Diffusion of Gases Chapter 16 dS dT D A R T C L MR 1 2 D diffusion coefficient which includes solubility of molecule in aqueous solution A surface area for diffusion C concentration gradient L path length or thickness of membrane MR molecular radius of gas molecule DCO2 DO2 WHY Figure 16 3 Solubility of O2 and CO2 in water Figure 16 3 Solubility of O2 and CO2 in water Diffusion Capacity of the Lung DL VGAS P1 P2 ml min mm Hg Oxygen Transport 95 carried by hemoglobin 5 dissolved in plasma Fig 16 4 O2 and CO2 in the Body Respiratory Considerations Surface area of capillaries in lung and tissues Thin membrane for diffusion MR for CO2 and O2 is very similar Solubility differs for CO2 and O2 Gases are warmed as they enter lungs Respiratory Considerations C in mm Hg Gas Air Alveolar Air Arterial O2 100 160 100 Venous 40 CO2 H2O N2 0 25 0 0 600 40 47 573 40 46 Fig 16 6 Transport of O2 Fig 16 8 Hb O2 Dissociation Curve Fig 16 7 Hb O2 Loading Hb O2 Saturation Curve Review Shift to the right decreases affinity increases P50 and increases unloading of O2 Caused by acidity Bohr effect increased temperature and elevated 2 3 DPG Increased by Epi thyroid hormones prolonged hypoxia etc CO2 in the blood 7 as dissolved CO2 23 as carbamino compounds on Hb Protein NH3 CO2 Protein NH2COOH 70 as HCO3 via carbonic anhydrase Carbonic Anyhydrase Reaction CO2 H2O H2CO3 H HCO3In the tissues the Bohr effect causes the increased release of O2 As CO2 increases H is formed and some is buffered by binding to Hb This decreases Hb affinity for O2 and promotes the unloading of O2in the tissues Haldane Effect in the Lungs O2 promotes the unloading of CO2 As Hb binds O2 Hb becomes a stronger acid i e it gives up an H This released H binds to HCO3 HCO3 H H2CO3 CO2 H2O The CO2 is then released or blown off in the exhaled air See also Figures 16 12 13 Fig 16 12 PO2 CO2 Transport Fig 16 11 Chloride Shift RBCs in the systemic capillaries Chloride Shift RBC Cl increases in systemic capillaries RBC volume and blood hematocrit Hct increases in systemic capillaries Venous Hct is 3 greater than arterial Hct Chloride Shift Reversed RBCs in the Lungs Gas Transport Summary O2 decreases amount of carbamino promoting unloading of CO2 Haldane Effect CO2 as H decreases O2 affintiy and increases unloading of O2 in systemic capillaries Bohr Effect Regulation of Ventilation Medullary Center Respiratory Neurons C Pool VRG B Pool Spontaneously Active A Pool DRG Dorsal Respiratory Group DRG Inhalation diaphragm and external intercostals Ventral Respiratory Group VRG Shuts off DRG and promotes active exhalation Fig 16 15 Brainstem Respiratory Centers Respiratory Input from the Pons Apneustic Center Prolonged inspiration Pneumotaxic Center Inhibits Apneustic Center Receives some input from vagal lung stretch receptors Fig 16 18 Peripheral Chemoreceptors Inputs to Medulla Inputs Higher Cerebral Centers C Pool VRG Muscle Proprioceptors A Pool DRG B Pool Lung Stretch Receptors Chemoreceptors pH PO2 PCO2 Respiratory Track Irritants Diaphragm CNS Medulla Sensitive only to pH due to PCO2 Periphery Aortic arch Carotid bodies Sensitive to PO2 and pH Oxygen only a factor at PO2 60 mm Hg Fig 16 19 Chemoreceptor Control Fig 16 20 Central Chemoreceptors Increasing Alveolar Ventilation A Pool Output Effects of alveolar ventilation on PO2 and PCO2 in the alveoli O2 Sensing Glomus Cells of the Carotid Bodies O2 Sensing Glomus Cells of the Carotid Bodies O2 Gated K Channel with PO2 100 mm Hg O2 K K Vm 70 mV O2 Sensing Glomus Cells of the Carotid Bodies O2 Gated K Channel in low P O2 K Vm 50 mV O2 Sensing Glomus Cells of the Carotid Bodies Increased Frequency of APs Dopamine K To VRG A Pool Sensory nerve Fig 16 23 Ventilation perfusion ratios Pulmonary Blood Flow To match perfusion with ventilation Increased alveolar air PCO2 dilate bronchioles and dilate systemic arterioles Decreased PCO2 constrict bronchioles and constrict systemic arterioles Increased PO2 dilate pulmonary arterioles and constrict systemic arterioles Decreased PO2 constrict pulmonary arterioles and dilate systemic arterioles