Respiratory System Health Article

Function

The main function of the respiratory system is the delivery of oxygen and removal of carbon dioxide. To achieve this purpose, the nervous system controls the flow of air in and out of the lungs while maintaining a regular rate and pattern of breathing. Regulation is controlled by the respiratory center, a cluster of nerve cells in the brain stem. These cells simultaneously send signals to the muscles involved in inhalation: the diaphragm and rib muscles. The diaphragm flattens out when stimulated by a nervous impulse. The thoracic or chest cavity contains the lungs. The volume of the cavity expands with the downward movement of the diaphragm, thus expanding the lungs. The rib muscles also contract when stimulated, which pulls the rib cage up and out, at the same time expanding the thoracic cavity. This movement reduces pressure in the chest. When the volume is increased in the thoracic cavity, air rushes into the lungs to equalize the pressure. This nervous stimulation is quick, and when it is over, the diaphragm and rib muscles relax and a person exhales.

Working in conjunction with the circulatory system, the oxygen-rich blood travels from the lungs through the pulmonary veins into the left side of the heart. From there, blood is pumped to the rest of the body. Blood that is oxygen-depleted, but carbon dioxide-rich, returns to the right side of the heart through two large veins called the superior and inferior venae cavae. This blood is then pumped through the pulmonary artery to the lungs, where oxygen is picked up and carbon dioxide is released. This process is repeated continually under normal circumstances.

Other functions the respiratory system assist in just by normal respiration are the regulation of acid–base balance in the body, a critical process for normal cellular function. It also protects the body against toxic substances inhaled as well as against disease–causing organisms in the air. The respiratory system also assists in detecting smell using the olfactory receptors located in the nasal passages. Furthermore, it aids in producing sounds for speech.

Role in human health

Breathing is an unconscious process carried out on a constant basis and is necessary for survival. Under normal conditions, a person takes 12–20 breaths per minute, although newborns breathe at a faster rate, at approximately 30–50 breaths per minute. The breathing rate set by the respiratory center can be altered by conscious control, for example, by holding the breath. This alteration occurs when the part of the brain involved in thinking, the cerebral cortex, sends signals to the diaphragm and rib muscles to momentarily ignore the signals from the respiratory center. If a person holds his or her breath too long, carbon dioxide accumulates in the blood, which then causes the blood to become more acidic. The increased acidity interferes with the action of enzymes, which are specialized proteins that coordinate all biochemical reactions in the body. To prevent too much acid from building up in the blood, special receptors located in the brain stem and in the blood vessels of the neck called chemoreceptors monitor the acid level in the blood. These chemoreceptors send nervous signals to the respiratory center when acid levels are too high, which overrides the signals from the cerebral cortex, forcing a person to exhale and then resume breathing. The blood acid level is brought back to normal levels by exhalation, which expels the carbon dioxide. Irreversible damage to tissues occurs, followed by the failure of all body systems, and ultimately, death if the respiratory system's tasks are interrupted for more than a few minutes.

Common diseases and disorders

The diseases and disorders of the respiratory system can affect any part of the respiratory tract and may range from mild to life-threatening conditions such as:

• Colds—A virus that targets the nasal passages and pharynx. Symptoms include a stuffy and runny nose.
• Hay fever and asthma—Allergic reactions that may occur when the immune system is stimulated by pollen, dust, or other irritants. A runny nose, watery eyes, and sneezing characterizes hay fever. In asthma, because the bronchi and bronchioles are temporarily constricted and inflamed, a person has difficulty breathing.
• Bronchitis—Characterized by inflamed bronchi or bronchiole membranes, resulting from viral or bacterial infection or from chemical irritants.
• Emphysema—A non-contagious disease that results from multiple factors including: smog, cigarette smoke, infection, and a genetic predisposition to the condition. Emphysema partially destroys the alveolar tissue and leaves the remaining alveoli weakened and enlarged. When a person exhales, the bronchioles collapse, trapping air in the alveoli. This process eventually impedes the ability to exchange oxygen and carbon dioxide, leading to breathing difficulties.
• Pneumonia—Infections caused by bacteria or viruses can lead to this potentially serious condition. The alveoli become inflamed and fill with fluid, impairing the flow of oxygen and carbon dioxide between the capillaries and the alveoli.
• Tuberculosis—A condition caused by a bacterium that attacks the lungs and occasionally other body tissues. Left untreated, the disease destroys lung tissue.
• Laryngitis—An inflammation of the larynx caused by such irritants as cigarette smoke, overuse of the voice, or a viral infection. A person with laryngitis may become hoarse, or they may be able only to whisper until the inflammation is reduced.

• Lung cancer—Occurs in those individuals who are exposed to such cancer-causing agents as tobacco smoke, asbestos, or uranium; or who have a genetic predisposition to the disease. Treatments are very effective if the cancer is detected before the cancer has spread to other parts of the body. About 85% of cases are diagnosed after the cancer has spread; thus the prognosis is very poor.
• Respiratory distress syndrome (RDS)—Refers to a group of symptoms that indicate severe malfunctioning of the lungs affecting adults and infants. Adult respiratory distress syndrome (ARDS) is a life-threatening condition that results when the lungs are severely injured, for example, by poisonous gases, in an automobile accident, or as a response to inflammation in the lungs.
• Wheezing—A high-pitched whistling sound produced due to air flowing through narrowed breathing tubes. It may have many causes such as asthma, emphysema, pneumonia, bronchitis etc.
• Shortness of breath or dyspnea—This condition may have mulitple causes such as asthma, emphysema, hyperventilation, obesity, cigarette smoking, lung disease, excessive exercise, etc.
• Chronic respiratory insufficiency (or chronic obstructive pulmonary disease; COPD)—A prolonged or persistent condition characterized by breathing or respiratory dysfunction resulting in reduced rates of oxygenation or the ability to eliminate carbon dioxide. These rates are insufficient to meet the requirements of the body and may be severe enough to impair or threaten the function of vital organs (respiratory failure).

Some of the most common symptoms of respiratory disorders are a cough, shortness of breath, chest pain, wheezing, cyanosis (bluish discoloration), finger clubbing, stridor (a crowing sound when breathing), hemoptysis (coughing up of blood), and respiratory failure. These symptoms do not necessarily signify a respiratory

problem, but can be a sign of another problem. For example, chest pain may be due to a heart or a gastrointestinal problem.

Cystic fibrosis is a genetic disease that causes excessive mucus production and clogs the airways.

Acidosis is a condition resulting from higher than normal acid levels in the body fluids. It is not a disease but may be an indicator of disease. Respiratory acidosis is due to a failure by the lungs to remove carbon dioxide, therefore reducing the pH in the body. Several conditions such as chest injury, block of the upper air passages, and severe lung disease may result in respiratory acidosis. Blockage of the air passages may be due to bronchitis, asthma, or airway obstruction resulting in mild or severe acidosis. Regular, consistent retention of carbon dioxide in the lungs is referred to as chronic respiratory acidosis. This disorder results in only mild acidosis because of an increased bicarbonate (alkali) production by the kidneys.

Alkalosis is a condition resulting from a higher than normal level of base or alkali in the body fluids. Respiratory alkalosis results from decreased carbon dioxide levels caused by such conditions as hyperventilation (a faster breathing rate), anxiety, and fever. The pH becomes elevated in the body. Hyperventilation causes the body to lose excess carbon dioxide in expired air and can be triggered by altitude or a disease that reduces the amount of oxygen in the blood. Symptoms of respiratory alkalosis may include dizziness, lightheadedness, and numbing of the hands and feet. Treatments include breathing into a paper bag or a mask that induces rebreathing of carbon dioxide.