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UNCG KIN 292 - Chapter 17: The Respiratory System: Gas Exchange and Regulation of Breathing

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Kin 292 1st Edition Lecture 30Outline of Last Lecture I. 17.1 Overview of Pulmonary CirculationII. 17.2 Diffusion of GasesIII. 17.3 Exchange of Oxygen and Carbon DioxideIV. 17.4 Transport of Gases in the BloodOutline of Current Lecture I. 17.4 Transport of Gases in the Blood - continuedII. 17.5 Central Regulation of VentilationIII. 17.6 Control of Ventilation by ChemoreceptorsIV. 17.8 Respiratory System in Acid-Base HomeostasisThis is the focus for Lab 9. Activity 4 includes exerciseCurrent Lecture- CO2 is more soluble in plasma than O2, but still not very soluble5–6% transported dissolved in plasmaCO2 can bind to hemoglobin to form carbaminohemoglobin5–8% transported bound to HbCO2 can be converted to bicarbonate in erythrocytes, then transported in plasma86–90% of transported CO2 dissolved in the plasma as bicarbonate- Carbon Dioxide Transport in Blood o Role of carbonic anhydrase in carbon dioxide transport Carbon dioxide exchange and transport in systemic capillaries and veins Carbon dioxide exchange and transport in pulmonary capillaries and veinso Effect of oxygen on carbon dioxide transport- At tissues:o As CO2 enters plasma a pressure (conc.) difference is produced compared to RBC,which pushes CO2 into RBC down pressure gradient.o Carbonic anhydrase (CA) immediately removes the CO2 by converting it to carbonic acid, which then dissociates into bicarbonate and hydrogen ionsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Law of mass action: an increase in CO2 causes an increase in bicarbonate and hydrogen ions; however, if these products remain in RBC enzyme activity slows down and CO2 would rise. Therefore, bicarbonate is immediately transported into plasma via a transport protein in exchange for a chloride ion (chloride shift) and free hydrogen ions are removed by bufferso At lung CO2 moves down conc. gradient RBC→plasma →alveolus As CO2 decreases in RBC, CA works in reverse to convert bicarbonate to CO2. Law of mass action again. Bicarbonate (substrate) is maintained by chloride shift working opposite direction. Also H+ is released form Hb and other buffers.17.5 Central Regulation and Ventilation - Neural control of breathing by motor neuronso Inspiration Phrenic nerve  diaphragm External intercostal nerve  external intercostal muscleso Expiration Internal intercostal nerve  internal intercostal muscleso Generation of breathing rhythm in the brainstemo Peripheral input to respiratory centers- Brainstem respiratory centerso Inspiratory neurons (blue) in VRG & DRGo Depolarize in a cyclical, ramplike fashion (next slide) signaling somatic motor nerves innervating diaphragm and external intercostal muscleso Expiratory neurons (yellow) in VRGo Depolarize only during active expirationo Activates neurons to expiratory muscles and/or inhibit inspiratory neurons- Source for this cycle is the Central Pattern Generator (CPG), a network of neurons located near the VRG and DRG in the medulla. - The mechanism for this apparent spontaneous action is unknown. - Thus medulla acts alone to control quiet breathing.- The CPG can receive information from other sources that can increase this cycle and we do know something about those- Chemoreceptors – our next topico Detect blood levels of O2 and CO2. Some of CO2 effects mediated by pHo Two types Peripheral chemoreceptors in carotid bodies Central chemoreceptors in medulla oblongata- Located in carotid bodies near carotid sinus- They have direct contact with arterial blood- Communicate via afferent neurons projecting to medullary respiratory control areas- Respond mainly to changes in blood pH that results from changes in CO2 (primary source) and many other routesChemoreceptors- Central chemoreceptorso Located on the ventral surface of medullao Respond to changes in pH of the CSFo Not directly responsive to CO2 Respond indirectly to CO2 via pH Increased CO2 decreases pHo Not responsive to changes in


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UNCG KIN 292 - Chapter 17: The Respiratory System: Gas Exchange and Regulation of Breathing

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