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Chapter 23 The Respiratory System: An Introduction ▪The respiratory system has five basic functions: ▪Organization of the respiratory system- can divided into upper and lower respiratory systems ▫The upper respiratory system▫The lower respiratory system▫The surface area of the lungs is very large, 35 times that of the body. ▫Respiratory mucosa▫Respiratory Defense SystemThe Upper Respiratory System ▪Nose and nasal cavity- the nose is the primary passageway for air entering the respiratory system ▫External nares▫Vestibule▫Nasal septum▫Olfactory region▫Nasal conchae▫Nasal meatuses▫Palates- 1 ▫Nasal mucosa▪The Pharynx- the chamber shared by the digestive and respiratory systems, is divided into three sections, nasopharynx, oropharynx, laryngopharynx. ▫Nasopharynx▫Oropharynx▫Laryngopharynx The Larynx- a cartilaginous structure that surrounds and protects the glottis ▪Cartilages and Ligaments of the Larynx ▫Thyroid cartilage▫Cricoid cartilage▫Epiglottis▫Smaller cartilages; arytenoids, corniculate, and cuneiform ▫Vestibular and vocal ligaments▫Vestibular and vocal folds▪Sound Production- air passing through the glottis vibrates the vocal folds and produces sound waves. ▪Laryngeal musculatureThe Trachea and Primary Bronchi ▪The Trachea- Windpipe, a tough, flexible tube, epithelia is continuous with the larynx ▫Tracheal cartilages- 15-20, serve to stiffen the tracheal walls and protect the airway. ▫Trachealis muscle2 ▪The Primary Bronchi- initial branches of the trachea, left and right branches ▫Right bronchus is larger in diameter than the left, and descends into the right lung at a steep angle. The Lungs ▪Lobes and surfaces of the lungs- the lungs have distinct lobes that are separated by deep fissures. ▪The Bronchi- the bronchi and their branches form the bronchial tree. ▪The Bronchioles- Each tertiary bronchus branches several times within the bronchopulmonary segment, giving rise to multiple bronchioles. ▫The autonomic nervous system regulates the activity of these smooth muscles. -Bronchodilation-Bronchoconstriction▫Pulmonary lobules-Each terminal bronchiole delivers air to a single pulmonary lobule -Within each lobule, the terminal bronchiole branch to form several respiratory bronchioles, the thinnest and most delicate branches of the bronchial tree. ▪Alveolar Ducts and Alveoli ▫Alveolar ducts▫Alveolar sacs▫Each alveolus is surrounded by an extensive network of capillaries ▫The capillaries are surrounded by a network of elastic fibers 3 ▫Alveolar epithelium contains simple squamous cells (pneumocytes type I) with roaming alveolar macrophages and pneumocytes type II cells. ▫Respiratory membrane- a composite structure containing: 1) 2) 3) -Gas exchange occurs across the respiratory membrane ▪Blood Supply to the Lungs ▫The respiratory exchange surfaces receive blood from arteries of the pulmonary circuit, continues to arterioles and capillaries that surround the alveoli. ▫The conducting portions of the respiratory tract receive blood from the bronchiole arteries. ▪The Pleural cavities and Pleural membranes ▫The two pleural cavities are separated by the mediastinum ▫Each lung occupies a single pleural cavity, which is lined by a serous membrane called the pleura, consisting of visceral and parietal layers. ▫Pleural fluid fills the pleural cavity, providing lubrication between membranes. 4 An Overview of Respiratory Physiology ▪Respiration usually refers to two integrated processes; external respiration and internal respiration ▫Internal respiration▫External respiration▫Three integrated steps involved in external respiration are: 1) 2) 3) Pulmonary Ventilation ▪Pulmonary ventilation is the physical movement of air into and out of the respiratory tract. ▪The movement of air- air moves from place to place in response to pressure changes. ▫Atmospheric pressure- ▫Boyle’s Law- ▫Air will flow from an area of higher pressure to an area of lower pressure ▫During inhalation: ▫During exhalation:. ▫Pleural fluid within the pleural cavity creates a relatively strong bond between the visceral and parietal pleura. 5 ▫Compliance▪Pressure changes during inhalation and exhalation ▫Intrapulmonary pressure▫Intrapleural pressure▫Respiratory cycle- ▪The mechanics of breathing ▫Muscles of inhalation- inhalation is an active process, involving the contraction of one or more of these muscles: ▫Muscles of exhalation- exhalation can be passive or active, when active, can include one or more of these muscles: ▫Modes of breathing- respiratory muscles are used in various combinations, depending on the volume of air that must be moved in or out of the system. -Quiet breathing- (eupnea), -Diaphragmatic breathing-Costal breathing-Forced breathing- (hyperpnea), -Accessory muscles assist with inhalation and exhalation involves contraction of the internal intercostal muscles 6 ▪Respiratory rates and volumes ▫Respiratory rate▫Respiratory minute volume▫Aveolar ventilation▫Relationships among VT, VE, and VA- The respiratory rate and tidal volume together determine the alveolar ventilation rate: ▫Respiratory Performance and Volume Relationships- only a small proportion of the air in the lungs is exchanged during a single quiet respiratory cycle. -Pulmonary Volumes include the following: -Resting Tidal Volume-Expiratory Reserve-Residual Volume-Inspiratory Reserve Volume-Pulmonary Capacities can be determined by adding the values of various volumes, they include: -Inspiratory capacity-Functional residual capacity-Vital capacity-Total lung capacity- 7 Gas Exchange ▪To understand the events of gas exchange, we need to consider 1) the partial pressures of the gases involved 2) the diffusion of molecules between a gas and a liquid ▪The gas laws- principles that govern the movement and diffusion of gas molecules ▫Daltons’ law- ▫Partial Pressures- ▫Henry’s Law- ▪Diffusion and respiratory function ▫The composition of alveolar air- 8 ▫Efficiency of diffusion at the respiratory membrane, there are five reasons gas exchange is efficient at the respiratory membrane: 1) 2) 3) 4) 5) ▫Partial pressures in alveolar air and alveolar capillaries: ▫Partial pressures in the systemic circuit Gas Pickup and Delivery ▪RBC continually remove O2 and CO2 from blood plasma, so the plasma continually absorbs gases. ▪The reactions between the plasma and RBC are temporary and reversible ▪Oxygen transport ▫Hemoglobin saturation- the percentage of heme units containing bound oxygen at any given moment. ▫Oxygen-hemoglobin saturation curve- 9 ▫Hemoglobin and pH▫Hemoglobin and temperature▫Hemoglobin and BPG▫Fetal hemoglobin- ▪Carbon dioxide transport ▫CO2 is generated by aerobic metabolism in peripheral tissues, after entering the bloodstream, a CO2 molecule is: 1) 2) 3) ▫Carbonic acid formation- 70% of absorbed CO2 is transported as carbonic acid. ▫Hemoglobin binding- roughly 23% of the CO2 carried by the blood is bound to the globular protein portions of the HB molecules inside RBC’s ▫Plasma transport- only about 7% of carbon dioxide is transported dissolved in the plasma. 10 Control of Respiration ▪Local regulation of gas transport and alveolar function ▫The rate of oxygen delivery in each tissue and the efficiency of oxygen pickup at the lungs are largely regulated at the local level. ▪Respiratory centers of the brain ▫Respiratory control has both involuntary and voluntary components ▫Respiratory centers in the medulla oblongata -respiratory rhythmicity centers- paired centers that set the pace of respiration -divided into a dorsal respiratory group (DRG) and a ventral respiratory group (VRG) -There is reciprocal inhibition between neurons involved with inhalation and exhalation. -Patterns of interaction between these groups of neurons differs between quiet and forced breathing. -During quiet breathing: -During forced breathing: ▫The apneustic and pneumotaxic centers- are paired nuclei of the pons that adjust the output of the respiratory rhythmicity centers. -Their activities regulate the respiratory rate and depth of respiration in response to sensory stimuli or input from other centers in the brain. 11 -Each apneustic center provides continuous stimulation to the DRG on that side of the brain stem. -The pneumotaxic centers inhibit the apneustic centers and promote passive or active exhalation -Interactions between the DRG and VRG establish the basic pace and depth of respiration. ▪Respiratory reflexes ▫Activities of the respiratory centers are modified by sensory information from several sources: ▫Information from these receptors alters the pattern of respiration, the induced changes have been called respiratory reflexes. ▫Chemoreceptor reflexes -Chemoreceptor inputs come from cranial nerves IX and X and receptors that monitor the composition of the cerebrospinal fluid: -stimulation of these chemoreceptors leads to an increase in the depth and rate of respiration. ▫Hypercapnia and hypocapnia -Hypercapnia- an increase in the PCO2 -Hypocapnia- an abnormally low PCO2, brought about by hyperventilation (rate and depth of respiration exceed the demand for oxygen delivery and CO2 removal) 12 ▫Baroreceptor reflexes -When blood pressure falls, the respiratory rate increases -When blood pressure rises, the respiratory rate declines ▫Hering-Breuer reflexes -The sensory information from these reflexes is distributed to the apneustic centers and the VRG. -The Hering-Breuer reflexes are not involved in normal quiet breathing or in tidal volumes under 1000 ml, there are two such reflexes: -Inflation reflex-Deflation reflex▫Protective reflexes- operate when there is an exposure to toxic vapors, chemical irritants, or mechanical stimulation of the respiratory tract. -Receptors are located in the epithelium of the respiratory tract -Sneezing, coughing, laryngeal spasms are examples of protective reflexes. ▪Voluntary control of respiration ▫Conscious thought processes tied to strong emotions affect the respiratory rate by stimulating centers in the hypothalamus ▫Emotional states can affect respiration through the activation of the sympathetic or parasympathetic division of the ANS ▫Anticipation of strenuous exercise can trigger an automatic increase in the respiratory rate ▫Conscious control has a limit; you can not “hold your breath ‘til death” 13