Kin 292 1st Edition Lecture 30 Outline of Last Lecture I 17 1 Overview of Pulmonary Circulation II 17 2 Diffusion of Gases III 17 3 Exchange of Oxygen and Carbon Dioxide IV 17 4 Transport of Gases in the Blood Outline of Current Lecture I 17 4 Transport of Gases in the Blood continued II 17 5 Central Regulation of Ventilation III 17 6 Control of Ventilation by Chemoreceptors IV 17 8 Respiratory System in Acid Base Homeostasis This is the focus for Lab 9 Activity 4 includes exercise Current Lecture CO2 is more soluble in plasma than O2 but still not very soluble 5 6 transported dissolved in plasma CO2 can bind to hemoglobin to form carbaminohemoglobin 5 8 transported bound to Hb CO2 can be converted to bicarbonate in erythrocytes then transported in plasma 86 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 veins o 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 ions These 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 buffers o 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 neurons o Inspiration Phrenic nerve diaphragm External intercostal nerve external intercostal muscles o Expiration Internal intercostal nerve internal intercostal muscles o Generation of breathing rhythm in the brainstem o Peripheral input to respiratory centers Brainstem respiratory centers o Inspiratory neurons blue in VRG DRG o Depolarize in a cyclical ramplike fashion next slide signaling somatic motor nerves innervating diaphragm and external intercostal muscles o Expiratory neurons yellow in VRG o Depolarize only during active expiration o 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 topic o Detect blood levels of O2 and CO2 Some of CO2 effects mediated by pH o 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 routes Chemoreceptors Central chemoreceptors o Located on the ventral surface of medulla o Respond to changes in pH of the CSF o Not directly responsive to CO2 Respond indirectly to CO2 via pH Increased CO2 decreases pH o Not responsive to changes in O2