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UNCG KIN 292 - Chapter 17: The Respiratory System: Gas Exchange and Regulation of Breathing

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KIN 292 1nd Edition Lecture 29 Outline of Last Lecture I. 16.1 Overview of Respiratory FunctionII. 16.2 Anatomy of the Respiratory SystemIII. 16.3 Forces for Pulmonary VentilationIV. 16.4 Factors Affecting Pulmonary VentilationV. 16.5 Clinical Significance of Respiratory Volumes and Air FlowsOutline of Current LectureI. 17.1 Overview of Pulmonary CirculationII. 17.2 Diffusion of GasesIII. 17.3 Exchange of Oxygen and Carbon DioxideIV. 17.4 Transport of Gases in the Blood – startCurrent 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 gaseso 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 liquidso 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 Lawo Gas mixtures Many gases are mixtures of different moleculesThese 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 × Ptotalo 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 humidityo 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- Tracheao 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 airo 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- Alveoluso Fresh atmospheric air mixes with air rich in CO2 and poor in O2 in the dead spaceof the conducting zoneo This decreases PO2 and increases PCO2 relative to outside airo 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 = kPo c = molar concentration of dissolved gaso 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 = kPo 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 lifeo 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 bloodDiffusion of Gases - Fick’s Law of Diffusiono 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 pressureo T = tissue thicknesso Lungs have large surface area and very thin membrane tissueDeterminants of Alveolar PO2 and PCO2- Factors affecting alveolar partial pressureso PO2 and PCO2 of inspired airo Minute alveolar ventilationo Rates at which respiring tissues use O2 and produce CO2o 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 constanto 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 increaseso Hyperventilation: ventilation exceeds demands Arterial PO2 increases  Arterial PCO2 decreasesTransport of Gases in the Blood- Oxygen transport in blood – start today. Magic trick: Hemoglobino 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 hemoglobino Oxygen binding to hemoglobin Hb + O2 HbO2 Hb = deoxyhemoglobin Hb-O2 = oxyhemoglobino 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 mLo 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


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UNCG KIN 292 - Chapter 17: The Respiratory System: Gas Exchange and Regulation of Breathing

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