<p> Diffusion of Gases Chapter 16 dS/dT = D A R T  C L (MR)1/2</p><p>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</p><p>DCO2 >>> DO2 - WHY?</p><p>Figure 16.3: Solubility of O2 and CO2 in water Figure 16.3: Solubility of O2 and CO2 in water</p><p>Diffusion Capacity of the Lung: DL = VGAS / P1 - P2</p><p>= ml / min / mm Hg</p><p>Oxygen Transport: 95% carried by hemoglobin 5% dissolved in plasma</p><p>Fig 16.4: O2 and CO2 in the Body</p><p>Respiratory Considerations</p><p> Surface area of capillaries in lung and tissues</p><p> Thin membrane for diffusion</p><p> MR for CO2 and O2 is very similar</p><p> Solubility differs for CO2 and O2</p><p> Gases are warmed as they enter lungs</p><p>Respiratory Considerations C (in mm Hg) Gas Air Alveolar Air Arterial Venous</p><p>O2 160 100 100 40 CO2 0.25 40 40 46 H2O 0.0 47 N2 600 573</p><p>Fig 16.6: Transport of O2 Fig 16.8: Hb - O2 Dissociation Curve Fig 16.7: Hb - O2 Loading</p><p>Hb-O2 Saturation Curve: Review</p><p> Shift to the right decreases affinity, increases P50, and increases unloading of O2</p><p> Caused by acidity (Bohr effect), increased temperature, and elevated 2,3 - DPG</p><p> Increased by Epi, thyroid hormones, prolonged hypoxia, etc.</p><p>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</p><p>Carbonic Anyhydrase Reaction + - CO2 + H2O <--> H2CO3 <--> H + HCO3</p><p>In 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</p><p>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</p><p>Fig 16.12: PO2 --> CO2 Transport Fig 16.11: Chloride Shift: </p><p>RBCs in the systemic capillaries: Chloride Shift</p><p> RBC [Cl-] increases in systemic capillaries  RBC volume and blood hematocrit (Hct) increases in systemic capillaries  Venous Hct is 3% greater than arterial Hct</p><p>Chloride Shift Reversed: RBCs in the Lungs</p><p>Gas Transport Summary:</p><p> 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)</p><p>Regulation of Ventilation Medullary Center Respiratory Neurons C P o o l ( V R G ) S p o n t a n e o u s l y - A c t i v e + A P o o l ( D R G ) B P o o l +</p><p>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 (?)</p><p>Fig 16.18: Peripheral Chemoreceptors</p><p>Inputs to Medulla I n p u t s H i g h e r C e r e b r a l C e n t e r s</p><p>C P o o l ( V R G ) - C h e m o r e c e p t o r s : M u s c l e - p H P r o p r i o c e p t o r s - P O 2 + A P o o l - P ( D R G ) C O 2 B P o o l + R e s p i r a t o r y + T r a c k + I r r i t a n t s L u n g S t r e t c h D i a p h r a g m R e c e p t o r s</p><p>CNS: Medulla</p><p> Sensitive only to pH (due to PCO2)</p><p>Periphery:  Aortic arch  Carotid bodies</p><p> Sensitive to PO2 and pH</p><p> Oxygen only a factor at PO2 < 60 mm Hg</p><p>Fig 16.19: Chemoreceptor Control Fig 16.20: Central Chemoreceptors</p><p>Increasing Alveolar Ventilation: A Pool Output</p><p>Effects of alveolar ventilation on PO2 and PCO2 in the alveoli</p><p>O2 Sensing Glomus Cells of the Carotid Bodies O 2 S e n s i n g G l o m u s C e l l s o f t h e C a r o t i d B o d i e s</p><p>+ O 2 G a t e d K C h a n n e l w i t h P O 2 = 1 0 0 m m H g</p><p>O 2</p><p>K+ K+</p><p>V m = - 7 0 m V</p><p>O 2 S e n s i n g G l o m u s C e l l s o f t h e C a r o t i d B o d i e s</p><p>+ O 2 G a t e d K C h a n n e l i n l o w P O 2 </p><p>K+</p><p>V m = - 5 0 m V O 2 S e n s i n g G l o m u s C e l l s o f t h e C a r o t i d B o d i e s</p><p>I n c r e a s e d F r e q u e n c y o f A P s D o p a m i n e</p><p>K + T o V R G A P o o l +</p><p>S e n s o r y n e r v e</p><p>Fig 16.23 Ventilation - perfusion ratios</p><p>Pulmonary Blood Flow  To match perfusion with ventilation:</p><p> Increased alveolar air PCO2 => dilate bronchioles and dilate systemic arterioles</p><p> Decreased PCO2 => constrict bronchioles and constrict systemic arterioles</p><p> Increased PO2 => dilate pulmonary arterioles and constrict systemic arterioles</p><p> Decreased PO2 => constrict pulmonary arterioles and dilate systemic arterioles</p>