Systemic Gas Exchange Systemic gas exchange the loading of CO2 and the unloading of O2 at the systemic capillaries In RBC CO2 H2O H2CO3 HCO3 In RBC H binds to Hb buffers both the intracellular and blood H CO2 loading pH chloride shift antiport called the chloride bicarbonate exchanger then pumps out HCO3 into plasma in exchange for Cl 22 1 Systemic Gas Exchange O2 unloading Blood entering O2 consuming tissues encounters a lower tissue fluid PO2 which cause a lower PO2 in plasma which lower the PO2 in RBC The lower PO2 in RBC causes oxygen to dissociate from Hb This dissociated O2 diffuses from RBC into plasma and then into tissue fluid Only dissolved O2 or O2 not on Hb is counted towards PO2 of the blood because actual O2 diffusion is drive by differences in dissolved O2 however the total amount of O2 that can diffuse is determined by mostly Hb H binding to HbO2 changes Hb shape lowers Hb affinity for O2 H HbO2 HHb dissolved O2 Hb arrives 97 100 saturated leaves 75 saturated Hb has released 22 25 of its oxygen load After the blood leaves the systemic cap bed of resting tissue the remaining O2 in the blood in veins is available for extraction if tissues need more because of exercise It is a venous reserve of O2 which can sustain life for 4 5 min in the case of respiratory arrest 22 2 Systemic Gas Exchange 22 3 Alveolar Gas Exchange Reactions are reverse of systemic gas exchange O2 loading The higher alveolar PO2 causes oxygen to diffuse from alveoli into blood plasma and then into RBC The new higher PO2 in RBC causes Hb to bind to oxygen and will achieve 100 saturation of Hb CO2 unloading as HHb loads O2 its affinity for H decreases H dissociates from pumped back into RBCs from plasma in HHb and binds with HCO3 exchange for Cl reverse chloride shift CO2 H2O H2CO3 HCO3 H The free CO2 CO2 gas dissolved in plasma and that released from carbaminohemoglobin diffuse into alveolus to be exhaled Blood gives up CO2 from dissolved gas and from the carbaminoHb cmpds during gas exchange more easily than it gives up the CO2 in bicarbonate 22 4 Alveolar Gas Exchange 22 5 Respiratory System Metabolic rate effect on Gas Exchange Neural Control of Breathing 22 6 Factors Affect O2 Unloading Hemoglobin unloads O2 to match metabolic needs of the tissues at different states of activity The Hb dissociation curve shifts right with increases activity This means that at any given PO2 Hb has less affinity for O2 At any given PO2 three factors affect the rate of O2 unloading to the tissues this in addition to the simple fact that the lower PO2 in tissues causes a decrease in O2 saturation of Hb compared to lungs In metabolically active tissues the following 3 factors lead to more O2 released from HbO2 Blood PCO2 active tissue has increased PCO2 temperature active tissue has increased temp Bohr effect active tissue has increased lactic acid and CO2 which 22 7 lowers pH Factors Affect O2 Unloading Protons and CO2 bind to globin portion of Hb and alter conformation of Hb molecule temperature also alters shape These factors do not matter as much in the lungs the for the normally high PO2 in lungs means shifting the curve to the right has only a small effect on Hb saturation and pul O2 loading In systemic cap where PO2 is the lower the effect causes a strong decreases in saturation of Hb with O2 for any given PO2 22 8 Oxygen Dissociation and Temperature 22 9 Oxygen Dissociation and pH 22 10 Factors Affect O2 Unloading The combined effect of increased PCO2 increased temp and lower ph which shifts dissoc curve to the right leads to Hb giving up more O2 in tissues than due to just the decrease in PO2 in tissues alone These three factors combined are much of the reason that saturation of Hb with oxygen decreases in very metabolically active tissue as compared to resting tissue In metabolically active tissue about 75 80 of oxygen load is released from Hb which results in only 20 25 saturation of Hb with oxygen in blood that leaves the capillaries of metabolically active tissue Need to know the saturation level of Hb has dropped by about 75 after leaving active tissue unlike only the 25 after leaving resting tissue Need rapid unloading of oxygen in metabolically active tissue which have an increased demand for oxygen 22 11 Factors Affecting CO2 Loading The rate of CO2 loading also adjusts to changing conditions of the tissues Haldane effect Low level of HbO2 as in metabolically active tissue enables blood to transport more CO2 As just explained active tissue uses more O2 thus less O2 bound to Hb which means more Hb or HHb Deoxyhemoglobin Hb or HHb binds CO2 better than HbO2 Hb or HHb binds more H than HbO2 as H are removed the CO2 H2O H2CO3 HCO3 H reaction shifts to the right towards products which produce more bicarb and H to compensate The shift of the reaction towards products removes both CO2 and water from RBC cytoplasm This means more dissolved CO2 diffuses from tissue fluid into plasma and then into RBC converted to bicarb to then be transported in plasma The effect is more CO2 is now being transported back to alveoli as HCO3 in blood 22 12 Neural Control of Breathing Breathing is under neural control for the skeletal muscles of ventilation cannot contract without nerve stimulation No autorhythmic pacemaker cells in lungs as in the heart Ventilation controlled by a central coordinating mechanism which involves repetitive impulses sent from brain to resp muscles Controlled at two levels of the brain one being cerebral and the other being automatic Neurons in three respiratory centers in medulla oblongata and pons control automatic unconscious breathing 22 13 Respiratory Control Centers Respiratory nuclei in medulla Ventral respiratory group VRG Generates the primary rhythm of breathing Nucleus in the medulla with three neural networks rhythm generating neurons inspiratory I neurons and expiratory E neurons In quiet breathing the VRG rhythm generating neurons activate VRG I neurons which depolarize inspiratory spinal motor neurons When the I motor neurons stop firing the inspiratory muscles relax allowing passive expiration During active expiration VRG expiratory neurons depolarize expiratory motor neurons causing expiratory muscles to contract During forced or active inspiration the firing of VRG I neurons inhibit the E neurons while activating the inspir muscle to contract While I neuron activity wanes E neruons begin to fire again if active expiration continues 22 14 Respiratory Control Centers Respiratory