chapter 10 Flashcards

Question

Define vital capacity

Answer 1

The maximal volume that you can exhale after a maximal inhalation is called your vital capacity. Your vital capacity is about 4,800 ml, almost 10 times your normal tidal volume at rest. The amount of additional air that can be inhaled beyond the tidal volume (about 3,100 ml) is called the inspiratory reserve volume, and the amount of the air that we can forcibly exhale beyond the tidal volume (about 1,200 ml) is the expiratory reserve volume. No matter how forcefully you exhale, some air always remains in your lungs. This is your residual volume, approximately 1,200 ml

Answer 2

Residual volume (RV) is the volume of air remaining in the lungs after maximum forceful expiration. In other words, it is the volume of air that cannot be expelled, thus causing the alveoli to remain open at all times. The residual volume remains unchanged regardless of the lung volume at which expiration was started

Answer 3

On average, only about 350 ml of each normal breath actually reach the alveoli and become involved in gas exchange. The other 150 ml remain in the airways, and because that amount does not participate in gas exchange, the air is referred to as dead space volume. Dead space volume is not measured by a spirometer.

Answer 4

Earth is surrounded by an atmosphere of gases. Like liquids, gases have mass and are attracted to the earth by gravity. Though it doesn’t really feel like we are pressed down by a heavy weight of gases, in fact, the atmosphere (air) exerts a total atmospheric pressure at sea level of about 760 mm Hg (millimeters of mercury). A normal atmospheric pressure of 760 mm Hg means that the pressure of the atmosphere will cause a column of mercury in a vacuum to rise 760 mm, or about 2.5 feet. The pressure seems like zero to us because the pressure inside our lungs is the same as atmospheric pressure, at least when we are resting between breaths. The primary gases of Earth’s atmosphere are nitrogen (78%) and oxygen (21%), with a trace amount of carbon dioxide (about 0.04%) and less than 1% of all other gases combined. In a mixture of gases, each gas exerts a partial pressure that is proportional to its percentage of the total gas composition. Partial pressure is represented by P and, like atmospheric pressure, it is measured in mm Hg. The pressure of the atmosphere is thus the sum of the partialBecause partial pressures in a mixture of gases are directly proportional to concentrations, a gas will always diffuse down its partial pressure gradient, from a region of higher partial pressure to a region of lower partial pressure. As we shall see, the exchanges of O2 and CO2, both between the alveoli and the blood and between the blood and the tissues, are purely passive. No consumption of ATP is involved; changes in partial pressures are entirely responsible for the exchange and transport of these gases.

Answer 5

Our discussion of external and internal respiration brings us to an important aspect of the overall subject of gas exchange, and that is how the respiratory gases (O2 and CO2) are transported between the lungs and tissues in the blood. The mechanisms of transport of oxygen and carbon dioxide are somewhat different; we’ll start with the transport of oxygen. Oxygen is transported in blood in two ways: either bound to hemoglobin (Hb) in red blood cells or dissolved in blood plasma (Figure 10.12a). The presence of hemoglobin is absolutely essential for the adequate transport of O2 because O2 is not very soluble in water. Only about 2% of all O2 is dissolved in the watery component of blood known as blood plasma. Most of it—98%—is taken out of the watery component by virtue of its binding to hemoglobin molecules. Without hemoglobin, the tissues would not be able to receive enough oxygen to sustain life. As described in the chapter on blood, hemoglobin is a large protein molecule consisting of four polypeptide chains, each of which is associated with an iron-containing heme group that can bind oxygen. Because there are four heme groups, each hemoglobin molecule can bind four oxygen molecules at a time, forming oxyhemoglobin (HbO2). We can represent this reaction as: Hb + O2 → HbO2 hemoglobin oxygen oxyhemoglobin This reaction is reversible and highly dependent on the partial pressures of O2 in plasma. When the PO2 rises (in the lungs), oxygen attaches to hemoglobin and is transported in arterial blood. When the PO2 falls (at the tissues), oxygen detaches from hemoglobin. Several other factors affect O2 attachment to hemoglobin as well. Hemoglobin binds O2 most efficiently in conditions of fairly neutral pH and relatively cool temperatures—similar to conditions existing in the lungs. Body regions with warmer temperatures and lowered pH— such as in body tissues—reduce hemoglobin’s affinity for binding O2. Consequently, O2 and hemoglobin tend to combine in the lungs, facilitating the transport of oxygen to the tissues, and to detach in body tissues, making O2 available to cells. Hemoglobin’s affinity for oxygen is also greatly reduced by carbon monoxide, a colorless, odorless, highly poisonous gas

Answer 6

Cellular metabolism in body tissues continuously produces carbon dioxide as a waste product. One of the most important functions of blood (other than the transport of oxygen) is to transport CO2 away from tissues and back to the lungs, where it can be removed from the body. Because the partial pressure of CO2 is higher in the tissues than it is in blood, CO2 readily diffuses from tissues into the bloodstream. Once in the blood, CO2 is transported in three ways: dissolved in blood plasma, bound to hemoglobin, or in the form of bicarbonate (Figure 10.12b). Only about 10% of the CO2 remains dissolved in blood plasma. Another 20% binds with hemoglobin to form carbaminohemoglobin (HbCO2). This reaction is represented as: Hb + CO2 S HbCO2 hemoglobin carbon carbaminohemoglobin dioxide Hemoglobin can transport O2 and CO2 molecules simultaneously because the two gases attach to different sites on the hemoglobin molecule: O2 combines with heme, CO2 with globin About 70% of all the CO2 produced by the tissues is converted to bicarbonate (HCO3 −) prior to transport. When bicarbonate is produced, CO2 combines with water (H2O) to become carbonic acid (H2CO3). This first reaction is catalyzed by an enzyme called carbonic anhydrase. The carbonic acid immediately breaks apart into bicarbonate and hydrogen (H) ions, as follows: CO2 + H2O S H2CO3 S HCO3 - + H+ carbon water carbonic bicarbonate hydrogen dioxide acid The formation of bicarbonate from CO2 occurs primarily inside red blood cells because this is where the carbonic anhydrase enzyme is located. However, most of the bicarbonate quickly diffuses out of red blood cells and is transported back to the lungs dissolved in plasma. Some of the hydrogen ions formed along with bicarbonate stay inside the red blood cells and bind to hemoglobin. Their attachment to hemoglobin weakens the attachment between hemoglobin and oxygen molecules and causes hemoglobin to release more O2. This is the chemistry behind the previously mentioned effect of pH on oxygen binding. The overall effect is that the presence of CO2 (an indication that cellular metabolism has taken place) actually enhances the delivery of O2 to the very sites where it is most likely to be needed. At the lungs, dissolved CO2 diffuses out of the blood and into the alveolar air. The loss of CO2 from the blood plasma causes the PCO2 to fall, which in turn causes the chemical reaction that formed bicarbonate in the first place to reverse, as follows: HCO3 - + H+ S H2CO3 S CO2 + H2O bicarbonate hydrogen carbonic carbon water acid dioxide Thus, as CO2 is removed by breathing, the bicarbonate and hydrogen ions formed in the peripheral tissues to transport CO2 are removed as well.

Answer 7

The basic cyclic pattern of inspiration and expiration and the rate at which we breathe are established in an area near the base of the brain called the medulla oblongata. Within this area, called the respiratory center (Figure 10.13a), groups of nerve cells automatically generate a cyclic pattern of electrical impulses every 4–5 seconds. The impulses travel along nerves to the diaphragm and the intercostal muscles and stimulate those muscles to contract. As these respiratory muscles contract, the rib cage expands, the diaphragm is pulled downward, and we inhale. As inhalation proceeds, the respiratory center receives sensory input from stretch receptors in the lungs. These receptors monitor the degree of inflation of the lungs and serve to limit inhalation and initiate exhalation. When nerve impulses from the respiratory center to the muscles end, the respiratory muscles relax, the rib cage returns to its original size, the diaphragm moves upward again, and we exhale. Any disorder that interferes with the transmission of these nerve impulses can affect breathing. Consider amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig’s disease, for the famous baseball player who succumbed to it). In ALS, the nerves to skeletal muscle become damaged and no longer conduct impulses properly. Over time, the skeletal muscles, including the diaphragm and intercostal muscles, weaken and waste away from lack of use. Most ALS patients die within five years of initial diagnosis. Although ALS is not a respiratory condition per se, the immediate cause of death is usually respiratory failure.

Answer 8

The body modifies, or regulates, the rate and depth of the breathing pattern to maintain homeostasis. Under normal circumstances, the regulation of breathing centers on maintaining homeostasis of CO2, H+, and O2, with the main emphasis on CO2. The sensory mechanisms for detecting changes in CO2 levels are actually indirect. Rather than detecting changes in CO2 levels, certain cells in the medulla oblongata near the respiratory center (Figure 10.13b) detect changes in the H+ concentration of the cerebrospinal fluid (the interstitial fluid around the cells in the brain). This is pertinent to control of CO2 because, as you may recall, a rise in CO2 concentration is accompanied by a rise in the hydrogen ion concentration according to the following reaction: CO2 + H2O S H2CO3 S HCO3 - + H+ Thus, when the PCO2 of arterial blood rises, the concentration of H+ in cerebrospinal fluid also rises. Receptor cells detecting an elevated H+ concentration transmit signals to the respiratory center, causing it to increase the rate of the cyclic pattern of impulses and the number of impulses per cycle. As a result, we breathe more frequently and more deeply, exhaling more CO2 and lowering blood levels of the gas back to normal. Our normal arterial PCO2 is maintained at about 40 mm Hg because the normal regulation of respiration keeps it there. Any rise above 40 mm Hg stimulates breathing, and any fall below 40 mm Hg inhibits it. Certain other receptor cells respond to blood PO2 rather than PCO2. These receptors are located in small structures associated with the carotid arteries (the large arteries to the head) and the aorta, called the carotid and aortic bodies (Figure 10.13c). Normally, PO2 in arterial blood is about 100 mm Hg. If PO2 drops below about 80 mm Hg, these receptors signal the respiratory center to increase the rate and depth of respiration in order to raise blood O2 levels back toward normal. The carotid and aortic bodies also can be stimulated by an increase in the blood concentrations of H+ and CO2 if they are great enough. Note that the receptors for O2 in the carotid and aortic bodies become activated only when arterial PO2 falls by at least 20%. In contrast, even a 2–3% change in PCO2 stimulates respiration. Under normal circumstances, then, respiration is controlled entirely by receptors that respond to CO2, rather than O2. In other words, the rate and depth of normal breathing is set by the need to get rid of CO2, not to obtain O2.It just so happens that the regulation of CO2 also keeps O2 within the normal range. There are circumstances, however, when the O2 receptors do come into play. These include certain disease states, drug overdoses, and breathing at high altitudes where the partial pressure of O2 is much lower than normal.

Answer 9

It increases it

Answer 10

Asthma is a condition characterized by spasmodic contraction of bronchial muscle, bronchial swelling, and increased production of mucus. An asthma attack causes partial closure of the bronchi, making breathing difficult. It is a recurrent, chronic lung disorder that affects 17 million people in North America. Its incidence is on the rise both in the United States and around the world. Symptoms of an asthma attack include coughing while exercising, shortness of breath, wheezing, and a sense of tightness in the chest. People with asthma often wheeze when they exhale. The symptoms can be triggered by any number of causes, including viruses, air particles, allergies (such as allergies to pollen, house dust, and animal fur), exercise (especially in cold temperatures), tobacco smoke, and air pollution. The symptoms may come and go. Most asthma attacks are caused by a hyperactive immune system. When a person with asthma breathes in allergens such as pollen or tobacco smoke, the body reacts with excessive production of immunoglobulin E. The IgE stimulates mast cells in the lungs to release chemical weapons such as histamine, leading to excessive inflammation and constriction of bronchiolar smooth muscle. Drugs are available to dilate the bronchi (bronchodilators), reduce the inflammation (corticosteroids), and restore normal breathing. Treatments also focus on preventing attacks by isolating the cause and avoiding it when possible

Answer 11

Emphysema is a chronic disorder in which the alveoli become permanently damaged. It begins with destruction of connective tissue in the smaller airways. As a result, the airways become less elastic, do not stay open properly, and tend to collapse during expiration. The high pressures in the lungs caused by the inability to exhale naturally through the collapsed airways eventually damage the fragile alveoli. The result is a permanent reduction in the surface area available for diffusion, and eventually breathlessness and reduced capacity to exchange gases across the lung. At least one form of emphysema is inherited, but most cases are associated with smoking or long-term exposure to air pollutants. The difference between asthma and emphysema is that asthma is an episodic, recurrent condition of increased airway resistance that largely goes away between episodes, whereas emphysema involves permanent damage to airways that eventually destroys alveoli.

Answer 12

Bronchitis refers to inflammation of the bronchi, resulting in a persistent cough that produces large quantities of phlegm. Bronchitis may be acute (comes on suddenly and clears up within a couple of weeks) or chronic (persists over a long period and recurs over several years). Both forms are more common in smokers and in people who live in highly polluted areas. Symptoms include wheezing, breathlessness, and a persistent cough that yields yellowish or greenish phlegm. Sometimes there is fever and a feeling of discomfort behind the sternum. Acute bronchitis can be treated by humidifying the lungs (using a home humidifier or inhaling steam), drinking plenty of fluids, and taking antibiotics if the infection is caused by bacteria. People with chronic bronchitis may need further testing to rule out other health conditions. Bronchodilators can widen the bronchi; oxygen may be prescribed to raise blood oxygen levels. Emphysema and chronic bronchitis are both characterized by poor airflow and difficulty breathing. Hence both conditions are generally referred to by the more general term, chronic obstructive pulmonary disease (COPD).

Answer 13

Cystic fibrosis is an inherited condition in which a single defective gene causes the mucus-producing cells in the lungs to produce a thick, sticky mucus. The disease affects other organ systems as well. In the lungs, the abnormally thick mucus impedes air flow and also provides a site for the growth of bacteria. People with cystic fibrosis tend to get frequent infections of the airways. Treatment of the disease includes consistent physical therapy to try to dislodge the mucus and keep the airways open. Several promising new drugs are now on the market for this disease. For more on cystic fibrosis, see the Health & Wellness feature in the chapter on genetics and inheritance.

Answer 14

Colds and the flu are common respiratory diseases; nearly everyone has had them at some time in their life. Both are caused by viruses. Colds (sometimes called an upper respiratory infection or URI) are generally caused by viruses of the rhinovirus or coronavirus families; both are highly contagious but not very virulent. The primary symptoms are coughing, runny nose, nasal congestion, and sneezing. The flu is caused by viruses of the influenza family, and although the symptoms are generally more severe, the flu is also not very virulent. Symptoms of the flu include sore throat, fever, and a cough, sometimes accompanied by aches and chills, muscle pains, and headache. The flu and a cold are easily mistaken for each other, except that colds are generally not accompanied by a fever. In any case, it hardly matters because there is no medical treatment for either of them. Rest and plenty of fluids are the best prescription. Only rarely, colds or the flu lead to inflammation of the lungs and pneumonia, accompanied by a bacterial infection that requires antibiotics (see the next section) Colds and the flu can be caught over and over again throughout a person’s lifetime. The reason is that these viral infections evolve rapidly, so that each year, they are just a little bit different from the previous year so are not recognized by the immune system.

Answer 15

Pneumonia is an inflammatory condition of the lungs. It is usually caused by a viral or bacterial infection. In pneumonia, the alveoli secrete excess fluid, impairing the exchange of oxygen and carbon dioxide. Symptoms typically include fever, chills, shortness of breath, and a cough that produces yellowish-green phlegm and sometimes blood. Some people experience chest pain when breathing due to inflammation of the membranes that line the chest cavity and cover the lungs. In North America, pneumonia ranks among the top 10 causes of death, primarily because it is a frequent complication of many serious illnesses. Treatment depends on the microorganism involved; if it is bacterial, antibiotics may be effective. In severe cases, oxygen therapy and artificial ventilation may be necessary. However, most people who develop pneumonia recover completely within a few weeks.

Answer 16

Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis. People pass the infection in airborne droplets by coughing or sneezing. The bacteria enter the lungs and multiply to form an infected “focus.” In most cases, the immune system fights off the infection, although it may leave a scar on the lungs. In perhaps 5% of cases, however, the infection spreads via lymphatic vessels to the lymph nodes and may enter the bloodstream. Sometimes the bacteria become dormant for many years, then reactivate later to cause more lung damage. Major symptoms include coughing (sometimes bringing up blood), chest pain, shortness of breath, fever, night sweats, loss of appetite, and weight loss. A chest X-ray usually reveals lung damage, such as cavities in the lungs or old infections that have healed, leaving scarred lung tissue. A skin test called the tuberculin test can indicate whether someone has been exposed to the infection. A century ago, tuberculosis was a major cause of death worldwide. With the development of antibiotics the incidence of tuberculosis declined precipitously, and most patients in industrialized countries now recover fully. The disease remains a major health problem in undeveloped nations, however, and recently the incidence of tuberculosis has increased in industrialized countries as well. Many authorities attribute this increased prevalence to immigration of people from developing nations. Worldwide, the increased prevalence of AIDS may also be a factor. Furthermore, some strains of tuberculosis are becoming resistant to antibiotics.

Answer 17

Botulism is a form of poisoning caused by a bacterium, Clostridium botulinum, occasionally found in improperly cooked or preserved foods. The bacterium produces a powerful toxin that blocks the transmission of nerve signals to skeletal muscles, including the diaphragm and intercostal muscles. Symptoms of botulism poisoning usually appear 8 to 36 hours after eating the contaminated food. They can include difficulty swallowing and speaking, double vision, nausea, and vomiting. If not treated, botulism can be fatal because it paralyzes the respiratory muscles.

Answer 18

A pneumothorax is collapse of one or more lobes of the lungs. The most common cause is a penetrating wound of the chest that allows air into the pleural cavity around the lungs, but it can also occur spontaneously as the result of disease or injury to a lung. Pneumothorax can be a lifethreatening event, because the inability to inflate the lung results in reduced exchange of oxygen and carbon dioxide. Treatment requires repairing the damage to the chest wall or lung and removing the air from the pleural cavity. Atelectasis refers to a lack of gas exchange within the lung as a result of alveolar collapse or a buildup of fluid within alveoli. In either case, there is no exchange of gases between the atmosphere and the blood in regions affected. Atelectasis is sometimes a complication of surgery, but it can also occur when the amount of surfactant is deficient. Treatment involves finding and reversing the underlying cause. Post-surgical patients in general are encouraged to take deep breaths, cough, and get up and start walking as soon as possible to avoid atelectasis. Sometimes positive pressure ventilation helps to force alveoli open again.

Answer 19

In the chapter on the heart, we discussed congestive heart failure as a cardiovascular condition in which the heart gradually becomes less efficient. Even though it starts as a heart disorder, heart failure eventually causes a severe impairment of lung function as well. Recall that in congestive heart failure, the heart begins to fail as a pump. When the left side of the heart fails, blood backs up in the pulmonary blood vessels behind that side of the heart. The result is a rise in blood pressure in the pulmonary vessels. When pulmonary capillary pressure increases, the balance of physical pressure and osmotic forces across the capillary wall favors fluid loss from the capillary. As a result, fluid builds up in the interstitial spaces between capillaries and alveoli and sometimes within alveoli themselves. This increases the diffusional distance and reduces diffusion of gases. Treatments focus on reducing this fluid buildup by helping the body get rid of fluid and improving the heart’s pumping action.

chapter 10 Flashcards

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