breath and coughing. The most common time for the coughing to occur is during the night or in the mornings (National heart Lung and Blood Institute, 2010).
The lungs and the other parts of the respiratory system makes it possible to inhale and exhale, to speak and make noises with the mouth, and to blow up a balloon. Awake, or asleep, air is inhaled in and out every minute of every hour, of every day, for your entire life.