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This chapter discusses the physiology of the respiratory system, including the function of the lungs and the process of gas exchange. It also covers various lung diseases such as COPD, chronic bronchitis, asthma, emphysema, cystic fibrosis, pneumonia, tuberculosis, and pulmonary edema. These diseases can be caused by factors like smoking, pollution, allergens, and infections, and they can lead to difficulty breathing, mucus buildup, and damage to the lungs. Treatment options include antibiotics, antiviral medications, and specialized antibiotics for tuberculosis. Chapter 8, Respiratory System Physiology. This chapter is all about the physiology of the respiratory system. The main organ involved in the respiratory system is the lung. There are two lungs, one on each side of the body. The two lungs have a couple of lobes. The right lung has three lobes and the left lung has two lobes. This is because part of the lung space is taken up by the heart on the left side of the body. The major function of the lungs is to exchange oxygen and carbon dioxide in the alveoli of the lungs. In this chapter, the function of the lungs will be discussed, as well as some diseases of the lungs that can adversely affect the way the lungs work. Basic Lung Physiology The lung has two separate zones. There is the respiratory zone, which consists of the respiratory bronchioles, the alveolar ducts, and the alveoli, or air sacs. The conducting zone consists of the bronchioles, bronchi, and trachea, which have the responsibility of bringing air into and out of the lungs. The alveoli of the lungs have an extremely large cross-sectional area so that there can be a rapid and efficient exchange of oxygen with carbon dioxide. The bronchioles of the lungs consist of cartilage and smooth muscle. These are smaller airways that have multiple branches. In fact, the bronchiole tree branches 23 times, from the trachea to the tiniest of bronchioles. The bronchioles secrete mucus and have cilia lining them. Large particles in the air are stopped by the hair and mucus in the nose, while the cilia in the bronchioles catch the smallest particles. Gas exchange in the lungs has four different components. There is ventilation, which is the movement of air into and out of the lungs. There is perfusion, which is the movement and distribution of blood through the lungs' circulation. There is diffusion, which is the movement of the two primary gases across the alveolar capillary membrane. Finally, there is control of breathing, which regulates the exchange of gas to meet an individual's immediate metabolic demands. The respiratory system has non-respiratory functions as well as respiratory functions. The lungs provide a route for water loss and heat elimination in the body. The upper airway warms and wets the air so the tiny alveoli don't dry out during gas exchange. The respiratory pump increases venous return to the heart. The lungs help normalize blood pH by changing the amount of carbon dioxide exhaled. The respiratory system also aids in speech formation and helps defend the body against any inhaled foreign matter. The nose provides a person with a sense of smell and the airway collectively removes or deactivates foreign material that is passing through the lung circulation. There are 300 million alveoli in the lungs. Each alveolus is 0.3 millimeters in diameter. The total surface area of the lungs is about 75 square meters or the size of a tennis court. The pressure between the alveoli is known as the intrapulmonary pressure. It opens to the air and is the same as the atmospheric pressure. The intrapleural pressure is the pressure between the lungs and the thoracic wall. It is about 700 millimeters mercury. The atmospheric pressure is about 760 millimeters mercury and this is equivalent to the pressure in the air spaces of the lungs. The difference between the atmospheric pressure and the intrapleural pressure is what allows for inspiration and expiration. There are two forces that keep the lungs close to the thoracic wall. These include the intrapleural fluid's cohesiveness that allows the lungs to slide against the thoracic wall and the transmural pressure gradient which allows for the exchange of gases in the alveoli. The pleural space has a slightly negative pressure because the lungs are pulling in and the chest is pulling out. There is no extra fluid to fill the space between the lungs and the chest wall. If a person develops a pneumothorax, there is air entering the pleural cavity and the pressure becomes equal to the atmospheric pressure. This causes the lungs to collapse and the thoracic wall to spring out. The major muscles of inspiration are the diaphragm and the intercostal muscles. As they contract, the thoracic cavity gets larger. The diaphragm is innervated by the phrenic nerve. It is responsible for 75% of the enlargement of the thoracic cavity during the act of inspiration. The rest of expansion happens when the intercostal muscles contract. As the lungs begin to expand, the pressure inside the lungs decreases resulting in an influx of air. The intrapleural pressure drops as well so the lungs can completely expand. It is the muscle contraction and pressure difference that causes air to move into the lungs and not the expansion of the lungs themselves. If the lungs need to expand fully, the accessory muscles are used as well as the diaphragm. When inspiration ceases, the muscles relax, the ribcage falls, and the volume of the lungs decreases. This increases the pressure in the airways of the lungs and the air flows out of the lungs. If a person is breathing quietly, the act of expiration is passive and is due to the elastic recoil of the lungs without an expenditure of muscle activity. Inspiration on the other hand is always an active activity. During heavy breathing, expiration is active and is secondary to contraction of the abdominal muscles that increase the intra-abdominal pressure so that the diaphragm is pushed upward. The intrathoracic pressure is increased and the internal intercostal muscles activate emptying the lungs out more forcefully. When expiration is forceful, the intrathoracic pressure is greater than the atmospheric pressure, but the lungs don't collapse because the pressure in the alveoli increases as well. Lung Diseases There are several diseases of the lungs that can be caused by hereditary factors or environmental factors. The greatest environmental factor affecting lung diseases is tobacco use. Tobacco users often suffer from lung diseases. The risk of lung diseases increases the longer a person smokes. This section talks about various lung diseases. One disease is known as chronic obstructive pulmonary disease or COPD. It is caused almost exclusively by tobacco smoking. There is narrowing of the lower passageways of the lungs and breakdown of the alveoli so that there are large alveolar blebs that inefficiently transfer gases in the lungs. Expiration is more difficult than inspiration so there are expiratory sounds during the expiratory phase. The lungs cannot be completely emptied in this disease and the individual is barrel-chested. Chronic bronchitis is another lung disease that is almost always caused by cigarette smoking, although it can be caused by pollution or allergens in the air. The lining of the airways thickens, making it more difficult for air to pass through. There is an increase in mucus production and the cilia lining the lungs are immobilized. The increased mucus production leads to an increase in bacterial infections because the mucus is a good place for bacteria to reside. Asthma is a lung disease that can affect individuals of just about any age. Children can be afflicted with this disease as much as adults. There is thickening of the walls of the bronchial tree secondary to inflammation and histamine induced edema of the respiratory tract. The airways become plugged by extremely thick mucus. The airways become hyper-responsive to allergens and other triggers. There can be spasms of the airway secondary to environmental triggers, such as infections, irritants, and allergens. Asthma is extremely common and is considered the most common chronic childhood disease. Allergies can trigger an exacerbation of asthma, as can other environmental triggers. Emphysema is a lung disease primarily caused by smoking. In emphysema, there is a collapse of the smaller airways and irreversible breakdown of the alveoli. The breakdown of alveoli can happen because of excessive release of trypsin from alveolar macrophages trying to defend the lungs against cigarette smoke and other irritants. The lungs are usually protected by alpha-1 antitrypsin, but can be overwhelmed in emphysema. In some cases, a person can have a genetic inability to make alpha-1 antitrypsin and can have hereditarily induced emphysema at a young age. Cystic fibrosis is a hereditary lung condition that results in poor clearance of mucus from the bronchial tree. The excess mucus builds up and provides a medium for repeated lung infections. There is a single defective gene involved in cystic fibrosis, which is inherited in an autosomal recessive manner. The repeated lung infections result in extensive damage to the lungs. The mucus also prevents the release of digestive enzymes that allow the body to digest nutrients. Many of these patients die from respiratory failure because their lungs become too damaged. Pneumonia is an environmentally caused lung disease that affects the alveoli and parenchyma of the lungs. It is caused by bacteria that invade the lung tissue and set up an infection. Viruses can also cause pneumonia. The infection affects older individuals, but can infect children and infants as well. The major treatment for the disorder is antibiotics. Viral illnesses of the lungs are treated with rest and fluids, although antiviral treatment is available as well. Tuberculosis is a type of pneumonia caused by the bacterium Mycobacterium tuberculosis. It is slowly progressing, but can be treated with specialized antibiotics directed at treating the infection. It affects people at any age and results in death unless treated. It is usually seen in developing countries, but can be seen in urban areas in the United States where there are a lot of immigrants who carry the infection with them from a developing country. Pulmonary edema results from excess fluid leaking out of the alveoli of the lung and entering the parenchyma of the lungs. It happens from heart failure, but can be caused by a heart attack, heart valve problems, and high blood pressure. The treatment is to draw fluid off the lungs using diuretics such as furosemide or Lasix. Lung cancer can happen at any age, but is more common in the elderly. It involves a genetic change in some of the cells of the body that go on to develop full blown cancer. Lung cancer is almost always a disease secondary to cancer, but it can be caused by other environmental problems such as asbestos exposure. There is no cure for lung cancer, but chemotherapy agents and surgery can be used to treat the illness. Acute respiratory distress syndrome, or ARDS, involves a sudden and severe injury to the lungs that is caused by a serious illness or injury to the lungs. Things like aspiration, inhalation of chemicals, lung transplants, pneumonia, septic shock, and trauma can also cause the disorder. The treatment is supportive, but the patient has a high chance of dying from the disease. Pneumoconiosis is a variety of lung conditions caused by the inhalation of substances that cause injury to the lungs. Asbestosis is a small needle-shaped substance that is mined from the ground. Black lung disease is caused by inhaled coal dust and is mainly seen in individuals who deal with coal substances. Interstitial lung diseases include a broad collection of lung disorders that affect the interstitium. This is the lining between the air sacs or alveoli in the lungs. Interstitial lung diseases include sarcoidosis, idiopathic pulmonary fibrosis, and autoimmune diseases. Pulmonary embolism, or PE, is a disease affecting the circulatory system of the lungs. A blood clot from a deep vein, usually in the calf, travels through the venous blood system and enters the pulmonary circulation. The blood oxygen level drops to extremely low levels, and death can result from hypoxia. Pulmonary hypertension involves various conditions that cause high blood pressure in the pulmonary arteries. This can lead to chest pain and shortness of breath. When no cause is identified, the patient is said to have idiopathic arterial hypertension. There are a lot of diseases that can cause this disease, including genetics, certain drugs, congenital heart disease, autoimmune diseases, left-sided heart failure, emphysema, pulmonary fibrosis, sleep apnea, high-altitude exposure, pulmonary emboli, blood disorders, metabolic disorders, and certain thoracic tumors. A pleural effusion is when fluid collects in the pleural space between the chest wall and the lungs. Pneumonia or heart failure can cause this condition. If there are large pleural effusions, the doctor must drain the lungs using a needle and an evacuation device. Mesothelioma is a rare cancer of the lungs in the pleura, the lining of the lungs, and the lining of the thoracic cavity. It is caused by asbestos exposure and can occur many decades after the exposure. It is not a common lung disease and is treated with surgery, chemotherapy, and radiation. Obesity can cause problems with breathing. It is a major cause of hypoventilation syndrome. The extra weight on the abdomen and chest makes it hard to expand the lungs. The individual cannot expand their lungs, so they underventilate, which causes shortness of breath with any exertion. Neuromuscular disorders can cause lung disease. Poor functioning of the nerves that control the muscles of breathing can cause respiratory failure from a lack of ability to breathe spontaneously. Examples of a neuromuscular disorder include amyotrophic lateral sclerosis or Lou Gehrig's disease and myasthenia gravis. Basic lung parameters. There are several lung parameters that you need to know about to understand the physiology of the lungs. This includes the tidal volume, which is the amount of air coming into or outside the lungs in a single breath. The inspiratory reserve volume is the extra air that can be breathed in using inspiratory muscles. The expiratory reserve amount is the extra air that a person breathes out using expiratory muscles and is higher than the tidal volume. The residual volume is the amount that can't be expired from the lungs. It is left over after a breath. The functional residual capacity is the volume of lungs after normal passive expiration. The vital capacity is the maximal volume change possible in the lungs with the greatest degree of inspiration. It is about 4,600 milliliters. The total lung capacity is 6,000 milliliters. The FEV1, or forced expiratory flow rate, is the amount of air that can be forced out of the lungs in one second. The peak expiratory flow rate, or PEFR, is the highest rate of flow achieved during expiration. Restrictive and obstructive lung disease. Restrictive and obstructive lung diseases are two different types of lung diseases that have the same symptoms, including shortness of breath during any type of exercise. Obstructive lung disease involves shortness of breath because the airways are so narrow that the air cannot escape from the lungs. At the end of a full exhalation, there is still a lot of air left inside the lungs. Types of obstructive lung diseases include chronic obstructive lung disease, cystic fibrosis, bronchiectasis, asthma, and chronic obstructive lung disease. Restrictive lung disease cannot fully bring air into the lungs. The lungs are restricted from being able to expand fully. Restrictive lung disease causes stiffness of the lung tissue. Symptoms like muscle weakness, chest wall stiffness, or damaged nerves can cause restriction of the lungs. Diseases that are classified as restrictive lung disease include interstitial lung disease, idiopathic pulmonary fibrosis, sarcoidosis, autoimmune diseases, obesity, scoliosis, muscular dystrophy, or amyotrophic lateral sclerosis. Key takeaways. The main organ of the respiratory system is the lungs. However, the nose, mouth, pharynx, trachea, and bronchi are considered parts of the respiratory system. Oxygen and carbon dioxide are exchanged in the alveoli of the lungs, which are small air sacs. There is a respiratory zone in the lungs and a conducting zone in the lungs. The main respiratory muscles are the diaphragm and the intercostal muscles. There are restrictive lung diseases and obstructive lung diseases. Lung diseases can involve the trachea, the bronchial tree, the alveoli, the lung parenchyma, or the lining of the lungs. Quiz. Number 1. Which of the following lung parts are considered part of the conducting zone? A. Trachea B. Alveoli C. Parenchyma D. Bronchioles Answer A. The trachea is part of the conducting zone of the lungs. The other answers are a part of the respiratory zone. Number 2. How do the lungs help control the pH of the bloodstream? A. By releasing factors that increase hemoglobin levels. B. By increasing the amount of oxygen in the bloodstream. C. By decreasing respirations so that more CO2 is in the bloodstream. D. By increasing respirations so more oxygen can be kept in the blood. Answer C. The lungs help control the pH of the lungs by underventilating so that more CO2 can enter the bloodstream. Number 3. What is the air pressure inside the trachea? A. Several millimeters mercury higher than the atmosphere to allow for exhalation. B. Several millimeters mercury lower than the atmosphere to allow for inhalation. C. The same as atmospheric pressure. D. Tobacco smoke. Answer D. The major cause of lung diseases is tobacco smoke. Number 6. Which lung disease is autosomal recessive and involves excessive mucus in the lungs? A. Cystic fibrosis. B. Amyotrophic lateral sclerosis. C. Pneumoconiosis. D. Pulmonary fibrosis. Answer A. Cystic fibrosis is an autosomal recessive lung disease that involves excessive mucus in the lungs. Number 7. Which lung disease is mainly associated with asbestos exposure? A. Lung cancer. B. Pneumonia. C. Pulmonary embolism. D. Mesothelioma. Answer D. Mesothelioma is almost exclusively secondary to asbestos exposure. Lung cancer can be caused by mesothelioma, but this is not the major cause of the disease. Number 8. Which of the following disorders is considered a restrictive lung disease? A. Asthma. B. Chronic obstructive lung disease. C. Pulmonary embolism. D. Obesity. Answer D. Obesity restricts lung motion, so it is considered a restrictive lung disease. Number 9. Which lung disease involves the circulation to the lungs? A. Chronic obstructive lung disease. B. Pulmonary embolism. C. Pneumoconiosis. D. Mesothelioma. Answer B. A pulmonary embolism involves a lack of circulation to the lungs so that air cannot be oxygenated. Number 10. Which lung disease is caused by cigarette smoking and involves excessive mucus in the lungs? A. Pneumoconiosis. B. Pulmonary hypertension. C. Chronic bronchitis. D. Pulmonary edema. Answer C. Chronic bronchitis is a disease that is caused by cigarette smoking and involves excessive mucus in the lungs.
