KIN 292 1nd Edition Lecture 29 Outline of Last Lecture I 16 1 Overview of Respiratory Function II 16 2 Anatomy of the Respiratory System III 16 3 Forces for Pulmonary Ventilation IV 16 4 Factors Affecting Pulmonary Ventilation V 16 5 Clinical Significance of Respiratory Volumes and Air Flows Outline of Current Lecture I II III IV 17 1 Overview of Pulmonary Circulation 17 2 Diffusion of Gases 17 3 Exchange of Oxygen and Carbon Dioxide 17 4 Transport of Gases in the Blood start Current Lecture Diffusion of Gases To understand the exchange of CO2 and O2 between the air and blood we need to know a little about Partial pressures of gases o Gases diffuse down pressure gradients High pressure low pressure A particular gas diffuses down its own pressure gradient Presence of other gases in a mixture of gases is irrelevant Solubility of gases in liquids o The concentration of a dissolved gas in a fluid is proportional to its partial pressure and its solubility CO2 is more soluble than O2 which has an impact on their respective ability to cross lipid membranes The solubility of both is very low in water Oxygen diffusing down its concentration gradient in the body Partial pressure measured in Atmospheres is directly proportional to concentration as we will see Partial Pressure of Gases Dalton s Law o Gas mixtures Many gases are mixtures of different molecules 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 The pressure exerted by a mixture of gases the sum of the pressures exerted by the individual gases in the same volume Dalton s Law Ptotal P1 P2 P3 Pn Partial pressure of a gas depends on fractional concentration of the gas Pgas gas Ptotal o Composition of air 79 nitrogen 79 of the molecules in a given volume are N2 21 oxygen Trace amounts of CO2 0 03 helium argon and other gases Water can be a factor depending on humidity o Pair 760 mm Hg PN2 PO2 PCO2 PN2 0 79 760 mm Hg 600 mm Hg PO2 0 21 760 mm Hg 160 mm Hg thus O2 concentration N2 concentration PCO2 0 0003 760 mm Hg 0 23 mm Hg tiny concentration o Composition of air at 100 humidity includes water vapor gas form of H2O Why do we need to know the effect of humidity o Pair 760 mm Hg PN2 PO2 PCO2 PH2O PN2 0 741 760 mm Hg 563 mm Hg PO2 0 196 760 mm Hg 149 mm Hg PH2O 0 062 760 mm Hg 47 mm Hg PCO2 0 00027 760 mm Hg 0 21 mm Hg Trachea o Composition of air at 100 humidity includes water vapor gas form of H2O Why do we need to know the effect of humidity Because our body is at maximum humidity and one role of conducting division is to add water vapor so this is your trachea air o Pair 760 mm Hg PN2 PO2 PCO2 PH2O PN2 0 741 760 mm Hg 563 mm Hg PO2 0 196 760 mm Hg 149 mm Hg PH2O 0 062 760 mm Hg 47 mm Hg PCO2 0 00027 760 mm Hg 0 21 mm Hg Alveolus o Fresh atmospheric air mixes with air rich in CO2 and poor in O2 in the dead space of the conducting zone o This decreases PO2 and increases PCO2 relative to outside air o Ventilation is adjusted as needed to maintain PO2 at 100 mmHg and PCO2 at 40 mmHg in the alveolar spaces at all times Solubility of Gases in Liquids Henry s Law Ability to dissolve depends on properties of the gas and properties of the liquid Henry s law c kP o c molar concentration of dissolved gas o k Henry s law constant higher number more soluble o P partial pressure of gas in atmospheres The partial pressure of a gas affects the amount of gas that goes into solution Carbonated beverages bottled with almost pure CO2 gas under high pressure High P higher c k does not change What happens when you pop the top Henry s law c kP o Henry s law constant k is low for CO2 and O2 in plasma mostly H2O so the concentration of dissolved CO2 and O2 in the blood at sea level is too low to support life o CO2 is more soluble than O2 k is higher but still too low for life o Red blood cells contain a bag of physiology tricks to greatly increase the CO2 and O2 carrying capacity in blood We ll discuss these later 17 3 Exchange of Oxygen and Carbon Dioxide Using a different version of Figure 17 4 to show equilibration at aveolus and blood Diffusion of Gases Fick s Law of Diffusion o The rate of gas transfer V gas is proportional to the tissue area the diffusion coefficient of the gas and the difference in the partial pressure of the gas on the two sides of the tissue and inversely proportional the thickness o V gas rate of diffusion D diffusion coefficient of gas solubility o A tissue area P1 P2 difference in partial pressure o T tissue thickness o Lungs have large surface area and very thin membrane tissue Determinants of Alveolar PO2 and PCO2 Factors affecting alveolar partial pressures o PO2 and PCO2 of inspired air o Minute alveolar ventilation o Rates at which respiring tissues use O2 and produce CO2 o What happens to alveolar partial pressures during exercise when there is an increased use O2 and production of CO2 The rate of alveolar ventilation increases to almost exactly match the rate of O2 use and CO2 production and keep alveolar partial pressures constant o Hyperpnea increased ventilation due to increased demand Minimal changes in arterial PO2 and PCO2 o Hypoventilation ventilation does not meet demands Arterial PO2 decreases Arterial PCO2 increases o Hyperventilation ventilation exceeds demands Arterial PO2 increases Arterial PCO2 decreases Transport of Gases in the Blood Oxygen transport in blood start today Magic trick Hemoglobin o Oxygen transport by hemoglobin O2 is not very soluble in plasma Only 3 0 mL of every 200 mL of arterial blood O2 is dissolved in plasma 1 5 Almost all of arterial blood O2 is transported by hemoglobin o Oxygen binding to hemoglobin Hb O2 Hb O2 Hb deoxyhemoglobin Hb O2 oxyhemoglobin o O2 carrying capacity of blood When 100 saturated 4 molecules O2 molecule Hb 1 g hemoglobin carries 1 34 mL O2 o Normal blood hemoglobin levels 12 17 g dL average 15 g dL where 1 dL 100 mL o O2 carrying capacity of hemoglobin in blood 1 34 x 15 20 mL dL or 200 mL O2 per 1 L blood CO at rest mL O2 pumped by left ventricle min at rest o Arterial blood Hemoglobin is 98 5 saturated o Venous blood Hemoglobin is 75 saturated Carbon dioxide transport in blood next lecture Magic trick Carbonic anhydrase Cooperativity among 4 Hb subunits is the reason for the shape of the curve O2 binding affinity decreases …