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Chapter 13 The Respiratory Systemright0The trillions of cells in the body require an abundant and continuous supply of oxygen to carry out their vital functions. We cannot "do without oxygen" for even a little while, as we can without food or water. Furthermore, as cells use oxygen, they give off carbon dioxide, a waste product the body must get rid of.The cardiovascular and respiratory systems share responsibility for supplying the body with oxygen and disposing of carbon dioxide. The respiratory system organs oversee the gas exchanges that occur between the blood and the external environment. The transportation of respiratory gases between the lungs and the tissue cells is accomplished by the cardiovascular system organs, using blood as the transporting fluid. If either system fails, body cells begin to die from oxygen starvation and accumulation of carbon dioxide.Functional Anatomy of the Respiratory System Name the organs forming the respiratory passageway from the nasal cavity to the alveoli of the lungs (or identify them on a diagram or model) and describe the function of each. Nose – air enters the nose by passing through the external nares , nostril, into the nasal cavity, which is divided by a midline nasal septum Olfactory receptors are located in the mucosa in the slit-like superior part of the nasal cavityRespiratory mucosa rests on a rich network of thin-walled veins that warms the air as it flows pastMucosa glands moisten the air and traps incoming bacteria and other foreign debrisCiliated cells of the nasal mucosa create a gentle current that moves contaminated mucus posteriorly toward the throat where it is swallowed and digested Conchae – mucosa-covered projections or lobes that greatly increase the surface area of the mucosa exposed to the air Pharynx – muscular passageway (throat) that serves as a common passageway for food and air – is continuous with the nasal cavity anteriorly via the internal nares Air enters the superior portion, the nasopharynx from the nasal cavity and then descends through the oropharynx and laryngopharynx to enter the larynx below Food enters the mouth and then travels along with air through the oropharynx and the laryngopharynx but is directed into the esophagus instead of entering the larynx Tonsils – small masses of lymphatic tissue that ring the pharynx, where they are found in the mucosa – function is to trap and remove any bacteria or other foreign pathogens entering the throatLarynx – voice box – routes air and food into the proper channels and plays a role in speechThyroid cartilage – protrudes anteriorly and is commonly called the Adam’s apple – the largest of the hyaline cartilages and is shield-shapedEpiglottis – protects the superior opening of the larynx – when we swallow food or fluids, the larynx is pulled upward and the epiglottis tips, forming a lid over the opening of the larynx routing the food into the esophagusIf anything other than air enters the larynx, a cough reflex is triggered to expel the substance Trachea – windpipe – lined with ciliated mucosa with cilia that beat continuously and in a direction opposite to that of the incoming air to propel mucus, loaded with dust particles and other debris, away from the lungs to the throat, where it can be swallowed or spat outPrimary bronchi – right and left formed by the division of the trachea – the right is wider, shorter, and straighter leaving foreign objects more likely to become lodged hereBy the time incoming air reaches the bronchi, it is warm, cleansed of most impurities, and well humidified Smaller subdivisions of the primary bronchi within the lungs are direct routes to the air sacsLungs – contain the alveoli, air sacs, where gas exchange occurs Describe several protective mechanisms of the respiratory system. See items above and below dealing with cilia, mucus, macrophages, coughing reflex, lymphatic tissue, and alveolar poresDescribe the structure and function of the lungs and the pleural coverings. A paired set that occupies the entire thoracic cavity except for the most central area, the mediastinum, which houses the heart, the great blood vessels, bronchi, esophagus, and other organsThe narrow superior portion of each lung, the apex, is located just deep to the clavicleThe broad lung area resting on the diaphragm is the baseEach lung is divided into lobes by fissures, the left lung has two lobes while the right lung has threeThe surface of each lung is covered with a visceral serosa called the pulmonary, or visceral, pleura and the walls of the thoracic cavity are lined by the parietal pleuraPleural membranes produce pleural fluid, a slippery serous secretion which allows the lungs to glide easily over the thorax wall during breathing movements and causes the two pleural layers to cling together The lungs are held tightly to the thorax wall, and the pleural space is more of a potential space than an actual one After the primary bronchi enter the lungs, they subdivide into smaller and smaller branches, finally ending in the smallest of the conducting passageways, the bronchioles resulting in a respiratory tree with all but the smallest branches having reinforcing cartilage in their wallsTerminal bronchioles lead into respiratory zone structures, even smaller conduits that eventually terminate in alveoli, or air sacs – the respiratory zone (respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli) is the only site of gas exchange while all other respiratory passages are conducting zone structures that serve as conduits to and from the respiratory zone The clusters of alveoli make up the bulk of the lungs leaving most of the lungs as air space and the rest of the tissue as stroma, an elastic connective tissueThe walls of the alveoli are a single, thin layer of squamous epithelial cells with alveolar pores connecting neighboring air sacs providing alternate route for air to reach alveoli whose feeder bronchioles have been clogged by mucus or are blocked The external surfaces of the alveoli are covered with a cobweb of pulmonary capillaries and together, the alveolar and capillary walls and their fused basement membranes construct the respiratory membrane (air-blood barrier), which has air flowing past on one side and blood flowing past on the other with gas exchange occurring by simple diffusionMacrophages wander in and out of the alveoli picking up bacteria, carbon particles, and other debrisChunky cuboidal cells present in amongst the epithelial cells produce a lipid molecule called surfactant, which coats the gas-exposed alveolar surfaces and lowers the surface tension of the film of water lining each alveolar sac so that the alveoli do not collapse between each breathRespiratory Physiology Define cellular respiration, external respiration, internal respiration, pulmonary ventilation, expiration, and inspiration.The major function of the respiratory system is to supply the body with oxygen and to dispose of carbon dioxide in a process that has four steps collectively termed respiration Pulmonary ventilation – breathing – air moving into and out of the lungs so gases in the air sacs of the lungs are continuously changed and refreshedExternal respiration – gas exchange between the pulmonary blood and alveoli Respiratory gas transport – gases must be transported to and from the lungs and tissue cells of the body via the bloodstreamInternal respiration – at the capillary level, gas exchange must be made between the blood and tissue cells – the use of oxygen and production of carbon dioxide by tissue cells is called cellular respiration Explain how the respiratory muscles cause volume changes that lead to air flow into and out of the lungs (breathing). Breathing is a mechanical process that depends on volume changes occurring in the thoracic cavityVolume changes lead to pressure changes, which lead to the flow of gasses to equalize the pressureOccurs in two phases – inspiration and expirationInspiration – the diaphragm and external intercostals contract and the size of the thoracic cavity increasesAs the diaphragm contract, it moves inferiorly and flattens out The superior-inferior dimension of the thoracic cavity increasesContraction of the external intercostals lifts the rib cage and thrusts the sternum forward, which increases the anteroposterior and lateral dimensions of the thoraxAs intrapulmonary volume increases, the gases within the lungs spread out to fill the larger spaceThe decrease in the gas pressure in the lungs produces a partial vacuum, which sucks air into the lungs and air continues to move into the lungs until the intrapulmonary pressure equals atmospheric pressureExpiration – largely a passive process that depends on the natural elasticity of the lungs instead of on muscle contraction As the inspriatory muscles relax and resume their initial resting length, the rib cage descends and the lungs recoilBoth the thoracic and intrapulmonary volumes decreaseAs the intrapulmonary volume decreases, the gases inside the lungs are forced more closely together and the intrapulmonary pressure rises to a point higher than atmospheric pressureThis causes the gases to flow out to equalize the pressure inside and outside the lungsUnder normal conditions, expiration is effortless, but if the respiratory passageways are narrowed by spasms of the bronchioles or clogged with mucus or fluid, expiration becomes an active process - forced expiration – the internal intercostal muscles are activated to help depress the rib cage, and the abdominal muscles contract and help force air from the lungs by squeezing the abdominal organs upward against the diaphragm The normal pressure within the pleural space (intrapleural pressure) is always negative, and this is the major factor preventing collapse of the lungsDefine the following respiratory volumes: tidal volume, vital capacity, expiratory reserve volume, inspiratory reserve volume, and residual air. Tidal volume – respiratory capacity – the amount of air inhaled or exhaled with a normal breathVital capacity – the sum of the TV + IRV + ERV – the volume of air that can be expelled from the lungs by forcible expiration after the deepest inspiration, total exchangeable air Expiratory reserve volume – the amount of air that can be forcibly exhaled after a tidal expiration Inspiratory reserve volume – the amount of air that can be taken in forcibly over the tidal volumeResidual air – the air that still remains in the lungs that cannot be voluntarily expelled – important because it allows gas exchange to go on continuously even between breaths and helps to keep the alveoli open/inflated Name several nonrespiratory air movements and explain how they modify or differ from normal respiratory air movements. Coughs – act to clear the lower respiratory passageways – clear the air passages of debris or collected mucus – clears the lower respiratory passageways Sneezes – similar to cough, except that expelled air is directed through the nasal cavities – clear the air passages of debris or collected mucus – clears the upper respiratory passagesCrying and laughing – inspiration followed by release of air in a number of short breaths – primarily an emotional induced mechanismHiccups – sudden inspirations resulting from spasms of diaphragm initiated by irritation of the diaphragm or phrenic nerves, which serve the diaphragm Yawn – very deep inspiration, taken with jaws wide open – ventilates all alveoli – not necessarily triggered by the need to increase the amount of oxygen in blood Describe the process of gas exchanges in the lungs and tissues. All gas exchanges are made according to the laws of diffusion, that is, the movement occurs toward the area of lower concentration of the diffusing substanceIn external respiration the blood picks up oxygen from the lungs while dropping off carbon dioxide to be exhaled At the systemic circulation level, oxygen is taken up by cells for use while carbon dioxide is released from the cells into the blood Describe how oxygen and carbon dioxide are transported in the blood. Oxygen is transported in the blood in two waysMost is attached to hemoglobin molecules inside the RBCs to form oxyhemoglobin – HbO2A small amount of oxygen is carried dissolved in the plasma Carbon dioxide is transported in two ways Within the plasma as the bicarbonate ion (HCO3-), which plays a very important role in the blood buffer systemBefore carbon dioxide can diffuse out of the blood into the alveoli, it first must be released from its bicarbonate ion form by combining with hydrogen ions (H+) to form carbonic acid (H2CO3), which quickly splits to form water and carbon dioxide allowing the carbon dioxide to diffuse from the blood and enter the alveoliA smaller amount is carried inside the RBCs bound to hemoglobinName the brain areas involved in control of respiration. The activity of the respiratory muscles, the diaphragm and external intercostals, is regulated by nerve impulses transmitted to them from the brain by the phrenic and intercostal nervesThe neural centers that control respiratory rhythm and depth are located in the medulla and ponsThe medulla, which sets the basic rhythm of breathing, contains a self-exciting inspiratory center, as well as other respiratory centers The pons centers appear to smooth out the basic rhythm of inspiration and expiration set by the medulla The communication between the pons and medulla centers maintains the normal respiratory rate called eupneaThe bronchioles and alveoli have stretch receptors that respond to over-inflation through impulses sent from the stretch receptors to the medulla by the vagus nerves to end inspiration and begin expirationDuring exercise, breathing becomes more vigorous and deep because the brain centers send more impulses to the respiratory muscles resulting in a respiratory pattern called hyperpnea Name several physical factors that influence respiratory rate. Physical factors – talking, coughing, exercise, and increased body temperature can increase the rate of breathingVolition (conscious control) – singing, swallowing, breath control such as holding our breath Emotional factors – being scared, gasping result from reflexes initiated by emotional stimuli acting through centers in the hypothalamus Chemical factors – levels of carbon dioxide and decreased blood pH lead to an increase in the rate and depth of breathing by acting directly on the medulla centers while levels of oxygen in the blood is detected by chemoreceptor regions in the aorta and carotid artery that send impulses to the medulla when blood oxygen levels are droppingExplain the relative importance of oxygen and carbon dioxide in modifying the rate and depth of breathing. The concentration of carbon dioxide in the blood is the more important stimulus for breathing in a healthy person while decreasing oxygen levels only becomes important when they are dangerously lowIn people with emphysema and chronic bronchitis, increased levels of carbon dioxide are no longer recognized as important by the brain and dropping oxygen levels become the respiratory stimulus, which is why these people are only given low levels of oxygen, otherwise they would stop breathing Explain why it is not possible to stop breathing voluntarily. The will to hold your breath can be overridden by respiratory centers when oxygen supplies are low or blood pH is falling – involuntary controls take over and normal respiration will begin againDefine apnea, dyspnea, hyperventilation, hypoventilation, and chronic obstructive pulmonary disease (COPD).Apnea – cessation of breathing often caused by hyperventilation, which is often brought on by anxiety attacksDyspnea – difficult or labored breathing, often referred to as “air hunger” Hyperventilation – when breathing becomes more deep and more rapid and is separate from hyperpnea of exercise – blows off more carbon dioxide and decreases the amount of carbonic acid, which returns blood pH to the normal range Hypoventilation – extremely slow or shallow breathing that allows carbon dioxide levels to increase in the blood and bring blood pH back to normal when it becomes too alkaline, or basic Chronic obstructive pulmonary disease (COPD) – the chronic obstructive pulmonary disease exemplified by chronic bronchitis and emphysema, Respiratory Disorders Describe the symptoms and probable causes of COPD and lung cancer. COPD patients Have four things in commonHistory of smoking – or exposure to air pollutionDyspnea, which becomes progressively more severeCoughing and frequent pulmonary infectionsHypoxia – retention of carbon dioxide and respiratory acidosisSmoking or exposure to air pollution can lead to continual bronchial irritation and inflammation, which leads to chronic bronchitis with excessive mucus production, coughing, and bronchospasms and/or it can lead to the breakdown of elastin in connective tissue of lungs, which leads to emphysema and the destruction of alveolar walls, lung fibrosis, and air trappingBoth can lead to airway obstruction or air trapping, dyspnea, and frequent infectionsUltimately lead to respiratory failure Lung cancer Typically caused by smokingWhich increases the heart rate, constricts peripheral blood vessels throughout the body, disrupts the flow of air in the lungs, and affects the brain and mood and ultimately to atherosclerosis and heart disease, strokes, cataracts, and early onset of osteoporosisWhich causes continuous irritation in the lungs causing an increase in mucus production but slowed cilia movements so mucus and irritants cannot be cleared from the lungs and decreases the activity of lung macrophagesWhich can cause the pooling of mucus in the lower respiratory tree and increased frequency of pulmonary infections including pneumonia and COPDUltimately, it is the irritating effects of the cocktail of free radicals and other carcinogens in tobacco smoke that leads to lung cancerEspecially nitrosamine and the tars in tobacco that contain carcinogens that cause the epithelial cells lining the bronchial tree to proliferate wildly and lose their normal structureThree main types of lung cancerSquamous cell carcinoma AdenocarcinomaSmall cell carcinoma Developmental Aspects of the Respiratory System Describe normal changes that occur in respiratory system functioning from infancy to old age. In the fetus, the lungs are filled with fluid and all respiratory exchanges are made by the placentaAt birth, the fluid-filled pathway is drained, and the respiratory passageways fill with air and the alveoli inflate and begin to function in gas exchange with lung inflation completed by two weeks of ageThe presence of surfactant, a fatty molecule made by the cuboidal alveolar cells that lowers the surface tension of the film of water lining each alveolar sac so that the alveoli do not collapse between each breath is only present in large enough amounts late in pregnancy – between 28 and 30 weeks The respiratory rate is highest in newborns and it continues to drop throughout life until old age when it can increase againThe lungs continue to mature throughout childhood and more alveoli are formed until young adulthood ................
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