Term
| Describe the structure and functions of the conducting and respiratory zones of the lungs: |
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Definition
| The region of the lungs where gas exchange with the blood occurs is known as the respiratory zone; includes the respiratory bronchioles and the terminal alveolar sacs. The trachea, bronchi and bronchioles that deliver air to the respiratory zone constitute the conducting zone. |
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Term
| Describe the location and significance of the pleural membranes: |
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Definition
| The structures of the thoracic cavity are covered in thin, wet pleurae. The lungs are covered by a visceral pleura that is normally flush against the the parietal pleura that lines the chest wall. The potential space between the visceral and parietal pleurae is called the intrapleural space. |
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Term
| Explain How intrapleural and intrapulmonary pressures change during breathing: |
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Definition
| The intrapleural pressure is always less than the intrapulmonary pressure. The intrapulmonary pressure is subatmospheric during inspiration and greater than the atmospheric pressure during expiration. Pressure changes in the lungs are produced by variations in lung volume in accordance with the inverse relationship between the volume and pressure of gas described in Boyle's law. |
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Term
| Explain how lung compliance, elascticity and surface tension affect breathing: |
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Definition
| The compliance of the lungs, or the ease with which they expand, refers specifically to the change in lung volume per change in transpulmonary pressure (the difference between intrapulmonary and intrapleural pressure). The elasticity of the lungs refers to their tendency to recoil after distension. The surface tension of the fluid in the alveoli exerts a force directed inward, which acts to resist distension. |
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Term
| Explain the significance of pulmonary surfactant: |
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Definition
| It would be seen that the surface tension in the alveoli would create a pressure that would cause small alveoli to collapse and empty their air into larger alveoli. This would occur because the pressure caused by a given amount of surface tension would be greater in smaller alveoli than in larger alveoli, as described in the law of Laplace. Surface tension does not normally cause the collapse of alveoli, however, because pulmonary surfactant (a combination of phospholipid and protein) lowers the surface tension sufficiently. |
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Term
| Explain how inspiration and expiration are accomplished: |
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Definition
| By contraction and relaxation of striated muscles. During quiet inspiration, the diaphragm and external intercostals contract, and thus increase the volume of the thorax. During quiet expiration, these muscles relax, and the elastic recoil of the lungs and thorax causes a decrease in thoracic volume. Forced inspiration and expiration are aided by contraction of the accessory respiratory muscles. |
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Term
| Describe lung volumes and capacities: |
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Definition
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Term
| Explain how pulmonary function tests relate to pulmonary disorders: |
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Definition
| Spirometry aids the diagnosis of a number of pulmonary disorders. In restrictive disease, such as pulmonary fibrosis, the vital capacity measurement is decreased to below normal. In obstructive disease, such as asthma and bronchitis, the forced expiratory volume is reduced to below normal because of increased airway resistance to airflow. |
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Term
| explain how partial gas pressures are calcvulated: |
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Definition
| According to Dalton's law, the total pressure of a gas mixture is equal to to the sum of the pressures that each gas in the mixture would exert independently. the partial pressure of a gas in a dry gas mixture is thus equal to the total pressure times the percent composition of that gas in the mixture. Because the total pressure of a gas mixture decreases with altitude above sea level, the partial pressures of the constituent gases likewise decrease with altitude. When the partial pressure of a gas in a wet gas mixture is calculated, the water vapor pressure must be taken into account. |
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Term
| Explain the signficance of partial gas measurements of arterial blood gases: |
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Definition
| According to Henry's law, the amount of a gas that can be dissolved in a fluid is directly proportional to the partial pressure of that gas in contact with the fluid. The concentrations of O2 and CO2 that are dissolved in plasma are proportional to an electric current generated by special electrodes that react with these gases, measuring the O2 and CO2 content of the blood. The PO2 and PCO2 measurements of arterial blood provide information about lung function. |
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Term
| Describe the factors that influence the partial pressure of blood gases and the total content of O2 in the blood: |
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Definition
| Normal arterial blood has a PO2 of 100 mmHg, indicating a concentration of dissolved O2 of .3ml per 100 ml blood; the O2 contained in RBCs (about 19.7 ml per 100 ml of blood) does not affect the PO2 measurement . In addition to proper ventiolation of the lungs, blood flow (perfusion) in the lungs must be adequate and matched to air flow (ventilation) in order foradequate gas exchange to occur. Abnormally high partial pressures of gases in blood can cause a variety of disorders, including O2 toxicity, nitrogen narcosis and decompression sickness. |
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Term
| Explain how ventilation is regulated by the CNS: |
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Definition
| The rythmicicity center of the medulla oblongata directly controls the muscles of respiration. Activity of the inspitratory muscles and expiratory neurons varies in a reciprocal way to produce an automatic breathing cycle. Activity in the medulla is influenced by the apneustic and pneumotaxic centers in the pons, as well as by sensory feedback information. Concious breathing involves direct control by the cerebral cortex via corticospinal tracts. Breathing is affected by chemoreceptors sensitive to the PCO2, pH and PO2 of the blood. The PCO2 of blood and consequent changes in pH are usually of greater importance than the blood PO2 in the regulation of breathing. Central chemoreceptors in the medulla oblongata are sensitive to changes in blood PCO2 because of the resultant changes in the pH of cerebrospinal fluid. The peripheral chemoreceptors in the aortic and carotid bodies are sensitive to changes in blood PCO2 indirectly, because of consequent changes in blood pH. |
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Term
| Explain how blood gases and pH influence ventilation: |
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Definition
| Decreases in blood PO2 directly stimulate breathing only when the blood PO2 is lower than 50mmHg. A drop in PO2 also stimulates breathing indirectly, by making the chemoreceptors more sensitive to changes in PCO2 and pH. At tidal volumes of 1L or more inspiration is inhibited by stretch receptors in the lungs (the Herin-Breuer reflex). a similar reflex may act to inhibit expiration. |
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Term
| Describe the changes in percent hemoglobin as a function of arterial PO2 and explain how this relates to oxygen transport: |
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Definition
| Deoxyhemopglobin combines with oxygen in the lungs (the loading reaction) and breaks its bonds with oxygen in the tissue capillaries (the unloading reaction). The extent of each reaction is determined by the PO2 and the affinity of hemoglobin for oxygen. High PO2 drives the equation to the right (favors the loading reaction); at the high PO of the pulmonary capillaries almost all deoxyhemoglobin combine with with oxygen. Low PO2 in the systemic capillaries drives the reaction in the opposite direction to promote unloading. The affinity between hemoglobin and oxygen influences the loading and unloading reactions; a strong bond would favor loading but inhibit unloading, a weak bond would hinder loading but improve unloading. |
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Term
| Describe various conditions that influence the oxyhemoglobin dissociation curve and oxygen transport: |
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Definition
| pH and temperature of the blood influence the affinity of hemoglobin for oxygen, and thus the extent of loading and unloading. A fall in pH decreases the affinity of hemoglobin for oxygen and a rise in pH increases the affinity. This is called the Bohr effect. A rise in temperature decreases the affinity of hemoglobin for oxygen. When the affinity is decreased, the oxyhemoglobin curve is shifted to the right. This indicates a greater unloading percentage of oxygen to the tissues. The affinity of hemoglobin for oxygen is also decreased by the organic molecule in the RBCs called 2,3 DPG. Oxyhemoglobin inhibits 2,3 DPG production, so 2,3 DPG concentrations will be higher in anemia, or when low PO2 decreases oxyhemoglobin. |
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Term
| Explain how CO2 is transorted by the blood: |
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Definition
| RBCs contain an enzyme called carbonic anhydrase that catalyzes the reversicle reaction whereby CO2 and H2O are used to form carbonic acid. This reaction is favored by the high PCO2 in the tissue capillaries, and as a result, CO2 produced by the tissues is converted into carbonic acid in the RBCs. Carbonic acid then ionizes to form H+ and HCO3- (bicarbonate). Because much of the H+ is buffered by hemoglobin, but more bicarbonate is free to diffuse outward, an electrical gradient is established that draws Cl- into the RBCs. This is called the chloride shift. A reverse chloride shift occurs in the lungs. In this process, the low PCO2 favors conversion of carbonic acid to carbon dfioxide, which can be exhaled. So, in summary, O2 is transported by the blood as 1) bicarbonate ion (described) 2) dissolved CO2, and 3) carbaminohemoglobin. |
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Term
| Explain the relationship between blood levels of CO2 and blood pH: |
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Definition
| By adjusting the blood concentration of CO2, and thus carbonic acid, the process of ventilation helps to maintain proper acid-base balance of the blood. Normal arterial blood pH is 7.4. A pH below 7.35 is termed acidosis, pH above 7.45 is termed alkalosis. Hyperventilation causes respiratory alkalosis, and hypoventilation causes respiratory acidosis. Metabolic acidiosis stimulates hyperventilation, which can cause a respiratory alkalosis as a partial compensation. |
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Term
| Describe the acid-base balance of the blood, and how it is influenced by the respiratory system: |
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Definition
| Carbonic is formed from CO2 and contributes to blood pH. It is a volatile acid because it can be eliminated in exhaled breath. Nonvolatile acids, such as lactic acid and ketone bodies are buffered by bicarbonate. Blood pH is maintained by a proper ratio of CO2 to bicarbonate. Lungs maintain the correct CO2 concentration. An increase in CO2 due to inadequate ventilation produces respiratory acidosis. Kidneys maintain the free-bicarbonate concentration. Abnormally low plasma bicarbonate concentration produces metabolic acidosis. Ventilation regulates the respiratory component of acid-base balance. Hypoventilation increases the blood PCO2, thereby lowering plasma pH and producing respiratory acidosis. Hyperventilation decreases plasma PCO2, decreasing formation of carbonic acid and thereby increasing plasma pH to produce respiratory alkalosis. Because of the action of chemoreceptors, breathing is regulated to maintain a proper blood PCO2 and thus a normal pH. |
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Term
| Describe the changes in the respiratory system that occur in response to exercise training: |
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Definition
| During exercise, there is increased ventilation, or hyperpnea, which is matched to the increased metabolic rate so that arterial blood PCO2 remains normal. This hyperpnea may be caused by proprioceptor information, cerebral input, and/or changes in arterial PCO2 and pH. During heavy excercise, the anaerobic threshold may be reached at 50-70% of the maximal O2 uptake. At this point, lactic acid is released into the blood by muscles. Endurance training enables the muscles to utilize the O2 more effectively, so that greater levels of exercise can be performed before the anaerobic threshold is reached. |
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Term
| Describe changes in the respiratory system that occur in response to high altitude: |
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Definition
| Acclimatization to a high altitude involves changes that help to deliver O2 more effectively to the tissues, despite reduced arterial PO2. Hyperventilation occurs in response to the low PO2. The RBCs produce more 2,3 DPG, which lowers the affinity of hemoglobin for O2 and improves the unloading reaction. The kidneys produce the hormone erythropoietin which stimulates the bone marrow to increase its production of RBCs, so that more oxygen can be carried by the blood at given values of PO2. |
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