Chapter 5Respiratory SystemIn this passage you will learn:● The organs of the respiratory system● The structure and function of these organs● The mechanism of breathing● The gas transport and cleaning systemAll living animals must take in oxygen and get rid of carbon dioxide. In the vertebrates——animals with backbones ——that get their oxygen from the air, both tasks are performed by special gas-exchange organs called lungs. The lungs provide a place where oxygen can reach the blood and carbon dioxide can be removed from it. They are equipped with tubes and a bellows system for drawing in air from the outside, while the pulmonary veins and arteries circulate blood through from inside. The lungs also have a cleaning system that traps, ejects, or destroys irritants and other harmful substances that travel in with the air.In the simpler cold-blooded amphibians and reptiles, the lungs are two balloon-like sacs. In active animals that require large amounts of oxygen, especially the warm-blooded birds and mammals , the lungs are a spongy labyrinth of sacs that supply an enormous surface area for the transfer of gases. In the adult human the total lung surface, if flattened out, would be larger than a badminton court, about 100 square yards (83 square meters).Air enters the body through the nose and passes through the nasal cavity, which is lined with a mucous membrane and fine hairs (cilia) to help filter out foreign bodies, as well as to warm andmoisten the air. Paranasal sinuses are hollow, air-containing spaces within the skull that communicate with the nasal cavity. They, too, have a mucous membrane lining and function to provide the lubricating fluid mucus. as well as to lighten the bones of the skull and help produce sound.After passing through the nasal cavity, the air next reaches the pharynx (throat). There arethree divisions of the pharynx. The nasopharynx is the first division, and it is nearest to the nasalcavities. It contains the adenoids, which are masses of lymphatic tissue. The adenoids (also known as the pharyngeal tonsils) are more prominent in children, and if enlarged, they can obstruct air passageways . Below the nasopharynx and closer to the mouth is the second division of the pharynx, the oropharynx. The palatine tonsils, two rounded massed of lymphatic tissue, are located in the oropharynx. The third division of the pharynx is the hypopharynx (also called the laryngopharynx). It is in the hypopharyngeal region that the pharynx, serving as a common passageway for food from the mouth and air from the nose, divides into two branches, the larynx (voice box) and the esophagus.The esophagus leads into the stomach and carries food to be digested. The larynx contains the vocal cords and is surrounded by pieces of cartilage for support. Sounds are produced as air is expelled past the vocal cords, and the cords vibrate. The tension of the vocal cords determines the high or low pitch of the voice.Since food entering from the mouth and air entering from the nose mix in the pharynx, what prevents the passing of food or drink into the larynx and respiratory system after it has been swallowed? Even with a small quantity of solid or liquid matter finding its way into the air passages, breathing could be seriously blocked.A special deterrent to this event is provided for by a flap of cartilage attached to the root of the tongue that acts like a lid over the larynx. This flap of cartilage is called the epiglottis. The epiglottis lies over the entrance to the larynx. In the act of swallowing, when food and liquid move through the throat, the epiglottis closes off the larynx, so that these things cannot enter.On its way to the lungs, air passes from the larynx to the trachea (windpipe), a vertical tubeabout 41 inches long and 1 inch in diameter. The trachea is kept open by 16-202C-shaped rings of cartilage separated by fibrous connective tissue that stiffens the front and sides of the tube.In the region of the mediastinum, the trachea divides into two branches called bronchi. Each bronchus leads to a separate lung and divides and subdivides into smaller and finer tubes, somewhat like the branches of a tree (see Figure 6-1) .DiaphragmFigure 6-1The smallest of the bronchial branches are called bronchioles. At the end of the bronchioles are clusters of air sacs called alveoli. Each alveolus is made of a one-cell layer of epithelium. The very thin wall allows for the exchange of gases between the alveolus and the capillaries that surround and come in close contact with it. The blood that flows through the capillaries accepts the oxygen from the alveolus and deposits carbon dioxide into the alveolus to be exhaled. Oxygen is combined with a hemoglobin in erythrocytes and carried to all parts of the body. Each lung is enveloped in a double-folded membrane called the pleura. The outer layer of the pleura, nearest the ribs, is the parietal pleura, and the inner layer, closest to the lung, is the visceral pleura. The pleura is moistened with a serous secretion that facilitates the movements of the lungs within the thorax.The two lungs are not quite mirror images of each other. The right lung, which is the slightly larger of the two, is divided into three lobes, or divisions, and the left lung is divided into two lobes. It is possible for one lobe of the lung to be removed without damage to the rest, which can continue to function normally; The uppermost part of the lung is called the apex, and the lower area is the base. The hilum of the lung is the midline region where blood vessels, nerves, and bronchialtubes enter and exit the organ.The lungs extend from the collarbone to the diaphragm in the thoracic cavity. The diaphragm is a muscular partition that separates the thoracic from the abdominal cavity and aids in the process of breathing. The diaphragm contracts and descends with each inhalation (inspiration) .The downward movement of the diaphragm enlarges the area in the thoracic cavity and reduces the internal air pressure, so that air flows into the lungs to equalize the pressure. When the lungs are full, the diaphragm relaxes and elevates, making the area in the thoracic cavity smaller, and thus increasing the air pressure in the thorax. Air then is expelled out of the lungs to equalize the pressure; this is called exhalation (expiration) . Other parts are also involved in the process. The cycle of respiration really begins when the phrenic nerve stimulates the diaphragm to contract and flatten. Also, the intercostal muscles between the ribs aid in inspiration by pulling the ribs up and out. The measure of how easily the lungs expand under pressure is compliance.Breathing is regulated unconsciously by center in the brainstem. These centers adjust the rate and rhythm of breathing according to changes in the composition of the blood, especially the concentration of carbon dioxide.Gas Transport.Oxygen is carried in the blood bound to hemoglobin in red blood cells. The oxygen is released to the cells as needed. Carbon dioxide is carried in several ways, but is mostly converted to an acid called carbonic acid. The amount of carbon dioxide that is exhaled is important in regulating the acidity or alkalinity of the blood. If too much carbon dioxide is exhaled by hyperventilation, body fluids tend to become more alkaline, a condition termed alkalosis. If too little carbon dioxide is exhaled as a result of hypoventilation, body fluids tend to become more acid, a condition termed acidosis.The cleaning system of the lungs has four main components. Lining the trachea and bronchial tree are cells that secrete mucus, which traps pollutants and bacteria. Also in the bronchi are cells containing tiny cilia, that project into the blanket of mucus and with constant wavelike motions push the mucus up out of the airways. Irritating chemicals, stagnant and excessive mucus, and large bitsof foreign matter are forcibly ejected as sputum from the bronchi by a cough. This third important cleaning device —— like breathing, under partial voluntary control —— is a rapid muscle contraction and bronchial-tube constriction that generates a wind force far stronger than a tornado. Small harmful substances that make their way into the alveoli are destroyed by the fourth line of defense, the macrophages. These are patrolling cells that "swallow up" foreign particles or destroy them with enzymes.New Words and PhrasesExercisesA. Discuss the following topics:1. Imagine you were lecturing in front of rural health workers on the topic ofrespiratory system, draw a picture to illustrate the whole system.2. Describe their structures and functions.3. How can epiglottis prevent the passing food and drink into the respiratory system?4. What role does the diaphragm play in the process of breathing?5. What are the four components of the cleaning system? How do they function?B. Fill in the blanks with the words given below and change their forms if necessary.alveolus capillary diaphragmhemoglobinthoraciccavitygas exchangeparietalpleuravisceralpleuramediastinumpleural spaceThe lungs are two cone-shaped, spongy organs consisting of alveoli, blood vessels, elastic tissue and nerves. Each of the two lungs consists of smaller divisions called lobes; the left lung hastwo lobes, while the right lung is divided into three lobes. In the lungs, ( 1 ) are surrounded by a network of tiny blood vessels called capillaries; oxygen from the lungs passes into these ( 2 ) for distribution to tissue cells, while carbon dioxide from the blood passes into the lungs to be expelled by exhalation. Once absorbed into blood cells, oxygen becomes attached to ( 3 ) and is released to tissue cells as needed. Thus, the primary function of thelungs is to bring airinto close contact with blood, which allows ( 4 ) to occur.The lungs are surrounded by a membrane called the ( 5 ) . The space that the lungs occupy within the chest is called the ( 6 ) , which is lined by a membrane called the ( 7 ). The parietal and visceral pleurae lie very close to each other; the small space between theses membranes, called the ( 8 ) , is filled with a fluid that prevents friction when the two membranes slide against each other during respiration. In the central portion of the thoracic cavity (in the area between the lungs) is a space called the ( 9 ) , which contains the heart. A group of smooth muscles called the ( 10 ) separates the lower portion of the thoracic cavity from the abdomen.C. Match Column I with Column n.Column I Column IIbronchiole[ 1 ]any of the small subdivision of the bronchicompliance[ 2 ]the peak portion of the lungshypoventilation[ 3 ]a condition in which there is too much carbon dioxidein the bloodintercostal[ 4 ]between the ribsparanasal sinuses[ 5 ]air-conditioning cavities in the bones near the nose acidosis[ 6 ]a condition in which there is too much carbon dioxidein the bloodapex[ 7 ]weak , inadequate exchange of gaspharynx[ 8 ]rounded masses of lymph tissue in the oropharynx ( palatinemeans roof of the mouth) .alkalosis[ 9 ]in agreement withpalatine tonsils[ 10 ]throat; composed of the nasopharynx, oropharynx, andlaryngopharynx.D. Define the following terms of the respiratory system in line with the text youhave just, learned (making use of the vocabulary provided in the brackets if necessary), for exam- ple:Oxygenfood, metabolism) 1. mirror image as if, left side, vice versa)2. adenoids ynx)3. alveolus respiration)4. bronchus mediastinum)5. epiglottis larynx, prevent, trachea)6. hyperventilation(extreme, rapid,deep, result in, alkalosis)7. diaphragm (dome-shaped, muscle,move, increase, decrease, space,thoracic cavity)8. pharynx ( common, passageway,esophagus, food, air, larynx)racic cavity)coughing, clearing the throat, res-piratory tract)E. Translate the following into English.1.副鼻窦2.口咽3.脊椎动物4.肺泡5.二氧化碳6.肺换气不足7.横膈膜神经8.双重折叠的9.威慑物10.润滑液11.滞痰12.食管13.纵隔14.哺乳动物15.碱中毒16.迷宫17.污染物质18.脑干19.上皮；上皮细胞20.刺激物Passage Two Respiratory Disorders and DiseasesIn this passage you will learn:● Various disorders and diseases of the respiratory system● Their definitions, causes and treatment●Detailed description of the signs and symptoms of chronic obstructive pulmonary disease● Medical terms pertaining to the diseases of the respiratory system● The respiratory system is subject to a wide variety of disorders and diseases. The most frequent attacks come from common cold and flu viruses. Other diseases that affect the lungs include bacterial infections such as pneumonia and tuberculosis. The lungs are especially vulnerable to allergic dis- eases such as asthma. There are more serious diseases such as respiratory distress syndrome, em-physema, chronic obstructive pulmonary diseases (COPD), lung cancer, etc.Influenza and pneumonia.Influenza is a viral disease of the respiratory tract. Different strains of the influenza virus have caused serious epidemics through history. Pneumonia is caused by several different microorganisms. The name represents any inflammation of the lungs caused by in-fection, so an alternate term for pneumonia is pneumonitis. Streptococcal pneumonia usually in- volves one or more lobes of the lung and described as lobar pneumonia.Other agents of pneumonialocalize in the bronchial tubes, causing bronchopneumonia.Pleurisy is severe chest pain accompanying each deep breath in a person with an inflamed pleura, the twin membranes around each lung and lining the chest cavity. Pleurisy can attend pneu-monia or result from direct infection of the pleura.Tuberculosis (TB)has increased in recent years along with the rise of AIDS and the appear-ance of resistance to antibiotics in the organism that causes the disease. The name of the disease comes from the small lesions, or tubercles, that appear with the infection. The symptoms of TB in-clude fever, weight loss, weakness, cough, and as a result of damage to blood vessels in the lungs, hemoptysis, i. e. the coughing up of phlegm (sputum) containing blood. Accumulation of exudatein the alveoli may result in solidification or consolidation of lung tissue. The tuberculin test is used to reveal tuberculosis infection, PPD (purified protein derivative) is the form of tuberculin commonly used.Asthma. Attacks of asthma result from narrowing of the bronchial tubes. The constriction, a-long with edema, swelling of the bronchial linings, and accumulation of mucus results in wheezing, extreme dyspnea and cyanosis. Although the cause of asthma is uncertain, foreign particles such as pollen or certain environmental pollutants are believed to be the culprits, which stimulate the smooth muscle of the bronchial tree to releases histamine causing the muscle to contract. The bronchial air- ways are consequently restricted. Treatment of asthma includes removal of allergens, administration of bronchodilators to widen the airways, and administration of steroids.Respiratory distress syndrome is a disorder of some prematurely bom infants. The alveoli of afflicted babies are lined with a protein material, limiting the amount of oxygen their blood can re-ceive. The disease is often fatal. Mechanical ventilators can be used to help infants breathe until their lungs become more mature. As a result of some accidents anddiseases, such as polio, the res-piratory center or nerves carrying its impulses may be paralyzed. Treatment may involve cutting a hole through the windpipe and passing a tube attached to a mechanical respirator through the hole. In other cases, the patient may be placed on a heart and lung machine that maintains respiration and heartbeat.Acute pulmonary edema results when fluid quickly accumulates in the lungs and fills the alveoli. The fluid buildup is caused by heart trouble that, in turn, produces back pressure in the pulmonary veins and the left atrium of the heart to which they carry oxygen-rich blood from the lungs. A person suffering acute pulmonary edema is suddenly breathless and turns blue because of oxygen-poor blood. The condition is treated with oxygen, digitalis to strengthen heart action, and diuretics to speed fluid removal by the kidneys.Pneumothorax occurs when air gets into the chest between the pleural lining. The lung then cannot fully expand and breathing becomes difficult. As a result, the lung may even collapse. Pneumothorax may result from a wound in the chest, such as a knife wound, or after a sudden tear in the lung. Infection of the pleural space by gas-producing microbes can also cause pneumothorax. Physicians treat pneumothorax by removing the gas by suction, surgically repairing the chest or lung, or prescribing antibiotics when an infection is present.Pneumoconiosis (black lung) means "dust disease." It can strike miners and industrial work-ers who inhale damaging amounts of dust over a long period of time. One of the most serious is sili-cosis, which results from inhaling quartz dust. Another, anthracosilicosis, arises from inhalation of coal and quartz dust. Pneumoconiosis often occurs in combination with other diseases, such as bron-chitis , emphysema, or tuberculosis. There is no treatment for it, but the disease can be prevented by minimizing dust inhalation.Emphysema.This is a chronic disease associated with overexpansion and destruction of the alveoli. Common causes are exposure to cigarette smoke and other forms of pollution, as well as chronic infection. Emphysema is the main disorder included under the heading of chronic obstructive pulmonary disease (COPD), which will be discussed in detail soon.Chronic obstructive pulmonary disease (COPD) is a rather broad term used to describe sim-ple chronic bronchitis, chronic obstructive bronchitis, asthmatic bronchitis and emphysema, for it is convenient to describe various combinations of these disorders that may coexist, for instance, pa-tients often have chronic obstructive bronchitis as well as emphysema.Unfortunately, chronic bronchitis has been used variably to refer to a simple smoker's cough or, as in the British literature, to severe COPD. In this discussion, chronic bronchitis will be con-sidered "simple," "obstructive," or "asthmatic" to reduce ambiguity. It is useful clinically to dif-ferentiate between the extremely common simple chronic bronchitis and the less common but often devastating form of chronic obstructive bronchitis.Simple chronic bronchitis, a syndrome characterized primarily by a chronic productive cough, is the result of low-grade exposure to bronchial irritants in an individual without hyperreac-tive airways. This syndrome is associated with enhanced mucous secretion, reduced ciliary activity, and impaired resistance to bronchial infection. Simple chronic bronchitis is defined in clinical terms: (1) excessive production of mucus; (2) presence of symptoms, largely cough, on most days for at least three months annually during two or more successive years; (3) exclusion of bronchiecta-sis, tuberculosis, or other causes of these symptoms. The term does not describe the underlying pro-cess , which may vary widely. The patient population ranges from those who are asymptomatic except for a morning "cigarette cough" productive of mucus in small amounts (simple chronic bronchitis) to patients with a severe disabling condition manifested by increased resistance to airflow, hypoxia, and often hypercatnia (chronic obstructive bronchitis) .Chronic obstructive bronchitis,which develops in a relatively small proportion of individuals with simple chronic bronchitis, results in irreversible narrowing of airways. Because the obstruction is in bronchioles and bronchi 2 mm or less in diameter, the term small airways disease has been used.Brochospasm. Exposure to bronchial irritants in individuals with hyperreactive or "twitchy"airways can lead to bronchospasm (i.e. , bronchial smooth muscle constriction), frequently accom-panied by excessive mucous production and edema of bronchial walls. Recurrent episodes of symp-tomatic bronchospasm are called asthma. The present discussion must consider bronchospasm, since a degree of reversible airways obstruction often accompanies other reactions to inhaled noxious a-gents. In fact, episodic airways obstruction is common in individuals with chronic bronchitis. This combination, called asthmatic bronchitis, may closely resemble classic asthma. The term chronic asthmatic bron'chitis is applied in patients with persistent airways obstruction, a chronic productive cough, and a major problem of episodic bronchospasm.Emphysema, another lung response to noxious stimuli, is characterized by abnormal, perma-nent enlargement of airspaces distal to the terminal bronchioles, accompanied by destruction of their walls, and without obvious fibrosis. The alterations of emphysema cause reduction in lung elastic re-coil, which permits excessive airway collapse upon expiration and leads to irreversible airflow ob-struction .These definitions are not mutually exclusive; there is considerable crossover between the em-physematous (type A) and bronchial (type B) signs and symptoms. For example, most individuals with emphysema also have a chronic productive cough. It may be difficult to determine the relative importance of emphysema and chronic obstructive bronchitis, with obliteration of small airways. Ac-cordingly, a general term such as chronic obstructive pulmonary disease (COPD)has been used to describe this clinical syndrome.New Words and Phrases（注：可编辑下载，若有不当之处，请指正，谢谢!）请预览后下载！。
