Physio free essay sample

Describe the gross structure of the lungs and pleurae. Mechanics of Breathing 7. Explain the functional importance of the partial vacuum that exists in the intrapleural space. 8. Relate Boyle’s law to the events of inspiration and expiration. 9. Explain the relative roles of the respiratory muscles and lung elasticity in producing the volume changes that cause air to flow into and out of the lungs. 10. List several physical factors that influence pulmonary ventilation. 11. Explain and compare the various lung volumes and capacities. 12. Define dead space. 13. Indicate types of information that can be gained from pulmonary function tests. Gas Exchanges Between the Blood, Lungs, and Tissues 14. State Dalton’s law of partial pressures and Henry’s law. 15. Describe how atmospheric and alveolar air differ in composition, and explain these differences. 16. Relate Dalton’s and Henry’s laws to events of external and internal respiration. Transport of Respiratory Gases by Blood 17. Describe how oxygen is transported in the blood, and explain how oxygen loading and unloading is affected by temperature, pH, BPG, and Pco2. 18. Describe carbon dioxide transport in the blood. Control of Respiration 19. Describe the neural controls of respiration. 20. Compare and contrast the influences of arterial pH, arterial partial pressures of oxygen and carbon dioxide, lung reflexes, volition, and emotions on respiratory rate and depth. Respiratory Adjustments 21. Compare and contrast the hyperpnea of exercise with hyperventilation. 22. Describe the process and effects of acclimatization to high altitude. Homeostatic Imbalances of the Respiratory System 23. Compare the causes and consequences of chronic bronchitis, emphysema, asthma, tuberculosis, and lung cancer. Developmental Aspects of the Respiratory System 24. Trace the embryonic development of the respiratory system. 25. Describe normal changes that occur in the respiratory system from infancy to old age. Lecture Outline I. Functional Anatomy of the Respiratory System (pp. 805–819; Figs. 22. 1–22. 11; Table 22. 1) A. The Nose and Paranasal Sinuses (pp. 806–809; Figs. 22. 1–22. 3) 1. The nose provides an airway for respiration; moistens, warms, filters, and cleans incoming air; provides a resonance chamber for speech; and houses olfactory receptors. 2. The nose is divided into the external nose, which is formed by hyaline cartilage and bones of the skull, and the nasal cavity, which is entirely within the skull. 3. The nasal cavity consists of two types of epithelium: olfactory mucosa and respiratory mucosa. 4. The nasal cavity is surrounded by paranasal sinuses within the frontal, maxillary, sphenoid, and ethmoid bones that serve to lighten the skull, warm and moisten air, and produce mucus. B. The Pharynx (p. 809; Fig. 22. 3) 1. The pharynx connects the nasal cavity and mouth superiorly to the larynx and esophagus inferiorly. a. The nasopharynx serves as only an air passageway, and contains the pharyngeal tonsil, which traps and destroys airborne pathogens. b. The oropharynx is an air and food passageway that extends inferiorly from the level of the soft palate to the epiglottis. c. The laryngopharynx is an air and food passageway that lies directly posterior to the epiglottis, extends to the larynx, and is continuous inferiorly with the esophagus. C. The Larynx (pp. 810–812; Figs. 22. 3–22. 5) 1. The larynx attaches superiorly to the hyoid bone, opening into the laryngopharynx, and attaches inferiorly to the trachea. 2. The larynx provides an open airway, routes food and air into the proper passageways, and produces sound through the vocal cords. 3. The larynx consists of hyaline cartilages: thyroid, cricoid, paired arytenoid, corniculate, and cuneiform; and the epiglottis, which is elastic cartilage. 4. Vocal ligaments form the core of mucosal folds, the true vocal cords, which vibrate as air passes over them to produce sound. 5. The vocal folds and the medial space between them are called the glottis. 6. Voice production involves the intermittent release of expired air and the opening and closing of the glottis. . Valsalva’s maneuver is a behavior in which the glottis closes to prevent exhalation and the abdominal muscles contract, causing intra-abdominal pressure to rise. D. The trachea, or windpipe, descends from the larynx through the neck into the mediastinum, where it terminates at the primary bronchi (pp. 812–813; Fig. 22. 6). E. The Bronchi and Subdivisions (pp. 813–815 ; Figs. 22. 7–22. 9) 1. The conducting zone consists of right and left primary bronchi that enter each lung and diverge into secondary bronchi that serve each lobe of the lungs. 2. Secondary bronchi branch into several orders of tertiary bronchi, which ultimately branch into bronchioles. 3. As the conducting airways become smaller, the supportive cartilage changes in character until it is no longer present in the bronchioles. 4. The respiratory zone begins as the terminal bronchioles feed into respiratory bronchioles that terminate in alveolar ducts within clusters of alveolar sacs, which consist of alveoli. a. The respiratory membrane consists of a single layer of squamous epithelium, type I cells, surrounded by a basal lamina. b. Interspersed among the type I cells are cuboidal type II cells that secrete surfactant. c. Alveoli are surrounded by elastic fibers, contain open alveolar pores, and have alveolar macrophages. F. The Lungs and Pleurae (pp. 815–819; Figs. 22. 10–22. 11) 1. The lungs occupy all of the thoracic cavity except for the mediastinum; each lung is suspended within its own pleural cavity and connected to the mediastinum by vascular and bronchial attachments called the lung root. 2. Each lobe contains a number of bronchopulmonary segments, each served by its own artery, vein, and tertiary bronchus. . Lung tissue consists largely of air spaces, with the balance of lung tissue, its stroma, comprised mostly of elastic connective tissue. 4. There are two circulations that serve the lungs: the pulmonary network carries systemic blood to the lungs for oxygenation, and the bronchial arteries provide systemic blood to the lung tissue. 5. The lungs are innervated by parasympathetic and sym pathetic motor fibers that constrict or dilate the airways, as well as visceral sensory fibers. 6. The pleurae form a thin, double-layered serosa. a. The parietal pleura covers the thoracic wall, superior face of the diaphragm, and continues around the heart between the lungs. b. The visceral pleura covers the external lung surface, following its contours and fissures. II. Mechanics of Breathing (pp. 819–826; Figs. 22. 12–22. 16; Tables 22. 2–22. 3) A. Pressure Relationships in the Thoracic Cavity (pp. 819–820; Fig. 22. 12) 1. Intrapulmonary pressure is the pressure in the alveoli, which rises and falls during respiration, but always eventually equalizes with atmospheric pressure. 2. Intrapleural pressure is the pressure in the pleural cavity. It also rises and falls during respiration, but is always about 4 mm Hg less than intrapulmonary pressure. B. Pulmonary Ventilation (pp. 820–822; Figs. 22. 13–22. 14) 1. Pulmonary ventilation is a mechanical process causing gas flow into and out of the lungs according to volume changes in the thoracic cavity. a. Boyle’s law states that at a constant temperature, the pressure of a gas varies inversely with its volume. 2. During quiet inspiration, the diaphragm and intercostals contract, resulting in an increase in thoracic volume, which causes intrapulmonary pressure to drop below atmospheric pressure, and air flows into the lungs. . During forced inspiration, accessory muscles of the neck and thorax contract, increasing thoracic volume beyond the increase in volume during quiet inspiration. 4. Quiet expiration is a passive process that relies mostly on elastic recoil of the lungs as the thoracic muscles relax. 5. Forced expiration is an active process relying on contraction of abdominal muscles to increase intra-abdominal pressure and depress the rib cage. C. Physical Factors Influencing Pulmonary Ventilation (pp. 822–824; Fig. 22. 15) 1. Airway resistance is the friction encountered by air in the airways; gas flow is reduced as airway resistance increases. . Alveolar surface tension due to water in the alveoli acts to draw the walls of the alveoli together, presenting a force that must be overcome in order to expand the lungs. 3. Lung compliance is determined by distensibility of lung tissue and the surrounding thoracic cage, and alveolar surface tension. D. Respiratory Volumes and Pulmonary Function Tests (pp. 824–826; Fig. 22. 16; Table 22. 2) 1. Respiratory volumes and specific combinations of volumes, called respiratory capacities, are used to gain information about a person’s respiratory status. a. Tidal volume is the amount of air that moves in and out of the lungs with each breath during quiet breathing. b. The inspiratory reserve volume is the amount of air that can be forcibly inspired beyond the tidal volume. c. The expiratory reserve volume is the amount of air that can be evacuated from the lungs after tidal expiration. d. Residual volume is the amount of air that remains in the lungs after maximal forced expiration. e. Inspiratory capacity is the sum of tidal volume and inspiratory reserve volume, and represents the total amount of air that can be inspired after a tidal expiration. . Functional residual capacity is the combined residual volume and expiratory reserve volume, and represents the amount of air that remains in the lungs after a tidal expiration. g. Vital capacity is the sum of tidal volume, inspiratory reserve, and expiratory reserve volumes, and is the total amount of exchangeable air. h. Total lung capacity is the sum of all lung volumes. 2. The anatomical dead space is the volume of the conducting zone conduits, which is a volume that never contributes to gas exchange in the lungs. 3. Pulmonary function tests evaluate losses in respiratory unction using a spirometer to distinguish between obstructive and restrictive pulmonary disorders. E. Nonrespiratory Air Movements (p. 826; Table 22. 3) 1. Nonrespiratory air movements cause movement of air into or out of the lungs, but are not related to breathing (coughing, sneezing, crying, laughing, hiccups, and yawning). III. Gas Exchanges Between the Blood, Lungs, and Tissues (pp. 827–830; Figs. 22. 17–22. 19; Table 22. 4) A. Gases have basic properties, as defined by Dalton’s law of partial pressures and Henry’s law (pp. 827–828; Table 22. 4). 1. Dalton’s law of partial pressures states that the total pressure exerted by a mixture of gases is the sum of the pressures exerted by each gas in the mixture. 2. Henry’s law states that when a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure. B. The composition of alveolar gas differs significantly from atmospheric gas, due to gas exchange occurring in the lungs, humidification of air by conducting passages, and mixing of alveolar gas that occurs with each breath (p. 828). C. External Respiration: Pulmonary Gas Exchange (pp. 28–830; Figs. 22. 17–22. 19) 1. External respiration involves O2 uptake and CO2 unloading from hemoglobin in red blood cells. a. A steep partial pressure gradient exists between blood in the pulmonary arteries and alveoli, and O2 diffuses rapidly from the alveoli into the blood, but carbon dioxide moves in the opposite direction along a partial pressure gradient th at is much less steep. b. The difference in the degree of the partial pressure gradients of oxygen and carbon dioxide reflects the fact that carbon dioxide is much more soluble than oxygen in the blood. . Ventilation-perfusion coupling ensures a close match between the amount of gas reaching the alveoli and the blood flow in the pulmonary capillaries. d. The respiratory membrane is normally very thin, and presents a huge surface area for efficient gas exchange. D. Internal Respiration (p. 830; Fig. 22. 17) 1. The diffusion gradients for oxygen and carbon dioxide are reversed from those for external respiration and pulmonary gas exchange. 2. The artial pressure of oxygen in the tissues is always lower than the blood, so oxygen diffuses readily into the tissues, while a similar but less dramatic gradient exists in the reverse direction for carbon dioxide. IV. Transport of Respiratory Gases by Blood (pp. 830–834; Figs. 22. 20–22. 22) A. Oxygen Transport (pp. 830–83 2; Figs. 22. 20–22. 21) 1. Because molecular oxygen is poorly soluble in the blood, only 1. 5% is dissolved in plasma, while the remaining 98. 5% must be carried on hemoglobin. a. Up to four oxygen molecules can be reversibly bound to a molecule of hemoglobin—one oxygen on each iron. . The affinity of hemoglobin for oxygen changes with each successive oxygen that is bound or released, making oxygen loading and unloading very efficient. 2. At higher plasma partial pressures of oxygen, hemoglobin unloads little oxygen, but if plasma partial pressure falls dramatically, such as during vigorous exercise, much more oxygen can be unloaded to the tissues. 3. Temperature, blood pH, Pco2, and the amount of BPG in the blood all influence hemoglobin saturation at a given partial pressure. B. Carbon Dioxide Transport (pp. 832–834; Fig. 22. 22) 1. Carbon dioxide is transported in the blood in three ways: 7–10% is dissolved in plasma, 20% is carried on hemoglobin bound to globins, and 70% exists as bicarbonate, an important buffer of blood pH. 2. The Haldane Effect encourages CO2 exchange in the lungs and tissues: When plasma partial pressure of oxygen and oxygen saturation of hemoglobin decrease, more CO2 can be carried in the blood. 3. The carbonic acid–bicarbonate buffer system of the blood is formed when CO2 combines with water and dissociates, producing carbonic acid and bicarbonate ions that can release or absorb hydrogen ions. V. Control of Respiration (pp. 834–839; Figs. 22. 23–22. 26) A. Neural Mechanisms (pp. 834–836; Fig. 22. 23) 1. Two areas of the medulla oblongata are critically important to respiration: the dorsal respiratory group near the root of cranial nerve IX, and the ventral respiratory group extending from the spinal cord to the pons/medulla junction. 2. The ventral respiratory group is a rhythm-generating and integration center containing separate groups of neurons, some that fire during inhalation and others that fire during exhalation. a. The inspiratory neurons, via phrenic and intercostal nerves, stimulate contraction of the diaphragm and intercostal muscles. b. When the expiratory neurons fire, output to the respiratory muscles stops, muscles relax, and lungs recoil. 3. The cyclic behavior of inspiratory and expiratory neurons produces a breathing rate of 12–15 breaths per minute, which is called eupnea. 4. The pontine respiratory group within the pons modifies the breathing rhythm and prevents overinflation of the lungs through an inhibitory action on the medullary respiration centers. . It is likely that reciprocal inhibition on the part of the different respiratory centers is responsible for the rhythm of breathing. B. Factors Influencing Breathing Rate and Depth (pp. 836–839; Figs. 22. 24–22. 26) 1. The most important factors influencing breathing rate and depth are changing levels of CO2, O2, and H+ in arterial blood. a. The receptors monitoring fluctuations in these parameters are the cen tral chemoreceptors in the medulla oblongata, and the peripheral chemoreceptors in the aortic arch and carotid arteries. b. Increases in arterial Pco2 cause CO2 levels to rise in the cerebrospinal fluid, resulting in stimulation of the central chemoreceptors, and ultimately leading to an increase in rate and depth of breathing. c. Substantial drops in arterial Po2 are required to cause changes in respiration rate and depth, due to the large reserves of O2 carried on the hemoglobin. d. As H+ accumulates in the plasma, rate and depth of breathing increase in an attempt to eliminate carbonic acid from the blood through the loss of CO2 in the lungs. 2. Higher brain centers alter rate and depth of respiration. a. The limbic system, strong emotions, and pain activate the hypothalamus, which modifies respiratory rate and depth. b. The cerebral cortex can exert voluntary control over respiration by bypassing medullary centers and directly stimulating the respiratory muscles. 3. Pulmonary irritant reflexes respond to inhaled irritants in the nasal passages or trachea by causing reflexive bronchoconstriction in the respiratory airways. 4. The inflation, or Hering-Breuer, reflex is activated by stretch receptors in the visceral pleurae and conducting airways, protecting the lungs from overexpansion by nhibiting inspiration. VI. Respiratory Adjustments (pp. 839–840) A. Exercise (p. 839) 1. During vigorous exercise, deeper and more vigorous respirations, called hyperpnea, ensure that tissue demands for oxygen are met. 2. Three neural factors contribute to the change in respiration: psychic stimuli, cortical stimulation of skeletal muscles and respiratory centers, and excitatory impulses to the respiratory areas from active muscles, tendons, and joints. B. High Altitude (pp. 839–840) 1. Acute mountain sickness (AMS) may result from a rapid transition from sea level to altitudes above 8000 feet. . A long-term change from sea level to high altitudes results in acclimatization of the body, including an increase in ventilation rate, lower than normal hemoglobin saturation, and increased production of erythropoietin. VII. Homeostatic Imbalances of the Respiratory System (pp. 840–842; Fig. 22. 27) A. Chronic obstructive pulmonary diseases (COPD) are seen in patients that have a history of smoking, and result in progressive dyspnea, coughing and frequent pulmonary infections, and respiratory failure (pp. 840–841; Fig. 22. 27). 1. Obstructive emphysema is characterized by permanently enlarged alveoli and deterioration of alveolar walls. 2. Chronic bronchitis results in excessive mucus production, as well as inflammation and fibrosis of the lower respiratory mucosa. B. Asthma is characterized by coughing, dyspnea, wheezing, and chest tightness, brought on by active inflammation of the airways (p. 841). C. Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis and spread by coughing and inhalation (pp. 841–842). D. Lung Cancer (p. 842) 1. In both sexes, lung cancer is the most common type of malignancy, and is strongly correlated with smoking. 2. Squamous cell carcinoma arises in the epithelium of the bronchi, and tends to form masses that hollow out and bleed. 3. Adenocarcinoma originates in peripheral lung areas as nodules that develop from bronchial glands and alveolar cells. 4. Small cell carcinoma contains lymphocyte-like cells that form clusters within the mediastinum and rapidly metastasize. VIII. Developmental Aspects of the Respiratory System (pp. 842–843, 846; Fig. 22. 28) A. By the fourth week of development, the olfactory placodes are present and give rise to olfactory pits that form the nasal cavities (p. 842; Fig. 22. 28). B. The nasal cavity extends posteriorly to join the foregut, which gives rise to an outpocketing that becomes the pharyngeal mucosa. Mesoderm forms the walls of the respiratory passageways and stroma of the lungs (p. 842; Fig. 22. 28). C. As a fetus, the lungs are filled with fluid, and vascular shunts are present that divert blood away from the lungs; at birth, the fluid drains away, and rising plasma Pco2 stimulates respiratory centers (p. 43). D. Respiratory rate is highest in newborns, and gradually declines to adulthood; in old age, respiratory rate increases again (p. 843). E. As we age, the thoracic wall becomes more rigid, the lungs lose elasticity, and the amount of oxygen we can use during aerobic respiration decreases (p. 846). F. The number of mucus glands and blood flow in the nasal mucosa decline with age, as does cili ary action of the mucosa, and macrophage activity (p. 846).